DEPARTMENT OF THE INTERIOR

FRANKLIN K. LANE, Secretary /

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, Director

Bulletin 700

THE ANALYSIS OF 

SILICATE AND CARBONATE ROCKS

A revised and enlarged edition 

of Bulletin 422

BY

W> F. HILLEBRAND

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1919

CONTENTS.

Page.

Introduction _______________________________________ 15

Object and scope of the present treatise __ __ __ __ _ _ _______ 15

Acknowledgments ___ __ __ __ 17

Silicate rock analysis ________ _ ___ ___ _ _____________ 18

I. Introduction ______________ _ ____________________ 18

1. Importance of complete and thorough analyses- _ __ 18

2. The constituents occurring in silicate rocks ___________ 24

3. The distribution and occurrence of certain minor constituents. 25

4. Summation of analytical results and limits of allowable

error _________ 30

5. Statement of analyses _______ _ __ ________ 31

6. Time needed for making an analysis ______________ 32

7. Useful appliances and apparatus ________ ' ________ 33

\. Crucible tongs ____________ __ _ _________ 33

B. Radiators for volatilizing liquids and solids ________ 33

C. Perforated disk for crucibles _ _ __ _ _____ 33

D. Weighing scoop or trough ___ _ _____________ 35

E. Colorimeters ___ __ _ _ _ ___ ___ 35

a. First Survey form _____________________ 35

b. Second Survey form (Steiger's) _____________ 37

s c. Schreiner's form _______ _ _____________ 39

S. Preliminary qualitative analysis __________________ 41

9. Quality of apparatus and reagents _ __ ________ 42

A. Glassware and porcelain__ __________________ 42

B. Platinum and substitutes __________________ 43

a. Platinum ___ _ ___ __ _____________ 43

b. Substitutes for platinum __________________ 44

C. Reagents _____ - _ ______ ____ 45

II. Methods applicable to silicate rocks ___ _ ___ 1 _______________ 48

1. Introductory remarks _ _ ______ ___ __ 48

2. Specific gravity (porosity)- _ ___ _ ____ __ 49

General remarks ______ __ ___ _ ___ __ _ _ _ 49

A. By suspension in water _ __ _ _ _ __ _ _ 50

a. Ordinary method for specific gravity _________ 50

b. Method for specific gravity and porosity combined _ 51

c. Penfield's method for mineral fragments ________ 53

B. Pycnometer method ___ _ _ 54

a. Ordinary method ____ __ __ __________ 54

b. Refined method ____________ _ _________ 55

C. Heavy solutions not suitable for rocks ____ _ _ 57

3. Preparation of sample for analysis _ _ _ __ _ 57

A. Quantity of rock to be crushed ________________ 57

B. Crushing _ __ _ _ _ _ _ 57

a. Survey methods ______________________ 57

b. Washington's method ___________________ 59

C. Grinding ________________________ _ ______ 60

D. Abrasion of mortar and pestle _________________ 63

E. Weight of sample _________________ : ______ 64

230935
4 CONTENTS.

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued. Page.

4. Water. General considerations__________________ 64

A. The role of hydrogen in minerals_______________ 64

a. Conditions in which hydrogen may occur_______ 65

b. Bearing of the classification on analytical procedure_ 67

a. Behavior of hydrogen on grinding the mineral_ 67

/3. Behavior of hydrogen on desiccation at constant

temperature______________________ - 67 

7. Behavior of hydrogen (expelled as water) on

heating ________________________ 68

c. Effect of dehydration on physical properties______ , 69

d. Conclusion______________________._____ 69

B. Water taken up or lost on grinding____________.'__ 69

C. Importance, of employing air-dry powder for analysis__ 71

D. Argument in favor of including hygroscopic water in the

summation __.________________________ 72

5. Water. Methods of determination.,______:_________ 73

A. Indirect methods ________________________ 73

a. General considerations__________________ 73

b. Methods involving the use of dehydrating agents___ 73

c. Methods involving the application of heat_______ 74

a. Fractional determinations ______________ 74

/3. " Loss on ignition " method for total water____ 76

B. Direct methods without absorption tubes Penfield's

methods____________________________ 77 

a. For minerals easily deprived of their water_____ 77 

b. For minerals not easily deprived of their water___ 78 

C. Direct methods with absorption tubes___________ 79 

a. General considerations___________________ 79 

b. Steiger's application of the toluene oven (for low temperatures) __________________________________________£.'_________________ 81

c. Chatard's oven for temperatures up to 300° and over__ 82 

d. Penfield's procedure (for low and high temperatures). S3 

e. Dittrich and Eitel's apparatus (for low and high temperatures)___________________ ___ 84 

f. Gooch's apparatus (for high temperatures)______ 85. 

g. Kuzirian's method (for hydrous sulphates)______ 88 

h. Merits of the several forms of apparatus_______ 89

6. Silica Separation from alumina, etc_______________ 89 

A. Alternative methods of decomposing the rock_______ 89 

a. General considerations __________________ 89 

b. Decomposition of refractory silicates by hydrochloric

acid under pressure___________________ 91 

c. The boric-oxide method of Jannasch and Heidenreich__________________________ 92 

a. Preparation of the boric oxide___________ 92 

p. Treatment of easily decomposable silicates___ 92

7. Treatment of refractory silicates_________ 92

8. Further treatment after fusion__________ 93 

c. Possible objections to the boric-oxide method__ 93
CONTENTS. 5

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued.

6. Silica Separation from alumina, etc. Continued.

A. Alternative methods of decomposing the rock Contd. Page, 

d. The sodium-carbonate method__ 94 

a. Advantages of sodium carbonate over sodiumpotassium carbonate ____ _ 94 

/3. Purity of the sodium carbonate _ 94 

" 7. The fusion with normal sodium carbonate____ 95 

8. Fusion with sodium bicarbonate____ __ 96 

c. Treatment after fusion__________ 97 

B. Subsequent treatment______________________ 97 

a. Separation of silica____________________ 97 

a. Reasons for adoption of accepted procedure___ 97 

ft. Procedure in absence of notable amounts of

fluorine ________________________ 99 

7. Procedure with rocks and minerals containing

fluorine ________________________ 102 

b. Ignition of silica____._____________ ____ 102 

c. Correction for impurities in the silica___ ___ 103 

d. Accuracy of the silica determination___ 104 

e. Composition of the residue obtained from the silica_ 104 

f. Platinum in filtrates____________________, 105

7. Metals precipitable by hydrogen sulphide_______ ______ 106

8. Joint precipitation of aluminum, iron, titanium, zirconium,

chromium, rare earths, phosphorus, and vanadium with

and without manganese_______________ _ 106

A. Preliminary remarks______________________ 106

B. Precipitation without manganese______________ 106

a. Precipitation by ammonia________________ 106

a. Preliminary remarks________________ 106

/8. Procedure ____________ ___ ___ 107

b. The basic-acetate precipitation_____________ 109

a. Preliminary remarks _________________ 109

/?. Procedure ______________________ 110

C. Precipitation together with manganese___________ 111

a. By ammonia and ammonium persulphate_______ 111

a. Preliminary remarks ________________ 111

]8. Procedure________________________ 112

b. By ammonia and ammonium sulphide_________ 113

D. Recovery of unprecipitated iron and aluminum from the

filtrates ____________________________ 113 

a. After an ammonia precipitation_____________ 113 

b. After a basic-acetate precipitation___________ 113 

c. After precipitation by ammonia and ammonium persulphate ___________ ___ __ ____ ' 114 

E. Ignition of the precipitate__________________ 114

9. Determination of the oxides of iron and silicon in the precipitate obtained under 8 ____________________ 115 

A. Preliminary remarks_______________________ 115 

B. Residual silica (barium)___________________ 116 

a. Silica_______________________________ 116 

b. Barium_____________________________ 118
0 CONTENTS.

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued.

9. Determination of the oxides of iron and silicon in the precipitate obtained under 8 Continued. Page. 

C. Iron Titrimetric determination in the ferrous state__ 119 

a. Without regard to vanadium_____________:_ 119 

a. Reduction of the iron by hydrogen sulphide___ ' 119 

j3. Titration of the iron and subsequent treatment

of the solution____________________ 120

7. Reduction with titanous sulphate_________ 121

b. Having regard to vanadium_______________ 121

c. True value for ferric iron________________ 123

D. Iron Titrimetric determination in the ferric state___ 123

a. Preliminary remarks ____________________ 123

b. Titration with titanous chloride_____________ 123

E. Iron Gravimetric determination after separating as

sulphide_____________________________ 124 

a. Preliminary remarks___________________ 124 

b. Procedure__________________________ 324 

F. Iron Special cases______________-_______ 125 

a. Glass sands_________________________ 125 

b. Ceramic clays_______________________ 126

10. Miscellaneous separations of the oxides obtained under 8_ 126 

A. Preliminary remarks_______________________ 126 

B. Recovery of aluminum, titanium, zirconium, and phosphorus from the filtrate from iron sulphide______ 126 

C. Direct fusion of the oxides obtained under 8 with sodium

carbonate and borax____________________ 127 

D. Separation of aluminum, titanium, and zirconium from

iron in the ferrous state__________________ 128

a. By phenylhydrazine__________________ 128

b. By sodium acetate_____________________ 129

a. According to Dittrich and Freund_________ 129

/3. According to Barbier________________ 130

E. Separation of titanium and zirconium from aluminum

and iron ___________________________ 130 

a. According to Baskerville________:________ 130 

b. According to Dittrich and Freund___________ 131 

F. Separation of aluminum from iron, etc., by a fixed

, caustic alkali_________________________ 132 

"G. Separation of iron from aluminum, etc., as volatile

chloride ____________________________ 133 

H. Separation of iron from titanium by hydrogen peroxide__ 133

11. Manganese, nickel, cobalt, copper, and zinc___________ 134 

A. Difficulties in the way of a correct gravimetric determination of manganese__________ __-____ 134 

B. Precipitation of the group and separation of its constituents______________________________ 135 

a. The ammonium-sulphide method____________ 135 

a. Its advantages and disadvantages_________ 135 

/3. Precipitation by ammonium sulphide and separation of manganese and zinc from nickel, cobalt, 

and copper_____________________ 135 

b. Manganese and zinc_____________ __ 136 

c. Nickel, cobalt, and copper_______ _ __ 136
CONTENTS. 7

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued.

11. Manganese, nickel, cobalt, copper, and zinc Continued. Page. 

C. Colorimetric determination of manganese________L_ 137 

a. Preliminary treatment__________________ 137 

b. Colorirnetric determination of manganese by ammonium persulphate__________________ 137 

D. Direct titration of manganese________________ 139

12. Calcium and strontium (barium)______________ 140 

A. Separation from magnesium________________ 140 

a. General considerations __________________ 140 

b. Separation when neither calcium nor magnesium

preponderates excessively _______ ____ 141

c. Ignition of the calcium oxalate_____________ 142

d. Separation of little calcium from much magnesium_ 142

a. Preliminary remarks ________________ 142

/3. Modified Stolberg method_____________ 143

7. Murmann's method__________________ 143

8. Author's method ___________________ 143

e. Separation of little magnesium from much calcium__ 144

B. Separation of strontium (barium) from calcium.____ 144

a. By ether-alcohol_____________________ __ 144

b. Other methods______________________ 144 

C. Behavior of barium______________________. 145 

D. Separation of barium from strontium___________ 145 

E. Other methods of determining calcium after precipitation

as oxalate__________________________ 146

a. Preliminary remarks___________________ 146 

b. Volumetric method ____________________ 147 

c. By weighing as the carbonate. __ __ 147 

d. By weighing as the sulphate _____ __ 147

e. By weighing as the fluoride______________ 148

13. Magnesium__________________________ _ 148

A. Precipitation ___________________________ 148

a. Conditions necessary for the production of a normal

' precipitate ________________________ 148 

b. Precipitation and filtration________________ 149

a. First precipitation__________________ 149 

/3. Second precipitation_________________ 150 

B. Ignition of the precipitate__________________ 150 

C. Contamination by and removal of barium, calcium, and

manganese ___________________________ 152

a. Barium______________,_____________ 152 

b. Calcium _____________________________ 152 

a. Preferred method __________________ 152 

/3. Alternative method _________________ 152 

C. Manganese__1______________________ 153 

D. Liability to error in the average magnesium determination__________________:____________ 153

14. Titanium ________________________________ 154 

A. General considerations____________________ 154 

B. Colorimetric determination with hydrogen peroxide- _ 155 

a. Principle of the method (Welter's) and the conditions

that affect it______________________ 155
8 CONTENTS.

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued.

14. Titanium Continued.

B. Colorimetric determination with hydrogen peroxide Con. Page,

b. Preparation of the standard______________ 157

c. The test solution_______________________ 157

d. The color comparison___________________ 159

e. Correction for the color of ferric sulphate ____ 160 

o. By allowing for the coloring power of the iron in

the test solution__________________ 160

/3. By addition of iron to the standard________ 160

7. By the use of phosphoric acid_____ __ 161

f. Correction for the effect of alkali sulphates________ 161

g. Correction for the effect of vanadium_________ 162

C. Gravimetric methods_______________________ 162

a. Gooch's method_______________________ 162

a. Description of the method_________ _ 162 

p. Gooch's method not directly applicable to rocks

containing zirconium _______________ 163

b. Thornton's method _____________________ 164

a. Preliminary remarks _________________ 164

/3. Procedure______________________ 165

c. Baskerville's method______________ ____ 166

cl. Method of Dittrich and Freund_____________ 166

D. Volumetric methods_______________________ 166

a. General considerations___:_______________ 166

b. Methylene blue method_________________ 168

c. Ferric alum method______:_____________ 168

d. Permanganate method_____,____________ 169.

15. Barium (zirconium, rare earths, total sulphur, chromium)_ 170

A. The general method_______________________ 170

B. The method without regard to zirconium and sulphur_ 172

16. Zirconium ________________________________ 172

A. Author's method_______________________ 173

a. Preliminary remarks___________________ 173

b. Procedure ________________-______________ 173

- B. Other methods__________________________ 175

17. Rare-earth metals other than zirconium_____________ 176

A. Usual method __________________________ 176

B. Alternative method ______________________ 177

18. Phosphorus____________________,________________ 177

A. Preliminary remarks_________..__________ 177

B. Procedure when material is ample_____________ 178

a. Washington's method of preliminary treatment___ 178

b. Alternative method of preliminary treatment_____ 178

c. Subsequent treatment___________________ 178

C. Procedure when material is scanty_____________ 179

19. Chromium_______________________________ 180

A. Gravimetric methods _________________ _ 181

a. Author's method _______________________ 181

b. Jakob's method __________ _____ 181
CONTENTS. 9

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued.

19. Chromium Continued. Page.

B. Colorimetric method _______________________ 182 

a. Preparation and strength of standard solution___ 1S2 

p. Preparation of test solution_______________ 182 

7. Comparison of colors___________________ 183

C. Comparative data_ ______________ _____ 183

20. Vanadium (chromium) and molybdenum____________ 184

A. Distribution of vanadium and molybdenum________ 184

B. Condition of vanadium in rocks_______________ 184

C. Author's method___ __________ ___.__ 185

a. Description of the method____ ________ 185

b. Confirmatory qualitative tests_____ _____ 187 

c. Application of the method in presence of relatively

much chromium__________ _ ____ 187 

D. Colorimetric method for vanadium_____________ 189

21. Ferrous iron _____ _ _ _____ ____ 189

A. Oxidation of ferrous iron in minerals by grinding 

preparation of sample ____________________ 189

B. Comparison of sealed-tube and hydrofluoric acid methods comparative worthlessness of the former in rock 

analysis ____ ____ ______ 193 

C. The modified Mitscherlich method______________ 195 

a. Strength of acid___________________ 195 

/3. Filling, sealing, and heating of the tube_____ 195 

7. Reason for introducing gas and sealing as above

directed ______ _,.______ 196 

D. The hydrofluoric acid method_________________ 196 

a. Principle of the method_________________ 196 

b. Defects of the method__________________ 197 

a. Oxidizability of divalent manganese by permanganate in presence of hydrofluoric acid____ 197 

j3. Extreme oxidizability of divalent iron by free 

oxygen in the presence of hydrofluoric acid or a 

fluoride _ _____________________ 199 

c. Influence of sulphides, vanadium, and carbonaceous 

matter on the determination of ferrous iron by 

the hydrofluoric-acid method___________ 201 

a. Sulphides________________________ 201 

/3. Vanadium _________,______________ 202 

7. Carbonaceous matter_________________ 203 

d. The method in its various modifications________ 203 

a. According to Pratt (modified) _ ____ 203 

|3. According to Cooke__________________ 204

7. According to Barnebey________________ 205

8. According to Treadwell_______________ 207 

E. Uncertainties of the ferrous-iron determination_____ 207

22. Alkalies ________________________________ 207

A. The J. Lawrence Smith method_______________ 207

a. Its advantages _______________________ 207

b. Reagents and apparatus___________________ 208

c. Treatment of the mineral powder___________ 208
10 CONTENTS.

Silicate rock analysis Continued. . . 

II. Methods applicable to silicate rocks Continued.

22. Alkalies Continued.

A. The J. Lawrence Smith method Continued. Page,

d. Separation of calcium and sulphuric acid___'. _______ 210

e. Precipitation of potassium________________ 210

f. Sodium and lithium____________________ 211

a. Gooch's method for separating lithium______ 212

B. Preliminary treatment by other methods__________ 213

a. The mercuric oxide method_______________ 213

b. The ammonium carbonate method___________ 213

c. The amyl alcohol method________,________ 214

C. Direct separation of potassium by sodium cobaltinitrite_ 214

a. Preparation of the reagent_______________ 215

b. Application of the method________________ 215

a. Determination as chlorplatinate__________ 216

p. Determination as perchlorate___________ 216

23. Carbon dioxide, carbon_______________________ 217

A. Qualitative test for carbon dioxide_____________ 217

B. Quantitative test for carbon dioxide____________ 217

C. Carbon _____________________________ 219

24. Chlorine__________________________________ 220

A. Condition in rocks_____ ____ ______ 220

B. Determination of water-soluble chlorine__________ 220

C. Determination of acid-soluble chlorine___________ 221

a. By nitric acid________________________ 221

b. By nitric and hydrofluoric acids_____________ 221

D. Determination of chlorine by alkali fusion_______ 221

25. Fluorine (silica in presence of fluorine)____________ 222

A. General remarks________________________ 222

B. Direct quantitative determination of fluorine_______ 222

a. Method of Berzelius___________________ 222

a. Procedure_______________________ 222

j8. Testing of the calcium fluoride__________ 224

7. Accuracy of the method_______________ 225

b. Determination of silica in the method of Berzelius___ 226

c. Other direct methods for fluorine___________ 226

C. Indirect quantitative determination of fluorine_______ 227

a: Steiger's method _____________________ 227

b. Merwin's modification of Steiger's method______' 227

a. Introductory remarks _______________ 227

/5. Procedure _______________________ 228

26. Sulphur ________________________________ 230

A. Determination of the condition of sulphur in rocks___ 230

B. Quantitative method general discussion_________ 230

C. Quantitative determination in rocks____________ 231

a. Total sulphur________________________ 231

b. Fractional determination________________ 233

27. Boron_________________________________ 234

A. General remarks________________________ 234

B. Distillation method as modified by Chapin_________ 235

a. Reagents ______________:_________ 235

b. Apparatus__________________________ 236

c. Procedure___________________________ 236

C. Qualitative tests for boron______ ___ 240
CONTENTS. 11

Silicate rock analysis Continued.

II. Methods applicable to silicate rocks Continued. Page.

28. Certain constituents in minute traces______________ 241

29. The gases and vapors expelled by heat_____________ 242

30. Special operations___ ___________________ 243 

A. Detection of nepheline in presence of olivine________ 243 

B. Determination of " soluble " silica _____________ 244

Carbonate rock analysis______________________________ 246

III. Introduction _________________________________ 240

31. Qualitative comparison of carbonate and silicate rocks___ 246

32. Mineral composition of carbonate rocks_____________ 248

33. Behavior toward different reagents as a means of distinguishing different carbonates____________________ 251 

A. Differing solubility in tartaric and citric acids and in

acid potassium sulphate__________1_______ 251 

B. Distinguishing calcite from aragonite___________ 251 

C. Distinguishing between calcite a'nd dolomite_______ 251

IV. Refined methods of analysis______________________ 253

34. Silica, its separation from alumina, etc_____________ 253 

A. Methods of decomposing the rock_____________ 253 

a. When the inorganic residue is to be separately

analyzed ______________:_______v 253 

b. When the inorganic residue is not to be separately

analyzed _____________ _____ 254 

a. By solution in acid after strong ignition_____ 254 

/3. By solution in acid after heating with sodium

carbonate _____________ ____ 255 

B. Separation of silica_______________ _____ 256

35. Aluminum, total iron, titanium (silica, manganese) ; precipitation in company with phosphorus..___ 257 

A. Precipitation of aluminum, iron, etc__:_________ 257 

a. Collective precipitation of aluminum, iron, manganese, titanium, and phosphorus by ammonium sulphide ____________________________ 257 

b. Precipitation of aluminum, iron, titanium, and phosphorus by ammonia__________ _____ > 258 

c. Precipitation of aluminum, iron, titanium, and phosphorus by the basic-acetate method_ ___ - 258 

B. Treatment of the filtrates from alumina, etc_______ 259 

C. Solution and separation of the oxides obtained in A and B_ 259 

a. Silica (barium)______________________ 259 

b. Iron_______________________________ 260 

c. Titanium ____________________________ 260 

d. Aluminum__________________ __ 260

36. Manganese__^___________________ 260 

A. In the filtrates from 350 B__________________ 260 

B. Separate determination of manganese________ 261

37. Copper, nickel, cobalt, lead, zinc, rare earths, chromium, vanadium, molybdenum____ ___ 261

38. Calcium, strontium, barium, magnesium (manganese) 262 

A. Ordinary procedures 262 

B. Separation of little calcium from much magnesium magnesite analysis ___ 263
12 CONTENTS.

Carbonate rock analysis Continued.

IV. Refined methods of analysis Continued. Page.

39. Phosphorus _______________________________ 263

40. Ferrous iron_____________________________ 264

A. In the absence of carbonaceous matter__________ 264

a. Ferrous iron soluble in sulphuric acid_________ 264

b. Ferrous iron in the insoluble residue__________ 265

c. Total ferrous iron_____________________ 265

B. In the presence of carbonaceous matter___________ 265

41. Alkalies __i______________________________ 265

42. Carbon dioxide, carbon (water)__________________ 266

A. Determination of carbon dioxide______________ _ 266

B. Determination of carbon of carbonaceous matter____ 266

C. Simultaneous determination of water and of total carbon_ 267

43. Chlorine_____________________________r_______ 267

44. Fluorine__________________________________ 268

45. Sulphur __,_____'_______________________'. _____ 268 

A. Tests as to its condition; determination of sulphate

sulphur ______________________________ .268

B. Determination of total sulphur________________ 268

a. Methods of converting sulphides to sulphates___.._ 268

'a. By ignition without flux_______________ 268

j8. By ignition with sodium carbonate._________ 269

b. Treatment after ignition_________________ 269

46. Water_______________________________^_ 269

A. Hygroscopic water_________________________ 269

B. Firmly held water________________________ 270

V. Condensed analysis___________________________: 271

47. Decomposition and solution ___________________ 271

48. Silica __._______________________________ . 271

49. Aluminum, iron, etc _________________________ 272

50. Calcium _________________________________ 273

51. Magnesium ______________________________ 273

52. Alkalies ________________1_______________ 274

53. Carbon dioxide _ __________________ 274

54. Sulphur __________________________________ 274

55. Water_________________________________ 274

56. Ignition loss ______ __________________ 274

Index_________________________________________ 275
ILLUSTRATIONS.

^ Page. 

FIGURE 1. Platinum-tipped crucible tongs__________________ 32

2. Radiator for rapid and safe evaporation____________ 33

3. Device for excluding flame gases from the interior of crucibles

during ignition___________________________ 34

4. Weighing trough of platinum_____________________ . 35

5. First Survey form of apparatus for colorimetric determinations___________________-__________ __ 36

6. Steiger's colorimeter (second Survey form) __ 38

7. Schreiner's colorimeter _______________________ 40

8. Moore's device to remove air from mineral powders______ 56

9. Ellis's mortar for crushing coarse materials_ __ ___ 58

10. McKenna ore grinder________________________ 62

11. Peufield's tubes for water determination in minerals.. ___ 78

12. Peufield's fire-brick and charcoal oven for use in determining

water____________ _ __ _ __ 79

13. Steiger's form of drying apparatus____________.___ 8,1

14. Chatard's form of drying oven for water determinations___ 82

15. Tube for water determination according to Penfield______ 83

16. Modified form of Gooch tubulated platinum crucible for the

determination of water______________________ 85

17. Arrangement, during drying, of Gooch apparatus for determining water___ ___ _ 87

18. Arrangement, during fusion, of Gooch apparatus for determining water______________________________ 88

19. Cooke's apparatus for ferrous-iron determination_______ 205

20. The J. Lawrence Smith crucible for alkali determinations__ 209

21. Compact form of apparatus for determination of carbon dioxide____________________________________ 218

22. Merwin's diagram for fluorine_____ ___ _ ___ 229

23. Distilling apparatus for boron_____________J_______ 237

13

THE ANALYSIS OF SILICATE AND CARBONATE

ROCKS.

By W. F. HlLLEBRAND.

INTRODUCTION. 

OBJECT AND SCOPE OF THE PRESENT TREATISE.

Prior to the publication of Bulletin 148 of the United States Geological Survey the literature relating ta the analysis of silicates, 

though extensive, was so widely scattered that in no single work 

was there to be found, in the light of modern methods, a satisfactory 

exposition of the procedures to be followed or the precautions to be 

observed, especially in the search for some of the rarer constituents 

or those which, without being rare, had come to be recognized as 

occurring persistently in small amounts. It was not the intention to 

make the chapter on rock analysis in Bulletin 148 a manual on mineral or even rock analysis, but to show primarily the principles and 

methods by which the major part of the analyses made up to that 

time in the laboratory of the Geological Survey had been conducted, 

and thus to afford a partial measure of the trustworthiness of those 

analyses. At the time it was felt that the experience gained by the 

chemists of the Survey since the establishment of its first chemical 

laboratory in Denver might be useful to most chemists engaged in 

mineral and rock analysis. The favorable reception accorded to it 

by chemists led to the republication of a portion of that bulletin in 

more extended form as Bulletin 176, and since then other enlarged 

revisions have appeared under the numbers 305 and 422. Bulletins 

148 and 176 treated only of the analysis of silicate rocks. In Bulletin 

305 there was added a section on carbonate rocks, for the reasons 

that the chief carbonate rocks form a most important element in the 

 earth's crust and that the knowledge of their composition is of 

moment to the geologist as well as to the cement worker, who now 

makes enormous use of them. The methods applied to their analysis 

differ in but unimportant respects from those used with the more 

siliceous rocks, for they are to a great extent themselves siliceous 

and contain essentially the same constituents, and therefore the same 

principles apply to both. Naturally they demand and receive briefer 

treatment.

A5
16 ANALYSIS OF SILICATE AND CARBONATE RQCKS.

The special problems often arising in the analysis of rocks of 

extraterrestrial origin the more or less stony meteorites will not 

be considered here. An analysis of those objects should never be 

intrusted to the novice but only to the chemist who has a knowledge 

of the comparison and properties of their peculiar mineral constituents and a judgment fit to cope with the difficult problems they 

present.

A suggestion was made to the author that the analysis of artificial 

glasses and of glazes, and possibly of other industrial silicate products, be covered in this.volume. To do so, however, would involve 

increasing the size of the volume materially, in order to take accqunt 

of the considerable number of elements occurring in such products 

that are not rock constituents in more than minute traces. Moreover, the elaborate treatise of J. W. Mellor* is available.

The third edition of Dr. H. S. Washington's "Manual of the 

chemical analysis of rocks," appeared just as the manuscript of this 

volume was completed too late for me to benefit largely by the extended revision of the earlier texts.

I regret that no reference could be made in the text to electrometric methods for determining iron in both the ferrous and ferric 

states. The subject has been well treated by J. C. Hostetter and 

H. S. Roberts in a recent paper.2 In a companion paper H. S. 

Roberts 3 describes the apparatus needed in applying the method. 

I can only urge upon all mineral analysts to consult both papers. 

High and low percentages of iron can be determined quickly, with 

high accuracy, and with fewer precautions than by the older methods, 

not only in sulphuric acid solution but also in hydrochloric or hydrofluoric acid as well as in mixtures of these acids.

The methods described in the later bulletins mentioned were not 

restricted to those actually in use at the Geological Survey, and a 

still further departure in this direction has been made in the present 

treatise. Many new methods and modifications of methods have been 

published in the last 10 years. Some of these may certainly be 

applied satisfactorily in rock analysis, and others seem promising. 

The most promising of the latter group have been described in the 

text in order to stimulate analysts to try them out, for it is well to 

have more than one good method for reaching a desired end. Another reason for presenting some simpler though perhaps less reliable 

methods is that a few of those preferred entail the use of expensive 

apparatus or complicated arrangements which are not at the com1 A treatise on quantitative inorganic analysis, being vol. 1 of A treatise on the 

ceramic industries, London, Griffin & Co., 1913. Among other publications on the subject of glass analysis a paper by E. C. Sullivan and W. C. Taylor (Jour. Ind. Eng. 

Chemistry, vol. 6, 1914, p. 897) deserves mention.

" Jour. Am. Chem. Soc., vol. 41, 1919, p. 1337.

8 Idem, p. 1358.
INTRODUCTION. 17

mand of all analysts. However, where silicate and limestone analyses 

are made in number it is a saving of time and, in the end, of money 

to set up permanent and even expensive arrangements for convenience in determining such constituents as water, carbon dioxide, ferrous iron, and boron, and in making reductions by hydrogen.

My transfer in 1908 from the Geological Survey to the Bureau of 

Standards has made it impossible for me to keep closely in touch 

with changes that may have been made in the analytical procedures 

and methods of the laboratory staff of the Survey. This statement 

is made in order to prevent possible misconception. The present 

work is to be considered as a general treatise on rock analysis, based 

on my own views and experience, often supported by those of others, 

rather than as an authoritative presentation of methods now practiced or approved by the present Survey staff.

Compared with its predecessor this bulletin shows many changes 

and additions, with some omissions. To enumerate them all is needless. A few, however, may be mentioned.

Additions have been made to the section on chemical reagents, 

especially by including information on porcelain, glass, and platinum ware and substitutes for platinum ware. The greater part of 

the chapter on the role of hydrogen in minerals has been rewritten 

for me in the light of modern views by Dr. E. T. Wherry, of the 

Department of Agriculture; Dr. H. E. Merwin, of the Geophysical 

Laboratory of the Carnegie Institution; and Mr. Elliot Q. Adams, of 

the Department of Agriculture.

Sections 8 to 14, in Part II, have undergone much modification, 

with the introduction of descriptions of new methods for the determination of individual constituents and for the fractional separation 

of complex precipitates, preliminary to the determination of the components of the less complex fractions. Two new sections have been 

introduced here in amplification of the matter that was previously 

presented in section 8. A detailed procedure for determining boron 

is given, in order to stimulate search for this very minor and hitherto 

entirely neglected element.

ACKNOWLEDGMENTS.

Drs. E. T. Wherry and H. E. Merwin and Mr. Elliot Q. Adams 

very kindly revised the chapter on the role of hydrogen in minerals, 

and Drs. Wherry and Merwin gave friendly advice on other points. 

My associate, Dr. G. E. F. Lundell, of the Bureau of Standards, 

rendered most valuable aid by his criticisms of the preliminary text 

and by tests of methods. Mr. H. B. Knowles, of the Bureau of 

Standards, was helpful in the experimental testing of certain methods. 

To all these gentlemen my thanks are gratefully tendered. 

131999° 19 2
SILICATE EOCK ANALYSIS.

I. INTRODUCTION. 

1. IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES.

The composition of the ultimate ingredients of the earth's crust 

the different mineral species which are there found and of many of 

which its rocks are made up was the favorite theme of the great 

workers in chemistry of the earlier half of the nineteenth century, and 

for the painstaking care and accuracy of Berzelius, Wohler, and 

others the mineralogists and geologists of to-day have reason to be 

thankful. Considering the limited facilities at their disposal in the 

way of laboratory equipment and quality of reagents, the general 

excellence of their work is little short of marvelous. As an outgrowth 

of and closely associated with the analysis of minerals came that of 

the more or less complex mixtures of them the rocks: to aid whose 

study by the petrographer and geologist a host of chemists have for 

many decades annually turned out hundreds of analyses of all grades 

of quality and completeness. With the growth and extraordinary 

development of the so-called organic chemistry inorganic chemistry 

gradually fell into a sort of disfavor. In many, even the best, European laboratories the course in mineral analysis, while maintained as 

a part of the curriculum of study, became but a prelude to the everexpanding study of the carbon compounds, which, multiplying 

rapidly and offering an easy and convenient field for original research and possible profit, proved more tempting to young chemists 

than the often worked-over and apparently exhausted inorganic field. 

For one student devoting his time to higher research in inorganic 

chemistry fifty perhaps were engaged in erecting the present enormous structure of carbon chemistry. The instruction afforded to the 

student in mineral analysis was confined to the ordinary separations 

of the commoner ingredients occurring in appreciable quantities, 

with little regard to supposed traces and with still less attempt to 

find out if the tabulated list really comprised all that the mineral or 

rock contained.

With the introduction of improved methods of examination by 

the petrographer, especially as applied to thin rock sections, and 

-the use of heavy solutions, whereby, on the one hand, the qualitative mineral composition of a rock could be preliminarily ascertained with considerable certainty, and on the other hand chemical 

examination of the more or less perfectly separated ingredients 

was rendered possible, a great help and incentive was afforded to 

the few chemists engaged in rock analysis. The microscope often 

18
IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES. 19

obviated in part the necessity for tedious and time-wasting qualitative tests, and the heavy solutions, by permitting the concentration 

and separation of certain components, facilitated the detection of 

elements whose existence had long been overlooked.

Meanwhile, in the progress of chemistry new methods and reagents 

for qualitative detection and quantitative separation and estimation 

were gradually being devised and discovered. The belief that some 

well-established methods were adequate was shown to be unwarranted; some had to be discarded altogether; others were still 

utilizable after modification. In the light thus shed it became 

possible to explain many hitherto incomprehensible variations in 

the composition of some rock species or types, as shown in earlier 

analyses, and in not a few cases it appeared that the failure to report 

the presence of one or more elements had obscured relations and differences which more thorough examination showed to exist. (See 

p. 21.) Consequently there arose a feeling of distrust of much 

of the older work in the minds of those chemists and petrographers 

wh6 were best fitted to judge of its probable qualities. This, and 

the incompleteness of nearly all the earlier work (and some of that 

of to-day, unfortunately), as shown by the largely increased list 

of those elements now known to enter into the normal composition 

of rocks, are rendering the old material less and less available to 

meet the increasing demands of the petrographer.1

And yet these demands were, with few exceptions, by no means 

so exacting as they should have been. Frequently the analysis was 

intrusted to a student without other experience than that gained by 

the analysis of two or three artificial salts and as many comparatively simple natural minerals, and with a laboratory instructor as 

adviser whose experience in rock analysis might be little superior to 

his own. In other words, one of the most difficult tasks in practical 

analysis was given to a tyro, and his results were complacently 

accepted and were published broadcast without question. Even to 

those who are thoroughly familiar with the subject rock analysis is a 

complex and often a trying problem. Although long practice may 

have enabled one to do certain parts of the work almost mechanically, 

perplexing questions still arise which require trained judgment to 

meet and answer properly, and there is yet room for important work 

in some of the supposedly simplest quantitative determinations. If

*Dr. Henry S. Washington, in Professional Papers 9£ (Chemical analyses of igneous 

rocks published from 1884 to 1913, with a critical discussion of the character and use 

of analyses) and 28 (The superior analyses of igneous rocks from Roth's Tabellen, 1869 

to 1884, arranged according to the quantitative system of classification) of the United 

States Geological Surrey, has done a most important work in sifting the great mass of 

data accumulated in the thousands of analyses published since 1869. After a systematic 

critical examination he has assigned to each analysis a certain value on a scale of 5. 

Many of these values may be incorrect, but most of them undoubtedly give a fairly true 

measure of the weight to be attached to the respective analyses.
20 . ANALYSIS OF SILICATE AND CARBONATE BOCKS.

the results are to have any decided value for purposes of scientific 

interpretation and comparison, they must be the outcome of the work 

of one who is able to find his way through the intricacies of an 

analysis in which from 15 to 25 components are to be separated and 

estimated with close approach to accuracy,, and this a beginner can 

not hope to do. The conscientious chemist should have a live 

interest in this matter. He should work with a twofold purpose in 

view that of lightening the labors of those who come after him by 

enabling them to use his work with less supplementary examination, 

and that of enhancing his own reputation by meriting encomiums on 

work that has stood the test of time.

How little understood may be the principles underlying the treatment of bodies so complex and the accurate separation and determination of their constituents, even when these are comparatively 

few, has been strikingly shown during recent years in the work of 

several committees of chemists charged with the investigation of the 

methods employed in various branches of technical chemistry involving the analysis or assay of zinc ores, slags from the smelting of 

copper ores, argillaceous limestones, and cements. In all cases a 

most woeful inability to obtain accordant results is apparent, not 

only among those less experienced but among those supposed to be 

most expert in each of the particular fields as well. Some improvement in commercial silicate analysis has resulted from the investigations set on foot and the recommendations mad© by these committees, and further improvement may be expected, but the situation is 

yet anything but satisfactory. A more marked improvement has 

been shown in the quality of analyses made for scientific study, but 

the art of analysis stands in great need of more thorough treatment 

in our educational institutions.

The petrographer, again, should seek to have his analyses made as 

complete as possible, and not, as was often the case, be content with 

determinations of silica, alumina, the oxides of iron, lime, magnesia, 

the alkalies, and water. The latter course, it is true, is entirely justifiable at times and may serve the immediate purposes of the 

analyses, but their incompleteness may, on the other hand, not only 

conceal points fruitful of suggestion to the attentive mind, but, what 

is of still greater importance, they may be actually misleading. 

Enough instances of totally inaccurate conclusions to be drawn from 

them have fallen under my own observation to fully justify this plea 

in favor of greater completeness in rock and mineral analysis made 

for purely scientific purposes.1

The importance of the points indicated in the foregoing paragraph 

is shown by the difference between the analyses given below. The

1 For further presentation of this subject from the viewpoint of an experienced petrographer, see Washington, H. S., Manual of the chemical analysis of rocks, 1919, pp. 7-1.7.
IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES.

specimens were taken and analyzed at widely separated times and by 

different persons, it is true, but they were unquestionably from the 

same rock mass, in which, however much the relative proportions of 

the different mineral constituents might vary within certain limits, 

there can be no reason to doubt the general distribution of all the 

elements shown by the second analysis.

Analyses of specimens taken from the same rock mass at different dates.

SiOa.. ........................

Ti02 . .........................

AUOs. ........................

Cr203 .........................

Fe203 . ........................

FeO. .........................

MnO..........................

CaO..... ......................

SrO...........................

BaO. .........................

MgO.. ........................

K20.. ........................

Na2 0.. .......................

Earlier 

analysis.

54.42

13.37

b. 61

&3.S2

4.38

6.37

10.73

1.60

Later 

analysis, a

53.70

1.02

11.16

.04

3.10

1.21

.04

3.46

10

.62

6.44

11.16

1.67

Li20. .........................

COj.. .........................

PjOs. ............... ..........

S03 .. .........................

F... ...........................

Cl... ..........................

Farlicr 

analysis.

Trace.

c2.76

1.82

99.58

Later 

analysis, a

o on

2.61

1.75

.06

.44

.03

100.40

.19

100.21

a A still more recent analysis of another of the series of rocks of which this is an example has shown that 

this "later analysis" is itself probably incomplete and incorrect in part incomplete because of the probable presence of 0.2 per cent or more of Zr02, incorrect because of the error in AljOs, resulting from having 

counted the ZrOa as Alj08, and from the fact that titanium is not fully precipitable in presence of zirconium by Gooch's method (the one employed). This latter error involves both the TiOs and the AljOs. 

(See 14. C. a. 0, p. 163.)

6 From the fact that repeated determinations of the iron oxides in this and related rocks from the same 

region show always a great preponderance of ferric oxide, it is not improbable that the figures given for 

the two oxides in the first analysis were accidentally transposed.

c In the published analysis it does not appear whether this is total water or, as seems probable, only 

that remaining above 100°.

Another instance of similar kind is given below. Here, again, certain differences are explainable by natural variations in the proportions of the constituent minerals, but it can hardly be doubted that 

Ti02 , BaO, SrO, P2 06 , and SO8 were present in both specimens in 

approximately the same amounts. In the earlier analysis determinations of some supposedly unimportant constituents were purposely 

omitted or made only qualitatively, with results that can not be 

otherwise than fatal to a full comprehension of the mineralogic 

nature of the rock.

Analyses of specimens taken from the same rock mass at different dates.

SiOa .. ........................

Ti02 . .........................

A12 03 . ........................

Fea08 . ........................

FeO..........................

MnO..........................

CaO..........................

SrO...........................

BaO..........................

MgO..........................

KaO.. ........................

Earlier 

analysis.

44.31

"Wnt flct

17.20

4.64

3.73

.10

10.40

fi 17

3.64

Later 

analysis.

44.65

.95

13.87

6.06

2.94

.17

9 <;7

o.37

.76

5.15

4.49

Na2 0. ........................

co2 . ..........................

PjOs. ......................... ci.............................

S08 . ..........................

Earlier 

analysis.

4.45

.77

3.30

99.11

Later 

analysis.

5.67

Trace.

.95

2.10

.11

1.50

Trace.

.61

99.92

a Not entirely free from CaO.
22 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

F. W. Clarke has shown that the combined percentages of titanio 

and phosphoric oxides in rocks of the earth's crust, averaged from 

hundreds of analyses, amount to 0.8 per cent. When the determination of these is neglected the error falls on the alumina. If the 

alumina is then used as a basis for calculating the feldspars, it is easy 

to see that a very large average error in the latter may result, amounting to several per cent of the rock.

In order to emphasize more strongly the importance of completeness in analysis, a few facts brought out by the hundreds of rock 

analyses made in this laboratory may be cited. It has been demonstrated most conclusively that barium and strontium are almost 

never-failing constituents of the igneous rocks of the United States 

and of many of their derivatives. The amounts are usually below 0.1 

per cent for each of the oxides of those metals, but higher amounts 

are by no means uncommon. Furthermore, the weight of barium is 

almost without exception in excess of that of strontium; but a still 

more important point is that the igneous rocks of the Rocky Mountain 

region, so far as examined, show much higher average percentages 

of both metals than the rocks from the eastern and the more western 

portions of the United States. The following examples serve to illustrate certain types of Rocky Mountain igneous rocks: Of seven rocks 

forming a Colorado series, six held from 0.13 to 0.18 per cent of BaO, 

while in the seventh the percentage was 0.43. The SrO ranged from' 

0.07 to 0.13 per cent for six and was 0.28 for that one highest in BaO. 

Of thirteen geologically related rocks from Montana, embracing basic 

as well as acidic and intermediate types, the range of BaO was from 

0.19 to 0.37 per cent, with an average of 0.30 per cent. Three others 

of the same series contained 0.10 per cent or less, while the seventeenth 

carried 0.76 per cent BaO. The SrO ranged from 0.37 per cent in the 

seventeenth rock to an average of 0.06 for the other sixteen. Certain 

peculiar rocks from Wyoming carry from 0.62 to 1.25 per cent BaO 

and from 0.02 to 0.33 per cent SrO. Surely this concentration of 

certain 'chemical elements in certain geographic zones has a significance which future geologists will be able to interpret, if those of today are not.

Again, vanadium is an element which few chemists ever thought 

of looking for in igneous rocks, though it has long been known to 

occur in magnetites and other iron ores. A. A. Hayes, in 1875, 

reported its occurrence in a great variety of rocks and ores. To 

quote from Thorpe's " Dictionary of chemistry:" " It is said to 

be diffused with titanium through all primitive granite rocks 

(Dieulafait) and has been found by Deville in bauxite, rutile, and 

many other minerals and by Bechi and others in the ashes of plants 

and in argillaceous limestones, schists, and sands." It is further 

reported to comprise, as the pentoxide, up to 0.1 per cent of many
IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES. 23

French and Australian x clays, 0.02 to 0.03 per cent of some basalts, 

0.24 per cent of a coal of unknown origin, and 0.45 per cent of a 

coal from Peru. Still later examinations in this laboratory of about 

100 rocks, chiefly igneous, covering nearly the whole continental 

territory of the United States, show not only its general qualitative 

and quantitative distribution, but that it predominates in the less 

siliceous igneous rocks and is absent, or nearly so, in those high in 

silica. In some of the more basic rocks it occurs in sufficient amount 

to affect seriously the figures for the oxides of iron unless separately estimated and allowed for (see 21. D. c. (3, p. 202), a matter of 

considerable importance, because the petrographer lays great stress 

on accuracy in their determinations.

The same investigation also threw some light on the distribution 

of molybdenum, which seems to be confined to the more siliceous 

rocks and to occur in quantities far below those commonly found 

for vanadium.

Finally, had it not been my practice during all the later years 

of my work to look for sulphur in rocks, even when no sulphides 

were visible to the eye, its almost invariable presence in the form 

of sulphide and consequent connection with the long mystifying 

lack of agreement between results for ferrous iron obtained by the 

Mitscherlich and the hydrofluoric-acid methods might not have 

been suspected. (See 21. B, p. 193.)

While strongly upholding the necessity for more thorough work, 

necessarily somewhat at the expense of quantity, it is far from my 

intention to demand that an amount of time altogether disproportionate to the immediate objects to be sought should be expended on 

every analysis. But I maintain that, in general, the constituents 

which are likely to be present in sufficient amount to admit of determination in the weight of a sample usually taken for analysis 

say 1 gram for Si02 , AI2O3 , etc., to 2 grams for certain other constituents should be sought for, qualitatively at least, in the ordinary course of quantitative work, and their presence or absence noted 

among the results. If present in little more than traces, that knowledge alone may suffice, for it is often more important to know whether 

or not an element is present than to be able to say that it is there in 

amount of exactly 0.02 or 0.06 per cent. In the tabulation of analyses a special note should be made in case of intentional or accidental 

neglect to look for substances which it is known are likely to be 

present. Failure to do this may subject the analyst to unfavorable 

criticism when, at some future time, his work is reviewed and the 

omissions are discovered by new analyses.

1 J. C. H. Mingaye has confirmed its wide distribution in Australian rocks, coals, etc. 

(Records Geol. Survey New South Wales, vol. 7, pt. 3, 1903, p. 213).
24 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

Finally, whenever possible, a thorough microscopic examination of 

the rock in thin section should precede the chemical analysis. This 

may be of the greatest aid to the chemist in indicating the presence of 

unusual constituents or of more than customary amounts of certain 

constituents, whereby, possibly, necessary modifications in the analytical procedure may be employed without waste of time or labor.1

If the point is raised that many of the published analyses emanating from the Survey laboratories, even my own earlier ones, are not 

in accord with the advocacy of completeness contained in the foregoing pages, it may be remarked that these ideas were to a considerable degree evolved during a personal experience of over 25 years 

in this kind of work, and that frequently the exigencies were such 

as to compel restriction in the examination. Where this was necessar}7", subsequent development in some cases showed it to be bad 

policy in every respect. It is better, for both the geologist and the 

chemist, to turn out a moderate amount of thorough work than a 

great deal of what may ultimately prove to be of more than doubtful 

utility.

2. THE CONSTITUENTS OCCURRING IN SILICATE ROCKS.

It is to the decomposition of the original igneous rocks or their 

magmas and their derivatives that nearly all ore bodies in the 

United States owe their origin by one or another process of concentration. A certain class of concentrates probably separated from 

magmas in the fluid state before solidification. Hence it is the 

natural and inevitable inference that sufficiently careful examination of these rocks would show them to contain all or nearly all 

the known elements, not necessarily all in a given rock, but many 

more than anyone has yet found.2 Mechanical and analytical difficulties have thus, far stood in the way of experimental proof that 

this is so, owing to the great scarcity of many of the elements. 

In exceptional cases it may be desirable to subject a given material 

to very exhaustive analysis, as, for instance, when searching for the 

origin of ore deposits. Ordinarily, however, the demands of the 

petrographer and geologist are satisfied with a knowledge of the 

quantitative relations of those constituents which can be determined

1 See also Washington, H. S., Chemical analysis of rocks, 1919, pp. 6-7. The foregoing 

tables and accompanying remarks, including several sentences preceding the tables, have 

been largely taken from my paper entitled, A plea for greater completeness in chemical 

rock analysis: Jour. Am. Chem. Soc., vol. 16, 1894, pp. 90-93; Chem. News, vol. 69, 1894, 

p. 163. See also Distribution and quantitative occurrence of vanadium and molybdenum 

in rocks of the United States: Am. Jour. Sci., 4th ser., vol. 6, 1898, p. 209; Chem. News, 

vol. 78, 1898, p. 216; and Bull. U. S. Geol. Survey No. 167, 1900, p. 49.

2 F. Sandberger's researches showed to what extent this is true of a large number of 

those elements contributing to the filling of metalliferous veins, and L. Dieulafait by his 

elaborate qualitative researches showed how universal was the distribution of copper, 

zinc, barium, strontium, etc., in the primordial rocks.
MINOR CONSTITUENTS. 25

in a limited amount of the sample say, from 0.5 gram to 2 or 

occasionally 5 grams. In general the discussion relating to silicate 

analysis in this volume will be confined to such separations as may 

be required in the analysis of an igneous, metamorphic, or sedimentary rock of complex mineralogical composition, in which the 

majority and possibly all of the ingredients in the list given below 

may occur in weighable or readily discoverable quantities:

SiO2 , TiO2 , Zr02 , A12 03 , Fe2 03 , Cr2 03 , V2 03 , FeO, MnO, NiO, 

CoO, MgO, CaO, SrO, BaO, ZnO, CuO, K2 0, Na2 0, Li2 0, H2 0, 

PaO« S,1 S03 , C,« C02 , F, Cl, N.

To the above list might be added'certain others, as the group of 

so-called rare earths, besides tin, platinum, tantalum, columbium, 

boron, glucinum,3 helium. Some of these occur at times in determinable amounts, though in my experience tantalum, columbium, and 

glucinum have not been met with. They may very well have been 

OArerlooked by reason of the absence of distinctive tests for identification. Thorium, cerium, and other rare earths are probably more 

common as constituents of silicate rocks than has been generally supposed. Their presence and amount can be so readily and certainly 

detected by the methods given in their proper place that the reason 

for neglecting to look for them is no longer so strong as it used to be, 

especially when there is microscopic or other evidence of the presence 

of minerals likely to contain them.

3. THE DISTRIBUTION AND OCCURRENCE OF CERTAIN MINOR CONSTITUENTS.

For the suggestion of this section and for much of its contents I 

am in no small degree indebted to Washington's book (Manual of 

the chemical analysis of rocks, 1919, pp. 17-21).

Washington says:

The increased number of analyses of igneous rocks, especially of those of 

unusual types, and the more frequent determination of the minor constituents, 

with the vast mass of data obtained by the use of the microscope, have shown 

that certain of the rarer elements are prone to occur in rocks of certain chemical characters. While our knowledge along this line is far from complete, a 

few words may be devoted to this subject, as it will often be of use to the 

analyst to know which elements should be especially looked for and which may 

safely be neglected.

Titanium. Not long ago held to be rare, titanium is now recognized to be one of the most universally distributed elements and 

about tenth in actual abundance in the explored crust of the earth. 

So far as my experience goes, it is entirely absent from no igneous,

1 Usually as pyrite, occasionally as lazurite, not Infrequently as pyrrhotite.

2 As graphite or coaly matter.

3 For probably the best method of separating even very small amounts of nlucinnm from 

iron and aluminum see Parsons, C. L., Jour. Am. Chem. Soc., vol. 28, 1906, p. 1589 ; Chem. 

News, vol. 9f>, 1907, p. 188.
26 - ANALYSIS OF SILICATE AND CARBONATE BOCKS.

metamorphic, or sedimentary rock of a more or less siliceous character. The recognition of this fact has been rendered possible and 

easy by its characteristic behavior, when in solution, toward hydrogen peroxide. Though seemingly present even in most siliceous 

rocks, it is most abundant in the so-called basic rocks. Its chief mineral occurrences are as rutile, octahedrite or anatase, ilmenite, titanite, 

and perof skite, but it is also a component in smaller amounts of many 

pyroxenes, hornblendes, biotites, garnets, and other ferromagnesian 

minerals, and is found in some magnetite and hematite. Owing to 

the refractory nature of some of its compounds it tends to concentrate in the residual products of decomposition of many rocks; hence 

its high percentage in clays as a class. It is very unusual to find 

titanium present in amounts that can properly be designated only as 

traces. In the great majority of cases its amount will not exceed 1 

per cent, but it may rise to over 5 per cent.

Zirconium,. The chemically related element zirconium is likewise 

now known to be more widely distributed than was formerly supposed, but it is much less common than titanium, rarely making ujy 

0.2 per cent of a rock and being usually under 0.05 per cent.

Zirconium * * * is apt to occur in granites, pegmatites, rhyolites, 

syenites, and in nephelite syenites, phonolites, and tinguaites. It is most 

abundant in rocks which are high in soda, such as the last three. It is rarely 

met with in rocks rich in lime, magnesia, and iron. Zirconium is usually found 

as the silicate zircon, especially in granites and syenites, but is also an ingredient of such rare minerals as eudialyte, lavenite, and rosenbuschite.

Rare earths. The rare earths * * * are found, so far as known, in 

notable amount only in rocks that are high in soda. They form part of allanite, 

a mineral that is rather widespread in granites, and also of monazite, mosandrite, xenotime, and other minerals of even greater rarity. They are almost 

always accompanied by notable amounts of zirconia. The rare earths, reckoned 

as (Ce, Y)2O8, seldom are present in more than one-tenth of 1 per cent, but two 

rocks are known in which they are present to the extent of 0.4 and 0.6 per cent. 

Scandium has been shown to be widespread in traces.

Chromium. Chromium is almost wholly confined to the femic [ferromagnesian] rocks, especially those which are high in magnesia and low in silica, 

and consequently contain abundant olivine, such as peridotite and dunite. It 

occurs as chromite and picotite (chrome-spinel) and in some augites, biotites, 

and oliyines. It may occur up to one-half of 1 per cent of Cr30s.

Vanadium. The distribution of vanadium has been covered in 

part by the remarks on pages 22-23. To leave out of account the 

well-characterized mineral vanadates, its most stable and normal 

form in the silicates seems to be that of trivalency, corresponding 

to the oxide V2O8 , in which form it replaces alumina and possibly 

ferric oxide to a very minor extent a few hundredths of 1 per cent 

in pyroxenes, hornblendes, and biotites. Hence it predominates in 

the less siliceous igneous rocks. As the mineral roscoelite, essen-
MINOR CONSTITUENTS. 27

tially a vanadio-alumino-potassic silicate, or some other similar 

silicate, it is rather widely distributed as a component of certain 

sandstones in western Colorado and eastern Utah, sometimes in 

large amount.1 It may well exist in a similar condition in clays 

and the ashes of coals. The conclusion being based on the above 

observations, it should not occur as a constituent of nonaluminous 

and nonferric rock-forming minerals. As to olivine, at least, this 

conclusion has been found to be justified. Vanadium is also a constituent of ilmenite in titaniferous iron ores. The existence of the 

copper sulphovanadate, sulvanite, and the occurrence of vanadium 

in apparent combination with sulphur in certain peculiar carbonaceous ores of eastern Utah and Peru 2 indicate a possible wider range 

of combination in exceptional cases.

Manganese. This element is found in ferromagnesian minerals in 

nearly all rocks, though as the result of their alteration it may appear sometimes, particularly on surfaces of limestones and sandstones, in a more or less peroxidized condition. Its amount will 

seldom exceed 0.3 per cent. I agree fully with Washington in regarding the high figures commonly reported as due to analytical 

error. There is no element which the average chemist is more prone 

to report too high, by gravimetric methods.

Nickel and cobalt. These elements are found in the olivine of 

peridotite rocks and also in pyrite and pyrrhotite, hornblende, and 

biotite. Even in peridotites the percentage of nickel will seldom exceed 0.1 per cent, while that of cobalt rarely if ever exceeds a trace. 

As with manganese, the percentage of nickel has often been reported 

too high.

Copper. Owing to the extreme precautions necessary to exclude 

its introduction from utensils and reagents during analysis, there is 

less positive information regarding the distribution of copper than of 

some other elements which do not exceed it in amount. Nevertheless, 

there is reason to believe that it is almost if not quite as universally 

distributed as most of the other minor constituents. Its particular 

Jiome appears to be in diabase, gabbro, amphibolite, and other basic 

rocks with pyroxene and amphibole. J. B. Harrison, in a report 

(1906) to the Science and Agriculture Department of British Guiana, 

shows its occurrence in hundredths of 1 per cent in many igneous 

rocks of that colony. So far as my experience goes, it can be found 

almost invariably, if looked for, in the rock analyses carried out in 

the Survey laboratory. But for the reason above given it is seldom

1 Hillebrand, W. F., and Ransome, F. L., Am. Jour. Sci., 4th ser., vol. 10, 1900, p. 120; 

Bull. U. S. Geol. Survey No. 262, 1905, p. 9.

2 As to the Peruvian occurrence see Hewett, Foster, Bng. arid Min. Jour., vol. 82, 1906, 

p. 385 ; Bravo, Jos6 J., Bol. Soc. ing. (Lima), vol. 8, 1906, p. 171; Hillebrand, W. F., Am. 

Jour. Sci., 4th ser., vol. 24, 1907, p. 141; Jour. Am. Chem. Soc., vol. 29, 1907, p. 1019.
28 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

reported unless extra precautions have been taken to prevent its 

extraneous entry into the analysis.

Barium and strontium. Feldspathic rocks are those most likely to 

carry barium and strontium, the former almost always in excess of 

the latter.

There is some evidence that barium is apt to be most abundant in rocks which 

are high in potash. Barium occurs in the feldspars, especially orthoclase, as 

the celsian molecule, in the rare hyalophane, in some zeolites, as well as in a 

few biotites and muscovites. We can at present form no definite conclusion as 

to the character of the rocks most likely to carry strontium, and more analytical 

data on this point would be of interest.

Barium has been found in a few peculiar rocks in excess of 1 per 

cent, in terms of the oxide, but in the greater part of the silicate rocks 

of the United States its percentage is well below 0.2. Strontium has 

been found as high as 0.3 to 0.4 per cent, but generally there is little 

more than a trace of it.

Lithium,. Although one of the most universally distributed of the 

elements, lithium is almost never found in rocks in more than spectroscopic traces. Aside from the lithium minerals lepidolite and spodumene, it is found in the alkali feldspars, in muscovite, beryl, and 

other minerals. According to Washington, there is reason for the 

belief that it is especially prone to occur in highly sodic rocks.

Phosphorus. This element is found in greatest abundance in the 

more basic igneous and metamorphic rocks and is practically never 

entirely absent. It affects especially those rocks "which are high in 

lime and iron rather than in magnesia." Its chief mineral occurrence 

is in apatite, though it may be found in xenotime and monazite. 

While the percentage is usually well under 1, it may considerably 

exceed this figure.

Sulphur. Aqueous extraction of a powdered rock will in many 

cases remove traces of sulphur and chlorine. These are to be regarded almost invariably rather as derived from infiltrating waters 

than as products of decomposition of the constituents of the rock 

itself. Essential rock-forming minerals containing sulphur in the 

oxidized condition are limited to hauynite and noselite, minerals 

v;hich are found chiefly in the more basic rocks, and especially those 

high in soda. In the sulphide condition the element is of very wide 

distribution, both as pyrite and pyrrhotite, less often as chalcopyrite 

and possibly other sulphides, also in the mineral lazurite, and here 

too in greater abundance in the basic rocks. It is a very common 

error of most chemists to report the sulphur in silicate and carbonate rocks, clays, etc., as SO3 instead of S. Now and then it may 

occur in both states, but much more often only in the sulphide condition.
.; . ' . ' MINOR CONSTITUENTS. 29

Chlorine. Washington says:

Chlorine is present most abundantly in rocks which are high in soda, and 

especially when so low in silica that nephelite is present, though it is also 

found sometimes in nephelite-free rocks and in a few cases in quartz-bearing 

ones. It is an essential component of sodalite and noselite and is also present 

in scapolite and in a few apatites.

Its amount when present rarely exceeds 0.2 or 0.3 per cent. When 

seeking for the chlorine of these minerals it is always well to extract 

the powder first with cold water. (See preceding paragraph.) It 

is to be remembered that fluid inclusions in minerals sometimes contain sodium chloride, which would be largely extracted from the 

powder by water.

Fluorine. Washington says:

Fluorine as a component of apatite, biotite, etc., seems to have no special 

preference as to magma, though, on the whole, it is found more frequently in 

silicic than in femic [ferromagnesian] rocks. It is, however, most apt to be 

met with as fluorite and some other rare fluorine-bearing minerals in rocks that 

contain nephelite, as foyaites and tinguaites. It is an essential constituent of 

fluorite and most apatite, and as an integral part of the last mineral is almost 

universally present. It also occurs in small amounts in biotites and other micas, 

in some hornblende and augite, as well as in tourmaline, topaz, chondrodite, etc.

When determined it is usually reported in amounts under 0.1 per 

cent, but freedom of the weighed calcium fluoride from contamination being assumed, the reported amount is invariably too low because 

of the inaccuracy of the method for its separation. (See 25. B. a. 7, 

p. 225.)

Other minor constituents. Washington says:

Glucinum, as a component of beryl and some other very rare minerals, is most 

frequent in granites, pegmatites, and quartzose gneisses; it seems to be most 

at home in sodic rocks. There is reason to think that the high alumina sometimes reported for these rocks may be in part glucina, which has not been separated from the alumina, and due to the presence of unidentified beryl. * * * 

Tin, as the oxide cassiterite, is confined to the highly silicic rocks, granites, and 

pegmatites, and its presence is due generally to pneumatolytic processes. It 

also may occur in traces in ilmenite, micas, and feldspars. Thorium would 

seem to be more abundant in highly sodic rocks, and the same is also apparently 

true of radium and the radioactive elements. Molybdenum, tungsten, and 

uranium are almost exclusively confined to the very siliceous rocks. Zinc has 

been met with in granite, as well as in basic rocks, but no generalization in 

regard to it is possible as yet [nor in regard to lead, which can often be 

found by using considerable amounts of rock material, as in some of the rocks 

of Leadville, Colo., and in those of British Guiana. W. F. H.]. Platinum is 

found almost exclusively in peridotites, but is occasionally met with in connection with gabbros. Boron, usually as a constituent of tourmaline, is most apt 

to occur in highly siliceous rocks.

Boron is also common in many contact-metamorphic schists. Gold 

and silver have been found repeatedly. According to Harrison,1

1 Rept. Set. and Agr. Dept British Guiana, 1906.
30 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

some of the rocks of British Guiana contain gold enough to account 

for the commercially valuable deposits in residual soils resulting 

from the rock decomposition. Tantalum and columbium occur in 

some granites and pegmatites but have never been reported in percentages in rock analysis, so far as known to me.

4. SUMMATION OF ANALYTICAL RESULTS AND LIMITS OF ALLOWABLE ERROR.

As is well known, a complete silicate-rock analysis which foots up 

less than 100 per cent is generally less satisfactory than one which 

shows a summation somewhat in excess of 100. This is due to several 

causes. Nearly all reagents, however carefully purified, still contain 

or extract from the vessels used traces of impurities, which areeventually weighed in part with the constituents of the rock. The 

dust entering an analysis from first to last is considerable, washings 

of precipitates may be incomplete, and if large filters are used for 

small precipitates the former may easily be insufficiently washed.

Given the purest obtainable reagents, an ample supply of platinum, 

facilities for working, and a reasonably clean laboratory, there is usually little excuse for failure on the part of a competent chemist to 

reach a summation within the limits 99.75 and 100.50. Failure to 

attain 100 per cent in several of a series of analyses of similar nature 

should be the strongest evidence that something has been overlooked. 

Excess above 100.5 per cent should be good ground for repeating portions of the analysis in order to ascertain where the error lies, for it 

is not proper to assume that the excess is distributed over all determined constituents. It is quite as likely in fact, more than likely 

to affect a single determination and one which may be of importance 

in a critical study of the rock from the petrographic side.

Washington would extend the allowable limits above given to 99.50 

and 100.75. If the analysis has to be made in other vessels than 

those of platinum a higher limit than 100.50 is certainly called for, 

but it is extremely doubtful if a lower one than 99.75 should be 

accepted, for, as has been said, there is a tendency toward too high 

results in any case, and a summation of less than 99.75 with vessels 

other than platinum would be indicative of rather gross error on the 

part of the analyst.

As to the allowable variation in duplicate determinations of the 

same constituent no rigid rules can be laid down. Washington has 

proposed the following,1 with which the independent experimental 

values of Dittrich 2 are in substantial agreement: For SiO2 and 

others which amount to 30 per cent and over, from 0.2 to 0.3 per cent; 

for A12O3 and others which amount to from 10 to 30 per cent, 0.1

1 Manual of the chemical analysis of rocks, 1919, p. 127.

2 Neuea Jahrb., 1903, vol. 2, p. 69.
STATEMENT OF ANALYSES. 31

to 0.2 per cent; for constituents which amount to from 1 to 10 per 

cent, 0.05 to 0.1 per cent. These percentages are in terms of the 

whole rock and not of the particular constituent.

While it is desirable sometimes, and for the beginner imperative, to 

make duplicate determinations, agreement is not to be taken as proof 

that the results are correct unless they have been arrived at by different methods.

Too great stress can not be laid upon the importance, especially for 

the analyst of limited experience, of consistently testing most of his 

final precipitates and filtrates as carefully as possible in order to be 

sure, on the one hand, that the substances reported by a given name 

are wholly such and, on the other, that all is reported. In no other 

way can an analyst so soon acquire the needed confidence in himself 

and his methods.

5. STATEMENT OF ANALYSES.

For many years it was the practice in the Survey laboratory to 

tabulate the constituents of a rock somewhat in the order of their 

determination, beginning with Si02 as the chief constituent and 

grouping together all chemically related oxides, as shown, for 

instance, on page 21.

From a strictly scientific point of view a chemical classification 

founded on a separation into basic and acidic atoms or radicals 

would be more satisfactory, but until we learn to find out what 

silicic radicals are present and in what relative amounts, also how 

much free silica there may be, it is useless to think of employing 

the arrangement so valuable in stating water analyses.

Petrographers now demand, with considerable reason, an arrangement " which shall bring the essential chemical features both the 

percentage figures and the molecular ratios prominently and compactly before the eye, so that the general chemical character and 

the relations of the various constituents may be seen at a glance."*

In accordance with this demand it is now the Survey practice 

to follow pretty closely the arrangement proposed by Pirsson and 

later strongly advocated by Washington,1 namely:

SiO2 , A12O3 , Fe2 03 , FeO, MgO, CaO, Na2O, K2O, H2O (above 

105-110°), H2O (below 105-110°), CO2 , TiO2 , ZrO2 , P2O5 , SO3 , Cl, 

F, S (FeS2 ), Cr2 03 , V2 03 , NiO, CoO, Cuo, MnO, SrO, BaO, Li,O, 

C, NH3 .

By this arrangement the nine constituents which in the great majority of cases determine the character of the rock are placed at 

the head of the list, thus facilitating greatly the comparison of dif1 Washington, H. S., The statement of rock analyses: Am. Jour. Scl., 4th sen, vol. 10, 

1900, p. 61.
32 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

ferent. analyses similarly arranged, especially when, as Washington recommends, the molecular ratios are calculated for these leading constituents and placed immediately after the corresponding 

oxides. The order of the remaining 'members 

is determined somewhat by the following considerations: CO2 is placed next after H2 0, for 

these two are generally a measure of the alteration the rock may have undergone. Ti02 and 

Zr02 naturally follow C02 on chemical grounds, 

and SO3 and Cl, being common constituents 

of the sodalite group, are conveniently placed together.

It may be said with regard to the use of the 

word "trace" that the amount of a constituent' 

thus indicated is supposed to be below the limit of 

quantitative determination in the amount of the 

sample taken for analysis. It should in general, 

for analyses laying claim to completeness and 

accuracy, be supposed to indicate less than 0.02 or 

even 0.01 per cent.

6. TIME NEEDED FOR MAKING AN ANALYSIS.

The question has often been put, "How long 

does it take to complete an analysis of this kind ? " 

This will depend, of course, on the mineral complexity of the sample and on the personal factor 

of the individual worker. If there is a competent 

assistant to do the grinding, and specific-gravity 

determinations are not required, it is quite possible 

after long experience for a quick worker to learn 

to so economize every moment of time in a working day of seven hours, with an abundance of 

platinum utensils and continuous use of air and 

water or steam baths through the night, as to finish every three day8' after the comp!etion of the 

first analysis, barring accidents and delays, one

of a series of rocks of generallJ similar character, each containing from eighteen to twenty 

quantitatively determinable constituents, excluding, for instance, fluorine, carbon as such, nitrogen, metals of the hydrogen sulphide group, and cobalt. But 

such an output of work implies an unusual freedom from those 

occasional setbacks to which every chemist is exposed.

FIGURE i. Platinumton"? TheUCpart3 

A, B, also of heavy

liw,^ 10°' serve h°as 

sockets for the

°£
ANALYSIS OF SILICATE AND CARBONATE ROCKS. 33

7. USEFUL APPLIANCES AND APPARATUS.

In connection with the foregoing remarks it is in place to mention 

a few aids to the chemist which are in constant use in the Survey 

laboratory and have come to be well-nigh indispensable. None is 

novel in principle and all are in use elsewhere, but some are not so 

commonly known as 

they deserve to be, 

hence this allusion to 

them. Certain cheap 

and simple forms of 

colorimeters have been 

found very useful, and 

as they are adapted to 

the determination of a 

variety of substances 

their description finds 

most appropriate place 

here.

A. CRUCIBLE TONGS.

Figure 1 represents 

a form of platinumtipped crucible tongs 

devised by A. A. Blair 

many years ago. With 

them a crucible can be 

securely grasped and 

brought into any desired position while 

still hot. To the contents, if in fusion over 

the blast flame, can be 

imparted the rotatory 

motion so often desirable. Above all, the 

cover need not be in the slightest degree displaced, as when using 

the common form of platinum-tipped tongs.

B. RADIATORS FOR VOLATILIZING LIQUIDS AND SOLIDS.

Figure 2 represents a very useful adjunct to the work table and 

especially to the draft cupboard, whereby the liquid contents of crucibles can be evaporated speedily at almost any desired temperature 

131999° 19 3

FIGURE 2. Radiator for rapid and safe evaporation. 

R is of sheet iron or aluminum, also nickel (Jannasch). A convenient height is 7 cm., width at top 

7 cm. and at bottom 5 cm. The base, B, may be of 

iron, nickel, or platinum, but not aluminum, which 

will not stand the temperature of the direct flame. 

Platinum is most satisfactory by reason of its long 

life and radiating power. The manner of attaching 

B to R is by turning the cogs of B up and over 

those of R. Evaporation may be greatly hastened 

when desired by placing upon R a cast-iron ring with 

its opening somewhat larger than the mouth of the 

crucible.
ANALYSIS OF SILICATE AND CARBONATE ROCKS.

and the dehydration of many solids effected much more safely than 

on an iron plate or sand bath. I do not recall who originated this form

of air bath, but it has been in 

use for over 30 years and is 

identical in principle with the 

" Nickel-becher" of Jannasch. 

Nickel undoubtedly has a certain advantage in not rusting 

like iron, but the form depicted 

in figure 2 can be made easily 

anywhere of sheet iron riveted 

at the joint, the bottom being 

securely held by a notched 

flange. at the extremity of the 

truncated cone. A crucible 

placed on the platinum triangle 

becomes heated uniformly by 

hot air, and large quantities of 

liquid, even sulphuric acid, can 

be volatilized thus in a short 

time without ebullition or spattering. The life and effectiveness of this appliance is greater 

if the bottom is of sheet platinum, but if an iron bottom 

wears out it can usually be replaced one or, more times before 

the sides fail. A coating of 

aluminum paint on the sides 

adds to their life.

By an extension of the principle illustrated in figure 2 very 

considerable amounts of ammonium salts and other easily 

volatile solids may be driven off 

from platinum dishes with little 

danger of loss by spattering and 

none by overheating. The dish 

containing the dry or nearly 

dry matter is placed in another 

of such size that the bottom of 

the inner dish is at some distance from that of the outer. 

The outer dish may be of iron, direct contact between it and the inner 

dish being prevented by wisps of asbestos overlapping its edge, but

FIGURE 3. Device for excluding flame 

gases from the interior of crucibles during ignition. A, Asbestos board ; B, stiff 

platinum foil of size suitable to the 

crucible used and having an opening to 

admit the crucible to about two-thirds 

of its depth. This disk may be used 

alone upon the ring of an ordinary 

stand and in horizontal position, or, 

preferably as shown in the figure, in 

combination with the asbestos board, 

in which is an opening considerably 

larger than the crucible. The combinar 

tion should then be given the inclined 

position shown, so as to allow the products of combustion to flow to one side 

without the possibility of tbeir enveloping the mouth of the crucible. In the 

lack of platinum a perforated asbestos 

board alone will yield fair service with a 

blast, but not as a rule with an ordinary 

burner.
USEFUL APPLIANCES AND -APPAKATUS. 35

the excellent conductivity and radiation of platinum recommends it 

above anything else. Aluminum will not stand the application of a 

full flame. If the contents of the dish are moist at first, a low flame 

will soon dry them, when the heat may be increased at will and the 

operation allowed to proceed without supervision. A sand bath may 

be substituted sometimes for the radiator.

C. PERFORATED DISK FOR CRUCIBLES.

Figure 3 shows an arrangement for the ignition of crucibles when 

it is desired to exclude flame gases from their interior, as in the ignition of ferric oxide and the determination of sulphur by fusion with 

an alkali carbonate. The original idea of J. Lowe 1 was to use perforated clay disks in determining the ash 

of coals. Later, Lunge and others advocated asbestos board, but this has the disadvantage that it lasts but a short time 

and the fibers adhere to the crucible to

, , T-> .,-, » ,, ... FIGURE 4. Weighing trough of

some extent. By neither of these is it easy platinum, to be balanced by 

to attain a very high temperature in the counterpoise of lead. Length

 11 mi f T i f i . of trough about 7$ cm.; width crucible. Inereiore a disk 01 platinum is bef0re bending, 5 cm. 

preferable because of its durability, cleanliness, and high conducting power, though its cost may preclude having a set to fit different sizes of crucibles. The platinum disk and 

asbestos board may be used conveniently in combination, as in the 

figure. The asbestos then has a large hole, over which a smaller 

perforated disk of platinum is laid.

D. WEIGHING SCOOP OR TROUGH.

Figure 4 represents a most convenient receptacle for the sample 

that is being weighed on the balance. It is made of platinum and is 

counterpoised by a leaden weight. It has the advantage over a 

watch glass in that its shape permits ready introduction of its contents into narrow-mouthed receptacles when desired.

E. COLORIMETERS, 

a. FIRST SURVEY FORM.

The Survey form of colorimeter shown in figure 5 consists of two 

glass reservoirs and a darkened box. The glasses, G, may be of 

square or oblong section, 8 to 12 cm. high and 3 to 3£ cm. inside 

measurement between those sides through which the liquid is to be

1 Zeitschr. anal. Chemle, TO!. 20, 1881, p. 224.
36 ANALYSIS OF SjILICATE AND CARBONATE ROCKS.

observed.1 These sides should, of course, be exactly parallel; the 

others need not be but should be blackened externally. In order to 

exclude further the effect of side light, it is very convenient to have 

a simple light box, B, that can be easily held in the hand, stained 

black inside and out and with one end closed by a piece of ground 

glass, W, the other being open. For a space equal to the width of 

the glasses the cover is removed at the top next the glass end to permit the insertion of the glasses side by side in such a way that no

FIGURE 5. First Survey form of apparatus for colorimetric determinations, different 

aspects. G, One of two glasses of square or rectangular section, 8 to 12 cm. high and 

3 to 3| cm. inside measurement between those sides through which the liquid is to be 

observed. The other sides are blackened on the outside. B, Rectangular box about 35 

cm. long and 12 cm. square, stained black inside and out, one end closed by a groundglass window, W, the other open, and a portion of the top removed. P, Blackened 

partition, with openings corresponding to the interior dimensions of the glasses when 

in position. S, Blackened cardboard shutter sliding stiffly up and down back of the 

partition.

light shall penetrate around'their sides or between them. Immediately back of the glasses is a partition, P, with openings of appropriate size cut in it. A stiffly sliding black cardboard shutter S, is 

movable up and down immediately back of the partition, so that all 

light can be cut off except that which comes through the liquid. The

1 The allowable error in distance between the corresponding pairs of sides of the two 

glasses should never exceed 1 per cent. Unfortunately there has been a disinclination on 

the part of dealers in this country to furnish glasses fulfilling this requirement, and held 

together by a durable cement which shall be proof against dilute sulphuric acid and 

alkali, though some have been obtained through Messrs. Eimer & Amend, of New York 

City. Canada balsam answers well for a time, but sooner or later it cracks, leaks then 

appear, and the sides soon drop off. However, it is but a simple matter to cement them 

on again. But the use of Canada balsam is precluded with alkaline solutions, and hence 

for the chromium determination, because the solution at once becomes turbid.
' USEFUL APPLIANCES AND APPARATUS. 37

ground-glass window, W, sliding up and down in slots, affords a 

much more uniform illumination than can be had without it.

Precautions of this kind are necessary if accurate results are to bo 

counted on. Except for mere traces, this combination of glasses 

and darkened box insures greater accuracy and rapidity of work than 

Nessler tubes and is likewise preferable, so far as my experience goes, 

to expensive instruments like the colorimeter of Soleil-Duboscq.

The manner of using the colorimeter is as follows: Any suitable 

amount of the standard solution, which is purposely made stronger 

than the solution to be tested, is placed in one of the glasses and an 

indefinite part or the whole of the test solution in the other. Water 

is then added from a burette to the standard until there is no distinction as to color. Perfect mixture is brought about by a glass 

rod flattened at one end. In making the color comparison the box 

is best held close to a window, so as to get a full, strong light. Daylight is far preferable to artificial light. The amounts of the substance to be determined and that in the standard cylinder are of 

course proportional to the volumes of the solutions.

b. SECOND SURVEY FOKM (STEIGEli's).

The colorimeter shown in figure 6 was devised by George Steiger. 

Though more elaborate in its construction than the one just described, it permits making any number of readings with the same 

standard solution and has given Steiger excellent service. Its construction and use are thus described by him.1

Instruments using the principle upou which this one is based the ratio of 

the thickness of the liquid through, and not the actual dilution to equal concentrations are not applicable to all colorimetric determinations. It will be 

found, in comparing such a solution as is used in the colorimetric determination of manganese and some other substances, that there is a change not only 

of the intensity of the color, but also of the color itself, making it impossible 

to find a point at which two solutions of different concentrations will have 

the same depth of tint. In some other cases, as for instance, the yellow color 

of the higher titanium salts, this principle gives perfect satisfaction.

The instrument to be described consists of two wooden boxes, the interior 

portions of which are finished in dead black. In fig. 6 (a), AA. is a piece of 

finely ground glass, and this should be illuminated with the full light of the 

sky. B is a mirror mounted to swing so that light may be thrown perpendicular^y through the hole C.

The second portion of the apparatus consists of a box, as shown in fig. 6 

(b), made with two parallel grooves in the bottom, in which the two glass 

cells CO can be moved back and forth, and the hole E, Avhich admits light 

reflected by the mirror B of fig. 6 (a). These cells are about 15 cm. long, 

2.5 cm. wide, and 5 cm. deep. On the bottom of each cell and near the outside edge is engraved a scale, a convenient unit for which is the millimeter. 

FF are glass tubes with mirrors, GG, attached to the lower ends at an angle

1 Jour. Am. Chem. Soc., vol. 30, 1908, p. 215.
38 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

of 45p. These tubes may be lifted up when it is desired to remove the cells; 

they may also be removed entirely from the clips RR for cleaning purposes, 

but- they should be pushed down when in use so that the lower edges of the 

mirrors touch the bottoms of the cells. When ready for use this box is 

placed in the space marked DD, fig. 6 (a). Care should be taken to place 

the mirrors at an exact angle of 45°.

Under these conditions, in each cell, all light coming through the bottom of 

the cell and reflected through the end K will go through the same thickness 

of liquid, and if the mirror were a reflecting surface coming in direct contact 

with the liquid this distance would be represented by. the line OP, fig. 6 (c).

FIGURE 6. Steiger's colorimeter (second Survey form).

There is a small error here, due to the converging of the rays to the eye ; this 

is so slight, however, as not to cause any perceptible uneven illumination.

The mirrors being made of ordinary looking glass, the reflecting surface will 

be the upper side GHG, fig. 6 (c), and the light must go through the glass of 

the mirror before striking the reflecting surface, and the same on leaving. 

The distance which the light travels through the glass of the mirror will be 

represented by twice the length of the hypotenuse of an isosceles right-angle triangle, the equal sides of which are each equal to the thickness of the glass, and 

must be deducted from the length OP.

A ray of light entering the glass at the point marked N will travel to Ji and 

then be reflected to t. From t to w it will go through the colorimetric solution, 

and this dista)ice is therefore the length to be measured. A point, H, is marked 

on the mirroi near the outer edge, so that it may be seen in the same line of
USEFUL APPLIANCES AND APPARATUS. 39

vision as the scale on the bottom of the cell, and perpendicularly above t. In 

looking through the end K, this mark will be recorded at the point t' directly 

below it on the scale, and t'P being the same as tw, the distance desired cun 

be read off. The position of the point H is determined by measuring off, on 

the back of the mirror, a distance from the lower edge equivalent to three 

times the thickness of the glass. It may be convenient, if thin looking-glass 

has been used, to have this point farther up on the mirror (H'), in order 

that it may be seen more plainly, but if so moved an addition must be made 

to the observed reading equivalent to one of the sides adjacent to the right 

angle of an isosceles right-angle triangle, the hypotenuse of which is equal to 

the distance this point has been removed from H. It is convenient in making 

the graduation on the cell to allow for this correction. The reading can then be 

made directly.

Glass cells to answer the purpose may be had of any of the large supply 

houses, but not graduated ; the graduation must be done in the laboratory. The 

supports FF can be made of rather heavy walled glass tubing, about 1 cm. 

outside -diameter.

The mirrors are made of a good grade of looking glass, the lower and top 

edges blackened, and cemented to the ground ends of the glass tubes with 

Canada balsam, after which the backs are coated with paraffin. Paraffin 

answers well as a coating for a large number of colorirnetric solutions. In 

case a liquid is to be used which attacks paraffin, a substitute must be employed 

which is unaffected by the liquid in question. It will be found necessary to 

replace the mirrors from time to time, as it is not possible to so protect the 

silvered surfaces as to prevent the gradual eating in from the edges by the 

various solutions used.

The comparison is made by pouring a solution of known strength into one of 

the cells. The unknown solution made up to a definite volume is put into the 

other. The left-hand cell is then placed at a convenient point, which should 

be determined by the depth of color of the solution it contains. The right-hand 

cell is then moved back and forth till, on looking in the end M of the apparatus, 

fig. 6 (a), the two mirrors appear to be of the same shade.

The strengths of the two colorimetric solutions being inversely proportional 

to the thickness of the liquids looked through, by substituting in the following 

equation the amount of the material to be determined may be found.

Let R equal the reading of the cell containing the known solution with a concentration C, and r the reading of the cell containing the unknown solution, 

which has a concentration c, then

RC

c. SCHBEINEB'S FORM.

Oswald Schreiner, of the United States Department of Agriculture, devised a colorimeter (fig. 7),1 which has done good service in 

colorimetric work on phosphates, etc. Its description, personally 

communicated by Dr. Schreiner, is as follows :

The colorimeter in its simplest form consists essentially of graduated glass 

tubes B, containing the standard and the unknown colorimetric solution, the 

column of the liquid in both tubes being changed by means of two smaller im1 Jour. Am. Chem. Soc., vol. 27, 1905, p. 1192.
40 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

mersion tubes A, also of glass. The upper ends of the tubes A are mounted in 

blocks of wood which fit into grooves on the body of the colorimeter. This permits the ready removal of the tubes from the colorimeter for cleaning when the 

liquids are changed. The graduated tubes B are supported by a block of wood 

about midway of the camera and are held in place by brass springs or clamps 

C, the tension of which can be regulated to suit the diameter of the tube, so as

to allow it to be moved freely up or 

down by hand and yet be firmly held 

in position when the setting is made. 

It will be noticed from the figure that 

the glass tubes diverge slightly. This 

has been found of advantage, as it 

allows the operator to look down the 

center of both immersion tubes, as 

well as to bring the upper parts of the 

tubes, and consequently the images, 

closer together. The openings to the 

immersion tubes can be covered by 

means of a microscope slide to prevent dust from falling into the tubes. 

The tubes are illuminated from the 

reflector D, below, which carries a 

white sheet of cardboard or opal 

glass, and after passing through the 

tubes the light is reflected by a mirror, E, in the upper part of the instrument to the eye of the observer 

at F. The dimensions of the camera 

are about 70 by 32 by 16 cm. Standard glass slides may be inserted at G 

below one of the immersion tubes in 

place of the tube containing the standard solution, the immersion tube being retained so as to give similar 

images when viewed from above.

The measuring colorimeter tubes, B, 

are 25 cm. long, with inside diameter 

as nearly as practicable 27 mm.; in no 

case less than 25 mm. and not greater 

than 29 mm. The glass should be 

colorless and the bottoms well ground 

and polished, with internal surfaces 

of the bottoms plane, in no case appreciably convex or concjave. The bottoms must be ground down sufficiently

to make the ground surfaces a little larger than the internal diameters of the 

tubes; each of the tubes is provided with an etched scale of one hundred 2-mm. 

divisions. The scale begins at the level of the inner surface at the bottom, the 

length of the marks being 6 mm. and every fifth mark 12 mm., and every tenth 

mark numbered on the right side, 10, 20, 30, etc., beginning at the bottom. On 

the reverse side of each measuring tube may be etched two capacity marks, if 

desired, one for 50 cm.8, the other for 100 cm.8.

FIGURE 7. Schrelner's colorimeter.
PEELIMINAKY QUALITATIVE ANALYSIS. 41

The smaller tubes are likewise 25 cm. long, with outside diameter not 

greater than 20 mm. and not less than 18 mm., with the thickness of the glass 

the same in all the tubes. The bottoms of these tubes must be carefully ground 

and polished and the inside of the bottom never sensibly convex or concave. 

They must be of colorless glass, with the bottoms so ground that the diameter 

of the ground portion exceeds the internal diameter of the tube. These tubes 

are to be provided with neither scale nor capacity marks.

The standard colorimeter solution is poured into one of the graduated tubes 

and put into place in the camera together with the immersion tube. The unknown colorimetric solution, made up to definite volume, is put into the other 

graduated tube and similarly placed in the instrument. The tube containing the 

solution of unknown strength is set at a convenient height, say fifty scale divisions, and the other tube containing the standard moved up or down, the 

operator watching the effect on the image in the mirror through the opening in 

' the front of the camera. By moving the tube so that the image is alternately 

weaker or stronger than the standard, the setting can be accurately and quickly 

made. When both images show the same intensity of color, the setting is read 

by noting the division mark on the graduated tube opposite the ground bottom 

of the immersion tube. This reading will give the height of column of the 

standard which exactly corresponds with the intensity of color of the column of 

the unknown solution. It follows that the strengths of these two colorimetric 

solutions are inversely as the heights of the columns that is, as the readings on 

the two tubes. If R is the reading of the standard solution of strength C, 

and r is the reading of the colorimetric solution of unknown strength c, then

R

. = C. The same formula, of course, applies when the standard is fixed and

the unknown solution moved up or down until the images are of equal intensity. 

8. PRELIMINARY QUALITATIVE ANALYSIS.

A complete qualitative analysis of a rock preceding the quantitative examination is in most cases a sheer waste of time. A few constituents may now and then be specially looked for, but in general 

time is saved by assuming the presence of most of them and proceeding on that assumption in the quantitative analysis.

This statement must not be misinterpreted, as it has been, so as to 

convey the impression that qualitative analysis receives little consideration in the chemical work of the Survey. For ores, mineral 

species, waters, etc., it is indispensable, as also in the testing of precipitates and filtrates during the course of quantitative analysis.

The student of qualitative analysis will find in papers by A. A. 

Noyes, W. C. Bray, and E. B. Spear 1 a vast fund of information, 

such as is to be had nowhere else, relating not only to the making of 

separations, but, and this is often of greater importance, to the completeness of these separations and to the possible limits of detection. 

The scope of these papers is less restricted than their titles might be 

thought to imply, for such elements as glucinum, uranium, vanadium, 

titanium, zirconium, and thorium are included.

1 Jour. Am. Chem. Soc., vol. 28, 1907, p. 137; vol. 30, 1908, p. 481; vol. 31, 1909, p. 

611;. Chem. News, vol. 95, 1907, pp. 89, etc.; vol. 98, 1908, pp. 6, etc.
42 ANALYSIS OF SILICATE AND CAKBONATE ROCKS. 

9. QUALITY OF APPARATUS AND REAGENTS.

Unquestionably the greatest hindrance to good work in otherwise 

well-equipped laboratories is the difficulty in obtaining satisfactory 

reagents and apparatus. This fact became apparent early to the 

Survey chemists, and it is due mainly to their strenuous complaints 

and initiative that the movement in favor of better quality arose.

A. GLASSWARE AND PORCELAIN..

Much of the glassware on the market was until recently of a very 

inferior grade, but the quality of the American glassware is now 

very much improved. It appears that several American manufacturers are turning out flasks and beakers that are equal or even superior to the Jena ware. The composition of a number of brands is 

given in the table below.1

Analyses of chemical glassware.

A1208 . ...............

FesOs.. ..............

ZnO... ..............

PbO....... ..........

MnO..... ............

CaO........ ..........

MgO...... ...........

NasO...... ...........

KsO...... ............

SiOj..... .............

BjOs..... ............ P2 o5 ...... ...........

S03 . .................

AssOj. ...............

SbjOs.. ..............

Kavalier 

beaker.

.14

.OS

.02

8.7

.17

7.1

7.9

75.9

.08

.20

Trace.

100.29

M. E. G. 

Co. 

beaker.

1.0

.35

5.6

.02

.66

4.3

10.8

.30

73.0

3.6

.02

.02

.60

100.27

Pyrex 

beaker.

2.0

.25

.01

.29

.06

4.4

.20

80.5

11.8

.70

100.21

Jena 

beaker.

4.2

.25

10.9

.01

- .63

.21

7.5

.37

64.7

10.9

.14

99.81

Jena 

flask.

4.2

.27

10.9

.01

.56

.25

7.8

.31

64.7

10.6

.19

99.79

Nonsol 

beaker.

2.5

.23

7.8

.01

.79

3.4

10.9

.30

67.3

6.2

Trace.

.62

100. 05

Fry 

beaker.

2.7

.22

3.6

.03

2.6

2.6

9.8

1.5

68.6

8.1

.18

99.93

Libbey 

beaker.

2.1

.44

i.6

.03

.42

.08

8.2

.67

75.9

10.8

.36

100.00

Selenium and fluorine were not found, but lithium was detected spectroscopically by Paul W 

Merrill in all samples.

Comparative tests of a number of brands of porcelain dishes and 

crucibles have been made by C. E. Waters.2 Two of these were of 

American origin. It appears that there was little choice between the 

five brands tested with respect to their resistance to reagents. A 

serious defect of the American porcelains, and also of one of the 

foreign brands, was the cracking of the glaze when the hot vessel was 

picked up with tongs. Tests made later on one of the American 

brands (Coors) showed an improvement in this respect.

1 Walker, P. H., and Smither, F. W., Tech. Paper Bur. Standards No. 107, 1918; Jour. 

Ind. Eng. Chem., vol. 9, 1917, p. 1090.

3 Tech. Paper Bur. Standards No. 105, 1917.
QUALITY OF APPARATUS AND REAGENTS. 43

J. W. Mellor 1 has discussed at some length and most pertinently 

the action of reagents on glass and porcelain. His discussion forms 

the basis for the following remarks.

The action of different solutions on glass is far more vigorous than on porcelain, but some types of glass resist better than porcelain with an unsuitable 

glaze. It is, therefore, bad on principle to allow filtrates, etc., to lie any length 

of time in porcelain or glass vessels particularly the latter. In some cases 

the contamination from the glass may be serious * * *. It is unfortunate 

that the impurities introduced from the glass or porcelain vessels are those very 

constituents which have to be specially determined.

The choice of the particular kind of glass to use is therefore sometimes of interest. For instance, glasses containing zinc should not bo 

used when zinc is to be determined, for alkaline solutions extract perceptible amounts of zinc from such glasses. Again, the use of the 

boro-silicate glasses is counterindicated when boron is to be determined.

Mellor gives the following rules to be observed:

(1) If possible, do not allow the solutions to stand in glass or porcelain 

vessels for any length of time, particularly in glass. (2) If the work be interrupted, so that the solutions must stand over, if there be no other objection, acidify the alkaline solutions before they are placed on the side. (3) If 

solutions must stand over, it is better to use good porcelain than glass vessels. 

(4) A resistant glass should be used for general work in place of the more 

soluble types of glass. (5) For exact work a blank experiment should be made, 

using nothing but the regulation reagents in similar quantities, and under conditions similar to those actually employed in the analysis proper. This plan 

not only corrects impurities in the -reagents, but it also enables us to practically 

eliminate the sources of error now under discussion. (6) Precipitations made 

in alkaline solutions which have stood for some time in glass vessels are almost 

certain to be contaminated with silica, and in exact work a correction must be 

made. (7) Remember that solutions of reagents are usually kept in glass vessels. Such solutions may accordingly be contaminated with silica, etc.

B. PLATINUM AND SUBSTITUTES, 

a. PLATINUM.

Practically all platinum ware contains some iridium, or copper, or 

copper and rhodium, added for hardening effect. Possibly certain 

ware carries rhodium only as an addition. The volatility loss occasioned by strong heating (above 1,100°) of some ware is due mainly 

to its iridium content. Therefore, the lower the iridium content is, 

consistent with requisite stiffness, the better.

Some years ago iron was found in large amounts in shipments of 

platinum ware fresh from the factory, and its presence must still be 

guarded against, although the quality of American-made ware has

1 A treatise on quantitative inorganic analysis, with special reference to the analysis of 

clays, silicates, and related minerals, London, Charles Griffin & Co. (Ltd.), 1913.
44 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

improved very much since 'then in this respect. Considerable 

amounts of iron can be detected readily by heating the ware to low 

redness, best in a muffle-furnace. The surface shows then a dark or 

even reddish color, due to oxide of iron. Proof of the presence of 

iron is afforded by digesting the heated ware in hydrochloric acid. 

A yellow color of the acid indicates iron, and further proof is furnished by a qualitative chemical test. It is seldom that a trace of 

iron can not be found in this way, even though the original metal 

may have been entirely free from it. Iron is taken up very readily 

by platinum from the rolls or tools used in preparing the ware, and 

such iron is superficially held. If so held it can be extracted for the 

most part by successive heatings and extractions of the ware until no 

more iron is found.

Sometimes, after ignition, a calcium content can be detected by the 

alkaline reaction imparted to a strip of moist litmus paper pressed 

upon the surface. Such reaction appears only in spots.

Platinum vessels should not be heated strongly in contact with 

metal of any kind except platinum.

b. SUBSTITUTES FOK PLATINUM.

If the restrictions imposed by its relatively low melting point are 

taken into account, gold may be used for many operations in place of 

platinum, especially in the form of dishes, which seldom have to be 

exposed to temperatures approaching the melting point of the metal.

Substitutes that have been put upoji the market under the trade 

names " palau " and " rhotanium " are alloys of gold and palladium. 

They may be used for many operations, with certain restrictions. 

Chief of these is that arising from the relatively strong action upon 

them of nitric acid. Their low melting point as compared with platinum is not an important defect, for it is considerably higher than 

that of gold alone. Nevertheless, a few reports have been received at 

the Bureau of Standards which indicate that these substitutes do not 

stand up as well in service as platinum. How much the failures may 

have been due to defective workmanship is unknown. A report of 

tests upon these two alloys, made at the Bureau of Standards, is cited 

for reference.1

" Auranium " and " platino " are trade names for alloys of gold 

and platinum intended for use in the form of crucibles and dishes. 

Nothing is known as to their serviceability.

Several papers have been issued from the Bureau of Standards 2 

that deal with the quality, behavior, and testing of ordinary platinum ware.

1 Gurevich, L. J., and Wichers, B., Jour. Ind. Eng. Chemistry, vol. 11, 1919, p. 570.

2 Burgess, G. K., and Sale, P. D., Jour. Ind. Eng. Chemistry, vol. 6, 1914, p. 452, vol. 

7, 1915, p. 561; Sci. Paper Bur. Standards No. 254, 1915. Burgess, G. K., and Waltenberg, R. G., Sci. Paper Bur. Standards No. 280, 1916.
QUALITY OF APPARATUS AND REAGENTS. 45 

C. REAGENTS.

All analyses performed in the Survey laboratory have been made 

with the purest reagents obtainable, either by purchase in the open 

market or by special preparation on the part of manufacturers or 

in the laboratory, but the most ceaseless vigilance has at all times 

to be practiced. As is now generally known, a " C. P." or " analyzed 

reagent" label is no guaranty whatever of the purity of a reagent. 

Every new purchase must be examined if it is one in which purity 

is a desideratum. In general, all so-called " C. P." chemicals should 

at least stand the tests laid down by Krauch.1 The " guaranteed " 

or special reagents, sold at high prices, have been found at times 

to be worse than those emanating from sources which make no claim 

to special purity for their goods.

Acids made in this country can be had of a high grade, and most 

of these need no redistillation except for special experiments, but 

exceptions have been noted.

Hydrofluoric acid had to be always freshly distilled with potassium permanganate until the introduction of ceresin bottles afforded 

an article sufficiently pure for the most exacting work. Care must 

be taken to see that no particles of paraffin or ceresin are floating 

on the acid as it is poured out, and that this is free from traces of 

hydrochloric acid whenever it is to be used for attacking silicates 

with a view to determining chlorine (24. C. b, p. 221). An important 

use for hydrofluoric acid is the decomposition of refractory silicates 

in the determination of ferrous iron. For this purpose it is necessary 

that it be free from any substance that will reduce permanganate. 

Sulphurous acid was found in one or two shipments, but this is a 

contamination against which care in manufacture can easily guard. 

On evaporation the acid should leave a nonvolatile residue so small 

as to be entirely negligible.

Ammonia water always ought to be redistilled at short intervals, 

after first shaking up with slaked lime in order to decompose any 

ammonium carbonate that it may hold. Glass stock bottles may be 

coated inside with ceresin so as to prevent contact between the glass 

and the ammoniacal solution, a device that may be serviceable with 

other reagents. For special purposes a small bottle of platinum or 

the cheaper gold can be used. Some manufacturers deliver in steel 

cylinders a very pure liquid ammonia,, the use of which is to be 

preferred to that of commercial aqua ammoniae. A solution of 

any desired strength can be prepared as often as called for by collecting the gas from a cylinder in a bottle half full of water kept 

immersed in a bath of flowing cold water.

1 Die Priifung der chemischen Reagentien, 3d ed., Berlin, Julius Springer, 1896. English 

translation by J. A. Williamson. D. Van Nostrand Co., 1902.
46 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Potassium bisulphate should be entirely free from silica, alumina, 

and heavy metals. The only correct way to get an accurate silica 

determination is to fuse the salt with a considerable amount of 

strong sulphuric acid, allow to cool, dissolve in water, and digest on 

the steam bath to coagulate the silica, which is then filtered; or the 

salt may be dissolved in water and evaporated with a large excess 

of sulphuric acid till fumes of the acid rise copiously. On cooling, 

the mass is dissolved and treated as above. If a satisfactory article 

is not to be purchased, it can be made from equivalent parts of 

potassium sulphate and sulphuric acid. Even then the normal salt 

must first be examined, for it has been found to contain notable 

amounts of lead, calcium, and silica. Sodium bisulphate is for some 

purposes preferable to the potassium salt. Both, however, should 

be converted to pyrosulphate by fusing in a large platinum dish 

and maintaining in fusion till all spattering has ceased and sulphuric 

acid rises copiously. The salt thus treated will not show the disagreeable frothing and spattering that is so objectionable when 

making fusions with the bisulphate, and it is more quickly effective.

The phosphorus ("microcosmic") salt used for precipitating 

magnesium has been found to contain iron and silicon.

Ammonium oxalate almost always contains calcium and must 

therefore be purified or specially prepared. The same may be said 

of oxalic acid. According to A. Classen,1 ammonium oxalate sometimes contains lead.

Ammonium chloride has been known to contain manganese.

Hydrogen peroxide sometimes contains fluorine, which renders it 

unfit for use as a chemical reagent. The test for fluorine is carried 

out as follows: To 50 cm.3 of the reagent add a slight excess of 

sodium carbonate and warm the solution. Filter if a precipitate 

forms, and to the boiling solution add calcium chloride in excess. 

Filter and ignite the precipitate gently. Treat it with dilute acetic 

acid, drop by drop, till the calcium carbonate is dissolved, filter, 

wash, ignite the residue gently, and test it with strong sulphuric 

acid in the usual way for fluorine. The perhydrol of E. Merck, 

now unobtainable in this country, is a very pure and strong peroxide 

(30 per cent).

Sodium carbonate, one of the most important reagents in silicate 

analysis, sometimes can be had which does not carry more than 2-| 

mg. of total impurity (see 6. A. d. (3, p. 94) in 20 grams (0.012 per 

cent). This should be reserved for the main portions, in which 

silica, alumina, etc., are to be determined. For other constituents, 

as phosphoric acid, fluorine, sulphur, a poorer grade is quite allowable, provided it is free from the element to be determined and from

^eitschr, anal. Chemie, vol. 42, 1903, p. 518.
QUALITY OF APPARATUS AND REAGENTS. 4?

any other which might interfere with its determination. Silica is 

to be tested for by evaporating the solution of the carbonate or the 

dry salt with sulphuric acid in large excess till fumes of the acid 

are copiously evolved, dissolving the cooled mass in water, and 

digesting on the steam bath in order to coagulate the silica before 

filtering. Evaporation with hydrochloric acid will not yield all of 

the silica. Once a very objectionable impurity in the otherwise acceptable article was encountered, namely, fluorine. The explanation 

of its presence is probably that cryolite had been used as the source 

of the carbonate. Sodium phosphate in small amounts seems to be 

a common contaminant of even good grades of sodium carbonate.

Sodium hydroxide made from sodium has been found with a large 

amount of lead, a fatal obstacle to successful mineral analysis, and 

also with small amounts of nickel.

Owing to the solvent action on glass of many solutions of solid 

reagents, these solutions should be made up at frequent intervals in 

small quantities, or, preferably, the solid should be dissolved as 

wanted. That this is no unnecessary refinement in really good work 

has been amply demonstrated, and it is particularly called for with 

such reagents as ammonium oxalate and microcosmic salt.

The quality of the distilled water used in analysis should be looked 

after particularly. The water should be tested at frequent intervals 

by evaporating at least a liter of it in a platinum dish with special 

precautions to exclude dust and chemical fumes. The best oncedistilled water, evaporated under proper conditions, is likely to show 

a residue unignited of about 1 mg. After gentle ignition and removal thus of volatile salts the weight may be reduced to about 

0.5 mg.
II. METHODS APPLICABLE TO SILICATE ROCKS. 

1. INTRODUCTORY REMARKS.

The order hereinafter followed in describing the various chemical 

separations has little relation to the affinities of the constituents of the 

rock, but those are grouped together which can be determined conveniently in the same portion of rock powder. Thus, in the main 

portion it is usual to determine Si02 , TiO2 , MnO, NiO, CaO, SrO, 

MgO, total iron, and the combined weight of all the following: 

A12 03 , Ti02 , P2 05 , Zr02 , all iron as Fe2 03 , and nearly if not quite all 

vanadium as V2 05 , also perhaps rare earths if present. In a separate portion is estimated FeO, and also the total iron, as well as BaO, 

if these last are desired as checks. The alkalies need a portion for 

themselves. In another it is convenient to determine ZrO2 , BaO, rare 

earths, and total sulphur. For V2O3 and Cr2O3 still another and 

usually much larger portion is to be used. Determinations of CO2 , 

C, H2O, F, and Cl are all made best in separate portions of substance, 

though various combinations are possible, as C02 and H2O, C and 

H2 0, or H2O, F, and Cl. In fact, by a judicious selection and combination of methods a very satisfactory analysis can sometimes be 

made on 4 grams of material without omission of anything of importance, though the time consumed will be greater than if ample 

material is available.

As an illustration of the advantage to be gained by a little judgment in the combination of methods, the case of sulphur, barium, 

zirconium, and rare earths may serve. Many chemists never look 

for any but the first of these, but by following the procedure given 

under 15. A (p. 170), not much more labor is expended in confirming 

their presence or absence than that of sulphur alone.

With only occasional exceptions nearly all the constituents mentioned on page 25 can be determined, if present, in portions of powder not exceeding 1 gram each in weight.

This is a convenient weight to take for the main portion, in which 

silica, alumina, etc., the alkaline earths, and magnesia are to be 

sought; but it should, in general, be a maximum, because if a larger 

quantity is taken the precipitate of alumina, etc., is apt to be unwieldy. It can not often be much reduced with safety if satisfactory determinations of manganese, nickel, and strontium are to be 

expected. For the alkali portion one-half gram is a very convenient 

weight. In general, it may be made a rule not to use more than 2 

48
SPECIFIC GRAVITY. 49

grams for any portion which has to be fused with an alkali carbonate, as for sulphur, fluorine, and chlorine. For carbon dioxide the 

weight may rise to 5 grams, or even more, if the amount of this 

constituent is very small, without expenditure of any more time than 

is required by 1 gram and with correspondingly greater approach 

to correctness in the result. For vanadium also usually a larger 

weight than 2 grams is demanded.

For the attainment of accurate results, such as are needed for the 

close classification of a rock in the system devised by Cross, Iddings, 

Pirsson, and Washington,1 too great stress can not be laid on the 

exercise of the utmost care throughout the analysis. This applies 

not only to routine manipulations, but even more in the matter of 

double precipitations, where these are called for, and in the testing 

of filtrates and precipitates to insure complete recovery of the desired substances, on the one hand, and freedom of them when obtained from matter which should not be there, on the other. These 

cautions are especially applicable to analysts who have little experience. It must always be remembered that analysis can at best 

afford but approximate results, which will be more serviceable the 

greater the care bestowed in obtaining them.

2. SPECIFIC GRAVITY (POROSITY).

GENERAL REMARKS.

Though a knowledge of the specific gravity of rocks is seemingly less prized now than formerly by petrographers, it is occasionally needed and is ever a most important criterion in the identification of mineral species. As ordinarily obtained, whether by 

the method of suspension or by the pycnometer, the results fall short 

of the accuracy which is generally credited to them. A really accurate determination of the specific gravity of solids by the pycnometer, in which the error shall not exceed one or two points in the 

third decimal, is to be achieved only with the most painstaking precautions. (See 2. B. pp. 55-56.) Without this care the error in 

the second decimal may and often does amount to several points. 2 

For these reasons the subject of specific gravity is treated in some 

fullness. Although the porosity of a rock is a constant seldom used 

by the petrographer, it is one that is most useful in the compara1 Quantitative classification of igneous rocks, 286 pp., Univ. Chicago Press, 1903.

2 H. LeChatelier and F. Bogitch (Compt. Rend., vol. 163, 1916,'p. 459) claim that 

the influence of the adhering film of air gives rise to low results when specific gravities 

are determined in water and that accurate results may be obtained by the use of carbon 

tetrachloride, benzene (crystallized), or petroleum ether (essence mine"rale). They measure the volume displaced in a simple form of apparatus. However, they employed only 

reduced pressure and not boiling to remove the air film when using water.

131999° 19 4
50 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

tive study of building stones, and since its determination as often 

carried out is likewise faulty and gives a value which does not represent the pore space in terms of the volume of stone, it has been 

deemed expedient to devote space to this subject also, especially as 

the determination of porosity involves that of specific gravity.

A. BY SUSPENSION IN WATER, 

a. ORDINARY METHOD FOB SPECIFIC GRAVITY.

The determination of specific gravity by suspension in water is 

best made on one or several fragments weighing up to 20 grams. 

They are held together by a fine platinum wire ready for suspension 

from the balance, and thus held are placed in a small beaker, to soak 

over night in distilled water under the exhausted receiver of an air 

pump side by side with a similar beaker of water. Boiling, while 

effective as a means of removing air, should not be resorted to, because the boiling water may exert an undesirable solvent and abrading effect. In the morning the wire is attached to the balance arm, 

the rock fragments remaining immersed in the water; a thermometer 

is placed in the companion beaker of water, now likewise in the balance case, and the weighing and temperature reading are made at 

once. Both vessels of water having precisely the same temperature, 

it is quite unnecessary to wait for the water to assume that of the 

balance should it not already possess it. The fragments are now 

lifted out, without touching the vessel, and transferred carefully to 

a tared crucible or dish. The wire is removed and at once reweighed, 

with the precaution that it dips just as far into the water now as 

when weighed. Hereby a special weighing of the wire out of water 

is avoided. The sample may now be dried on the water bath and 

then at 110° for some hours to expel with certainty all absorbed 

water, and weighed after prolonged cooling in the desiccator. It is 

better to ascertain the weight of the dry rock after soaking in water 

than before, in order to avoid the error due to possible breaking off 

of a few grains between the two weighings. Should the density of 

the rock in air-dry condition be required, it may be left exposed to 

the air for a long period after drying and before weighing; 1 but 

the difference will affect the second decimal by more than a single

l ln view of the uncertainty as to what constitutes hygroscopic water (see p. 72), this 

course is perhaps more to be commended than the former, and seems imperative for certain zeolitic rocks. In such cases it is best to weigh the fragments before putting to 

soak, and afterward, to collect on a Gooch crucible the grains which may have fallen 

off in the water. Should no crucible of. this kind be available, a paper filter may be 

used unhesitatingly and incinerated with the powder. Owing to the small amount of 

powder the error due to loss of even all its water during ignition is quite negligible.

Since the first publication of the foregoing in Bulletin 148, a series of determinations 

on eight rocks, in which the weighing was done after drying, led to an interesting observation. The lumps were heated for a short time on the steam bath until dry on the surface, 

then allowed to cool in air and weighed from time to time during two or three days. It
SPECIFIC GRAVITY. 51

unit only in exceptional cases. For instance, an undried rock of 

2.775 specific gravity containing in the uncrushed state the high percentage of 0.3 hygroscopic moisture will have a density of 2.79 when 

dry; a rock of 2.982 specific gravity, undried, will have a density of 

3 after removal of 0.3 per cent of moisture. The difference becomes 

greater as the density of the rock increases.

This method of ascertaining the specific gravity of rocks is certainly more convenient than, and for compact rocks is believed to be 

decidedly preferable to, that of the pycnometer, in which the fragments must be reduced to small size with consequent formation of 

more or less powder, which is subject to slight loss in the various 

manipulations. To exclude this powder and employ only small fragments would introduce a possible source of error, for the powder is 

likely to consist largely of the most easily abraded minerals and consequently the fragments might not have the average composition of 

the mass. By following the instructions given above, loss of material 

is avoided absolutely, a decided saving in time is effected, and considerable weights can be employed with consequent lower probable 

error in the results. To vesicular rocks, however, notably certain 

lavas, the above procedure is of course inapplicable, as it is probable 

that many of the interior pores would be inaccessible to penetrating 

water.

b. METHOD FOIl SPECIFIC GBAVITY AND POROSITY COMBINED.

E. R. Buckley 1 has called deserved attention to the faultiness of 

the methods generally employed for the determination of specific 

gravity and porosity as applied to building stones, and has brought 

together the fruits of his experience. His recommendations are 

essentially as follows:

The specimens should be cubes, such as are commonly employed 

for the other physical tests, measuring usually 2 inches square.

was observed that some lumps lost weight from the start, while others gained. For 

instance :

14.3803 9.5342 17. 0846

. 3730 . 5178 . 1089

. 366G . 5121 . 1159

. 3483 . 5024 . 1413

.3481 . 5016 . 1388

. 3450 . 5016 . 1370

.3457

The losses in the first and second cases may reasonably be ascribed to the gradual 

evaporation of water absorbed in the pores, while the increase in the third case is doubtless indicative of the presence of zeolitic constituents, from which even brief exposure to 

the heat of the steam bath had sufficed to drive out a good deal of their loosely held 

water. Subsequent careful analysis confirmed this view, for each rock that gained in 

weight was found to hold a relatively large amount of water removable at 105°, and the 

microscope revealed the presence of zeolitization in them and not in the others. Hence, 

this procedure may sometimes be of value as a test for the presence of zeolltic minerals 

in advance of or as confirmation of the microscopic diagnosis.

1 Building and ornamental stones of Wisconsin : Bull. Wisconsin Geol. Nat. Hist. Survey 

No. 4. 1898, pp. 63, 70.
52 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

 These are dried for at least 24 hours at 110° (100° is not high 

enough to insure the removal of all interstitial water) and weighed 

to centigrams. They are then placed on the bottom of a large 

bottle, the cork of which can be hermetically sealed. Through the 

cork pass three tubes, two of which end below the cork and connect with a vacuum pump and manometer, respectively. The third 

tube, provided with a gtopcock, ends near the bottom of the bottle and 

leads on the outside into a basin of water which can be heated to boiling. The bottle itself rests in a water bath, so that its contents 

can be kept hot all the time. At first the cubes rest in a shallow 

layer of water only, the better to facilitate the escape of air and 

entrance of water under reduced pressure, which should not exceed 

one-twelfth of an atmosphere. The cubes should remain in this state 

for 72 hours, experiment having shown that little or no absorption 

takes place after this lapse of time. Water is let in slowly from time 

to time, till the cubes are wholly immersed. In this way, it is thought 

thorough saturation can. be attained. The saturated samples are 

transferred to an open dish filled with water and taken to the balance, where their weight in water is ascertained by .suspension. They 

are then removed from the water, rapidly dried on the surface with 

bibulous paper, and the weights then taken in air. 1 They are dried at 

110° for 24 hours and again weighed. The second dry weight was 

found by Buckley to vary from the first rarely by as much as 0.2 

gram, and often by not more than 0.01. " When reckoned in per cent, 

the error would be such a small fraction of 1 per cent as not to be 

worthy of attention. The specific gravity was determined by dividing the average of the two dry weights by the difference between the 

dry weight and the weight of the cube suspended in water." For 

arriving at the true porosity or actual pore space compared with the 

volume of the sample tested, the following formula is to be used:

(B-A) sp. gr. 100 _p 

(B-A) sp. gr. + A

in which A is the average dry weight, B the saturated weight, and P 

the percentage of porosity or actual pore space. The value thus

1 The above procedure differs from that of Buckley in the inversion of the order of 

weighing in water and after wiping. The more perfect the vacuum the less need be the 

temperature of the bath of immersion to insure the effictive aid, by boiling of the water 

drawn up into the pores of the specimen, in securing expulsion of the inclosed air. A 

vacuum desiccator can perhaps be substituted for the bottle with much advantage. It will 

not be necessary to open the desiccator for the periodic introduction of water if to the 

evacuating tube is attached a Y or T with stopcocks, one branch leading to the pump 

and manometer, the other to a basin of water. By proper regulation of the cocks water 

can be drawn in at pleasure. In a later publication (Missouri Bureau Geol. and Mines, 

2d ser., vol. 2, 1904) Buckley states that he has reduced the time of immersion to 24 

hours and the vacuum to one-fourth of an atmosphere without finding appreciable differences in the results obtained.
SPECIFIC GRAVITY. 53

obtained is always much higher than that ordinarily taken as the 

measure of porosity. This last would better be called, according 

to Buckley, "ratio of absorption," being found by dividing the 

weight of water absorbed by the dry weight of the stone and multiplying by 100. Buckley finds no definite relation between porosity 

and ratio of absorption, although in a general way the former is a 

little more than twice the latter.

In calculating the weight of a stone in pounds per cubic foot the 

pores should be included in this volume. The weight sought is found 

by multiplying the apparent specific gravity by 62.5 that is, by the 

weight of a cubic foot of water. The apparent specific gravity can be 

calculated from the above data by the formula

B-C

in which A is the dry weight, B the saturated weight, and C the 

weight in water.

T. W. Thorner 1 and H. Seger and E. Cramer 2 have described 

apparatus alike in principle for determining porosity by the use of 

which a direct specific-gravity determination is avoided and the operations are very simple. The apparatus of Seger and Cramer are of 

simpler construction than those of Thorner, and have stood the test 

of many years' use. By both, however, the true porosity as well as 

the " ratio of absorption " is ascertainable.

In the Proceedings of the American Society for Testing Materials 

for 1918, page 588, is given a tentative standard method for the determination of .porosity and volume changes in refractory materials.

c. PENFIELD'S METHOD FOE MINERAI, FRAGMENTS.

Penfield 3 recommends the following modification of the suspension 

method as more convenient than that by the pycnometer in many 

cases for small fragments of minerals.

After boiling in water, the substance is transferred with water to 

a small glass tube about 8 by 35 mm., provided with a fine platinum 

wire for suspension. This is weighed full of water in another vessel 

of water, and again after the removal of the mineral, the weight of 

which is found after drying.

The method is of course more applicable to homogeneous minerals 

than to rock fragments and will therefore be applied in rock analysis 

chiefly to the determination of the specific gravity of the mineral 

grains separated by heavy solutions or acids.

'. ^hem. Zeitung, vol. 29, 1005, p. 744. 

2 Idem, p. 884. 

8 Am. Jour. Sci., 3d ser., vol. 50, 1895, p. 448.
54 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

B. PYCNOMETER METHOD, 

a. OEDINAEY METHOD.

For determining the specific gravity of materials of fine grain the 

pycnometer method has to be used. A good procedure is that 

adopted in the Survey laboratory by L. G. Eakins a number of years 

ago, provided there is no evaporation whatsoever around the stopper 

of the pycnometer, a condition seldom, if ever, fulfilled, unless a 

thin film of vaseline is used, the weight of which need not exceed 

half a milligram. The pycnometer used is one with a capillary stopper, 

provided with a millimeter scale etched in the glass, the divisions 

being numbered both ways from the center and calibrated by mercury, so that the value of each one in weight of water is known. The 

capacity of the flask filled with water to the zero division is then 

calculated for every half degree of temperature from 0° to 30° by 

making a series of careful weighings in which, the capacity of the 

stem being known, it is quite immaterial at what level the water 

stands, provided it is within the limits of the scale. The exact 

temperature is obtained by an accurate thermometer placed in a 

companion vessel of shape similar to that of the pycnometer and 

containing a like amount of water, both being left in the balance case 

till its temperature has been nearly or quite assumed, as shown by a 

second thermometer. The weighing must of course be made before 

the thread of water has sunk beneath the lowest division, which it 

will do after a time, even though at first filling the bore to the top of 

the stopper; and the corrected weight of the flask full of water to 

the zero mark is found by adding or subtracting the needed amount, 

as shown by the height of the thread on the scale.

For each of the pycnometers in use, and they are of different 

sizes, is prepared a table showing its weight, the value of each scale 

division in grams of water, and the capacity of the flask at different 

temperatures, as indicated above. The preparation of such a series 

of flasks is time saved in the end, for the weighing of the flask full 

of water each time a density determination is made is rendered superfluous. All that is necessary is to look up in the table the weight 

corresponding to the temperature.

The density of the previously weighed substance is now determined in much the same way as in A. a, page 50, after the unstoppered pycnometer containing it and nearly filled with water has stood 

with its companion vessel of water under the air pump the necessary 

length of time. The water needed to fill the flask is taken from its 

companion.

All who have used the pycnometer method for fine substances know 

the difficulty experienced in preventing some of the material from
SPECIFIC GRAVITY. OJ

being held at the surface, despite all attempts at making it sink. 

Hence it often happens that a very small portion runs out around 

the sides of the stopper on inserting it. If the flask rests in a small 

tared dish the grains thus forced out may be washed down into it 

and weighed after evaporation in order to get the correct weight of 

what is in the flask; or, after weighing, the contents of the flask may 

be emptied into a tared dish and the water slowly evaporated off in 

order to get the weight of the mineral. Usually this way is less to 

be recommended than the other.

b. REFINED METHOD.

In their elaborate study of the thermal properties of the feldspars x 

A. L. Day and E. T. Alien found the ordinary methods of specificgravity determination of powders by the pycnometer to be affected 

with grave errors. To eliminate these in great degree they use 

special pycnometers and precautions (slightly modified since publication) which are described in the paragraphs that follow. With 

25-cm.3 pycnometers and 5 to 10 grams of material of from 2.50 to 

2.75 specific gravity the error from all causes should never be greater 

than one unit (±1) in the third decimal place.

A chief source of error is the evaporation of water around the stopper. In order to reduce this to a negligible quantity, the grinding 

should be very fine and the stopper should be vaselined slightly before the final weighing. If the exc,ess of vaseline is carefully wiped 

off, the error due to its weight will not affect the result in the third 

decimal with 25-cm.3 flasks. The best flasks are those with capillary 

stoppers, made with the glass of the necks 2 mm. thick, so as to 

avoid springing when the stopper is pressed in, and ground square 

off to prevent the adhesion of a film of water between stopper and 

neck above the joint. With the stopper slightly vaselined, such a 

flask does not lose at 30° more than 1 to 1£ milligrams of water per 

half hour.2

To obviate another serious source of error,3 incomplete removal of 

air from the powder and undue loss of powder during filling and 

stoppering, the device of G. E. Moore 4 is used, slightly modified, as 

shown in figure 8. The flask containing the powder is attached to a

1 Pub. Carnegie Inst. Washington No. 31; and in less detail in Am. Jour. Sci., 4th ser., 

vol. 19, 1905, p. 93 ; Zeitschr. phys. Chemie, vol. 54, 1905, p. 1.

2 J. Johnston and L. H. Adams (Jour. Am. Chem. Soc., vol. 34, 1912, p. 567) have 

modified the pycnometer with the object in view of attaining still greater accuracy. The 

new feature is a plane ground joint between bottle and stopper. The neck of the bottle 

is made especially thick at the upper end in order to provide sufficient surface for the 

cap to rest upon. The cap is not perforated, but its lower face and the top of the neck 

are made optically flat so as to give a perfect Joint that allows no escape of water. 

Such perfect surfaces are very difficult to prepare. With this instrument the results differ 

only in the fourth decimal, a degree of accuracy quite uncalled for with rock powders.

3 See footnote 2, p. 49.

* Am. Jour. Sci., 3d ser., vol. 3, 1872, p. 41: Jour, prakt. Chemie, vol. 2, 1870, p. 329.
56 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

water pump, with the intervention of a tube and bulb attachment, as 

shown. The bulb A contains boiled water. When the system has 

been nearly freed from air by the pump, water from A is made to 

flow into the flask. Then by tapping and plunging the flask into 

 water warmed to 40° to 50°, in order to produce boiling within the 

flask, the air is soon removed. During the boiling powder will 

usually be thrown up into the connecting tube; but this can be washed 

back by water from A or, after disconnecting, by boiled water from 

a wash bottle. Should any particles remain in the tube, they are 

washed into a tared dish and weighed, after evaporation of the water. 

It is absolutely essential that not the smallest grain be caught between 

the stopper and the neck. To this end the neck is wiped out with a 

bit of filter paper, which is burned in the tared dish in order to obtain the proper correction.

Aspirator

Pycnometer 

with-charge

FIGURE 8. Moore's device to remove air from mineral powders.

Constant temperature is attained in a water thermostat electrically 

regulated to tenths of a degree at a temperature slightly above that of 

the balance case. In the thermostat there is also placed a small vessel 

with water for the final filling. If the powder is very fine, the flask 

may have to remain in the thermostat several hours to allow complete settling before wiping the neck, vaselining, and stoppering. 

When the flask is filled and stoppered, it should be returned to the 

thermostat for a time, with a short piece of rubber tube slipped part 

way over the end of the stopper, so as to form a cup for a drop of 

water and insure that the capillary remains filled. At the proper 

time the rubber is removed and the flask wiped quickly with bibulous 

paper and weighed without delay. A blank test must of course be 

made with water alone, or the pycnometer may be calibrated once 

for all within any desired range of temperature. A determination of
PREPARATION OF SAMPLE. 57

the accuracy attainable in this way is subject to a correction for 

buoyancy.

(See p. 70 for remarks by Day and Alien on another source of 

error in the determination of the specfic gravity of powders.)

0. HEAVY SOLUTIONS NOT SUITABLE FOR ROCKS.

Because of their roughness, porosity, and complex mineral composition the density of rock fragments can not be determined accurately 

by that of heavy solutions in which they may remain suspended.

3. PREPARATION OF SAMPLE FOR ANALYSIS. 

A. QUANTITY OF ROCK TO BE CRUSHED.

The amount of -material that must be used in preparing the 

analysis sample varies. Most rocks are well represented by a few 

chips from a hand specimen, but if a rock in which porphyritic 

structure is strongly developed is to be analyzed a large sample 

should be provided, gaged according to the size of the crystals, and 

the whole of this should be crushed and quartered down for the 

final sample. Unless this is done, it is manifest that the analysis 

may represent anything but the true average composition of the 

rock. The geologist should see that a fairly representative sample is 

provided, else the chemist's work, however careful, may count for 

little.

B. CRUSHING.

/

For accurate analyses the use of steel power crushers and mortars 

is out of the question because of the danger of contamination by 

particles of metal and the impossibility of cleansing the roughened 

surfaces after they have been in use a short time. Extraction, by 

the aid of a magnet, of steel particles thus introduced into the 

powder is quite inadmissible, for the rocks themselves, almost without exception, contain magnetic minerals.

a. SURVEY METHODS,

For breaking large pieces of rock to small sizes a thick steel plate 

with specially hardened surface and a similarly hardened pounder, 

such as street pavers use, will probably render the best service, but 

the hardening must be done with extreme care.

A method of rough crushing on a small scale that gives fair satisfaction in practice is to place each fragment as received on a hard 

steel plate about 4r| cm. thick and 10 cm. square, on which is likewise 

placed a steel ring 2 cm. high and of about 6 cm. inner diameter, to 

prevent undue flying of fragments when broken by a hardened ham-
58 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

mer. In this way a considerable sample can soon be sufficiently reduced for transfer to the agate grinding mortar with a minimum of 

metallic contamination.

This method is now superseded in the Survey laboratory by one 

devised by C. W. H. Ellis, mechanician in the geophysical laboratory 

of the Carnegie Institution, which entirely obviates loss of material 

by flying fragments. The method of operating is apparent from

figure 9. The block, cylinder, 

and pestle are of the best 

chilled tool steel, surface 

hardened to the utmost limit. The cylinder fits snugly 

into a depression in the block, 

after the manner of an ordinary " diamond " mortar, but 

the pestle has a diameter less 

than the inner diameter of 

the cylinder. The crushing is 

done by the pestle, without 

the aid of a hammer, and may 

be carried so far, if necessary 

(see C, p. 60), as to furnish 

by the aid of a fine sieve, preferably of the best silk bolting 

cloth, a powder that is fit for 

analysis without needing further pulverization in a mortar. For very many rocks 

and minerals a material that 

passes a sieve of 30 meshes 

to the linear centimeter can 

be used directly for the analysis. Much the greater part 

of this will consist of grains of a diameter less than that of the 

mesh of the sieve, even when the intervals between successive applications of the pestle and siftings are very short.

Metal sieves must on no account be used if search is to be made 

for elements identical with those of which the sieves are made.

An imperative precaution, when using either of these methods, 

however, is to refrain absolutely from the least grinding or rubbing 

motion, with the hammer in the one case or the pestle in the other. 

Even quartz can be broken down by vertical blows to a size fit for 

the agate mortar without showing any darkening in color, whereas 

if a rubbing motion has been employed to even a slight extent, the 

powder will, by contrast, be perceptibly dark after grinding in the

FIGURE 9. Ellis's mortar for crushing coarse 

materials. All parts of best chilled and surface-hardened tool steel. A, Block, 12| by 

12J by 6 cm., with depression in center 0.6 

cm. deep; B, pestle, 20 cm. high, 3.5 cm. 

diameter at base; C, cylinder, 12J cm. high, 

5 cm. outside diameter, 4.4 cm. inside diameter, fitting accurately the depression in the 

block.
PKEPAKATION OF SAMPLE. 59

mortar. The hardest steel is very susceptible to abrasion by minerals 

less hard than quartz. 1 The crushing must be carried to such a 

degree of fineness that after transferring the grains to the mortar 

the grinding motion of its pestle will not occasion further loss of flying particles because the portions lost will not have the same composition as those retained unless the material is glassy or very finegrained.

If grinding is not to follow crushing, the sieve should be chosen 

of a mesh that will afford a powder susceptible of complete or nearly 

complete decomposition within 20 minutes by boiling with dilute 

hydrofluoric acid (see C, below, and 21. A, p. 192). In order to obtain the minimum of " flour " it is important to sift at very frequent 

intervals. Some flour is, however, essential to the production of a 

homogeneous sample when flaky minerals, like the micas, are present. 

If the flour is first separated from a micaceous powder, no amount 

of mixing of the coarser material will afford a sample in which the 

mica does not show in streaks instead of being uniformly distributed. 

The sample finally obtained is to be very thoroughly mixed on glazed 

paper or by gentle shaking in a clean bottle. 

b. WASHINGTON'S METHOD.

The rock is first reduced, as by the methods described in a, to lumps 

that will fit into a " diamond " steel mortar of Plattner's form, the 

bottom of the cavity being hemispherical and matched in shape by 

the end of the pestle. The lumps are crushed, one by one, in the 

mortar by a dozen blows of a half-pound hammer (billet of wood, 

Dittrich), and the contents of the mortar are emptied into a cylindrical glass box about 3.5 cm. deep and 7.5 cm. in internal diameter, 

with walls about 2 mm. thick. When the whole sample, or a quartered portion if large, has been thus crushed a piece of best silk bolting cloth with about 25 meshes to the linear centimeter is stretched 

over the open side of the box and clamped fast by a brass ring 1 cm. 

in height. The box is now inverted and the finest powder gently 

sifted onto a sheet of glazed paper. The material left on the cloth, 

is recrushed in the mortar and resifted, these operations being repeated until nearly all has passed the sieve. The final small oversize 

portion is ground in an agate mortar. It will, of course, not do to

1 When the crushing has been done with proper care, the amount of steel contaminating 

the sample is so small as to cause no important error. This steel is for the most part apparently not in splinters but as thin films on the mineral grains. Its presence can be 

shown readily by grinding the crushed sample to a very fine powder in presence of 

water. The films thus become separated from the grains and still further flattened, 

and as the grinding progresses they rise as a visible scum to the surface of the water, 

whence they can be removed by careful handling of a magnet. This behavior of the 

films might perhaps afford a means of testing for native iron in rocks, provided the use 

of steel for crushing could be avoided altogether.
60 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

reject any portion, for thereby the composition of the mass will be 

affected.

Washington finds that in this way there is no danger of serious 

contamination by metallic iron (see preceding footnote) and that 

any error resulting from the introduction of cloth fiber is negligible. 

This last will hardly be true of the method practiced in parts of 

Europe (the German "beuteln"), which, at1 least as it was carried 

out in Bunsen's laboratory, differs in essential points from the 

gentle sifting recommended by Washington.

C. GRINDING.

Ordinarily an extremely fine state of division of the analysis 

sample is unnecessary, except for those portions in which alkalies 

and ferrous iron' are to be determined or where soluble constituents 

are to be removed by acids, etc., and for such portions the final 

grinding can be done at the balance table on a small quantity of the 

crushed sample.

Not only is fine grinding for most purposes needless, but it may 

be positively harmful, allowing escape of contained gases, and, as 

R. Mauzelius has shown,1 it is absolutely imperative for the correct 

determination of ferrous iron to use the coarsest powder that can 

be decomposed completely by the method of attack employed. I 

have since shown 2 that this is true for the water that is not given 

off at 100°-110°. Mauzelius finds that the finer the material (containing ferrous iron) is ground the less ferrous iron is found. In all 

his experiments on rocks and on iron-bearing minerals separated 

from rocks the oxidation was marked and in the most extreme case 

amounted to about 40 per cent of the total ferrous iron (3.13 per 

cent FeO found in the finest powder against 5.13 per cent in the 

coarsest). This totally unexpected behavior has been confirmed by 

me. (See 21. A, p. 189.) The necessity for an entire reversal of the 

hitherto prevalent practice of preparing a very fine powder for the 

ferrous-iron determination is obvious.

The preparation of two samples, one coarse for the ferrous iron 

and another much finer for the other constituents, though perhaps 

unavoidable at times, is objectionable for several reasons. (1) The 

finer the powder the more loosely held (hygroscopic) water it contains, easily 5 to 20 times as much as unground grains, and also the

1 The determination of ferrous iron in rock analysis: Sveriges geol. Undersokning, 

Arsbok 1, 1907, No. 3.

2 The influence of fine grinding on the water and ferrous iron content of minerals and 

rocks: Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120; Chem. News, vol. 98, 1908, pp. 

205, 215. J. W. Mallet (Phil. Trans., vol. 171, 1880, p. 1017) seems to have been the 

first to notice that mechanical crashing could expel water from hydrous minerals (alum). 

He ascribed the effect to heat developed by the crushing, a view with which I am in 

accord. Carey Lea (Phil. Mag., vol. 34, 1892, p. 36; vol. 37, 1894, p. 31), however, 

regards mpdiflFic*! stress, especially shearing stress, as the effective factor.
PREPARATION OF SAMPLE. 61

more water that is not given off at 100°. If two samples are used 

the water given off both below and above 100° must be determined 

in each and a correction applied to the other constituent or constituents that may be determined in the finely ground sample. (2) The 

composition of the unground sample will differ in another respect 

from that of the ground material by the amount of silica derived 

from the mortar. This may easily reach or exceed one-half of 1 per 

cent of the weight of the mineral powder (see p. 63), depending on 

the hardness of the minerals and on the length of grinding.

In order to obviate the need for two samples I have made experiments with a view to secure fine grinding and at the same time avoid, 

oxidation. These experiments need to be multiplied before positive 

conclusions can be reached and precise directions formulated. So far 

as they go, however, they show that grinding in a nonoxidizing 

medium, such as absolute alcohol, is fairly satisfactory. Water is 

somewhat less satisfactory, notwithstanding the lower solubility in 

it of oxygen.1 Alcohol does not seem to exercise a reducing effect on 

ferric minerals when they are ground in it. These experiments have 

served to show at the same time that the oxidation of the iron is not 

due merely to the greater exposure of surface, but-that it is probably 

aided by intense local heat from friction and fracture of the grains 

uncler the pestle. Probably grinding in an inert gas would be more 

satisfactory, but while this might be arranged with a mechanical 

grinder, it would be impossible when the grinding has to be done by 

hand, and in any case it would involve much inconvenience and 

trouble. When alcohol is used, it should be in small quantities at a 

time, enough to wet the powder thoroughly and to give a very liquid 

mass. A second and third application of alcohol are sometimes 

needed, because of the rather rapid evaporation. When the grinding 

is finished the alcohol is allowed to evaporate spontaneously under 

a cover placed a few centimeters above the mortar and pestle, so as 

to exclude falling dust and yet allow free circulation of air. When 

thoroughly free from alcohol the powder is removed gently from 

mortar and pestle with a flexible knife blade and then bottled.

Formerly all rock samples in the Survey laboratory were, after 

crushing, reduced to powder by hand grinding, with expenditure of 

much time and labor. Since then, except in special cases, the work 

has been done by mechanical grinders run by a small electric motor. 

It will be evident from the foregoing statements, however, that hereafter such grinders are likely to be less used than they have been.

The grinder manufactured by the McKenna Brothers Brass Co. 

(Ltd.), Pittsburgh, Pa., is shown in figure 10, with the addition of 

simple attachments intended to keep metal dust and oil out of the

1 Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120; Chem. News, vol. 

98, 1908, pp. 205, 215.
62 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

mortar. These additions have been found to be quite essential for 

the Survey work. As made for the technical industries the machine 

is largely of brass, nickel plated, but the latest made for the Survey

FIGURE 10. McKenna ore grinder, slightly modified by the addition of the following 

attachments to prevent oil and dust from belts and bearings from entering the 

mortar. A, Copper cup soldered to head of pestle holder. This partakes, without 

the slightest friction, of the .motion of the latter. B, Tin plate with deep sinus, the 

latter being covered in turn by the rubber cloth, C, which fits closely about the metal 

shaft. " The spring at the top of the sliding rod, to which the agate pestle is attached 

at the bottom, can be adjusted to give any desired pressure or can be thrown back 

entirely to allow the pestle to be raised in removing the agate mortar. This is accomplished by loosening a set screw and dropping one of the four posts holding the 

mortar in place. The pestle should make about 200 revolutions per minute, the mortar 

moving very slowly in the same direction. The scraper keeps the ore in the center of 

the mortar and the combined rolling and sliding motion controlled by the b&ll and 

socket supporting side arm reduces the hardest ore very rapidly." Iron Age.

is of steel throughout, without plating. It was found that the pulley 

belts caused too much abrasion of the softer metal to permit its use 

for much of the Survey work, on account of the danger of copper,
PREPARATION OF SAMPLE. 63

zinc, and nickel getting into the sample in traces, and that in spite of 

a very limited use of oil this invariably became scattered over the contents of the mortar, though its presence never became visible to the 

eye except when white materials were ground. The last contamination is prevented by the copper cylinder, A, soldered securely onto 

the pestle holder so as to form a cup large enough for the purpose 

intended. The tin shield, B, with a superposed rubber cloth, C, covering the slit required for the proper adjustment of the shield, 

greatly lessens the danger of metallic contamination, even with the 

all-steel machine. At first it was thought that a rubber cloth covering the mortar, with the pestle snugly fitting a hole in the cloth, 

would be an effective protection, but it was found that there was sufficient friction on the rubber itself to cause contamination of the 

powder beneath.

With this apparatus a large amount of work can be done in a short 

space of time though there is much loss of fine powder if the speed of 

revolution is too high. In the Survey laboratory three of these machines are operated, one or all, on a single table from the same shaft, 

the whole being covered with a glass case divided by glass partitions, 

so as to exclude dust from the room and to separate the grinders.

D. ABRASION OF MORTAR AND PESTLE.

The abrasion of crushing apparatus has been touched on in B.

The abrasion of pestle and mortar becomes far more manifest 

with machines like that shown in figure 10 than with hand grinding, notwithstanding the fact that each has its motion simulating as 

far as possible that of the hands. There is undoubtedly a very considerable introduction of silica into the sample from these sources, 

but in comparison with the amount invariably present in an igneous 

rock the quantity abraded is hardly of moment. Rocks normally 

free from silica, or nearly so, like many iron ores, are as a rule softer 

than igneous rocks and consequently cause less abrasion of the grinding implements.

E. T. Alien, in order to get an idea of the amount of silica introduced into an ordinary rock sample through the abrasion of the 

grinding implements, caused 200 grams of quartz sand to be ground 

in portions at a time till all passed a sieve of 150 meshes to the 

linear inch (60 to the centimeter), the time required being 19.5 

hours,. The mortar (635 grams) lost 0.189 gram in weight and the 

pestle (268 grams) lost 0.102 gram, a total of 0.291 gram, or 0.145 per 

cent of the weight of the sand. The powder obtained in this case 

was less fine than that ordinarily sought at that time by rock 

analysts, but, on the other hand, the material was all quartz, a mineral much harder than most of those constituting the average rock.
64 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

W. Hempel 1 has tested experimentally the effect of grinding in 

mortars of agate, glass, iron, and hardened steel and has found that 

for hard bodies, like glass, hardened steel is far superior to agate, 

and that even mortars and pestles of green bottle glass showed much 

less abrasion than agate. In grinding 10 grams of glass to very 

fine powder the agate mortar and pestle, weighing 416 grams, lost 

0.052 gram in weight (or 5 mg. per gram of glass), against a tenth 

of that loss with a hardened steel mortar and pestle of the same 

weight that had been some time in use.

Notwithstanding these observations in favor of steel, the use of 

metal in rock analysis is, as said above, forbidden by the conditions 

of the case. Still more so is that of glass because of its complex 

composition. If impurity can not be avoided, it is far better that it 

should be of one kind only, and that one productive of less disturbance than any other.

E. WEIGHT OF SAMPLE.

The sample when crushed or ground should weigh not less than 

10 grams, and preferably 20 in case it should be necessary to repeat 

or advisable to employ unusually large portions for certain determinations, notably carbonic acid. Eock analysis has in this respect 

an advantage over mineral analysis, as rock material is almost always 

available in- ample quantity and any desired number of separate 

portions may be used, whereas with a mineral the analyst is frequently compelled to determine many or all constituents in a single, 

perhaps very small portion of the powder. This course often involves delay and the employment of more complicated methods of 

separation than are usually necessary in rock analysis.

4. WATER GENERAL CONSIDERATIONS.

A. THE ROLE OF HYDROGEN IN MINERALS.2

As the purpose of this bulletin is primarily the instruction and 

guidance of the analyst, it has been thought best to curtail the discussion of the role of hydrogen in minerals given in the last edition, 

and to include here only such data as are likely to be of direct aid 

in the interpretation of the analytical results. Fuller discussions of 

certain more general aspects of the subject will be found in the

1 Zeitschr. angew. Chemie, 1901, p. 843.

2 This section was prepared by Edgar T. Wherry, H. E. Merwin, and Elliot Q. Adams, 

on the basis of the matter on this subject in Bulletin 422.
WATEK. 65

works listed in the footnote,1 although it should be noted that the 

changes in viewpoint as to crystal structure, solid solution, etc., 

during recent years render many of the conclusions of the earlier 

writers of doubtful validity.

a.. CONDITIONS IN WHICH HYDROGEN MAY OCCUR.

The table which follows presents a classification of the ways in 

which hydrogen (especially that given off as water) may occur in 

minerals, representing an enlargement upon the " provisional classification " given in Bulletin 422. In using this table it should be 

borne in mind that the subdivisions are not, in general, sharply 

delimited, but that .a certain amount of gradation between them 

exists; that a given mineral may contain hydrogen in several different 

forms; and that some of the hydrogen originally present in one form 

may pass into another on grinding or on heating.

Classification of the condition of hydrogen in minerals, mineral aggregates, and

mineral powders.

A. Essential hydrogen present in regular atomic arrangement in molecular 

or crystal structure.

I. Present in definite, stoichiometric proportions.

a. As hydrogen called acidic by analogy to behavior in solutions. 

b. As hydroxl the hydrogen called basic, again by analogy, 

c. As water especially water of crystallization.

II. Not present in stoichiometric proportions with reference to the substance as a whole, but present, in one of the above forms, 

in one or more of the constituents of mix crystals, including isomorphous mixtures. 

B. Nonessential hydrogen its presence not necessary for characterization of the

mineral. (Considered as water or other compounds.) 

I. In liquid solution, specially in deliquescent powders, also in amorphous material, including undercooled liquids. 

II. Held by surface forces.

a. Absorbed on surfaces in films of molecular thickness.

1. On walls of cavities within grains of aggregates.

2. On exteriors of grains.

1 Le Chatelier, H., Zeitschr. physikal. Chemie, vol. 1, 1887, p. 396; Compt. Rend., vol. 

104, 1887, pp. 1443, 1517 ; Bull. Soc. frang. min., vol. 10, 1887, p. 204.

Hamberg, A., Geol. Foren. Forh. Stockholm, vol. 12, 1890, p. 591.

Tammann, G., Zeitschr. physikal. Chemie, vol. 10, 1892, p. 255; idem, vol. 27, 1898, p. 

323 ; Zeitschr. anorg. Chemie, vol. 15, 1897, p. 319.

Van Bemmelcn, J. M., Zeitschr. anorg. Chemie, vol. 13, 1897, p. 233, and subsequent 

volumes.

Tschermak, G. Zeitschr. physikal. Chemie, vol. 53, 1905, p. 349; Zeitschr. anorg. 

Chemie, vol. 63, 1909, p. 169.

Panichi, U., Pubbl. Inst. studi pract, etc., Sez. di sci. fls. e nat., 1908, p. 1. Lengthy 

abstract in Neues Jahrb., 1910, Band 2, p. 2 of Referate.

Zambonini, F., Mem. Accad. sci. fls. mat. Napoli, vol. 14, ser. 2, No. 1, 1908, 127 pp.

Lowenstein, B., Zeitschr. anorg. Chemie, vol. 63, 1909, p. 69.

Thugutt, S. J., Centralbl. Mineralogie, 1909, p. 677.

Beutell, A., and Blaschke, K., Centralbl. Mineralogie, 1915, pp. 4, 195.

Langmuir, I., Jour. Am. Chem. Soc., vol. 40, 1918, p. 1361.

131999° 19 5
66 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

B. Nonessential hydrogen, etc. Continued.

II. Held by surface forces Continued.

b. Held by capillarity, in liquid form.

1. In colloids with mesh structure.

2. In definite openings within grains of aggregates.

3. In spaces between separate grains. 

III. Included.

a. As liquid droplets in cavities.

b. As included grains of minerals belonging to one of the abore 

listed classes.

The following notes will help to interpret the table.

A. I. Investigations by X-rays and infra-red radiation indicate that groups, 

such as OH and H3O, may have identity within crystals, so the separation of 

essential, stoichiometric, hydrogen into three classes, a/b, and c, is believed to 

be justified.1

A. II. This class is intended to include such minerals as topaz, which is believed to consist of an isomorphous mixture of two end members, one hydrous and 

the other anhydrous, Al2 (OH) 2Si04 and ALFzSiO*. As the proportion of these 

members may vary widely, the hydrogen content may vary also; but even though 

the hydrogen is not present in stoichiometric proportions with reference to the 

mineral as a whole, it does bear definite relations to one of the constituent members and is therefore properly considered as essential. It is not necessary, however, that the members entering the substance be isornorphous in the strictest 

sense that is, of homologous formula type; for instance, the mineral turgite is 

believed to be made up of two components Fe2Oa (hematite) and FeO(OH) 

(goethite), in variable proportions, forming mix crystals.2

B. I. The liquid surrounding deliquescing crystals belongs here. A part of 

the water in opal may be dissolved, but probably most of it falls in B. II. b. 1, 

where the water of most hydrous " amorphous minerals " is thought to belong. 

Such substances as liquid hydrocarbons and volcanic glass, though not strictly 

minerals, may be mentioned here.

B. n. a. Adsorption of water in molecular films upon surfaces is believed 

to be a general property of solids, and if the surface exposed is large in proportion to the amount of material involved, the quantity of water thus held may be 

analytically significant. The increase in-water content shown by many minerals 

upon fine grinding represents, thus, chiefly an increase in class B. II. a. 2. A few 

instances are known where water of class B. II. a. 1 is present in appreciable 

amount, one being the fibrous form of goethite, which is generally known as 

limonite."

B. II. b. 1. With reference to this class it may be pointed out that recent 

studies of colloids, among which are to be included many " amorphous minerals," have shown that they often possess a submicroscopic mesh structure, 

water (or other liquid phase) being held in the interstices of this structure. It 

is possible that certain crystalline substances, and in particular certain of the 

zeolite minerals, may contain water in this form also, but this has not been convincingly demonstrated. Classes 2 and 3 under this heading are of special 

significance in connection with finely fibrous minerals, such as the above-mentioned goethite which often contain considerable amounts of capillary water.

1 Coblentz, W. W., Pub. Carnegie Inst. Washington No. 65, 1906; Bull. Bur. Standards, 

vol. 2, 1906, p. 457. Schaefer, C., and Schubert, Martha, Ann. Physik, vol. 50, 1916, p. 

339, Johnson, A., Physikal. Zeitschr., vol. 15, 1914, p. 712.

2 Posnjak, E., and Merwin, H. B., Am. Jour. Sci., 4th ser., vol. 47, 1919, pp. 325, 337.

sIdem, pp. 311-348.
WATER. 67

B. III. Liquid inclusions of either water or hydrocarbons and solid inclusions 

of hydrous minerals may be the source of a considerable content of hydrogen.

b. BEABINQ OF THE CLASSIFICATION ON ANALYTICAL PBOCEDTJEE.

a. Behavior of hydrogen on grinding the mineral. The fine grinding of minerals may lead to either an increase or a decrease in 

total hydrogen content. (See B, p. 69.) An increase is the result 

of the subdivision of grains and the consequent development of a 

greater surface upon which water can be absorbed and otherwise 

held. A decrease is for the most part due to decomposition caused 

by local heating by pressure or by mere change in grain size.

As in general (though by no means invariably) the decomposition 

temperatures of minerals containing water of crystallization are 

lower than those of minerals belonging to other classes, a marked 

loss of hydrogen on grinding may be regarded as pointing to the 

probable existence of the hydrogen in this form (A. I. c). Members 

of other classes, however, show low decomposition temperatures 

with sufficient frequence to render it unsafe to depend too much on 

this criterion. A decrease may of course also be due to the evaporation of water or other hydrogen-bearing liquids originally included 

as droplets (class B. III. a) when the grinding exposes them. 

It is to be inferred from the foregoing discussion that in order to 

be representative of the mineral the sample to be used for determination of water should be ground as little as possible; still the material must be fairly well subdivided in order that the water shall 

be liberated within reasonable limits of time and temperature. The 

effect of grinding on the water content may have at least confirmatory value in the final conclusion as to the role of hydrogen in 

the substance.

@. Behavior of hydrogen on desiccation at constant temperature. 

On exposure of a mineral containing essential hydrogen which is 

given off as water to an atmosphere in which the partial pressure of 

water vapor is being continuously diminished, water is likely to be 

lost discontinuously. Hydrogen of class A. II may, however, behave 

differently; this class requires further investigation.

The behavior of nonessential hydrogen is likely to vary with the 

class concerned. If it is included (class B. III. a and b), no loss is 

to be expected. If it is held by capillarity (B. II. b), the mode of 

loss will depend on the size and shape of the capillary openings. 

Water absorbed on the surfaces of grains probably will be lost continuously that is, it will be given off gradually as the water-vapor 

pressure diminishes, and dehydration will not be complete at any 

definite pressure. Hydrogen dissolved in " amorphous" material 

(B. I) would be expected to behave likewise.
68 ANALYSIS OF SILICATE AND CARBONATE ROCKS. ,

The change here described is often reversible, water that has been 

lost by decreasing the aqueous vapor pressure being taken up again 

when this pressure is increased. Such rehydration may often be more 

readily followed than the original loss of water, and the continuity 

or discontinuity of the effect be more certainly determined thereby. 

In any thorough study of the role of hydrogen in a mineral, both 

dehydration and rehydration data should be obtained and preferably 

represented graphically, for conclusions as to the relations existing 

are often best drawn from the examination of curves.

 f. Behavior of hydrogen (expelled as water] on heating* The 

behavior of hydrogen which is expelled as water on heating a 

mineral substance may be considered under three heads.

1. Heating to approximately constant weight at each step of a 

series of increasing temperatures in an atmosphere of uniform or 

regularly changing and usually small water-vapor pressure.

Minerals containing essential hydrogen are likely to lose it discontinuously that is, at one or more rather definite temperatures. 

The temperatures at which dehydration occurs in dry air depend 

chiefly on the element or elements with which the hydrogen, hydroxyl, or water is associated. But, aside from this, in class A. I. a, 

" acidic " hydrogen, the dehydration temperature is likely to be relatively high ; in A. I. b, " basic " hydrogen, somewhat lower ; and in 

A. I. c, water of crystallization, relatively low, especially for the 

first water given off from a series of hydrates. In this case the 

water from two or more states of hydration may come off at one 

temperature unless the surrounding atmosphere has a carefully controlled and rather high-water content.

The escape of water from mix crystals is likely to be gradual as 

temperature increases, but experimental results are lacking.

Nonessential hydrogen is most likely to be given off continuously, 

but there are exceptions. For example, included water may escape 

discontinuously as the cavities containing it are burst open (decrepitation of the mineral) ; and even capillary water may escape more 

or less discontinuously if the heating changes the size of the pore 

spaces.

2. Heating with continuously increasing temperature, the watervapor pressure being largely determined by the dehydrating substance.

The rate of loss of water as determined by frequent weighings 2 

or by Le Chatelier's method of heat absorptions is either discontinuous or continuous, about as stated in the preceding section, except

1 Thermal dehydration may give some other hydrogen compound, HC1 from 

for example.

2 Hillebrand, W. F., Merwin, H. E., and Wright, F. E., Proc. Am. Philos. Soc., vol. 53, 

1914, p. 45; Zeitschr. Kryst, vol. 54, 1915, p. 221.
WATER. 69

that the temperatures at which discontinuities occur are much influenced by such factors as rate of heating, state of subdivision of the 

material, and method of agitating the material during heating; the 

discontinuities themselves, however, tend to be more marked, especially in case of a series of hydrates.

3. Determination of vapor-pressure curves in cases of reversible 

changes in water content.

This determination gives very definite information concerning the 

state of hydration of a substance, but it is not commonly made as an 

analytical procedure.

C. EFFECT OF DEHYDRATION ON PHYSICAL PBOPERTIES.

In general the crystallographic, optical, and other properties are 

likely to be profoundly changed by dehydration when the hydrogen 

is essential, and but slightly changed when it is nonessential. There 

are here, however, as in most other phenomena, important exceptions 

to the rule. In particular, some of the zeolite minerals, in which the 

water is presumably in part essential, may show only minor changes 

in their properties when they are partly or even completely dehydrated. In minerals of class A. II, also, the change in properties incident to loss of water may be but slight. On the other hand, when 

minerals contain considerable quantities of nonessential water, 

marked changes in properties may result upon its removal.1

d. CONCLUSION.

From the foregoing discussion it is evident that while determination of the condition of hydrogen in minerals is by no means a simple 

matter, considerable information upon it may be obtained by appropriate analytical procedure. No conclusions should be drawn from 

single observations, but when the results of several methods of study 

show converging indications, it is quite possible to decide, for the 

majority of minerals, the condition in which their hydrogen is 

present.

B. WATER TAKEN UP OR LOST ON GRINDING.

Before considering methods of determining water attention must 

again be called to the effect of fine grinding of mineral powders on 

their ability to take up from the air and retain at temperatures far 

above 100° very appreciable amounts of water, even in excess of 1 

per cent. (See p. 60.) The following table contains typical data 

on this subject. For fuller details see the paper already cited.2

1 Larsen, E. S., and Wherry, E. T., Jour. Washington Acad. Sci., vol. 7, 1917, pp. 178, 

208.

3 Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120; Chem. News, vol. 98, 1908, pp. 205, 215.
70 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Water content of powders of varying fineness, ground in air.

No.

la 

Ib

1C

2a 

2b 

3a 

3b 

4a 

4b 

5a 

5b 

6a 

6b

Material.

1 Diabasic norite or gabf bro.

\Altercd basaltic greenf stone.

JMeerschaum ..........

\Unglazed Berlin porce- 

/ lain.

Condition.

<60 meshes to 1 cm .................... ..............

<CO meshes to 1 cm ...................................

Water.

Below 

100°.

Per cent. 

0.03 

.10 

.74 

.22 

1.70 

1.01 

1.18 

None. 

.35 

5.76 

6.33 

None. 

.62

Above 

100°.

Per cent. 

0.66 

.66 

1.00 

3.13 

4.19 

3.40 

3.54 

.06 

.45 

6.79 

9.81 

None. 

.18

On the other hand, water of crystallization may be expelled from 

minerals by long-continued grinding. Thus the content in water of 

a specimen of gypsum was reduced from over 20 to about 5 per cent. 1 

The inference is obvious that water of crystallization should be determined on unground material, if possible.

The following excerpt from the work of Day and Alien 2 on the 

feldspars, already cited, has direct relation t'o the above:

There is another error to which accurate specific-gravity determinations upon 

powdered minerals will be subject unless suitable precaution is taken. The 

exposure to the air during the period of grinding the samples gives opportunity 

for the condensation of sufficient atmospheric moisture upon the grains to affect 

the weight in air. The amount varies measurably with the size of the grains, 

as will be seen from the accompanying data, and probably with the degree of 

saturation of the atmosphere and the time of exposure.

Determination of moisture in 1 gram of powdered mineral upon exposure to

the air. 

[ <=flner than. >=coarser than.]

Mineral.

Orthocla 

AbiAns 

AbiAns 

AbiAni 

AbiAni 

Ab (nati

Orthocla 

Orthocla 

Do.

Orthocla 

Orthocla

artificial glass) ...................................................

artificial crystal) .................................................

artificial glass) ...................................................

artificial crystal) .................................................

se (portion of same) ..............................................

Fineness (meshes to 

the linear inch).

<150..............

Selected, coarse. .. 

<100>120. ........

<100>120.........

<100>120.........

<150..............

<120>150.........

<150. ...........

Still finer.........

E very thing> 100. . 

>150. .............

Moisture.

Gram. 

0.0006 

.0001 

.0010 

.0007 

.0010 

.0006 

.0069

.0011 

.0031 

.0059

.0065 

.0022

1 Jour. Am. Chem. Soc.. vol. 30, 1918, p. 1120 ; Chem. News, vol. 98, 1908, pp. 205-215.

2 Pub. Carnegie Inst. Washington No. 31, pp. 56-67 ; Am. TOUT. Sci., 4th ser., vol. 19, 

1905, p. 93. Consult also Mauzelius, R., Sveriges geol. Undersokning, Arsbok 1, 1907, 

No. 3; and Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120; Chem. 

News, vol. 98, 1908, pp. 205, 215 ; and the footnote on p. 50 of the present volume.
WATER. 71

In the last two groups note that the moisture in graded portions of the same 

sample varies with the fineness.

We also verified the conclusion of Bunsen * that this absorbed moisture is not 

altogether removed at temperatures only slightly\above 100° but requires 600° 

to 800° equivalent to low red heat. Several samples for which the moisture 

had been determined were laid away in corked test tubes for a number of 

weeks, after which redetermination gave exactly the former value.

It is worth noting in this connection that these measured quantities of absorbed water are of the same order of magnitude as those usually obtained 

for the water content in feldspar analyses, where, again, of course, the finer 

the sample is ground for the analysis the greater the possible error from this 

cause. It may be that a part and occasionally all of the moisture usually 

found in these analyses is absorbed and the significance of its presence there 

mistaken.

C. IMPORTANCE OF EMPLOYING AIR-DRY POWDER FOR ANALYSIS.

The time-honored custom of drying a powdered specimen before 

bottling and weighing has long seemed to me one that has no sound 

basis in reason. Its object is plain, namely, that of securing a uniform hygroscopic condition as a basis for convenient comparison of 

analytical results, because some rock powders contain more hygroscopic moisture than others and the amount is dependent further on 

the degree of fineness of the powder. Nothing, however, is more 

certain than that by the time the dried substance is weighed it has 

reabsorbed a certain amount of moisture, small, indeed, in most cases, 

but very appreciable in others; and, further, that with every opening 

of the container tube moisture-laden air enters and is inclosed with 

the remainder of the dry powder. Therefore it may very well 

happen that a powder which has been dried will, after several openings of the tube, especially at considerable intervals, be nearly as 

moist as it was at first. Dittrich has expressed views similar to the 

above. Of course, it is understood that no deliquescent substance is 

present.

It is preferable to weigh the air-dry powder and to make a special 

determination of moisture. If all the portions necessary for an 

analysis are weighed out one after another, or even at different 

times on the same day, the error due to difference of hygroscopicity 

in dry and moist weather, which for most of the separate portions 

is an entirely negligible quantity, is eliminated. Only in the main 

portion, in which silica and the majority of the bases are to be estir 

mated, can it ever be an appreciable factor. Especially is this true 

if a rather coarse powder is employed, such, for instance, as passes a 

sieve of 30 to 60 meshes to the linear centimeter. In many powders 

of this grade the moisture wilL fall below 0.1 per cent, whereas in 

those that have been ground for one to two hours it may easily exceed 

1 per cent.

1 Wiedemann's Annalen, TO!. 24, 1885, p. 327.
72 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

P. "ARGUMENT IN FAVOR OF INCLUDING HYGROSCOPIC WATER IN THE

SUMMATION.

The question has been asked: " If the so-called hygroscopic water 

is not always such, but not infrequently includes essential water, 

why are not its separate determination and entry in the analysis 

unnecessary? Why make a distinction which after all may not be 

a true one ? " The question involves the further consideration of the 

need in any event of including the loss at 100° or 110°.

It would seem to be a reasonable desire on the part of petrographers 

to have all analyses referred to a moisture-free basis in order that 

they shall be strictly comparable. This involves the omission of the 

" hygroscopic " water from the list of constituents, which would be 

eminently proper were it always possible to be sure that the loss at 

100° to 110° truly represents such water. As it very often represents more, and the determination as to whether or not it does in 

each case is not always possible and would add to the time required 

for the analysis, it seems necessary to include this water. What 

errors may arise from its exclusion the following rather extreme case 

well illustrates: Certain rocks of Wyoming in powder form lost 

from 1 to 2 per cent of moisture at 110°. That not even an appreciable fraction of this was truly hygroscopic is fully demonstrated by 

the fact that the uncrushed rocks lost the same amount; yet the rule 

followed by many chemists and petrographers would have involved 

the removal of all this water as a preliminary to beginning the 

analysis, and not only would a most important characteristic have 

passed unnoticed, but the analyst would have reported an incorrect 

analysis, inviting false conclusions and possibly serious confusion. 

(See also second paragraph of footnote, p. 50, and examples cited 

on p. 75.)

Hence it may be said that the estimation of the loss at 100° or 110° 

and its separate entry in the analysis are advisable as affording to the 

lithologist an indication of the mineral character of one or more of 

the rock constituents, thus perhaps confirming the microscopic evidence or suggesting further examination in that line. A marked 

loss in weight at 100° by a coarse powder other than that of certain 

igneous glasses may be taken as almost positive proof of the presence 

of zeolites or other minerals which characteristically contain loosely 

held water. It has been objected that the hygroscopic moisture 

varies with the degree of comminution of the sample and with the 

condition of the air at the time of weighing, and that therefore it 

should not be incorporated in the analysis, but this variation is 

ordinarily not at all great if the powder is coarse.
WATER. 73 

5. WATER METHODS OF DETERMINATION.

With the coarse powders that are needed to afford a true value for 

the hydrogen content of rocks and minerals, one or another of the 

methods described in this section will be found more or less unsatisfactory, especially with those materials that lose their hydrogen 

at very high temperatures or that are difficult to decompose with 

fluxes. Unfortunately at present no directions can be given to cover 

all such cases. The analyst must exercise judgment in the selection 

of a method. In any event duplicate determinations should be made 

until he has acquired the experience that Avill permit him sometimes 

to make exceptions. M. Dittrich 1 has compared different ignition 

methods.

A. INDIRECT METHODS, 

a. GENERAL CONSIDERATIONS.

The means employed for the indirect determination of water differ 

according as fractional or total amounts are needed. For the latter 

simple ignition is adopted; for the former exposure to the effects of 

dehydrating reagents or different temperatures. These methods, as 

ordinarily carried out, while exceedingly simple, are affected in most 

cases by serious errors, which will be considered in turn in their 

proper places. The methods should not be employed, therefore, 

when accuracy is essential, unless it is known that the errors are too 

slight to be significant or unless modifications are introduced to guard 

against them. A complication, sometimes serious, is added by the 

fact that with coarse powders the time required for expulsion of the 

water may be much greater than when a fine powder is used.

b. METHODS INVOLVING THE USE OF DEHYDRATING AGENTS.

Calcium chloride, sulphuric acid, and phosphorus pentoxide are 

the chemical dehydrants commonly employed in mineral analysis. 

Of these sulphuric acid finds most extended use, generally in a condition of high concentration, but in varying degrees of known concentration if detailed study of the behavior of a mineral during dehydration is in progress. I have shown 2 the importance of employing in desiccators only sulphuric acid of maximum dehydrating power 

when the full effect of the acid is desired. That which has stood 

long in desiccators that are in constant use is by no means so effective 

as fresh strong acid. Furthermore, the acid becomes dark from access of organic matter from dust or from the lubricant of the vessel, 

and this gives rise to the formation of appreciable amounts of sulphur 

dioxide.

^eitschr. anorg. Chemie, vol. 78, 1912, p. 191. 

2 Am. Chein. Jour., vol. 14, 1892, pp. C-7.
74 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

A mineral which loses much water over a strong dehydrant may 

need an exposure of several days or even weeks for its complete 

extraction. If the weighings are made from day to day, the apparent 

limit may be reached long before all water really removable has been 

taken up by the acid. Whenever the crucible, after weighing, is 

replaced in the desiccator it is no longer in a dry but a more or less 

moist atmosphere, and its contents, even when covered, sometimes 

absorb a part of this moisture and retain it so persistently that the 

acid is unable to bring the powder beyond its previous state of dryness in the next 24 hours. In fact, it may be unable even to reach 

it unless greater time is allowed. An experiment on tyrolite, made 

and published many years ago, illustrates this point in part:

Experiment of drying 1 gram of tyrolite over strong sulphuric acid.

Time 

exposed.

Hours. 

18 

26 

23 

24 

23 

24 

25

Loss.

Gram. 

0.0231 

.0083 

.0029 

.0012 

.0008 

.0001 

.0003

Time 

exposed.

Hours. 

24 

24 

48 

24

283

Loss.

Gram. 

0.0002 

.0003 

.0006 

.0002

' .0380

The experiment might reasonably have been considered ended after 

the 138th hour, when a loss of but 0.1 milligram was shown during 

24 hours; but nevertheless a nearly steady loss of 0.3 milligram per 

day took place for six days more, and might have been observed longer 

but for the interruption of the experiment.1 The sample was in fine 

powder. Had it been coarse, the rate of dehydration would have been 

much slower. The time can of course be greatly reduced by operating 

in a vacuum.

The indirect method can be made more accurate by heating the 

mineral or rock in a weighed tube, through which a current of air or 

other gas can be passed, either dry or of definite moisture content, 

according to the object in view, and then determining the loss in 

weight of the tube and its contents. If the drying agent for the gas 

is phosphorus pentoxide, it is well to cause the gas to pass first over 

or through calcium chloride or sulphuric acid, for the effectiveness of 

the pentoxide rapidly lessens as it becomes glazed with metaphosphoric acid.

C. METHODS INVOLVING THE APPLICATION OF HEAT.

a. Fractional determinations. As to the temperature to be adopted 

for drying in order to determine so-called hygroscopic moisture, the

1 Consult Mallet, J. W., Phil. Trans., vol. 171, 1880, p. 1006, for an example of slow 

loss of water from alum in air in an experiment lasting six months.
WATER. 75

practice has varied at different times and with different workers, 

ranging from 100° to 110°. For the great majority of rock specimens it is quite immaterial which of these temperatures is adopted, 

for no greater loss is experienced at the higher than at the lower 

temperature, given a sufficient time for the latter. It is the practice 

in the Survey laboratory to employ a toluene bath giving a temperature of about 105°. Should the results show a very unusually high 

loss, the powder is reheated at, say, 125°, in order to learn if the loss 

is progressive with increased temperature, as this knowledge is important for the interpretation of results. To insure accuracy this 

experiment should never be made in crucibles or dishes which must 

be cooled in a desiccator. One instance will suffice: A gram of a mineral mixture containing about 17 per cent of water, of which about 

3 per cent was driven off at 100° and 8 or 9 per cent at 280°, was 

placed in a desiccator over sulphuric acid, after several hours' heating at the latter temperature, and weighed as soon as cold, and then 

replaced and again weighed the next day. It had regained 1£ per 

cent of its original weight, although the desiccator was tightly closed 

and the crucible covered, showing apparently a drying power superior to that of the acid, or having, in other words, a vapor tension 

less than that of the acid.

A specimen of tyrolite was found on one occasion to lose 10.34 per 

cent at 280°, and on another occasion 14.33 per cent. In the latter 

case the drying and heating at progressive temperatures had continued during a period of 528 hours, the weighings being made 

usually from day to day; whereas in the former the duration of the 

experiments was much shorter and the intervals between weighings 

were but a few hours each.

An important research of G. Friedel 1 well shows what errors are 

possible in the determination of this easily removable water, as he 

found that certain zeolites which had been largely dehydrated but not 

heated to the point of rupture of the molecular net could then absorb, 

instead of water, various dry gases in which they might be placed, as 

carbon dioxide, ammonia, carbon disulphide, and others, even air in 

large quantities, and certain liquids. In the light of this observation 

the cause of the great increase of 1-| per cent in weight of the partly 

dehydrated mineral mentioned above may very possibly be attributed 

to air from the desiccator instead of moisture, as was at the time supposed. At any rate, as Friedel says, the danger of accepting a loss in 

weight as an index of the amount of water lost is clearly shown, and 

thus that method of determining water is for many cases fully discredited. Just what method to adopt must be left largely to the 

judgment of the operator, who will often be guided by the mineral

1 Bull. Soc. min., vol. 19, 1896, pp. 14, 94 ; Compt. Rend., vol. 122, 1896, p. 1006.
76 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

composition of the rock as revealed by the unaided eye or the microscope.

Friedel indicates a means for determining the true weight of water 

lost by minerals behaving like the zeolites, even without collecting the 

water lost, namely, by driving out of the dehydrated and weighed 

mineral, under proper precautions, any air it may have absorbed in 

the process of drying and cooling, and collecting and measuring this 

air and thus finding its weight, which, added to the apparent loss, 

gives the true content of water.

But aside from the above reasons for avoiding the use of indirect 

methods-of water determination, there is another very important one. 

They never give correct results where air baths are used in the ordinary way, for the reason that the drying is performed in an atmosphere far from dry, and therefore the substance can not lose all its 

moisture. As examples, if the indirect method shows 0.12 and 0.75 

:per cent in two samples, the direct method may afford 0.17 and 1.00 

per cent, respectively. Similar observations have been repeated many 

times and admit of no dispute. They apply as well to rocks as to 

minerals. Therefore, if the moisture content is more than an insignificant factor the indirect method must be avoided or so arranged as 

to insure a constantly changing dry atmosphere.

To effect this the powder should be heated in a weighed tube, 

through which a current of dry air can be passed, and allowed to 

cool therein, after which a second weighing gives the loss of moisture. 

The degree of drying will depend on the nature of the reagent used 

for drying the air, sulphuric acid being more effective than calcium 

chloride, and phosphorus pentoxide most effective of all. When 

using the last, it is well to cause the air first to pass over or through 

one of the first-named dehydrants, for its effectiveness rapidly lessens as it becomes glazed with metaphosphoric acid. For experiments carried out at room temperature no bath is required, but for 

artificial temperatures the - tube should pass through a suitable 

thermostat.

(3. " Loss on ignition " method for total water. In a few cases the 

simple loss on ignition of a rock will give the total water with accuracy, but in the great majority there are so many possible sources of 

error that this old-time method can seldom be used with safety. 

Only when the rock is free from fluorine, chlorine, sulphur, carbon, 

carbon dioxide, and fixed oxidizable or reducible (MnO2 ) constituents can the loss be accepted as the true index of the amount of water 

present, and it is seldom that a rock is met with fulfilling these conditions, especially as to the absence of ferrous iron. Blast ignition in 

presence of carbon dioxide alone of the above list may give a correct 

result, after separate estimation of the carbon dioxide, provided this
WATER. 77

emanates from carbonates of the earths and not from those of iron or 

manganese. Another source of error lies in the fact that from some 

minerals the hydrogen is not all driven out, even at the highest temperature obtainable by a blast lamp. Such heat may, on the other 

hand, drive out other difficultly volatile constituents, as the alkalies. 

This happens particularly when mixtures of alkaliferous silicates 

and alkaline-earth carbonates are concerned, such as argillaceous 

limestones.

The long-maintained idea that in presence of ferrous iron a sufficiently correct result is obtainable by adding to the observed loss an 

amount needed for oxidizing all ferrous iron is not justifiable. There 

can be no certainty that the oxidation has been complete, especially 

in the case of readily fusible rocks, and at the high temperature of 

the blast a partial reduction of higher oxides is not only possible but 

sometimes certain.1 The inability to insure complete oxidation by 

simple ignition is illustrated in the case of precipitated ferric hydroxide which has been ignited in contact with its filter paper. If 

the quantity was in any degree large, it is sometimes decidedly magnetic, presumably from presence of magnetic oxide, which no amount 

of heating wholly oxidizes, especially in the larger grains. Neither 

is evaporation with nitric acid and reignition sufficient to destroy 

the magnetic property of the oxide, as has been claimed.

P. G. W. Bayly,2 in a paper on recent methods of rock analysis, 

gives the following method for determining water. The total ignition loss is corrected for carbon dioxide when this is present, and 

for ferrous oxide by determining the ferrous iron both before and 

after ignition. Deduction of the separately determined moisture 

gives finally the more firmly held water. It need hardly be said 

that this method presupposes very exact determinations of both 

moisture and ferrous oxide.

B. DIRECT METHODS WITHOUT ABSORPTION TUBES PENFIELD's METHODS.

a. FOR MINEBALS EASILY DEPRIVED OF THEIR WATER.

If no other volatile constituents than water are present, the beautifully simple method first used by G. J. Brush and extended by 

S. L. Penfield 3 leaves nothing to be desired for accuracy, provided 

that the expulsion of water can be effected at relatively low temperatures. It consists simply in heating the powder in a narrow tube of 

hard glass, enlarged at the closed end and provided with one or two

1 H. Warth (Chem. News, vol. 84, 1901, p. 305) also mentions this and draws attention 

to the effect of alumina, not only in decolorizing ferric oxide when the two are heated 

together, but also in restraining the reduction of the latter to the magnetic oxide.

2 Australasian Assoc. Adv. Sci., Adelaide meeting, 1907.

8 Am. Jour. Sci., 3d ser., vol. 48, 1894, p. 31; Zeitschr. anorg. Chemie, vol. 7, 1894, p. 22.
78 ANALYSIS OF SILICATE AND CABBOFATE BOOKS.

further enlargements in the middle to hold the water and prevent 

its running back and cracking the hot glass. A capillary glass stopper fitted in with rubber tubing prevents loss of water by circulating 

air currents. The tube being held horizontally, the bulb is heated to 

any required degree by the Bunsen or blast flame. Moistened filter 

paper or cloth wound about the cooler parts of the tube insures condensation of all water. The heated end being finally pulled off, the 

tube is weighed after cooling and external cleansing, and again after 

the water has been removed by aspiration. For most rocks, as they 

contain little water, central enlargements of the tube are hardly 

needed.

Various forms of tubes used by Penfield are shown in figure 11.

Before using, even if apparently dry, "these tubes must be thoroughly dried inside, which is best accomplished by heating and

FIGURE 11. Penfleld's tubes for water determination in minerals, a, 6, c, Different forma 

of tubes; d, thistle tube for introducing the powder; e, capillary-tipped stopper.

aspirating a current of air through them by means of a glass tube 

reaching to the bottom."

How this simple tube is made to afford entirely satisfactory results 

with minerals, even when carbonates are present, is fully set forth 

in the paper cited.

Comparatively few rocks are altogether free, from other volatile 

constituents. Hence for refined work the application of this apparatus in the simple manner above set forth is limited. However, 

it may be used with the addition of a retainer for fluorine, sulphur, 

etc., such as the oxide of calcium, of lead, or of bismuth. It gives, 

of course, the total water.

b. FOB MINERALS NOT EASILY DEPBIVED OF THEIR WATER.

When minerals are present that do not give up their water wholly, 

even over the blast, as talc, topaz, chondrodite, staurolite, Penfield
WATER. 79

recommends the use of the simple combination of fire-brick and 

charcoal oven, which is depicted in figure 12, either with or without 

a retainer in the tube for fluorine, as circumstances demand. The 

part of the tube in the fire is to be protected by a cylinder of platinum 

foil tightly sprung about its end, and the part outside by asbestos 

board, as well as by wet cloth or paper. A piece of charcoal is likewise laid on the tube, as well as beneath and behind, and the blast 

flame is given a horizontal direction, so as to play upon the side 

of the apparatus. In this way a most intense temperature can be 

reached, but the platinum foil does not last long.

M. Dittrich1 condemned the above method as giving variable results, after comparative trial of different methods, but it would seem 

that he did not use a retainer for fluorine or sulphur.

In whichever way the apparatus may be used the water found is 

the total water, from which that found separately at 105° may bo 

deducted if desired.

FIGURE 12. Penfleld's fire-brick and charcoal oven for use In determining water.

C. DIRECT METHODS WITH ABSORPTION TUBES.

a. GENERAL CONSIDERATIONS.

In general it is preferable to collect and weigh the water in suitable absorption tubes after its expulsion from the rock or mineral. 

The method is especially suited for the determination of total water 

or of that escaping above 105° when the apparatus of Gooch (f, p. 

85) or of Dittrich and Eitel (e, p. 84) is employed. It is less suited 

for those fractional determinations where the escape of water is 

very slow at the different temperatures, for the absorption tube in 

such cases may gain weight, other than that of water from the mineral, sufficient to introduce appreciable error. This may sometimes 

be corrected to a certain extent by running a parallel blank test.

Absorption, following ignition without a flux, is not suited for 

rocks or minerals which yield other volatile substances than water 

and carbon dioxide, unless some substance is employed to retain 

these before they pass into the absorption tube. Even so, at extreme

^eitschr. anorg. Chemie, vol. 78, 1912,'p. 191.
80 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

temperatures the results are likely to be in error, so that for materials which yield their water only at very high temperatures fusion 

with a flux is imperative.

A precaution too often overlooked is to see that the drying agent 

used for the air current (always forced, not drawn) is the same as 

that in the absorption tube in which the water from the sample is 

collected not only the same in kind, but as near as may be in strength 

also, especially with calcium chloride. Therefore the contents of 

drying and absorption apparatus should be 'changed often, and when 

the apparatus is refilled the reagents should be taken from the same 

stock. Fresh calcium chloride in absorption tubes should be exposed 

to a current of carbon dioxide and the excess removed by air before 

use. Furthermore, all connections should be as nearly as possible 

glass against glass, with the least possible inside exposure of rubber. 

With long rubber connections the error may be a very sensible plus 

one. Again, the direction of the air current through the absorption tube should always be the same as long as a filling lasts. Care 

must also be taken that the conditions at the several times of weighing 

of the tubes are nearly alike as to temperature and hygrometric state 

of the atmosphere, for the afternoon weight of a tube may be appreciably different from that on the following morning. It is well, 

therefore, to avoid error from this cause by approximately counterpoising the absorption tube by another of about the same volume and 

weight. Finally, the electrifying effect of wiping a tube before 

placing it on the balance must not be overlooked. In my experience 

this has often amounted to as much as 1 to 2 centigrams in a balance 

resting on glass (always an increase in weight) after wiping with a 

clean linen handkerchief. The charge can be removed by repeated 

application of the hand, but disappears slowly without such aid. 

A strongly electrified condition makes itself apparent by marked 

irregularities in the swing of the needle. While more pronounced in 

cold weather, the phenomenon is not peculiar to winter. 1

The absorption tubes should not weigh in general over 30 grams 

each, filled with calcium chloride. Those preferred by me are shown 

in figure 14 (p. 82), and are 10 to 11 cm. over all in height. Sulphuric 

acid as an absorbent has no apparent advantage over calcium chloride 

if the drying apparatus for the air contains also calcium chloride of 

the same absorptive power as that in the collecting tube.

The methods of P. Jannasch that were given in preceding editions 

of this work are omitted here because of the error introduced by the 

taking up of water during grinding of the sample to the excessive 

fineness which the methods call for.

i With regard to electrification, consult also Bornemann, Ernst, Chem. Zeitung, 1908, pp. 

125, 220.
WATER. 81

b. STEIGEB'S APPLICATION OK THE TOLUENE OVEN (FOB LOW TEMPEBATTJRES).

The apparatus devised by George Steiger consists simply of a 

U-tube of home construction and a small toluene oven, in the cover 

of which is an opening of suitable shape to receive the tube (fig. 13). 

The open space between the uprights is closed when in operation "by 

a piece of asbestos board. The horizontal end of the tube is made 

long, so that in the event of much water being given off it can be 

readily driven over into 

the absorption tube by a 

low flame, which if applied from the first may 

prevent any appreciable 

condensation of water 

before reaching the calcium chloride. The interior of the tube having been first freed from 

adhering moisture by a 

current of dry air and 

the absorption tube attached, the stopper is 

lifted without shutting 

off the air current, and 

the weighed powder is 

quickly introduced by 

means of the clean metal 

trough in which it has 

been weighed (fig. 4, 

p. 35). The stopper is 

replaced as quickly and 

the dehydration begins 

at once and often is 

nearly finished by the 

time the thermometer 

indicates the maximum 

temperature.

If the sample has no 

easily oxidizable constituents, it would be quite possible, by employing 

a U-tube with glass stoppers, like A, figure 14, page 82, to ascertain the 

loss in weight of the powder as well as the gain of the absorption tube, 

or to do away with the tube altogether. In this case, however, it would 

.be necessary to vaseline the stoppers very lightly, and perhaps to introduce the powder through a dry funnel because of the vaseline film 

on the inner side of the end of the tube. The moderate heat on the top 

of the bath would suffice to prevent condensation of moisture before 

131999° 19 6

FIGURE 13. Steiger's form of drying apparatus. A, 

Toluene oven ; B, condenser, about 50' cm. high ; C, 

cover of bath, showing openings; D, tube for mineral 

powder; E, asbestos board cut so as to close central 

opening In cover.
82 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

reaching the absorption tube, or to soon remove what might condense 

at first, but there must be no long rubber connections.

By employing a suitable oven this form of tube can be used for 

higher temperatures, but the stoppers must fit air-tight, for vaseline 

can not be employed.

c. CHATARD'S OTEW FOB TEMPERATURES UP TO 300" AND OVER.

A form of drying oven devised by T. M. Chatard 1 gave good seryice in the Survey laboratory for determining water at different temPIGURB 14. Chatard's form of drying oven for water determinations. B, Copper box, 18 

cm. long, 10| cm. high, 9 cm. wide, open in front, its sides and top covered with 

asbestos board ; S, two slides of different sizes to close openings, O, after the tube is 

in position ; F, asbestos-board front stiffened by an interlaid sheet of copper; R, metal 

rod to hold front in place; T, glass ignition tube; A, calcium-chloride absorption 

tube. For mineral substances with very high water content the tubes T and A may 

preferably have the original form given them by Chatard, as depicted in Bulletin 176, 

p. 37. The use of a straight tube, as shown above, permits a less complicated construction of box and stand than that here shown, as round holes in opposite ends of the 

box admit the ignition tube, and the roller base is then superfluous.

peratures up to 350°. It is an asbestos-covered copper box shown in 

different aspects and parts in figure 14. The box is so constructed 

that the tube with its contents can be removed without detaching 

from either the drying or collecting tubes, which is a great advantage 

if it is desired to apply afterward the direct heat of a lamp in order

1 Am. Chem. Jour., vol. 13, 1891, p. 110; Bull. U. S. Geol. Survey No. 78, 1891, p. 84.
WATER. 83

to expel the water retained at 300° to 350°. To facilitate this removal 

the stand is on rollers, so that after clamping the projecting end of 

the tube and removing the front of the box, F, and the little side 

pieces, S, closing the horizontal slits, the oven can be rolled bodily 

backward, leaving the tube and its attachments in their original position, ready for further heating over a burner or blast. The removable front, F, of the oven is made of two pieces^ of sheet asbestos 

board stiffened by an interlaid piece of sheet copper. The inner 

piece of asbestos board fits snugly into the box, while the outer oner 

being slightly larger, by its projecting edges hinders the door from 

falling in and helps to prevent air currents. This door is held in 

place by the metal rod, R. The little slides, S, are made in a somewhat similar manner, and are intended to slip in from the front - 

and close the two openings, 0, after the tube is in place, but before 

closing the front.

(1. PETWIELD'S PROCEDURE (FOR LOW AND HIGH TEMPERATURES).

The simplest of these methods as to apparatus, and one permitting, by the use of auxiliary arrangements such as are shown and 

described on page 82, the determination of the hygroscopic as well

PIGDBH 15. Tube for water determination according to Penfleld. A, Outer protecting 

covering of platinum foil. A second similar foil on the inside prevents the glass from 

collapsing when heated to softness, &, Cross section of platinum boat.

as any other fraction of the water, is the following glass-tube arrangement (fig. 15) of Penfield,1 whereby the brick and charcoal oven 

already referred to (fig. 12) comes again into play, but without the 

half brick shown in that figure.

The tube is of about 15 mm. internal diameter and is fitted with 

two platinum cylinders at A, one inside, the other outside, where the 

heat exposure is to be most intense.

These are made from pieces of platinum foil, about 0.07 mm. in thickness 

and 8 by 11 cm. in size, which have been previously bent around glass tubes 

of such a diameter that when applied to the combustion tubing the spring of 

the metal will hold them in place. A large platinum boat, 7 to 8 cm. long 

and 11 to 12 mm. in diameter, with a cross section like 6, should be used, 

since this will readily hold a gram of mineral mixed with 5 grams of sodium 

carbonate. * * * The tube is placed in the angle formed by the charcoal 

lining, some pieces of charcoal are placed at the sides in front, leaving an 

opening through which the flame may be directed, and an additional piece is 

laid on top. The tube can readily be brought to a full white heat, and by 

forcing a slow current of dry air through the apparatus the carbon dioxide

1 Am. Jour. Sci., 3d ser., vol. 48, 1894, p. 37; Zeitschr. anorg. Chemie, vol. 6, 1894, 

p. 22.
84 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

resulting from the decomposition can be removed and the water carried over 

into the weighed absorption tube. The glass fuses between the platinum 

casings, and in a number of experiments that have been tried there has not 

been a single instance where the glass tube has broken or shown any indication of breaking. After heating, the tube will not crack if it is left to cool 

slowly on the charcoal, but it can not be used a second time. * * * At the 

high temperature to which the glass is subjected it of course becomes very soft 

and the ends must be properly supported; also the rubber connections and 

absorption apparatus must be carefully screened by asbestos board. By constructing a cover for the boat no material need be lost by splattering, and 

after making the water determination the contents may be used for the remainder of the analysis.

The inner cylinder of platinum serves to prevent the glass from 

collapsing as it softens, whereby distortion of the boat would result 

and its withdrawal for further examination of its contents would be 

impossible.

6. DITTEICH AND EITEL'S APPABATUS (FOR LOW AND HIGH TEMPERATURES).

M. Dittrich and W. Eitel 1 recommend a tube of fused quartz of 

45 cm. length, 22 nun.. diameter, and 0.5 mm. wall thickness, drawn 

out at the exit end and provided with a stopper and inlet tube of the 

same material in one piece. The stopper and end of the large tube 

are ground to fit and rubbed with a little graphite to insure tightness. 

Further surety against loosening is provided by two pairs of quartz 

hooks on both stopper and tube, over which wire springs can be 

stretched.

For holding the sample, mixed with 5.5 to 6 grams of dry sodium 

carbonate, a boat of platinum-iridium (10 per cent iridium), 12 cm. 

long, is used, having a cover of the same alloy. To protect against 

injury to the tube by spilling of the contents of the boat a cylindrical 

shield of platinum-iridium is provided. Boat, cover, and shield 

weigh 42 grams.

Fusion is brought about by the heat of a row of burners, increased 

toward the end of the operation by that of a large blast lamp. An 

electric resistance furnace is preferred to gas as a source of heat. The 

temperature for complete fusion is 1,000° to 1,050°.

In a later paper 2 Dittrich and Eitel describe the determination of 

water and carbon dioxide simultaneously, without flux, in a similar 

apparatus but at higher temperatures (up to nearly 1,400°). The 

tube, however, is of platinum-iridium and of much smaller bore than 

that used with the flux. The boat is also smaller than the one described above, as it has to hold only the rock or mineral powder. For 

the purpose of retaining sulphur, fluorine, etc., a spiral of silver, 

4 to 5 cm. long, is held at the exit end of the tube just before it 

narrows.

1 Zeitschr. anorg. Chemie, vol. 75, 1912, p. 373. 

" Idem, vol. 77, 1912, p. 365.
WATEB. 85

In view of the cost of the apparatus and the possibility of error 

arising from volatile constituents other than carbon dioxide and 

water, the use of this apparatus offers no advantages over the less 

expensive one before described, especially as carbon dioxide can be 

determined easily in a separate sample by another method.

f. GOOCH'S APPARATUS (FOR HIGH TEMPERATURES).

Of more elaborate apparatus, designed to be used with fluxes, the 

tubulated platinum crucible invented by F. A. Gooch 1 is capable 

of affording most ex- . _______ 

cellent service, and it 

is the one by which 

far the larger number of water determinations have been 

made in the Survey 

laboratory. Its high 

cost, which puts it 

beyond ordinary 

reach, is the only 

hindrance to its general employment.

Figure 16, which 

hardly needs detailed description, 

shows it in a modified form, which differs from the original forms of Gooch 

in that the tubes for 

connecting with both 

the drying and absorption vessels are 

constructed wholly 

of platinum instead 

of lead glass. With inlet and exit tubes of the lengths shown in the 

figure there is absolutely no danger of the ends becoming hot enough 

by conduction to scorch or soften the rubber connection.

As an adjunct to its convenient use there is needed an ordinary 

upright iron ring stand, with two small sliding rings, and a sliding 

ring burner provided with entering ducts for gas and air blast. 

Across the uppermost ring there is an arrangement of stout platinum 

wire (S, fig. 17), forming at the center of the ring a secure seat for

FIGURE 16. Modified form of Gooch tubulated platinum 

crucible for the determination of water, one-half natural 

size. Weighs about 75 grams.

Am. Chem. Jour., vol. 2, 1880, p. 247; Chem. News, vol. 42, 3880, p. 326.
86 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

the upturned flange of the crucible proper. Both rings and burner 

can be clamped firmly at any height.

The rock powder, having been placed in the cylindrical crucible 

(C, fig. 16), is there mixed with not more than 3 or 4 grams of fully 

dehydrated sodium carbonate,1 or more of lead chromate if carbon is 

to be likewise determined. The crucible is sunk in its seat, S (fig. 17), 

in the upper ring, E/, and the tubulated cap, T (fig. 16), is fitted on 

and attached to the calcium-chloride drying towers preceded by 

one containing potassium hydroxide if carbon dioxide is likewise to 

be estimated on the one side, and to a sulphuric-acid bulb tube, B 

(fig. 18), on the other. Powdered sodium tungstate 2 free from 

arsenic, which would soon ruin the crucible lips is now poured into 

the flanged lip, L (fig. 16), in which the cap rests, and a metal vessel of 

cold water having been raised by the lower ring, R" (figs. 17 and 

18), until the platinum crucible is immersed sufficiently, the flame of 

an ordinary blast lamp is turned on to melt the tungstate. As soon 

as this is fused the flame is removed and the salt solidifies and makes 

an air-tight joint, the test of which is the permanence of the column 

of sulphuric acid in the bulb tubes caused by the contraction of the 

air in the platinum apparatus as it cools.

After drying by a current of air at 105° for two hours, more or 

less, by means of an air or toluene bath, as shown in fig. 17, 

the absorption tube, A (fig. 18), is interposed between the sulphuric-acid bulbs and the apparatus, and while a slow current of 

air continues to pass the gradual heating and subsequent fusion of 

the flux is brought about by the blast-fed sliding ring burner, R'" 

(figs. 17 and 18). The sodium-tungstate joint is shielded from the 

flame by small pieces of asbestos board, P (fig. 18), cut out so as to 

fit the crucible. It is well to begin fusing at the top of the mixture 

in the crucible and to lower the blast gradually till the bottom is 

reached. In this way may be avoided all danger of the outlet tube 

becoming stopped by flux carried up by the escaping carbon dioxide. 

When fusion is complete, as shown in the case of sodium-carbonate 

flux by the decided slackening of the gas current through the safety 

bulbs attached to the drying tube, the flame is extinguished and a 

current of air is allowed to continue until the apparatus is cold.

This apparatus suffers from the drawback of being slightly permeable to combustion gases at high temperatures. The defect can be

1 This has been heated for a length of time to near its fflSing point over a free flame 

or in an air bath, to decompose the bicarbonate it usually contains, and then placed in a 

desiccator. Thus heated it is not very hygroscopic. Penfleld found that 2.5 grams of it, 

spread out on a watch glass, gained only 0.0002 gram in 15 minutes. Potassium carbonate and potassium-sodium carbonate are too hygroscopic by far to be available.

2 Private advice from B. W. Morley conveys the information that sodium carbonate is 

perfectly satisfactory as a substitute for the tungstate. If so, its use is preferable when, 

the contents of the crucible are to be used for other determinations.
WATER. 87

overcome by causing the flame to play upon an outer ordinary 

platinum crucible, kept permanently filled with sodium-potassium 

carbonate. This protective crucible, however, is soon ruined for 

other purposes, being distorted by the alternate expansion and contraction of the carbonate, unless this is poured out before it solidifies 

after each fusion.

It has been found that if the operation is carried out expeditiously 

and the final full heat applied for but a few minutes, the error due to

FIGURE 17. Arrangement, during drying, of Gooch apparatus for determining water. 

S, Seat of stout platinum wire resting on ring R' and serving as a support for 

the crucible ; R'", blast-fed ring burner; R", support for air or toluene bath, 0 ; F, 

asbestos-board shield.

penetrating water gases is inappreciable. This hastening may be 

rendered safer by using rather finely powdered calcium chloride in 

the central section of the U-shaped absorption tube to avoid large air 

channels. Through this or any other apparatus based on similar 

principles the air current should always be forced, not drawn. A 

warm air blast directed upon the exit tube near its entrance into the 

absorption tube greatly shortens the time required and is to be 

recommended.
88 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

In this apparatus only the water expelled above 100° to 110° should 

be determined as a rule. The reason why it is unsafe to attempt to 

determine " hygroscopic " moisture in this apparatus is that the luting 

of the two parts must be done by direct application of a flame to 

the tungstate, and considerable water vapor may enter the apparatus 

and be retained in part by the dried sodium carbonate.

FIGURE 18. Arrangement, during fusion, of Gooch apparatus for determining water. R'", 

Blast-fed ring burner; P, protective asbestos shield resting on ring R" ; F, asbestosboard shield; A, calcium-chloride tube; B, sulphuric-acid bulbs serving to show the 

rate of gas flow through the absorption tube and at the same time to prevent back. 

entry of moisture from the air into A.

g. KUZIBIAN'S METHOD (FOB HYDROUS SULPHATES).

For the determination of water in those hydrous sulphates which 

are apt to lose some of their acid radical when heated S. B. Kuzirian T 

has developed a method which may find application for hydrous 

salts other than sulphates. An ignition tube, which may be of hard

1 Am. Jour. Sci., 4th ser.,. vol. 36, 1913, p. 401; Chem. News, vol. 109, 1914, p. 173; 

Zeitschr. anorg. Chemie, vol. 85, 1914, p. 127.
SILICA. 89

glass, is used for heating the mineral. The sample is mixed in a bout 

of porcelain or platinum with six times its weight of sodium paratungstate 1 and inserted into the tube, which has been dried thorough^ by passing through it a rapid current of dry air. The ignition is started gently while dry air passes over the boat at a rate of 

three bubbles a second for 15 minutes. Then the temperature is increased gradually until the mixture forms a clear fusion. The usual 

precautions for drying the air and absorbing the water evolved from 

the mineral are to be observed.

Kuzirian's experiments were carried- out on sulphates of copper, 

aluminum, and nickel and the potassium alums of chromium and 

aluminum. They gave good results, the sulphate radicle being retained quantitatively by the paratungstate.

h. MERITS OF THE SEVERAL FORMS OF APPARATUS.

The apparatus described in d, e, and f permit the determination of 

other constituents besides water in the same portion if necessary, and 

by the use of lead chromate instead of sodium carbonate, graphite, 

or the carbon of organic matter, can be simultaneously determined 

with the water. If carbonates are present, together with graphite or 

organic matter, the total carbon is obtained.

To one accustomed to its use, and with a drying and suspension 

attachment permanently set up, the Gooch apparatus, considering 

its limitations above set forth, offers perhaps the most handy and 

convenient means for the determination of water in rocks. Its high 

first cost, in comparison with the glass or quartz tube, is made up 

in time by its durability.

6. SILICA SEPARATION FROM ALUMINA, ETC.

A. ALTERNATIVE METHODS OF DECOMPOSING THE ROOK.

a. GENERAL CONSIDERATIONS.

The almost universal practice in silicate analysis is to determine 

silica, titanium, and most of the basic elements in one and the same 

portion of the sample. The practice of separating alumina, etc., by 

the usual methods, after first attacking the rock powder by hydrofluoric and sulphuric acids silica being estimated in a separate portion while attractive in principle, was long ago abandoned by me 

after fair trial, owing to the disturbance sometimes occasioned by

1 In order to purify the commercial paratungstate, which ordinarily contains sodium 

carbonate, it is fused in a large platinum dish over the blast, and pure tungsten trioxlde 

is added until carbon dioxide ceases to bubble out.
90 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

incomplete expulsion of fluorine* and to a less degree by the presence 

of sulphates instead of chlorides. With the exception of a comparatively few analyses made thus the sodium carbonate method of attack has always been employed. In the case of rocks rich in fluorine 

strict accuracy requires the separation of silica to be made as in the 

Berzelius method for fluorine determination (see p. 226; also footnote, p. 93), but in practice it is not often necessary to resort to this 

tedious procedure, for the amount of fluorine is usually small and it 

could by no possibility cause a loss of much more than three-fourths 

its own weight of silica if it were all to volatilize as silicon tetrafluoride when the sodium-carbonate fusion is evaporated with hydrochloric acid. The loss is, however, less, as silicon fluoride is unstable 

in presence of moisture. Some of the fluorine escapes perhaps as 

hydrofluoric acid, and more is fixed in fluosilicates.2 In any event 

the error is of comparatively slight importance, for it attaches always 

to the constituent that is present in greatest amount.

Various fluxes other than alkali carbonates have been recommended 

for breaking up silicates insoluble in ordinary acids, such as lead and 

bismuth oxides, lead carbonate, borax, and boric oxide. Jannasch 

and his pupils were especially active in this line of work. One of the 

advantages most of these fluxes possess over the alkali carbonates is 

their removability after serving their purpose, thus allowing the 

various separations to be made more perfectly and without the annoying interference of several grams of foreign fixed salts, which are 

most troublesome in that part of the analysis devoted to the separation of silica, alumina, iron, lime, and magnesia.

Another of their advantages is that with some of them it is possible 

to estimate in one portion the alkalies in addition to those constituents that are usually determined in the silica portion. Where the 

material is limited, as so often it is in mineral analysis, this is a most 

important advantage, sufficient to outweigh all possible objections; 

but in rock analysis, where the supply of material usually is ample, 

it is seldom worth considering. A still further point in their favor

1 The presence of fluorine renders the precipitation of aluminum very incomplete. See 

also Veitch, F. P., Jour. Am. Chem. Soc., vol. 22, 1900, p. 246; also Hinrichsen, F. W., 

Ber. Deutsch. chem. Gesell., vol. 40, 1907, p. 1497; Zeitschr. anorg. Chemie, vol. 58, 1908, 

p. 83; and Cavaignac, H., Compt. Rend., vol. 158, 1914, p. 948. The reason for the sometimes incomplete precipitation of aluminum by ammonia from sulphate solution, after 

attacking a rock by hydrofluoric and sulphuric acids, is ascribed by E. Selch (Zeitschr. 

anal. Chemie, vol. 54, 1915, p. 395) to incomplete removal of fluorine. He obtained complete recovery after a second evaporation with sulphuric acid, the first residue of sulphates being brought to a clear solution with dilute sulphuric acid before proceeding 

with the second evaporation. Contrary to some statements, Selch found that evaporation of alumina with hydrofluoric acid involves only a negligible loss by volatilization.

2 A supposition confirmed by G. E. F. Lundell, at the Bureau of Standards. The 

fluosilicates, if eventually ignited with the silica, would undergo at least partial decomposition and on treatment of the ignited silica with hydrofluoric and sulphuric acids 

the metal of the fluosilicates (presumably sodium) would be weighed eventually as 

sulphate if not volatilized by the heat of ignition.
SILICA. 91

is that it is probably more easy to obtain them entirely free from fixed 

impurities than an alkali carbonate.

There are, however, objections to their use. With some of them an 

extraordinary amount of time must be devoted to grinding the mineral to an impalpable powder, with the result of introducing serious 

analytical complications. (See ante, p. 60.) And the flux itself 

may need considerable hand pulverization. Once introduced, they 

must be removed before the analysis can be proceeded with, and this 

removal takes much time and is always a possible source of error.

In mineral analysis these objections are entitled to far less weight 

than in rock analysis, for the object sought usually the deduction 

of a formula warrants the expenditure of much time and painstaking care. Finally, it has been found that one or more of these fluxes 

are not available for altogether general use, because certain minerals 

do not succumb fully to their attack under simple conditions, as 

andalusite with boric oxide and others with lead oxide (Jannasch). ( 

Therefore, however well adapted one or the other of these methods 

may be for the analysis of homogeneous minerals, the anticipations of 

Jannasch, to the effect that the boric-oxide method "would soon supersede the alkali-carbonate fusion method in rock as well as in mineral 

analysis, have not been realized. Nevertheless the boric-oxide fusion 

method, owing to its evident merit, will be" described in detail after 

brief reference to a means of bringing refractory silicates into solution without employing any solid reagent.

The methods of decomposition and the subsequent treatment of 

the silica hereinafter described are with few exceptions applicable to 

definite silicate mineral species as well as to complex mixtures of 

them.

b. DECOMPOSITION OF REFRACTORY SILICATES BT HYDROCHLORIC ACID UNDER

PRESSURE.

Jannasch 1 pours upon the finely ground rock powder contained in a 

platinum tube of about 26 cm.3 capacity a somewhat diluted hydrochloric acid (4 acid to 1 water), places over the open end a cap which 

does not hermetically close the tube, inserts the latter in a larger 

tube of potash glass likewise partly filled with the diluted acid, seals 

the glass tube, places it in turn in an inclined position in a steel 

Mannesmann tube containing ether or benzine to equalize the pressure, and heats to any desired temperature up to 400°.

The chief drawback seems to be a somewhat incomplete decomposition, doubtless due to the necessarily inclined position of the tube, 

which causes the powder to collect at the lower end, and thus renders

1 Ber. Deutsch. chem, Gesell., vol. 24, 1891, p. 273; Zeitschr. anorg. Chemie, vol. 6, 1894, 

p. 72.
92 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

decomposition less complete than if the material were spread evenly 

throughout the length of the tube. Further, the acid attacks the platinum strongly unless the air in both the platinum and the glass tubes 

is replaced by carbon dioxide. Even when this is done, several milligrams of platinum is found in the silicate solution.

Nevertheless, to those possessing the necessary platinum and steel 

tubes the method can render efficient service in special cases when 

economy of material is imperative.

C. THE BORIC-OXIDE METHOD OF JANNASCH AND HEIDENREICH.1

<x. Preparation of the boric oxide. The boric-oxide method demands, if the alkalies are to be estimated in the same portion as silica, 

etc., an absolutely alkali-free boric acid, which can be prepared by 

two or three recrystallizations of a good commercial article. The 

purified crystals are dehydrated and fused in a large platinum 

crucible. This is then cooled suddenly to cause the anhydride to 

crack into pieces of a size convenient for powdering, which are to be 

kept in a tight glass vessel and powdered as needed, since the anhydrous oxide is hygroscopic."

(3. Treatment of easily decomposable silicates. To this flux Jannasch 

and Heidenreich found that nearly all silicates readily succumb over 

the ordinary blast lamp. The fusion is made in a large crucible holding 40-65 cm.3 , and the proportion of flux to be used is gaged according to the nature of the silicate, ranging from 3 to 8 and more parts 

to 1 of mineral. This last must be finely powdered, especially if very 

resistant to attack by the flux, the authors recommending the expenditure of one-half to one hour's time for the grinding of one-half to 

1 gram of powder. Heat from a burner turned low is applied for 

5 to 10 minutes till water is expelled; the heat is then increased gradually till the gas is fully turned on. Bubbling and rising in the 

crucible is prevented as far as possible by using a short platinum 

rod which does not reach above the edge of the crucible. When the 

mass has been in quiet fusion for a time in the covered crucible the 

blast flame is applied. The average duration of the entire operation 

is 20 to 30 minutes but depends much on the character of the mineral.

Y. Treatment of refractory silicates. For those minerals which, like 

andalusite, cyanite, and topaz, are not fully decomposable by the 

heat of the ordinary blast flame, P. Jannasch and H. Weber 2 used a

1 Zeitschr. anorg. Chemie, vol. 12, 1896, p. 208. This method of decomposing rocks 

with a view to the determination of their contained alkali originated with Sir Humphrey 

Davy, as shown in his paper " On a method of analyzing stones containing fixed alkali 

by means of the boracic acid " (Phil. Trans., 1805, p, 231 ; Ann. d. chim., vol. 60, 1806, p. 

294; Gilbert's Annalen, vol. 30, 1808, p. 369; Tulloch's Phil. Mag., 1806, p. 146). 

Original with Jannasch and Heidenreich is the manner of getting rid of the. Introduced 

boric oxide.

2 Ber. Deutsch. Chem. Gesell., vol. 32, 1899, p. 1670.
SILICA. 93

flame fed by oxygen instead of air. The blast lamp, of 2£ mm. opening, is supplied with gas from at least five or six ordinary gas cocks, 

and the flame is made broad and free from luminosity. The mineral 

having been first heated as above described, but with a much larger 

proportion of flux as high as 30 to 1 a few grams additional of 

boric oxide is added and the oxygen blast is applied till, in 10 or 

15 minutes, the fusion is as transparent as glass. 1

S. Further treatment after fusion. From this point the further 

treatment is the same in both cases and, as modified by Jannasch and 

Weber,2 is as follows:

The hot crucible is cooled in cold water and the contents are turned 

into a very large porcelain or platinum dish, to which, after covering 

with a glass, a saturated solution of hydrochloric-acid gas in methyl 

alcohol is added. 3 The cover being then removed, the liquid is heated 

to boiling, over asbestos board, by an inch-high flame, with constant 

stirring, or it is left'without attention over a lower flame or on a 

water bath heated short of boiling. The crucible is cleansed in a 

similar manner, and its contents are added to the dish. In 10 to 15 

minutes, with occasional addition of the methyl chloride, solution 

is complete and the liquid is then boiled down to a small volume and 

evaporated to dryness on the bath. The residue is then digested on 

a bath at 80° to 85° three or four times in succession with the ether 

solution, in order to remove the last traces of boron as boric ether. 

Care should be taken to wash down from the sides of the dish, with 

methyl-chloride solution, the boric acid formed and deposited thereon 

during the evaporation.

e. Possible objections to the 'boric-oxide, method. Very much was 

claimed by Jannasch for this method, but with all its undoubted merit 

there are several points which militate against it. (1) The boric 

ether, driven off in such quantities, at once decomposes in contact with 

moisture, and boric acid settles over all objects with which it comes 

in contact. The hood must become thickly coated. Hence a special 

hood for these evaporations alone seems to be called for, otherwise 

boric acid may at any time fall into other dishes and cause untold 

trouble. (2) The second objection attaches to the use of the oxygen 

flame when alkalies are to be estimated in the fusion, and the ability 

to so determine them is one of Jannasch's chief claims in favor of the 

method, for it can not be doubted that at the high temperature of 

this flame alkalies are volatilized. Borax can be volatilized slowly

1 An interesting and important observation reported by Jannasch and Weber is that 

when the oxygen blast has been used for silicates carrying fluorine or mixed with 

fluorides the fluorine seems to be wholly expelled as boric fluoride without loss of silica. 

No verification of this by any one has been made up to the present (1919).

 Ber. Deutsch. chem. Gesell., vol. 32, 1899, p. 1670.

8 Made by passing dry hydrochloric-acid gas into cooled methyl alcohol for from one to 

two hours.
94 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

but wholly over the ordinary blast, hence there is great reason.to 

fear sufficient loss at this much higher temperature to give rise to 

serious error. (3) Incomplete expulsion of the boric acid gives rise to 

errors later in the analysis.

d. THE SODIUM-CABBONATE METHOD.

a. Advantages of sodium carbonate over sodium-potassium carbonate. Except in special cases, as when fluorine or chlorine are to be 

determined, there is no advantage in using the much recommended, 

because more fusible, double carbonate of sodium and potassium, or 

the equimolecular mixture of the normal carbonates, or of sodium 

carbonate and potassium bicarbonate. As Dittrich says,1 potassium 

salts are more prone to pass into precipitates than sodium salts, and 

it may be that the higher melting point of sodium carbonate is a distinct advantage. Certainly, for effective decomposition of some rock 

constituents, a far higher temperature than that of the fusing point 

of the double salt is required.

P. Purity of the sodium carbonate. Notwithstanding the most 

earnest efforts for years, it has been impossible to procure, either in 

the open market or by special arrangement with manufacturers, a 

grade of sodium carbonate which can be called chemically pure. 

With special precautions small lots can be prepared in the laboratory 

that will contain less than 1 mg. total impurity in 10 grams; but 

such an article can not be purchased in the market, and rarely will 

the so-called chemically pure dry sodium carbonate contain as little 

as 1 mg. in 10 grams. The invariable contaminating substances 

aside from sand and straw, which have sometimes been found 

are silica, alumina, iron, lime, magnesia, and sometimes phosphoric 

oxide, all of these going into aqueous solution with the carbonate. 

The chief of these impurities are usually silica, alumina, and lime. 

Sulphur can be found almost always in minute amount, but this is 

not objectionable for the present purpose. An article of the above 

degree of purity (1 mg. in 10 grams) is satisfactory in almost 

all imaginable cases, as the use of the usually extravagant amount of 

10 grams for a fusion would introduce an error of but 0.1 per cent 

in the analysis, supposing 1 gram of mineral to be operated on, and it 

would, moreover, be distributed over several constituents. Undoubtedly this error is fully equaled by the introduction of dust from the 

air in the various long evaporations.

It is to be borne in mind that the so-called dry sodium carbonate, 

" C. P.," almost always contains some bicarbonate and hence yields 

water on heating. This, however, in no way detracts from its usefulness, and it is not necessary to convert it wholly to the normal salt

1 Anleitung zur Gesteinsanalyse, 1905, p. 5.
SILICA. 95

for fusion of the kind now contemplated. In fact, C. Holthof * 

most strongly recommends using the bicarbonate itself as a flux 

instead of the normal carbonate. (See 8, p. 96.)

f. The fusion with normal sodium carbonate. Ordinarily from 4 

to 6 parts of the flux should be used to 1 part of rock powder, thoroughly mixed in a crucible of 20 to 30 grams weight. It is inadvisable to use the much larger proportion of flux recommended by 

some writers, except as it may be shown to be needed in isolated 

instances. The larger amounts introduce more impurity than the 

smaller and necessitate longer washing of precipitates. At first, the 

crucible (covered) is placed over a moderately low Bunsen flame, 

which is gradually increased to the maximum and maintained there 

till the mass is quiescent. There should be no violent action. The 

contents of the crucible will then appear, in the case of highly 

feldspathic or quartzose rocks, as a viscous liquid, occasionally 

almost clear, though generally more or less turbid, and when placed 

over the blast little or no further effervescence occurs. Melts of 

this character disintegrate very readily in water. With less siliceous 

rocks the fusion is less perfect and may be far from complete, though 

this does not necessarily imply incomplete decomposition of the silicates. It is generally advisable and often necessary to place these 

less fusible mixtures over the blast lamp, when a further and very 

marked escape of carbon dioxide takes place, and the crucible cover 

should be lifted cautiously at intervals to avoid loss by boiling over. 

This boiling is due not merely to further action of the carbonate on 

the rock-forming minerals, but oftentimes more to the decomposi- 

, tion of the alkaline earth carbonates, whose bases then enter into 

combination with other constituents of the flux and rock to form 

compound silicates and probably aluminates. It is a great mistake 

to regard, as many seem to have done, the alkaline-earth metals, 

magnesium, iron, and manganese as present in the form of carbonates after a blast fusion. They are rarely in that state even when 

only the Bunsen flame has been used.

The blast flame during fusion should not be directed vertically 

against the bottom of the crucible, but at an angle against the side 

and bottom, nor should the flame be allowed to envelop the whole 

crucible. These precautions apply in all ignitions of reducible substances, and yet they are too often neglected. In neither case, if 

neglected, will there be the necessary oxidizing atmosphere within 

the crucible; on the contrary, reduction may occur fraught with 

serious consequences. This is especially true if the rock contains 

more than traces of pyrite or other sulphide, when, after cleansing 

and igniting the crucible, there may appear on its interior a darken1 Zeitschr. anal. Chemie, rol. 23, 1884, p. 499.
96 ANALYSIS OF SILICATE AND CARBONATE HOCKS.

ing due to oxidation of reduced iron which had alloyed with the 

platinum. In exceptional cases this may amount to several milligrams in weight, and can be removed only^ by repeated ignitions, 

followed each time by scouring or treatment with hydrochloric acid 

or acid potassium sulphate. In order to avoid the use of niter in 

case of pyritiferous rocks, it is well to first roast gently the weighed 

powder in the crucible in which the fusion is to be made, turning 

the crucible around a few times to expose all of the powder to the 

air. With rocks exceptionally high in pyrite the roasting is done 

best in a porcelain crucible. In such case, after transferring the 

greater part to the platinum crucible, if brushing with a camel's 

hair brush does not remove the last of any adhering dust, scouring 

with a little sodium carbonate will be effective.

It is unsafe to make sodium carbonate fusions in a muffle. Tests 

made at the Bureau of Standards by E. Wichers with sodium carbonate by itself have shown a marked attack of the platinum above 

the melt, owing probably to the absence of an atmosphere charged 

with carbon dioxide and consequent formation of sodium hydroxide. 

This explains probably the conflicting statements that have been 

made regarding the effect on platinum of molten sodium carbonate.

It happens sometimes that the cooled flux, and even its solution, 

will indicate the absence of manganese when it is really present in 

quantity to give normally a strong coloration. Two fusions made 

side by side or successively, under apparently similar conditions, 

may in one case show little or no manganese, in the other considerable. 

This observation has been made frequently, and therefore the absence 

of a bluish-green color in the fusion is not to be taken as a proof of 

the absence of manganese. This difference of behavior I can ascribe 

to no other cause than that of a reducing atmosphere in one of the 

crucibles and an oxidizing one in the other, even though the conditions were apparently alike. It is, of course, not to be expected that 

the green color can show until all other oxidizable components of the 

rock, like sulphides, ferrous iron, and organic matter, have been fully 

oxidized, which, however, is soon the case if air has access to the surface of the melt.

8. Fusion with sodium bicarbonate. C. Holthof,1 who strongly 

recommends sodium bicarbonate as a flux, uses 12 to 15 parts of it to 

1 part of the sample. One quarter of this is placed on the bottom 

of the crucible, a second quarter is mixed thoroughly with the rock 

powder in a small warmed dish, and the composite is then mixed 

with a third quarter on glazed paper and poured into the crucible. 

The last quarter is used for rinsing the dish and paper and covering 

the contents of the crucible, which may be half full. The crucible

1 Zeitschr. anal. Chemie, vol. 23, 1884, p. 499.
SIIJCA. 97

is heated over a low flame till the bottom is dull red, then during 

15 minutes the flame is increased till the lower quarter of the crucible is dull red, in which state it is maintained for 15 minutes. Then 

fusion is brought about by the full flame and maintained for a time. 

Holthof claims that action between the silicate and carbonate takes 

place at a lower temperature than with the normal carbonate before 

fusion, and that for this reason there is almost no spattering onto 

the lid of the crucible.

e. Treatment after fusion. When fusion is complete, the crucible 

is seized with the tongs (fig. 1, p. 32), and the contents are caused to 

solidify in a thin sheet over the sides and bottom by imparting an 

appropriate gyratory motion with the arm during the cooling process. 

Separation of the mass from the crucible is usually easy, especially 

if aided by gentle pressure, and much less time is required for. its 

disintegration than when allowed to solidify as a thick cake. If time 

is no object it is perhaps better to avoid all risk of deforming the 

crucible and proceed as follows: Let the melt solidify at the bottom 

of the crucible, first placing in it the bent end of a stout platinum 

wire. When all is solid, apply the flame again to melt only a thin 

layer next the crucible, when the cake can be lifted out with ease 

except for the little that still adheres to the vessel.

The contents of the crucible are placed in a rather tall covered 

beaker with some water, and hydrochloric acid of 1.1 specific gravity 

is added gradually in excess. The depth of the evanescent pink color 

usually produced on addition of the acid allows of judging approximately the amount of manganese present. The beaker is placed on 

the water bath, and when disintegration is complete, having been 

assisted by gentle pressure with a blunt glass rod, the contents are 

transferred to a large platinum dish and evaporated on the bath. It 

is permissible to dispense with the beaker and to perform the whole 

operation of solution in the platinum dish, but there will be greater 

solution of platinum in this case by reason of the action of the 

hydrochloric acid on sodium manganate, etc., in direct contact with 

platinum.

B. SUBSEQUENT TREATMENT.

From this point the treatment will be the same ordinarily whether 

the boric-oxide or the sodium-carbonate method of decomposition 

has been employed.

a. SEPARATION OF SILICA.

a. Reasons for adoption of accepted procedure. The once universal practice of employing a single evaporation with hydrochloric 

acid for the dehydration of silica has been thoroughly discredited 

131999° 19 7
98 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

by the work of a number of writers. K. Bunsen 1 was aware of the 

impossibility of separating silica by a single evaporation, and he 

corrected the alumina in his silicate analyses for the silica it was 

always found to contain. Later E. Ludwig 2 and still later C. 

Meineke 3 drew renewed attention to the fact and insisted on the 

importance of correcting the alumina in the manner indicated. 

Ludwig and, at first, Meineke contented themselves with a single 

evaporation, and maintained that all of the unprecipitated silica 

was to be found with the subsequently precipitated iron and alumina. 

In his second paper Meineke prescribes two evaporations (presumably with intervening filtration) and the rejection of the silica subsequently recovered from the alumina as due to impurity in the 

ammonia or derived from the vessels, unless these were of platinum. 

He furnishes quantitative data.

In spite of these publications the practice continued of employing 

but a single evaporation. Some years later Alexander Cameron,4 

seemingly in ignorance of the earlier work, reopened the subject with 

additional quantitative data, and insisted on more than one evaporation with intervening filtration instead of trying to recover the remaining silica from the alumina. He also showed, as Ludwig had 

asserted, that a common practice of evaporating to dryness several 

times with fresh portions of acid without intervening filtrations did 

not reduce the silica in the filtrate, and that the presence of aluminum, iron, and calcium was without influence on the results; further, 

that the dehydration was more complete when a high temperature 

was employed, but that it could not be made complete at one treatment by any modification of the process.

According to J. P. Gilbert,5 a drying temperature above that of the 

steam bath offers no advantage unless much magnesium is present, 

when the most favorable temperature is 120°. He found that much 

calcium chloride seems to facilitate dehydration of the silica, but that 

magnesium chloride above 120° by decomposing forms a silicate 

which dissolves in hydrochloric acid and increases the amount of 

silica carried into the filtrate. He confirmed the earlier belief that 

drying temperatures higher than that of the steam bath increase the 

amount of insoluble impurity in the silica, and that this amount 

can not be overcome by long digestion with hydrochloric acid. Further, he confirmed D. Lindo's statement 6 that evaporation with sulphuric acid till the appearance of white fumes gives a higher result

»Ann. Chem. Pharm., vol. 61, 1847, p. 265. 

"Zeitschr. anal. Chemie, vol. 9, 1870, p. 321. 

8 Repert. anal. Chemie, vol. 7, 1887, pp. 215, 757. 

*Chem. News, vol. 69, 1894, p. 171.

6 Tech. Quart., vol. 3, 1890, p. 61; abstract in Zeitschr. anal. Chemie, rol. 29, 1890, 

p. 688.

8 Chem. News, vol. 60, 1889, p. 14.
SILICA. 99

in silica than with hydrochloric acid. But for general rock analysis 

the use of sulphuric acid at this stage must be rejected utterly.

Some of the above experiments of Cameron and Gilbert were 

repeated and confirmed by me.1 In the course of this work it was 

found that hydrochloric acid itself exerts a marked solvent action on 

silica that has been separated from solution in any of the ways above 

outlined, whence it becomes plain how a portion of the silica always 

found in the filtrates gets there, and that it is hopeless to expect to 

prevent this by a single prolonged drying.2 Other explanations commonly offered for the observed solubility are the formation of soluble 

silicates by interaction between the silica and salts present during 

drying and the protective influence of those salts. The former of 

these should become more active with increasing temperature, though 

Gilbert's work does not seem to indicate this except when magnesium 

is present in quantity.

A. B. Trickett'3 and Lenher and.Truog* have shown that the 

sodium chloride always present after acidifying a solution of a 

sodium carbonate melt has a solvent action on silica. F. G. Hawley 5 

and H. A. B. Motherwell 6 add confirmation, and Motherwell shows 

that other salts exert solvent action. Hawley found that concentrated hydrochloric acid is less active than that of 18 to 25 per cent 

strength, and, further, that, as was to be expected, the amount of 

silica dissolved is proportional to the amount of acid used.

C. Friedheim and A. Pinagel 7 prescribe washing the silica with 

dilute hydrochloric acid instead of hot water because of the marked 

solubility in water observed by them. But, according to experiments 

made by myself to test this point, the direction is a vain one, for the 

results obtained by following it in the ordinary course of rock analysis were worse, if anything, than when pure water was used.

P. Procedure in absence of notable amounts of -fluorine. From the 

above observations the following procedure is deemed best adapted 

for general rock analysis in the absence of more than 0.2 or 0.3 per 

cent of fluorine.

The evaporating dish should be of platinum and as large as possible to permit considerable surface distribution of the dry mass. 

The dishes used in the Survey' have a capacity of about 1 liter.

» Common errors in the determination of silica : Jour. Am. Chem. Soc. vol. 24, 1902, p. 

262; Chem. News, vol. 86, 1902, pp. 79, 89. For details of experiments referred to here 

and on several of the following pages the reader will do well to refer to this paper.

2 Max Wunder and A. Suleiman (Ann. chim. anal., vol. 19, 1914, p. 45) and V. Lenher 

and E. Truog (Jour. Am. Chem. Soc., vol. 38, 1916, p. 1050) confirm this statement. 

The former give quantitative data for the solubility of silica in hydrochloric, nitric, and 

sulphuric acids, and the lattei" for hydrochloric and sulphuric acids.

a Mellor, J. F., Quantitative inorganic analysis, p. 175.

*Jour. Am. Chem. Soc., vol. 38, 1916, p. 1050.

B Eng. and Min. Jour., vol. 103, 1917, p. 541.

"Idem, p. 1155.

7 Zeitschr. anorg. Chemie, vol. 45, 1905, p. 411.
100 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Porcelain may be used, but never glass, if platinum is not available. 

Water or steam bath temperature suffices is, indeed, demanded^ 

for the evaporation to approximate dryness. If the analysis is begun 

in the morning the first filtration can be made late in the afternoon. Nothing is gained by continuing the evaporation long beyond 

apparent dryness this first time, for the slight reduction in the soluble 

silica gained by so doing is offset by a large loss of time; nor is there 

much advantage in crushing the residue to powder, whereby, moreover, the dish is easily scratched. The amount of silica passing into 

the filtrate will generally vary from 1 to 3 per cent of the amount 

present, and is but little less after 20 hours drying than after onetenth of that time.1 Upon the seemingly dry mass is poured enough 

strong hydrochloric acid to drench it thoroughly,2 then an equal 

bulk of water, and the dish is placed covered on the bath for 10 to 

30 minutes and the contents are stirred occasionally. It is quite 

permissible and sometimes advisable to defer adding the water till 

the strong acid has been in contact with the salts for 10 or 15 minutes. More water is then added and filtration proceeded with, first 

by decantation, leaving nearly all the silica in the bottom of the 

dish. The silica is generally in a coarse condition, and may be 

ground finer with a pestle. If there is a good deal of iron in the rock, 

it may be advisable at this stage to add hydrochloric acid of half 

strength and heat, after which the silica is brought onto the filter. 

It is not necessary to remove at this time the film of silica that may 

adhere to the dish in spots beyond the power of a stiff feather to 

remove, for in the subsequent evaporation it will disappear.3 The 

washing should be done with cold water or with hot dilute acid till 

the absence of any yellow color in the precipitate or paper indicates 

removal of most of the iron. Hot water may be used with advantage 

for the last washings, and the paper should be sucked dry at the 

pump.

The filtrate is evaporated again in the same dish to dryness. Usually this state will be reached by the following morning. It may be 

hastened, if desired, by placing the dish in an air bath at 110° or 

120°. It is probable that a much higher temperature would have no 

bad effect in the majority of cases except to increase the amount of 

insoluble matter other than silica. If the data of experiments 6 to 9

1 See Jour. Am. Chem. Soc., vol. 24, 1902, p. 366; Chem. News, vol. 86, 1902, p. 80.

2 E. Jordis and W. Ludewig (Zeitschr. anorg. Chemie, vol. 47, 1905, p. 180) warn against 

loss by incautious moistening of the dry powder with water or acid, especially when 

these are hot, due to the throwing off of a cloud of dustlike particles. They recommend 

covering the dish and moistening cautiously with water before adding 'the acid. With a 

very capacious dish this is hardly called for.

3 Where but a single evaporation is contemplated this film may be removed by warming with ammonia and recovered by reevaporation with acid after driving off the ammonia. 

(See Kortright, F. L., Chem. Engineer, vol. 5, 1905, p. 19, who gives data to show tlie very 

material error that often results from neglect to recover this silica.)
SILICA. 101

in the paper already cited 1 are conclusive, they show that at this 

stage thorough drying exercises an appreciable effect in reducing the 

silica in the next filtrate, though the small amounts there reported 

when experimenting with pure quartz are not to be expected in rock 

work. If time is no object, and great accuracy is sought, a third 

evaporation and filtration should be made, for the silica in the second 

filtrate will amount to 2 to 4 mg.2 Nearly the whole of this can be 

recovered later from the alumina, but not all, hence the advisability 

of securing as complete separation here as possible. The second and, 

if need be, third filtrations with their attendant operations consume 

less time than the first, and, of course, smaller filter papers are to be 

used. It is to be noted that these later silicas are more colored than 

the first, and if the rock is even moderately titaniferous they are by 

no means pure silica.8

Lenher and Truog in their paper already cited base the following 

procedure on their experimental work:

The cold fusion is treated with 60 cm.3 of hydrochloric acid (sp. g. 1.07). After all carbonates are decomposed and the lumps are broken up, evaporation 

on a steam or water bath is proceeded with until the residue begins to powder 

or crumble. Further evaporation should be avoided. Breaking up of lumps 

or crusts greatly expedites the evaporation near the end. The residue is treated 

with 15 cm.3 of hydrochloric acid (sp. g. 1.1), covered, and heated on the water 

bath for 10 minutes. After diluting with 10 cm.3 of water, filtration is proceeded with immediately, and the silica is washed with a hot solution consisting of 5 cm.3 of hydrochloric acid (sp. g. 1.2) to 95 cm.3 of water. This filtration 

is preferably performed with suction. The filtrate is evaporated *o dryness and 

until the smell of acid has practically disappeared. The residue is dehydrated 

at 110° for two hours, taken up with 8 cm.3 of hydrochloric acid (sp. g. 1.1), 

covered, and heated on the water bath five to ten minutes, diluted to about 50 

cm.9, and filtered immediately. This filtration is performed without suction, 

and the washing is done with cold water containing 1 cm.3 of concentrated hydrochloric acid to 99 of water.

By this procedure Lenher and Truog found the recovery of silica 

on a third evaporation not in excess of 0.3 mg. if a platinum dish was 

used, but more if the dish was of porcelain. The inference is that the 

glaze was attacked.

1 Jour. Am. Chem. Soc., vol. 24, 1902, p. 306; Chem. News, vol. 86. 1902, pp. 79, 89.

2 Lenher and Truog's more favorable results, Jour. Am. Chem. Soc., vol. 38, 1916, p. 

1050, are not based on positive proof but merely on what they obtained by evaporation. 

They may have overlooked the possibility of a normal solubility of silica in the solution 

silica which is not recoverable by evaporating to dryncss.

8 Without giving quantitative data, A. LeC16re (Compt. Rend., vol. 137, 1903, p. 50) 

claims that, silica and titanium dioxide are rendered completely insoluble by acidifying the 

aqueous solution of the sodium carbonate melt with enough formic acid to give 5 

per cent of free acid and keeping at a temperature of 100" for two days. As to 

titanium dioxide this claim has been verified at the Bureau of Standards by G. E. P. 

Lundell only if the solution is boiled during the two days, but not even so as to 

silica, very much of which remains in solution. The method need not be considered 

for rock analysis, both on account of the time required and the introduction of 

foreign matter from the glass vessel-in which the boiling is done.
102 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

With minerals like the zeolites, or 'artificial products such as Portland cements, which are directly soluble in hydrochloric acid, the 

drying may be very much hastened by placing the covered dish, 

after bringing to approximate dryness on the bath, on a sand bath 

or on a triangle which itself rests on a hot plate. The temperature 

may rise in the dish to 200° ; in fact, according to Bertram Blount 1 

it should not be lower. After an hour's exposure to this temperature 

less silica will perhaps pass into the filtrate than after prolonged 

drying at steam-bath temperature, but this is usually at the expense 

of greater contamination of the filtered silica. As this contamination is very large (see e, p. 104) with highly titaniferous and ferruginous rocks and minerals, the operator should use discretion in his 

choice of a high drying temperature.

Y. Procedure with rocks and minerals containing fluorine* This 

subject has been touched on in commenting on the boric-oxide and 

sodium-carbonate methods of fusion,2 and will be considered in, 

detail under the heading "Fluorine" (p. 222).

b. IGNITION OF SILICA.

The application of a strong blast heat or its equivalent 3 for 20 to 

30 minutes with crucible covered is absolutely necessary to expel all 

moisture from the silica, and the latter is then not hygroscopic. The 

first of these statements, long extant in the literature, has been disputed by G. Lunge and C. Millberg * on the basis of experiments 

made on silica obtained by the decomposition of silicon tetrafluoride 

by water. It has been shown,5 however, that while the objection holds 

good for silica thus prepared, it does not for silica obtained by the 

decomposition of an alkali silicate by means of an acid. F. P. Treadwell confirmed the observation as to the difference in behavior of the

Soc. Chem. Ind., vol. 21, 1902, p. 1217.

2 See A. a, p. 89, and footnote, p. 93.

a It must be borne in mind that some platinum crucibles lose weight steadily and very 

appreciably on long blasting, not only when new but even after long use. When a crucible 

suffers from this defect the rate of loss should be ascertained from time to time and allowance made accordingly, or else the weight of the crucible should be taken after and 

not before ignition of the precipitate. (See on this subject Hall, R. W., Jour. Am. Chem. 

Soc., vol. 22, 1900, p. 494, and Hulett, G. A., and Berger, C. W., Jour. Am. Chem. Soc., 

vol. 26, 1904, p. 1512.) It was hoped that with the advent of the electric furnace 

prolonged ignitions would not be subject to this source of error, but it was soon found 

that at 1,250°, the maximum temperature v attainable in the furnace at the Survey, 

medium-sized crucibles lost approximately 1 mg. in weight per hour. Similar losses have 

since been noticed and published by others. Their cause seems to be chiefly the distillation of iridium out of the alloy. At one time an error of about the same magnitude in 

the opposite direction caused perplexity until it was found that the platinum wire in 

the bedplate of the furnace was burned out. The crucible, then occupying the coolest 

place in the furnace, received a deposit of some of the metal volatilizing from the wires 

in the side plates. Iron has also been found repeatedly in platinum ware in large 

amount. (See p. 43.)

*Zeitschr. angew, Chemie, 1897, p. 425.

5 Hillebrand, W. P., Jour. Am. Chem. Soc., rol. 24, 1902, pp. 372-373; Chem. News, 

vol. 86, 1902, p, 91,
SILICA. 103

two forms of silica, but regarded the blast as unnecessary if a Teclu 

instead of a Bunsen burner is used. Lenher and Truog say also that 

pure silica comes quickly to constant weight after ignition over a 

Meker burner. My experience is not in agreement with theirs.1

Although with a powerful blast the above time limit usually suffices, and may be shortened materially for small amounts of silica, 

such as are usually found, in limestones and even in cements, there is 

need occasionally to prolong it in very exact work until repeated 

weighings give the same value or a loss no greater than that suffered 

by the crucible itself. 2

C. CORRECTION FOB IMPURITIES lit THE SILICA.

The weight of the crude silica should always be corrected for 

impurities, which are never, entirely absent, by evaporating with 

sulphuric and hydrofluoric acids, which should be free from nonvolatile impurities, and again blasting for a minute or less, according 

to the amount of residue. It is a mistake to neglect another weighing 

at this point, even if the residue may appear insignificant. In my 

experience it has never been found to be unweighable, and, furthermore, the error due to loss in weight of the crucible itself is eliminated if the weighing is made. The silica in the crucible should bo 

moistened with water before adding the hydrofluoric acid, though 

with strongly blasted silica the action is not so violent as with that 

which has not been thus treated. With rocks carrying 60 to 80 per 

cent of silica one or two dr,ops of sulphuric acid diluted one-half 

suffice, but with less siliceous rocks the amount ought to be increased, 

not only in order surely to afford acid enough for the conversion of

1 It was thought that the observation reported by E. Jordis and E. H. Kanter (Zeitschr. 

anorg. Chemie, vol. 35, 1903, p. 16), to the effect that artificially prepared silica when 

digested with hydrochloric acid takes up chlorine and holds it in a chemical combination that is only incompletely broken up. on ignition, might have bearing on this point. 

To test this, precipitated silica was fused with sodium carbonate, the melt was dissolved 

in water and evaporated with hydrochloric acid as in silicate analysis, and the separated 

silica was washed with cold water till free from all but a hardly detectable trace of 

chlorine (wash-water test) and dried at gentle heat Instead of the large amount 

of chlorine reported by Jordis and Kanter, this silica yielded only the minute trace 

that blank tests with the reagents afforded, and sodium in weighable amount was 

also absent. Evidently, as stated by Jordis and Kanter, the chlorine compound, if it 

exists, is readily decomposed by water. The tests for chlorine were made by dissolving 

the silica in presence of silver nitrate in hydrofluoric acid free from chlorine, also by 

fusing with chlorine-free sodium carbonate, dissolving in water, acidifying with nitric acid, 

and then adding silver nitrate. Th. Bauer (Thonind. Ztg., vol. 37, 1913, p. 89) believes 

also that incompletely washed silica contains an oxychloride of silicon, soluble in water 

but not readily decomposed by ignition. If he prepared his silica from alkali melts it 

may have held sodium chloride.

1 For the proof see Hillebrand, W. P., Jour. Am. Chem. Soc., vol. 24, 1902, p. 373 ; 

Chem. News, vol. 86, 1902, p. 91. The duty of every analyst to test the efficiency of 

his blast or muffle can not be emphasized too strongly. The discordance of many statements and results on a variety of subjects is to bo attributed to a difference in the 

ignition temperature employed by different writers. A really good blast will readily 

melt a few centigrams of orthoclase powder in the bottom of a 15-gram platinum crucible, 

showing a temperature of probably 1,200".
104 ANALYSIS OF SILICATE AND CABBO^&TE EOCKS.

all the contaminating bases to sulphate, but also to prevent loss of 

titanium by volatilization as fluoride, for with increasingly basic 

character of the rocks the percentage of this element in the residue 

is likely to increase.

Precipitated silica is easily removed by one evaporation with a 

sufficiency of hydrofluoric acid, but if quartz happens to be present 

this is not the case, for it is dissolved but slowly, and more than one 

treatment may be necessary.

The subsequent precipitate of alumina, etc., is usually ignited in 

the crucible containing the residue from the silica.

d. ACCURACY OF THE SILICA DETERMINATION.

By observing the above rules use of platinum, repeated evaporations and filtrations, proper blast ignition, and correction for foreign 

matter the determination of silica, from being one subject to grave 

error, has become one of the most exact of which I have cognizance, 

provided precautions are taken to recover, as hereinafter described, 

the portions that are to be found inevitably with the alumina. With 

careful work variations of 0.1 per cent are the exception in duplicate 

analyses.

6. COMPOSITION OF THE RESIDUE OBTAINED FROM THE SILICA.

The qualitative composition of the residue obtained from the silica 

varies with different rocks less than its quantity. The residue will 

contain alumina and ferric, titanic, and phosphoric oxides invariably 

if these are present in the rock. If the "rock is low in the last three, 

particularly the last two, the residue should be slight, occasionally 

less than 1 mg. Usually it is much greater, and it may amount to 2 or. 

even 3 per cent with basic rocks very rich in titanium and phosphorus. 

It is, however, a great mistake to suppose, as some chemists still seem 

to, that all or nearly all the titanium is to be found with the silica. It 

may reach one-third of the total amount.

If in correcting the silica, toward the end of the evaporation, when 

the hydrofluoric acid has been driven off and the sulphates begin to 

appear in solid form, the residue has a peculiar milky or enamel-like 

appearance, it may be taken as evidence of much phosphorus and 

titanium, though possibly the appearance may be due to zirconium 

with the other elements named. Although observed in but one series 

of rocks,1 the appearance is so unusual and striking that it was 

deemed worthy of record.

It might be supposed that the residue would contain most of the 

barium of those rocks carrying that element together with sulphur or 

sulphates, but in my experience this is not so. Only when there is 

considerable excess of SO3 over BaO will any of the latter be present

1 See first footnote, p. 119.
SIIICA. 105

in the residue, and in the vast majority of cases there is none at all. 

This is due to the appreciable solubility of barium sulphate in hot 

hydrochloric acid, coupled with the fact that barium is so minor a 

constituent of most rocks. Should some of it be present in the residue, its removal and estimation at this stage are not necessary, as 

it can be recovered more conveniently later, together with the silica 

accompanying the precipitate of alumina, etc. (9. B. b, p. 118).

Quite as rarely is calcium ever a component of the residue if the 

decomposition of the rock powder was complete at the outset. I have 

found frequently that the residue, after re-solution, is quantitatively 

precipitable by ammonia in presence of an ammonium salt. W. R. 

Bloor,1 however, in analyzing clays, invariably found calcium and 

magnesium as well as alkalies in this residue in amounts that were 

surprisingly large, considering the relatively small percentages of 

these elements in clays. I have since tested the matter carefully as 

to calcium and magnesium, finding none of the former and but 0.2 

to 0.3 mg. of MgO, when present at all.

F. A. Gooch, F. C. Keckert, and S. B. Kuzirian 2 and later Kuzirian 8 assume without proof that sodium chloride is one cause of persistent loss of weight when silica is ignited. My own observations, 

like later ones of Lenher and Truog,4 are quite opposed to this.

f. PLATINUM IN FILTRATES.

The filtrates from the silica always contain notable amounts of 

platinum. This arises in very small degree from the crucible fusion, 

unless niter was added; in a larger degree indirectly from the action 

of hydrochloric acid on the manganate, vanadate, and sometimes 

chromate of sodium; and, if much iron is present, in no small degree 

from the reduction of ferric chloride to ferrous by the platinum of 

the dish. This last reaction has attracted little attention until recently, but it is mentioned by Gmelin-Kraut 5 and can be demonstrated readily by evaporation of ferric chloride in platinum.

The removal of this platinum before precipitating, alumfna and 

iron is not necessary (but see footnote, p. 119) and to do so involves 

the reoxidation of all iron and subsequent boiling to remove or 

destroy the excess of oxidizing agent, together with the expenditure of much valuable time. The iron is already oxidized by the 

fusion, and needs no further help in that direction. In the following descriptions it is assumed that the platinum has not been eliminated at this stage.

1 Jour. Am. Chem. Soc., vol. 29, 190T, p. 1603.

2 Am. Jour. Sci., 4th ser., vol. 36, 1914, p. 598 ; Chem. News, vol. 110, 1914, p. 202; 

Zeitschr. anorg. Chemle, vol. 85, 1914, p. 430.

«Am. Jour. Sci., 4th ser, vol. 37, 1914, p. 61; Chem. News, vol. 109, 1914, p. 184; 

Zeitschr. anorg. Chemie, vol. 85, 1914, p. 430.

«Jour. Am. Chem. Soc., vol 38, 1916, p. 1050.

s Anorganlsche Chemie, 6th rev. ed., vol. 3, 1875, p. 359.
ANALYSIS OF SILICATE AND CARBONATE BOCKS. 

7. METALS PRECIPITABLE BY HYDROGEN SULPHIDE.

The presence in appreciable amounts of metals precipitable by 

hydrogen sulphide, except perhaps copper, is of so infrequent occurrence in most rocks that discussion is unnecessary in their connection. In case it is necessary to precipitate them at this stage, however, it is always well to bear in mind that a little titanium may be 

thrown down along with them. Separations of the silica should be 

made in porcelain, to eliminate platinum; or, better still, the quantitative determination of these metals should be made in a separate 

portion of the rock broken up by the action of hydrofluoric and sulphuric acids.

The warning may here be repeated that the samples should never 

be passed through copper or brass sieves when copper or copper and 

zinc are sought.

8. JOINT PRECIPITATION OF ALUMINUM, IRON, TITANIUM, ZIRCONIUM. CHROMIUM, 

RARE EARTHS, PHOSPHORUS, AND VANADIUM, WITH AND WITHOUT MANGANESL

A. PRELIMINARY REMARKS.

The difficulties are very great in the way of successfully producing 

and handling the complex precipitate which is obtained in the next 

stage of the analysis and which should contain the aluminum, iron, 

titanium, and phosphorus, besides chromium, vanadium, zirconium, 

and rare earths if present, and according to some preferences the 

manganese. It is recognized fully that there are objections to parts 

of the procedure that has been followed in the Survey laboratory, 

but the same may be said of any other that is known. It is believed 

that the Survey procedure, which in its main features is closely 

modeled after old and well-known methods, will give in competent 

hands quite as satisfactory if not better results than any other.

© B. PRECIPITATION WITHOUT MANGANESE, 

a. PRECIPITATION BY AMMONIA.

a. Preliminary rema/rJcs. Two precipitations by ammonia at boiling heat are usually quite sufficient to separate iron, aluminum,1 

phosphorus, vanadium, chromium, titanium, rare earths, and zirconium, if all these are present, from nickel, manganese, the alkalineearth metals, and magnesium, in the relative proportions in which 

these elements ordinarily occur in rocks, provided ammoniacal salts 

are present in sufficient quantity. This last point is of special im1 It is well to bear in mind that in presence of fluorine, aluminum is precipitated very 

incompletely by ammonia. See footnote, p. 90.
ALUMINUM, IRON, ETC. 107

portance as regards magnesium, and failure to observe it is doubtless the reason why many old analyses, and sometimes modern ones, 

show utterly improbable percentages of alumina, especially as chemists were formerly often satisfied with a single precipitation. The 

necessary ammonium chloride is obtained better by the use of purified ammonia water and hydrochloric acid than by the addition of 

the solid salt, which is seldom pure. The chemist should satisfy 

himself what amounts of ammonium salt are needed to hold in ammoniacal solution the maximum percentage of magnesium that the 

rock he is analyzing might contain. With extremely high magnesian 

rocks a third precipitation is generally requisite, and a minute 

amount of calcium will sometimes be found in the third filtrate, unless the procedure given under (J is followed carefully.

The precipitations are made in a bulk of 300 to 400 cm.3 , at boiling 

heat, in a platinum dish if possible, otherwise, in one of the borosilicate beakers of the " pyrex " type (free from zinc). The ammonia 

should be as free from carbonate as possible, as well as from any 

nonvolatile matter.

Very many inconclusive researches have been conducted to determine the best conditions for the precipitation of aluminum as the 

hydroxide. Some writers have regarded even a slight excess of 

ammonia as objectionable; others not. The failure to come to agreement seems to be due to the fact that the hydroxide has a certain 

solubility in ammonia and that the hydroxyl concentration at which 

this solubility is least was unknown. Recent work of W. Blum 1 at 

the Bureau of Standards has settled the latter point in favor of the 

concentration which is indicated by the change of color of methyl 

red or rosolic acid in acid solution that is, [H] + =10~T (about). 

Methyl red is preferred because of its sharper color change. Blum's 

recommendations for precipitation are the following:

(}. Procedure. To the solution containing at least 5 grams of ammonium chloride per 200 cm. 3 of solution, or an equivalent amount of 

hydrochloric acid, add a few drops of methyl red (0.2 per cent alcoholic solution) and heat just to boiling. Carefully add dilute ammonium hydroxide drop by drop until the color of the solution changes 

to a distinct yellow. Boil the solution for one to two minutes and 

filter at once. Wash the precipitate thoroughlv with hot ammonium 

chloride or nitrate solution (2 per cent).

The correct end point would be difficult to determine in presence 

of much iron were it not for the fact that ferric iron precipitates 

before the solution is alkaline to methyl red; hence it is easy to 

obtain the correct end point by adding at first only enough ammonia 

to precipitate the iron upon short boiling and allowing the ferric

1 Scl. Paper Bur. Standards No. 286, 1916; Jour. Am. Chem. Soc., vol. 38, 1916, p. 1282.
108 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

hydroxide to settle, after which the color of the indicator can be 

recognized readily in the supernatant liquid and more ammonia 

added if necessary, or any large excess may be neutralized with 

dilute acid.

Blum found that, after a single precipitation, separation from 

calcium and barium is perfect, and from magnesium nearly so; and 

that aluminum itself was so completely precipitated that a maximum 

of only 0.3 mg. A12O3 could be found in the combined filtrates and 

Avashings. :

As to the behavior of manganese, G. E. F. Lundell and H. B. 

Knowles, of the Bureau of Standards, found that after two precipitations less than 0.1 mg. of it, calculated as Mn3 04 , had been carried 

down when there was present originally 10 mg. of MnO, and less 

than 1 mg. with 200 mg. MnO originally present. The separation 

seems therefore to be practically perfect for rock analysis.

Further experiments by Lundell as to the behavior of vanadium 

seemed to show that in rock analysis practically all the vanadium 

will be in the precipitate when R2O3 is high, with Fe2O3 preponderating and V2O5 low, a point which is of importance in the subsequent determination of the iron. When A12O3 preponderates the 

precipitation of vanadium is less complete. Vanadium in the quadrivalent state is more completely precipitated than vanadium in the 

quinquivalent state. ... It is probable that the evaporation with hydrochloric acid to dehydrate silica reduces the vanadium to the former 

state. These observations bear out a statement made by F. J. Pope* 

that vanadium can not be precipitated completely with aluminum by 

ammonia, but that it is precipitated with iron and titanium when in 

the quinquivalent state provided that no excess of amomnia is present.

The use of a dilute solution of an ammonium salt as a wash liquid 

instead of water is necessary in order to avoid as much as possible 

resolution of some of the aluminum hydroxide. S. L. Penfield and 

D. N. Harper 2 recommend washing with a dilute solution of ammonium nitrate (20 cm.3 nitric acid neutralized with ammonia to 

the liter), and also the solution of the first precipitate in nitric instead of hydrochloric acid in order to shorten the washing, there 

Toeing no chloride to remove.3

1 Trans. Am. Inst. Min. Eng., vol. 29, 1899, p. 372.

2 Am. Jour. Sci., 3d ser., vol. 32, 1886, p. 112. C. F. Sideuer and E. Pettijohn's statement (Jour. Ind. Bug. Chemistry, vol. 8, 1916, p. 714) that ammonium nitrate exerts 

about as much solvent effect as pure water on aluminum hydroxide is opposed to that of 

Penfield and Harper and to the experience of Blum (op. cit.).

8 A single objection, and that of a practical nature, weighs against these suggestions. 

It will not do to evaporate to dryness filtrates containing both chlorides and nitrates 

In the same platinum dish, still less to drive off the mixed ammoniacal salts in platinum. 

Contrary to numerous earlier statements there is no danger of loss of aluminum chloride 

Ly volatilization when the 'precipitate is ignited before complete removal of ammonium 

chloride, an assertion which has been confirmed by more than *bne recent writer. Iron 

also is not volatilized by ignition in presence of as much as 1 per cent of ammonium 

chloride (Daudt, II. W., Jour. Ind. Eng. Chemistry, vol. 7, 1915, p. 847).
ALUMINUM, IRON, ETC. 109

For a reason mentioned under E (p. 114) the final precipitation 

may be made with advantage in the presence of macerated filter 

paper, as recommended by Dittrich,1 and the precipitate should be 

sucked dry.

In the presence of little or no manganese, and also in the absence of 

iron, the ammonia method of precipitation is preferable by far to the 

basic-acetate method described in the following section, but it will 

occasionally happen that the separation from even very small amounts 

of manganese is altogether incomplete, and the uncertainty of insuring this separation led me to employ the basic-acetate method for the 

first precipitation in all cases where manganese is present and the 

exceptions are few even though the precipitation of alumina is sometimes less complete than by ammonia, and in spite of other admitted 

defects, as, for instance, a tendency of the precipitate to run through 

the filter on washing.2

The most likely explanation of the persistent retention of small 

amounts of manganese by the precipitates produced by ammonia or 

acetates, even after repeated precipitation, seems to be that a portion 

of the manganese becomes oxidized to the Mn203 state and remains so 

when redissolved, being then in a fit condition for reprecipitation.

b. THE BASIC-ACETATE PRECIPITATION.

a. Preliminary remarks. Although for the basic-acetate precipitation most writers seem to prescribe or prefer sodium acetate, except 

when the presence of a fixed alkali would interfere with subsequent 

operations, there does not seem to be any valid reason why ammonium 

acetate should not do quite as good service, besides having the advantage of easy removability afterward in case of need. Also, there 

is probably no good reason why the corresponding carbonates instead 

of the hydroxides should be used for neutralizing the hydrochloric 

solution before adding the acetate other than the fact that they were, 

when the methods originated, and still are easier to obtain comparatively free from silica and alumina.'. It is to be borne in mind that 

with precipitates low in iron and high in aluminum the separations 

are less satisfactory than when the reverse condition prevails. In 

rocks alumina usually predominates, often largely, over iron oxide, so

1 Anleitung zur Gesteinsanalyse, 1905, pp. 10, 11, 14; Ber. Deutsch. chem. Gesell., vol. 

37, 1004, p. 1840.

2 The fact must not be overlooked that certain of the rare earths may pass completely into the filtrate if 'the basic-acetate method is followed. If, then, later, on rendering the combined filtrates ammoniacal, an unexpectedly large precipitate appears, this 

.should be examined carefully as to its nature. In an analysis of piedmontite from Maryland over 2 per cent of rare earths, including cerium and others not identified were 

quantitatively separated in this way from iron" alumina, etc. On the other hand F. J. 

Pope (Trans. Am. Inst. Min. Eng., vol. 29, 1899, p. 372) says that quinquivalent vanadium is completely precipitated, which is a very desirable effect.
110 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

that none of the methods of making the basic-acetate separation that 

involve the presence of notable quantities of free acetic acid are permissible, because of the solubility of aluminum hydroxide in this acid 

even when it is very ^dilute.

(3. Procedure. The cold and not excessively acid solution, not exceeding 100 cm.3 in bulk and contained in a beaker of resistant glass, 

is first neutralized with great care by adding a freshly prepared solution of sodium carbonate drop by drop. When the solution begins to 

deepen in color, the addition of the carbonate is continued with less 

speed and with longer stirring between the successive drops. When, 

now, the precipitate that each drop causes begins to dissolve very 

slowly, no further addition may be made till the liquid becomes quite 

clear again. With practice, it is not difficult to recognize this condition, even when the liquid is very dark. The intensity of the color 

will depend on the amount of iron present and the degree of dilution; therefore with small amounts of iron one is much more liable 

to overstep the end point than with solutions rich in iron. When, in 

spite of vigorous stirring, the turbidity after a final drop seems rather 

to increase than diminish, one or, if need be, two drops of acid are 

added. If this does not clear the liquid, it is best to add a slight 

excess and to repeat the neutralizing process.

Two or three grams of sodium acetate dissolved in a small amount 

of water are now poured in and then boiling water till the total bulk 

is about 400 cm.3 The beaker is placed over a lamp and its contents 

are brought to boiling and kept in that state for two or three minutes. 

As soon as settling has taken place filtration is proceeded with. It is 

generally best to dispense with the pump at this stage and to use a 

filter of such size that the whole of the precipitate can be brought 

upon it conveniently without filling to the top. The washing is to 

be done with hot water, to which has been added a very little sodium 

acetate for the purpose of guarding against an otherwise inevitable 

turbid filtrate.

The precipitate, having been sucked dry at the pump, is redissolved 

in hydrochloric acid, reprecipitated by ammonia as in B. (3 (p. 107), 

washed, sucked dry, and treated as in E (p. 114), after recovery as in 

D. b (p. 113) of the portions of aluminum and iron that may have 

passed into the filtrates. 1

1 Modifications of the basic acetate separation. Borck's method. H. Borck (Zeitschr. 

angew. Chemie, vol. 25, 1912, p. 719) makes the basic acetate precipitation by adding 

ammonia in presence of methyl orange until the color changes, then ammonium acetate, 

and finally boiling for a short time.

S&nchez's metJwd,. J. A. Sanchez (Bull. Soc. ehim., vol. 9, 1912, p. 880) separates 

ferric iron from bivalent ^manganese i§ neutral or faintly acid solution by adding 

pyridine and then beating.' The ferric hydroxide is washed with hot water holding 

pyridine and then with pure water. It is claimed that half a milligram of manganese 

can be separated thus from a gram of iron. If much manganese is present the precipitate 

is to be dissolved in hydrochloric acid and the separation repeated. Zinc accompanies the
ALUMINUM, IRON, ETC. Ill

0. PRECIPITATION TOGETHER WITH MANGANESE, 

a. BY AMMONIA AND AMMONIUM PERSULPHATE.

a. Preliminary remarks. This method has for its object the coprecipitation of manganese with a view to simplifying subsequent operations. It is, however, defective in case the rock carries appreciable 

amounts of barium and strontium or is very high in calcium, by 

reason of the certain partial precipitation of some of one or both of 

the first two as sulphates and its possibility in the case of calcium.

iron In part, but can be separated from it, after dissolving In hydrochloric acid, by ammonia in presence of ammonium chloride.

Mittasch's method. A study of the conditions necessary for successful separations of 

large or small quantities of niaaiganese from iron by one treatment has been made by 

A. Mittasch (Zeitschr. anal. Chemie, vol. 42, 1903, p. 492), who gives the following 

directions for the use of ammonium acetate. It must be borne in mind, however, that 

this method is not applicable to aluminous materials.

The solution containing not much free acid (hydrochloric) and preferably cool, whose 

volume should not exceed 100 cm.3, is neutralized in a beaker with concentrated ammonium-carbonate solution (200 grams per liter, about double molar) till the precipitate 

that is formed begins to redissolve slowly, then with weaker solution (about one-tenth 

molar) till a slight precipitate persists for one or two minutes in spite of stirring. 

Next is added, according to the amount of this precipitate, 3 to 5 cm.3 of acetic acid 

(double normal) if the commercial article of ammonium acetate, which nearly corresponds 

to the acid salt (NHJCaHsOa-CaEUOz, is used, or 10 cm.» if the normal salt is used. 

The last is made by neutralizing acetic acid with ammonia. The solution is then diluted 

with water to about 400 cm. 3 and brought nearly to the boiling point. Any precipitate 

that may have appeared being disregarded, 20 cm.1 of the acid acetate (one-half 

molar) or 5 cm.a of acetic acid and 10 cm.8 of the normal acetate (molar) Is added, and 

the boiling temperature is maintained for a minute longer. Precipitation is complete 

even at 60°, but nitration is easier if the boiling temperature is reached. As soon as 

the solution is settled filtration, is begun and the washing performed with, hot water at 

first, then with hot water containing some acetate and a little acetic acid. Any adhering fllm is removed from the glass with hydrochloric acid and reprecipitated with ammonia. If this is added to the main filter it must not be done till the large precipitate has been washed completely, because of the danger of precipitating, by the ammonia, 

manganese that has not yet been washed out.

Brunch-Funk method. The following method of 0. Brunck (Chem. Zeitung, vol. 28, 

1904, p. 514), slightly modified and extended by W. Funk (Zeitschr. anal. Chemie, vol. 

45, 1906, p. 181), is claimed to afford a complete separation, by one treatment, of iron 

from manganese, zinc, nickel, and cobalt. Its applicability to aluminous materials, however, has not been tested, and it is quite improbable that it would work with rocks containing phosphorus and titanium.

The method differs from other modifications of the acetate process in the avoidance 

of the delicate neutralization, by removing excess of acid by evaporation, and in the 

addition of potassium chloride to form a double salt with ferric iron and thus prevent 

the separation of a basic chloride during the drying. As given by Funk for materials 

soluble in acids the procedure la as follows:

To the chloride solution in a large dish is added potassium chloride (about 0.35 gram 

to 0.1 gram of iron), and the solution is evaporated to apparent dryness on the steam 

bath but without expelling all of the free acid. The residue is broken up superficially, 

and the drying on the bath continued for 5 to 10 minutes. It is then taken up in 10 to 

20 cm.3 of cold water, with which it should give a clear solution. It is requisite that 

there shall remain a slight amount of free acid to set free acetic acid from the acetate 

in the next stage of the operations. One and a half to two times the theoretically needed 

quantity of sodium acetate (3 molecules of NaC2H3O2 .3HoO to 1 atom of iron) is now 

added, in a solution which has been rendered slightly acid with acetic acid if originally 

alkaline. After diluting with cold water (to 400 to 500 cm.3 for 0.2 gram iron) the 

solution Is gradually heated with stirring to the point of precipitation (60° to 70°), 

allowed to settle, and decanted, the precipitate being collected on. the filter and washed 

with hot water.
112 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

It is probable that calcium can be completely held in the filtrates by 

two precipitations in analyzing almost any silicate rock, but this is not 

at all certain with respect to limestones, a point that has not yet been 

investigated. If neither strontium nor calcium is present in sufficient amount to be retained in the precipitate, there is no vital objection to the method on this score, for barium can be recovered, as in 

9. B. b (p. 118).

The applicability of the method as above limited being assumed, it 

may be carried out as follows, though too few tests have thus far been 

made to warrant its unqualified recommendation.

P. Procedure.' To the filtrate from the silica contained in a platinum dish, and in bulk from 100 to 200 cm.3 , is added enough hydrochloric acid to prevent precipitation of magnesium when made ammoniacal (see B. a. a, p. 106). Heat is applied, and about 1 gram of 

ammonium persulphate 1 free from all interfering impurities is added. 

When the liquid begins to boil ammonia is added carefully until in 

decided excess, as shown by the odor, and boiling is kept up for 

several minutes.2 The precipitate is allowed to settle, is filtered 

quickly, washed three or four times with 2 per cent ammonium chloride solution, and sucked dry by the pump. It has not been determined if such a very dilute solution of persulphate has any appreciable effect on glass, but apparently not, to judge from my own 

limited experience. The precipitate is then dissolved in a small 

amount of hot hydrochloric acid containing a few drops of sulphurous 

acid, and after addition of well-macerated filter paper is reprecipitated precisely as the first time, washed three or four times with 2 

per cent ammonium chloride solution, then ignited in the paper, and

1 This reagent may have to he purified hefore use. Jannasch (Praktlsche Leitfaden der 

Gewiclitsanalyse, 2d ed., 1904, p. 179) does this as follows: To a warm saturated solution (not over 95°) ammonia is added until its odor persists. [More will have to be added 

at intervals, for the continual decomposition of persulphate sets free sulphuric acid. 

W. F. H.] When the precipitate of alumina, etc., has settled, the solution is filtered 

as rapidly as possible through asbestos, a porcelain funnel being used, because the 

strong solution attacks both paper and glass markedly. When cooled to about 30° the 

clear filtrate is poured into twice its volume of alcohol and further cooled by ice applied 

(xternally. After half an hour the precipitated persulphate is collected on a filter, 

washed with alcohol and then with ether, and dried in the air. The alcohol must be 

removed thoroughly.

A commercial article purified thus by me was found to contain no interfering impurities, though not free from alkali, and it held moreover much ammonium sulphate 

nearly 50 per cent in one preparation.

The reagent as bought should be tested always as to strength as well as for 

alumina and other impurities. B. E. Sive, at the Bureau of Standards, recently found 

an article^ of domestic make, purchased in 1912 and labeled 97.9 per cent, to contain only 

3.5 per cent of persulphate. Two other lots, one of domestic and one of foreign 

origin, purchased in the same year, held 95 and 99.25 per cent, respectively.

Because of the decomposition and consequent loss that results when Jannasch's method 

of purification is employed, H. E. Merwin has suggested (private communication) that, 

if aluminum is the only interfering element, its content be determined and a correction 

made for it, using of course a weighted amount of the reagent for the rock analysis.

2 It has not been determined if Blum's manner of precipitating (8. B. 0. p. 107) is permissible under the conditions here existing.
ALUMINUM, IKON", ETC. Il3

weighed as A12 03 , Fe2 03 , Mn3 04 , Ti02 , and P^Og. 1 Any chromium 

in the rock should be in the filtrates, wholly oxidized by the persulphate, but it will be recovered with the unprecipitated traces of 

alumina, as detailed under D. c, page 114, and should be added to 

the main precipitate ahove. It is not best to attempt to determine 

the chromium colorimetrically in the filtrate.

b. BY AMMONIA AND AMMONIUM SULPHIDE.

Although the old method of precipitation by ammonia and ammonium sulphide can be employed in special cases, it is not well 

adapted generally to silicate rocks and therefore will not be described 

in this connection.

D. RECOVERY OF UNPRECIPITATED IRON AND ALUMINUM FROM THE

FILTRATES.

a. AFTER AN AMMONIA PRECIPITATION.

- The filtrates are evaporated to a small volume, always in platinum 

if possible and allowable. If ammonium salts are present in abundance it is advisable to evaporate the filtrates separately, the second 

to dryness. Its dry contents, almost wholly ammonium salt, are expelled by heat, the slight residue being taken up with hydrochloric 

acid and added, whether wholly soluble or not, to the other filtrate 

reduced in bulk. To this ammonia is now added and the evaporation 

continued, the solution being kept alkaline, in order to coagulate the 

small amount of alumina that will invariably and the iron hydroxide 

that will usually be found. This is collected on a small filter and the 

filtrate caught in a flask of 150 to 200 cm.3 capacity, if manganese 

is to be determined, otherwise in a platinum dish of suitable capacity 

for the calcium precipitation. The small precipitate is washed with 

2 per cent ammonium chloride solution, burned, and added to the 

main one.

b. AFTER A BASIC-ACETATE PRECIPITATION.

The first filtrate is evaporated to or nearly to dryness, in order to 

get rid of the excess of acetic acid. The residue is then taken up with 

only enough hot water to keep it in solution, and the dish is replaced 

on the bath for a short time. The precipitate, which will generally 

be appreciably larger than that obtained in a, is collected on a small 

filter (7 cm.), and the filtrate in a flask of 150 to 200 cm.3 capacity. 

The second or ammoniacal filtrate, having been separately evaporated 

to small bulk, with the addition of a few drops of ammonia toward 

the end, serves as first wash water for the other dish and for the preiThe mixture will contain also Zr02, V205, and the rare earths, If present. 

131990° 19 S
114 ANALYSIS OF SILICATE AND CAKBONATE KOCKS.

cipitate on the filter. Both dishes and the filter are finally rinsed with 

2 per cent ammonium chloride solution. The ammoniacal filtrate contains enough ammonium salts to prevent precipitation of magnesium 

in the first filtrate when the two come together.

If manganese peroxide has been deposited on the surface of the 

dish it is removed by hydrochloric acid and a drop or two of sulphurous acid, which mixture is then passed hot through the filter, the 

filtrate being caught in a small beaker. A reprecipitation by ammonia is then made, and the precipitate collected again on the filter 

and added to the main one, the filtrate passing into the flask containing the previous filtrate. If much manganese is present, of course, a 

second precipitation by ammonia of the small precipitate may be 

required. In these cases there is no difficulty in getting all the 

manganese into the filtrate.

C. AFTEB PRECIPITATION BY AMMONIA AND AMMONIUM PERSULPHATE.

The filtrates are evaporated as in a. The second filtrate is carried 

to dryness and the ammoniacal salts are removed by ignition. The 

residue is treated with a little hot hydrochloric acid and added, to the 

first. A drop or two of sulphurous acid is then added if chromium 

is present, as will be shown usually by a yellowish color of the solution. The aluminum, chromium, and trace of iron are then precipitated by ammonia in slight excess and the digestion is allowed to 

proceed on the bath till the slight precipitate has coagulated. This 

is collected on a small filter (7 cm.) and washed with hot water, the 

filtrate being collected as in a and b if nickel or zinc are to be looked 

for, otherwise in a large platinum dish for treatment as in 12 (p. 140).

The precipitate is redissolved in hydrochloric acid, reprecipitated 

in small bulk of solution by ammonia, and finally added to the main 

precipitate obtained in C. a (p. 111).

E. IGNITION OF THE PRECIPITATE.

The combined precipitates of alumina, etc., obtained in either B, 

or C, and D, are ignited without preliminary drying in the crucible 

containing the residue from the silica (6. B. c, p. 103), unless considerable iron is present. In that case the main precipitate is dried and 

removed as far as possible from the paper, which is ignited separately to prevent partial reduction of a portion of the iron oxide. 

This is especially necessary when the precipitates were obtained without using macerated filter paper, in which case they are lumpy after 

ignition, and any magnetic oxide that may have been formed can not 

be reoxidized wholly by heating or by treatment with nitric acid. 

(See 5. A. c. (3, p. 76.) They are also slow to yield to subsequent treatment. A precipitate formed in presence of thoroughly macerated
OXIDES OF IRON AND SILICON. 115

paper, as recommended by Dittrich, on the other hand, yields on ignition a powder, and the fine state of division makes reoxidation of any 

reduced iron easy, besides wonderfully shortening the time required 

for subsequent re-solution.

M. F. Connor,1 instead of using macerated paper, moistens the 

washed and dried precipitate, separated from the paper, with an 

alcoholic solution of ammonium nitrate, dries again, and ignites. 

The paper is ignited separately.

Alumina in the quantities usually found can not be dehydrated 

completely by the full heat of the ordinary Bunsen burner.2 It must 

be blasted for 5 or 10 minutes. If iron is present in large amount 

this blasting must be so conducted as to insure access of air to the 

crucible (6. A. d. 7, p. 95).

For ignitions of this kind, which involve no very prolonged heating, an electric furnace is well adapted,by reason of its nonreducing 

atmosphere, provided the temperature is not high enough to cause by 

temperature alone reduction of ferric to magnetic oxide of iron.

The crucible itself may have changed in weight since the silica 

was ignited in it. Its correct weight is found after treatment of its 

contents as explained in the next section.

9. DETERMINATION OF THE OXIDES OF IRON AND SILICON IN THE PRECIPITATE

OBTAINED UNDER 8.

A. PRELIMINARY REMARKS.

The common practice in the Survey laboratory has been to find 

alumina by difference after deducting from the precipitate produced 

by ammonia, sodium acetate, or ammonia and ammonium persulphate the sum of all other oxides this precipitate may contain. Of 

these only ferric oxide, titanic oxide, and the small amount of residual silica not recovered by the procedure detailed in section 6, and 

in rare instances perhaps a little barium, are determined in this portion. (See also footnote 2, p. 119, regarding possibly contaminating 

platinum.) The oxides of phosphorus, vanadium, chromium, rare 

earths, and sometimes manganese are looked for in other portions of 

the rock powder. Glucinum and uranium are not considered. This 

throws on the alumina all errors that are involved in their separate 

determination, but these may balance. In any event the probable 

error can hardly be as high as that involved in the direct determination of the alumina itself, considering the difficulty of effecting a 

satisfactory separation of it from the other components of the mixture, an operation which would, moreover, extend immoderately the 

time required for each analysis.

l Cong. g<5o1. Internal, 12° sess. Canada, 1913, p. 885.

3 A statement which perhaps originated with A. Mitscherlich (Zeitschr. anal. Chemie, 

vol. 1, 1862, p. 67) aud has been confirmed by me and very many other authors.
116 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Phosphorus can not be determined in the ignited oxides after 

these have been fused with pyrosulphate (B. a, below), for the reason that the treatment volatilizes some of it. Fuming of a phosphate 

with sulphuric acid also volatilizes P2 05 . H. Eose, in his " Handbook of quantitative analysis," mentions this possibility, and the fact 

was long ago confirmed by me and again recently by careful tests, as 

yet unpublished, that were made at the Bureau of Standards. The 

loss may be large, depending upon the amount of sulphuric acid used 

and the rate at which it is driven off.

In section 10, below, are presented various procedures of separation 

differing from those which immediately follow here and which may 

be used under special conditions or by preference of the experienced 

analyst. In the main they are described only in so far as they have 

to do with the mixture of oxides treated of in section 8, the ultimate 

determination of the constituents of the fractions being described 

fully under the sections on titanium, zirconium, chromium, phosphorus, and vanadium.

The first step is to obtain the ignited oxides in a suitable solution. 

Some earlier writers recommended dissolving the oxides in hydrochloric acid, but this is a most ineffective mode of attack. Perfect 

solution is effected in the manner detailed in the next paragraph.

B. RESIDUAL SILICA (BARIUM).

a. SILICA.

The weighed precipitate is transferred as far as possible to another 

crucible of 25 to 30 grams weight.1 The small adhering residue, 

chiefly that originally derived from the main silica, is brought into 

solution by fusion with a small amount of sodium or potassium pyrosulphate. This fusion takes but a few minutes, and must not be continued beyond the time actually needed, otherwise it will be impossible, after cleaning and igniting, to get the correct weight the crucible 

possessed after the ignition of the alumina.2 The hot liquid is poured 

onto the main mass of precipitate in the other crucible, more pyrosulphate is added (up to 7 grams in all),3 and the fusion is renewed

1 This crucible may be of gold, as that metal is less attacked by the subsequent treatment than platinum. If gold is used the remarks in the text concerning the recovery of 

dissolved .platinum apply to the dissolved gold.

2 It will be remembered (see p. 102, footnote 3) that long blasts or furnace ignition 

of the silica may have reduced the weight of the crucible by an appreciable amount, 

hence the need for getting its weight empty at this point.

8 The total weight of pyrosulphate used should be known approximately in order to 

correct later for its effect on the colorimetric determination of the titanium (p. 161).

A chief objection raised by many to the use of an alkali bisulphate for bringing this 

precipitate into solution is that so much care is needed during a fusion to prevent frothing 

and boiling over, which involves a very gradual application of the heat and consequent 

greater expenditure of time. The objection is sound as applied to the bisulphate, but is 

swept away if the latter is first converted into pyrosulphate, which is always its condition after th<> frothing has ceased. To effect this change it is only necessary to melt a
OXIDES OF IRON AND SILICON. .u 117

and continued until the whole has been dissolved, which in the case 

of the potassium salt is always easy to be seen, even when the liquid 

appears dark red and opaque, by removing the crucible from the 

flame to a good light and allowing to cool. At one point in the cooling 

the liquid becomes transparent and allows the bottom of the crucible 

to be seen. This is less the case with the sodium salt.

When all is dissolved 1 the melted mass is poured into a large, dry 

platinum dish, what adheres to the two crucibles is removed by 

diluted sulphuric acid, and the solution, with rinsings, is poured into 

the dish. Much more dilute sulphuric acid is added and the dish 

heated till the solid is dissolved. The solution is evaporated as far as 

can be done on the steam bath, then gradually heated higher till fumes 

of sulphuric acid come off copiously. During this heating the mass 

is apt to darken from reduction and separation of dissolved platinum. 

The acid should have been used in such quantity that after cooling the 

mass is pasty and not solid, for it then dissolves readily, on heating, 

in the water which is now to be added, the sodium salt dissolving 

much more readily than the potassium salt. It is important that 

the amount of absolute acid used shall be approximately known, so 

that in the subsequent reduction of iron the volume of the solution 

can be so adjusted as to contain from 1.5 to 2.5 per cent by volume 

of acid.

The dish is placed on the bath and soon the silica can be seen in 

coagulated form at the bottom. It is collected on a small filter, well

large amount of the salt In a platinum dish and keep it in fusion till spattering 

ceases and white fumes begin to come off freely. If the liquid is then poured out into 

other dishes it cools in thin sheets or cakes, which can be readily broken up and bottled 

for future use. With such material the fusion is always tranquil, and the action on 

the alumina, etc., much more intense and speedy than with the ordinary bisulphate. If 

a good article of the latter is not to be had by purchase, it is only necessary to mix 

and melt together equivalent weights of sulphuric acid and pure normal sulphate until 

the water of the acid has been mostly expelled and the conversion to pyrosulphate accomplished.

The recommendation of J. Lawrence Smith (Am. Jour. Sci., 2d ser., vol. 40, 1865, p. 

248) to use the sodium instead of the potassium salt has been followed with satisfaction. This salt acts more quickly and forms a more soluble double salt with aluminum, 

but has the slight disadvantage that the progress of decomposition of the ignited mass 

is not so readily followed because of the greater tendency of the sodium salt to crust 

over.

A further objection is the action on the crucible of the fused pyrosulphate and the 

consequent necessity of removing the dissolved platinum. To obviate this and likewise to effect more speedy solution of the oxides E. Deussen (Zeitschr. anorg. Chemie, 

vol. 44, 1905, pp. 423 426), fuses the finely powdered oxides with acid potassium fluoride 

(about 1 gram). The mass melts at first over a low flame, then solidifies. Its solution 

is evaporated with sulphuric acid to expel most of the fluorine, then reduced with 

hydrogen sulphide or sulphurous acid and titrated for iron. The use of the fluoride is, 

however, incompatible with accurate work in silicate analysis, because the silica in the 

ignited oxides can not be determined. Moreover, the oxides must be finely powdered 

and consequently an aliquot part only can be taken for the fusion. The expulsion of 

fluorine by sulphuric acid must furthermore be thorough if titanium is to be determined 

in this solution.

1 Should a small portion of the precipitate have escaped solution no particular harm is 

done. The further treatment is not thereby changed.
118 .ANALYSIS OF SILICATE AND CAKBONATE BOCKS.

washed with hot water, burned, and weighed in a platinum crucible. 

Being seldom pure, it has to be corrected by a few drops of hydrofluoric and a single drop of sulphuric acid, and the crucible reweighed. 

The slight residue in the crucible is brought into solution by pyrosulphate and added to the main portion, for the treatment of which see 

C. a (p. 119) after filtering from barium if present. (See b, 

below.) The amount of silica recovered thus ranges usually between 

2 and 4 mg. after two filtrations of the main silica and is of course 

to be added to this. Only in this way is the full amount of the 

silica in the ignited oxides to be recovered.1 Formerly it was customary to regard that remaining undissolved when the pyrosulphate 

melt was taken up with water or dilute acid as the total amount 

present. It is, however, but a small portion of what the alumina 

held, the greater part having formed alkali silicate during the fusion 

and remaining in solution afterward, unless set free and rendered 

insoluble by the treatment above given.

The silica thus recovered does not, however, represent quite all of 

that which originally escaped separation by evaporation with hydrochloric acid. A small part (roughly 1 to 2 mg. for a single precipitation and a total of 1 centigram of silica in the experiments 

detailed elsewhere 2 is not precipitated with the alumina and escapes recovery altogether. It is therefore apparent why a thorough 

separation of silica at the start is so urgently called for.

In case the recovery of the residual silica is not required, the procedure of W. Trautmann 3 for removing it from alumina may be 

serviceable. He recommends the evaporation of hydrofluoric and 

sulphuric acids in the crucible containing the ignited alumina, after 

which the alumina is to be again ignited and weighed. E. Selch 4 

maintains that there is only a negligible loss of aluminum by volatilization as fluoride when this procedure is followed.

I). BABIUM.

Should by any chance the alumina precipitate have held barium 

sulphate, something which has not happened in my experience with 

rocks, unless ammonium persulphate w,as used as in 8. C. a (p. Ill), 

it will be found as a contaminant of the silica recovered after the 

pyrosulphate fusion. The weighed residue remaining after expulsion of this silica by hydrofluoric acid is dissolved (except the platinum it may have held) by a little pyrosulphate and the cooled melt 

redissolved in dilute sulphuric acid. Any barium will then be left

1 For proof see Jour. Am. Chem. Soc., vol. 24, 1902, pp. 368-370; Chem. News, vol. 86, 

1902, pp. 79, 89.

2 Jour. Am. Chem. Soc., vol. 24, 1902, p. 369 ; Chem. News, vol. 86, 1902, p. 90. 

3 Zeitschr. angew. Chemle, vol. 26, 1913, p. 702. 

*Zeitschr. anal. Chemle, vol. 54, 1915, p. 395.
OXIDES OF IRON 4ND SILICON. 119

in the form of sulphate l and can be separated by flotation from the 

heavier platinum.

C. IRON TITRIMETRIC DETERMINATION IN THE FERKOUS STATE, 

a. WITHOUT REGARD TO VANADIUM.

a. Reduction of the iron by hydrogen sulphide. Into the cool filtrate obtained in B. a, b (pp. 116-118), held in a beaker and containing from 1.5 to 2.5 per cent by volume of free acid, is introduced 

hydrogen sulphide for the reduction of the iron to the ferrous state 

and the precipitation of the platinum resulting from the pyrosulphate 

fusion. This last effect is rendered complete by causing the solution 

to boil 2 with continued passage of the gas, whereby the sulphur becomes coagulated and readily filterable. The gas current is not interrupted till the solution has cooled somewhat. This is then filtered *

1 Some years ago, In a series of analyses of rocks from the Leu cite Hills, in Wyoming, 

there was obtained at this stage, when it was customary to dissolve the melt in 

cold water preliminary to precipitation of titanium by boiling the neutralized sulphuric 

solution in presence of sulphur dioxide, a white, more or less flocculent residue which 

amounted to 1 to 3 per cent of the rock and which was at first taken to be a mixture 

of tantalic and columbic acids. Eventually, it was found to consist apparently of 

nothing but Ti02 and P205, with perhaps a little Zr02. By repeated fusion with acid 

potassium sulphate and leaching with cold water it could be brought gradually into solution. It was these rocks which furnished the most striking instance of the peculiar 

milky sulphate residues mentioned ou page 104 as derived from the ignited silica.

A. Knop (Zoitschr. Kryst, vol. 10, 1885, p. 73) seems to have obtained a similar mixture in analyzing minerals from the Kaiserstuhl in Baden, but its nature was not ascertained, though it was suspected to be, if not silica, columbiferous titanic acid.

3 The precipitation of platinum from a hot sulphate solution is far quicker and 

cleaner than from hydrochloric acid. Further, this platinum sulphide, when ignited In the' 

crucible in which the bisulphate fusion was made, should weigh together with the 

crucible itself what the latter weighed before the main oxide precipitate was fused in it; 

in other words, the weight of the platinum recovered by hydrogen sulphide should equal 

the loss in weight of the crucible due to attack by the bisulphate.

In somewhat rare instances this will not be so, but the weight will be greater, showing a gain in platinum which may amount to a milligram. Tests have shown that this 

is not due to retention of platinum by the main A120», etc., precipitate; hence, it must 

come from platinum mechanically loosened from the dish during the drying and powdering of the silica preparatory to its collection on the filter, or to some insoluble compound of platinum formed during evaporation and drying of the silica. It may also be 

in part or wholly due to contamination from platinum reduced during evaporation of 

the filtrate from the basic-acetate separation. It will be remembered that from this 

filtrate a small amount of iron oxide and alumina is recovered and added to the main precipitate. Hence it is always well in fine work to collect the sulphide and weigh the 

platinum in the original crucible, deducting any excess from the alumina, or else to 

get rid of the platinum by hydrogen sulphide before proceeding to the precipitation of 

alumina, etc. (See 7, p. 106.)

3 Through a Gooch crucible lined with asbestos or platinum sponge. A paper filter 

may be used if first washed with hot water in order to remove a small amount of reducing matter (McBride, R. S., and Scherrer, J. A., Jour. Am. Chem. Soc., vol. 39, 1917, p. 

928).

Filtration is not necessary if only precipitated sulphur and no sulphides are in suspension, for the sulphur is without reducing action on cold permanganate solution, as 

II. L. Wells, and W. L. Mitchell and others before them have pointed out. These authors 

used this method of reducing ferric iron in titanic iron ores (Jour. Am. Chem. Soc., vol. 

17, 1895, p. 878; Chem. News, vol. 73, 1896, p. 123). The observation of A. Coppadoro 

(Gazz. chim. ital., vol. 31, pt. 2, 1901, p. 217) that the precipitate of sulphur caused 

by reducing ferric solutions with hydrogen sulphide carries some iron as sulphide, even in 

strongly acid solutions and after thorough washing, need not be regarded. He seems 

to have operated on very concentrated solutions as compared with those here in question.
120 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

warm into a half-liter flask, hydrogen sulphide is again introduced 

for a few minutes, with production of slight milkiness if any iron had 

become oxidized during filtration, the flask is then connected with a 

carbon-dioxide generator already in action for a time, and the solution brought to boiling to expel the hydrogen sulphide. The expulsion is aided by a rapid current of carbon dioxide,1 the end point being 

found by occasional testing of the escaping gas with lead-acetate 

paper.2 When this point is reached, the flame is removed and the 

flask allowed to cool without interrupting the gas current. The 

cooling is hastened by placing the flask in a basin of cold water.

(i. Titration of the iron and subsequent treatment of the solution. A burette with permanganate solution having been made 

ready, the gas tube is rinsed into the flask and the permanganate at 

once run into the latter without further dilution of the solution, which 

is kept in rotary agitation by an appropriate movement of one hand. 

The bulk of the solution will be from 100 to 200 cm.8 The drops of 

the titrating fluid that may fall upon the neck of the flask are washed 

down by aid of a wash-bottle. The strength of the permanganate 

solution would best not much exceed 0.0025 gram of iron to the cubic 

centimeter, for the amounts of iron to be determined are moderate 

and often very small.3

1 The gas generated from every new lot of marble must be tested carefully for 

hydrogen sulphide. Even pure white marble is frequently not free from soluble sulphides probably pyrrhotite, sphalerite, or galena and the amount may be enough to 

affect appreciably the result of titration for iron. A good precaution to take is to wash 

the gas by passing it through a large U tube containing glass beads and a solution of 

copper sulphate.

3 The test is most delicate when the flask is provided with a two-hole stopper fitted 

with inlet and outlet tubes of glass. If the outside opening of the outlet tube is small, 

the concentration of the escaping steam and gas contributes to the sharpness of the 

test. Because of the possibility, of the introduction of organic matter from the stopper 

by the action of the hot steam, it is safer to. employ a cap of platinum foil with two 

holes, one for the gas entry tube, the other for its escape in a concentrated stream.

If the solution was free from milkiness at the start', the operation of expelling 

hydrogen sulphide need not take more than 10 to 20 minutes; otherwise a longer time 

will be required to remove the last traces. The immediate effect of boiling on any 

moderate amount of suspended sulphur is to coagulate it and clear up the solution 

completely. Some of the sulphur volatilizes with the steam, but a further portion appears 

to be converted by it to hydrogen sulphide, so that a faint reaction for that gas can be 

obtained as long as any sulphur remains. This is probably the explanation for Washington's direction (Manual of the chemical analysis of rocks, 1904, p. 112) to boil for 

about two hours, since by this method of reducing the iron, without coagulating the 

sulphur, the filtrates are always strongly milky. It is important to bear in mind that 

excess of hydrogen sulphide at this stage is not proof that all ferric iron has been 

reduced. Alkali sulphocyanate occasionally reveals the presence of unreduced iron. Due 

caution therefore renders it advisable to test a drop of the solution and to introduce more 

hydrogen sulphide if the result shows that it Is needed. Experiments made under my 

direction at the Bureau of Standards by R. S. McBride show that perfect results are 

to be had only when the acid concentration is kept within very narrow limits. For 

the average run of rocks these may range from 1.5 to 2.5 per cent sulphuric acid by 

volume, but for iron ores a variation of even 0.5 per cent from 2 per cent produces a 

sensible error. Reduction is then incomplete with more than 2 per cent of absolute 

acid ; with less than this amount too much permanganate is required.

3 The permanganate should be standardized against pure sodium oxalate, such as the 

Bureau of Standards provides. Ferrous sulphate and ferrous-ammonium sulphate are 

less reliable. Iron wire should not be used under any circumstances.
OXIDES OF IKON AND SILICON. 121

The results are strictly accurate, with the limitations set forth in b 

below, when care is taken with the reduction by hydrogen sulphide. 

The method is superior to that involving the use of zinc, for no foreign impurity affecting the result is introduced and the ever-present 

titanium is not affected, nor is vanadium reduced below the condition 

of V2 04 , whereas nascent hydrogen converts it in part at least to 

V2 0,

The solution, after titration, is returned to a dish, which may be 

of porcelain, and evaporated to a volume of much less than 100 cm.3 

if the rock is supposed to carry less than 1 per cent of titanic oxide. 

For each additional 1 per cent the final volume may be larger by 

100 cm.3 The solution is then transferred to a graduated flask having 

a capacity of 50,100, 200 cm.3 or more, as the case may be, and enough 

hydrogen peroxide free from fluorides is added to peroxidize the 

titanium fully, the flask is filled with water to the mark and well 

shaken, and the titanium is determined colorimetrically. (See 14. B, 

p. 155.)

Or, as the presence of large amounts of alkali sulphates is detrimental in the color determination, an ammonia precipitation can be 

made and the precipitate, after filtering and washing, dissolved in 

the requisite amount of sulphuric acid. (See 14. B. c, p. 157.)

y. Reduction with titanous sulphate. H. D. Newton 1 reduces the 

iron by titanous sulphate, oxidizes the excess of the sulphate by bismuth oxide, and titrates the remaining ferrous salt by permanganate.

The titanous solution is prepared by fusing 20 grams of commercial titanic oxide with alkali carbonate, dissolving the finely ground 

melt in concentrated sulphuric acid, cooling, diluting somewhat, 

filtering through asbestos, reducing with zinc, and diluting with 

about 2 liters of water. The solution is to be kept in a reservoir 

connected with a burette and a hydrogen generator.

The determination is made as follows: Add to the sulphuric acid 

solution of the ferric iron in the cold an excess of the titanous solution, destroy the excess with a little bismuth oxide, filter from the 

excess of bismuth oxide and the precipitated bismuth into cold water, 

and titrate with permanganate. The titanous solution must be 

treated in a similar manner in order to be able to correct for an iron 

content.

Because of the added titanium this method precludes the determination in this solution of the titanium in the rock or mineral.

b. HAVING REGARD TO VANADIUM.

If vanadium is present the value found for iron will be in error, 

whether the reduction was brought about by hydrogen sulphide, as

1 Am. .Tour. Sci., 4th sor., vol. 25, 1908, p. 343; Chem. News, vol. 97, 1908, p. 218; 

Zeitschr. anorg. Choraio, vol. 58, 1908, p. 378.
122 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

in a. a, or by titanous sulphate, as in a. f, °r by nascent hydrogen. 

The first of these reagents reduces V205 to V2O4 , which in its action 

on permanganate solution is equivalent to 2 molecules of FeO. After 

the first transitory pink blush throughout the liquid, the more slowly 

acting vanadium may require the addition of a drop or two more 

of permanganate before a fairly permanent coloration appears.

How far titanous sulphate reduces vanadium is not known to me. 

If below the V2 04 stage, the bismuth oxide, as used in a. y, may not 

convert it wholly to V2O4 again, for Newton in a private communication stated that vanadium which has been reduced by zinc to V202 

is oxidized by bismuth oxide only to V2 03 if the solution is strongly 

acid (10 per cent H2SO4 ) by volume and cool, but toward V2 04 if 

the solution is warm or less acid.

Nascent hydrogen reduces the higher vanadium compounds to 

V2O2 , which for its conversion to V2O5 requires an amount of permanganate equivalent to 6 molecules of FeO.

In view of what has been said, it seems advisable to use only the 

method of reduction by hydrogen sulphide when vanadium is present. 

When the amount in the rock is known, a correction can be applied 

on the assumption that practically all the vanadium is here collected, a point that needs further investigation. Various authors 

assert its precipitability with alumina and iron by ammonia and 

ammonium acetate, though Carnot 1 states that repeated precipitation by ammonia, ammonium carbonate, or ammonium sulphydrate 

separates it from iron. My experience with ores very rich in vanadium shows that precipitation along with iron and aluminum is 

only partial. Ridsdale 2 has determined its precipitability with 

various metals and gives numerous figures which show an approximation to 90 per cent thus thrown down under the conditions prevailing in analysis of iron slags, the remainder passing into the 

filtrates and appearing in small part with the lime and to a greater 

extent with the magnesium phosphate. For all practical purposes 

it is probably safe to assume that the small amounts of vanadium met 

with in rocks are wholly in the alumina precipitate.

If the amount of vanadium in the rock is not known and great 

accuracy is necessary, caution requires the determination of the 

total iron to be made either in a separate portion or after reprecipitation from the above solution, as follows: Fuse with sodium carbonate, extract with water, bring the insoluble residue into sulphuric 

solution, reduce, and titrate as above directed. But unless a certain 

precaution is here observed an error greater than that which it is 

designed to avoid will be committed. Contrary to general belief, 

the aqueous extract from the sodium-carbonate fusion carries a small

1 Compt. Rend., vol. 104, 1887, p. 1803; Zeitschr. aual. Chemie, vol. 32, 1893, p. 223.

2 Jour. Soc. Chem. Industry, vol. 7, 1888, p. 73.
OXIDES OF IRON AND SILICON. 123

but appreciable fraction of 1 per cent of iron, as I have found repeatedly by actual test. This iron is thrown out with the alumina 

(and silica, if present) by the usual methods of neutralizing the alkaline solution, and can be brought to light when the precipitate thus 

formed is treated with a fixed caustic alkali, or again fused with 

sodium carbonate and leached with water, when it remains wholly 

or in part undissolved. Hence it is necessary to collect this iron and 

add it to the main portion before titration.

The differential method of Graham Edgar 1 for determining iron 

and vanadium in presence of each other is not well suited to rocks, 

because of the very small amounts of vanadium involved.

C. TBUK VALUE FOB FERRIC IBON.

The total iron in the rock having been found in one way or another, it remains to deduct an amount equivalent to the ferrous oxide 

the rock contains and a further amount corresponding to the sulphides often present, in order to get what may pass for the true 

value for ferric iron. That this is often only an approximation 

appears from the difficulties due to the presence of vanadium and the 

generally indeterminable effect of sulphides on the ferrous-oxide 

determination. (See pp. 201-202.)

D. IRON TITRIMETRIO DETERMINATION IN THE FERRIC STATE. 

a. PRELIMINARY REMARKS.

Chemists have long felt the want of a method for determining 

ferric iron directly by titration, both for the purpose of avoiding 

prior reduction to the ferrous state and as a check on the ferrous 

iron determination, especially when the metal exists in both states 

side by side. The method given below would seem to be applicable 

to the mixture of oxides obtained as under 8 (pp. 106-113), but its 

applicability to the direct determination of ferric iron in rocks has 

not been studied. If suitable for minerals that are readily soluble 

in sulphuric or hydrochloric acid, it might not be so for rocks, for 

these would have to be attacked by hydrofluoric acid with exclusion 

of air (21. d, p. 203), the resulting condition being then quite 

different from the conditions under which the authors of the method 

worked.

b. TITRATION WITH TITANOTJS CHLORIDE.

E. Knecht and Eva Hibbert 2 titrate with a solution of titanous 

chloride of about 1 per cent strength. For standardizing this solution they used a ferric solution prepared from ferrous ammonium 

sulphate, with potassium thiocyanate as ind ator. added directly

*Am. Jour. Sci., 4th ser., vol. 26, 1908, p. .9. 

3 Ber. Deutsch. chem. Gesell., vol. 30, 1903, p. 1549.
124 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

toward the end of the titration or used preferably in spot tests. 

With the standard a ferric solution of unknown content is titrated in 

the same way.

If ferrous and ferric salts are present together the solution is first 

titrated with permanganate for the ferrous iron and then with titanous chloride for the total iron.

E. IRON GRAVIMETRIC DETERMINATION AFTER SEPARATING AS SULPHIDE.

a. PEELIMINAEY EEMARKS.

In view of the slight errors involved in the titrimetric determination of the iron it may be advantageous occasionally to determine it 

gravimetrically as the oxide, after first precipitating as the sulphide 

from a solution containing ammonium tartrate, the function of 

which is to hold in solution the other elements. If manganese, nickel, 

and cobalt are not present, this method yields a pure product. If 

manganese is present the purity of the resulting iron oxide will depend upon the amount of manganese and whether the iron hydroxide 

was precipitated by ammonia or by sodium or ammonium acetate. 

If there is doubt the purity of the final product can be determined 

by a colorimetric test for manganese (11. C, p. 137). The procedure 

does not admit of conveniently determining titanium colorimetrically, 

as in the method described in 9. C (p. 119).

b. PROCEDURE.

In the filtrate from the residual silica (9. B. a, p. 116), which should 

be brought to a volume of 100 to 400 cm.3 , according to the amount of 

iron present, and held in a flask or beaker, is dissolved tartaric acid 

(3 to 4 times the weight of the oxides operated upon). In order to 

provide the best conditions for the next step the solution is made 

neutral with ammonia and acid again with 2 cm.3 of sulphuric acid 

(1:1). Hydrogen sulphide is then introduced until the solution has 

become colorless, the iron being then reduced to the ferrous state. If 

not reduced in acid solution before the next step is taken there is a 

possibility of precipitating a little titanium.1 The solution is then 

made decidedly ammoniacal, and more hydrogen sulphide is introduced. After the ferrous sulphide settles in the corked flask or covered beaker, it is filtered and washed thoroughly with water containing a little ammonium sulphide and enough ammonium chloride (sulphate if the preliminary operations noted under 10. B, p. 126, are to 

follow) to prevent passage of the filter by colloidal iron sulphide. 

The funnel should be kept covered as much as possible, and the precipitate finally sucked fairly dry.

Precipitate and paper are then placed in a beaker of suitable size, 

hydrochloric acid (1:1) is added, the vessel being covered, and heat

1 falli! -in, A., Zeitsehr. Eryst., vol. 6, 1882, p. 243; vol. 7, 1883, p. 250.
OXIDES OF IKON AND SILICON. 125

is applied until all black particles have disappeared. The paper is 

then shredded by vigorous stirring with a rubber-tipped glass rod, 

the iron is oxidized by a few drops of nitric acid, the solution diluted 

if necessary, and the iron precipitated by ammonia. As aluminum is 

absent it is not necessary to avoid overstepping neutrality.

As soon as the precipitate has settled it is filtered, washed only a 

few times with hot water, sucked dry, wrapped in its paper, and 

placed moist in a weighed platinum crucible, the paper is carefully 

charred, and when the carbon has disappeared the full heat of the 

burner or of a blast of moderate power is applied for 5 to 15 minutes 

according to the weight of the oxide.

The filtrate from the iron sulphide can be treated as in the first 

paragraph of 10. B and then in a variety of ways, either directly as 

given under 10. B or by suitable application of the procedure indicated under 10. C, D, and E (pp. 127-132), 14 (p. 154), and 16 (p. 

172).

F. IRON SPECIAL CASES, 

a. GLASS SANDS.

Materials used in making certain kinds of glass, especially optical 

glass, should contain no more than a very minute amount of iron. 

For the iron determination in glass sands it is customary to attack 

the sand with hydrofluoric and sulphuric acids until the silica disappears, whereupon heat is applied to drive off the excess hydrofluoric acid and most of the sulphuric acid. J.- B. Ferguson 1 has 

drawn attention to the fact that this procedure fails to decompose 

certain minerals in these sands that are iron-bearing, like magnetite, ilmenite, tourmaline, and staurolite, and that the iron reported represents but a part of that actually in the sand. He points 

out properly that the slight residue left on treating the sand with 

hydrofluoric and sulphuric acids and evaporating till white fumes 

appear should be collected on a filter paper and treated further, as 

follows:

The residue left after igniting the filter is fused with a little ironfree potassium pyrosulphate. If after the melt is dissolved in dilute 

sulphuric acid no dark particles are to be seen, the operation is 

ended. If dark particles (staurolite) are still evident, they are to 

be collected on a filter, ignited, and fused with sodium carbonate 

free from iron. The sulphuric acid solution of the melt should show 

no undecomposed matter. The filtrates are combined for the iron 

determination.

Ferguson prefers to reduce the iron with stannous chloride and 

then to titrate with bichromate, determining the end point electro1 .Tour. Ind. Eng. Chemistry, vol. 10, 1918, p. 041.
126 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

metrically as suggested by J. H. Hildebrand,1 and for this reason 

dissolves the fusions in hydrochloric acid (1:1) instead of sulphuric 

acid.

Needless to say, freedom of the reagents used from iron and the 

use of a platinum crucible that is also iron free are of prime importance. Blank runs on the reagents will eliminate the error due to 

an iron content if the work is very carefully done, but such correction is not entirely safe.

b. CEBAMIC CLAYS.

For clays low in iron J. W. Mellor 2 uses a colorimetric method 

based on the color imparted to an ether-amyl alcohol solution of 

ferric iron by potassium thiocyanate.

10. MISCELLANEOUS SEPARATIONS OF THE OXIDES OBTAINED UNDER 8.

A. PRELIMINARY REMARKS.

Although, as said in 9. A, it is customary to determine aluminum 

by difference, special cases may call for treatments that are different 

from those recorded in the foregoing section. Thus it may happen, 

though not in ordinary rock analysis, that only a very small amount 

of aluminum is present, and that a direct determination of it is 

necessary or desirable in order to ascertain its amount with greater 

certainty than is possible by the method of difference or even to 

determine whether it is actually present. Again, in view of the 

errors incidental to the colorimetric determination of titanium, it 

may be desired to determine this element with greater precision than 

is possible in the presence of much iron and alkali salts, in which 

case the procedures allowable will enable one to take account of 

zirconium also.

A direct determination of aluminum is feasible by the procedures 

given below only when phosphorus is absent. It is possible when 

titanium and zirconium are present, but 'then further operations 

are called for.

As to phosphorus, see second paragraph under 9. A (p. 116).

In addition to the procedures that follow others will be found 

in the sections on phosphorus (p. 177) and chromium (p. 180).

B. RECOVERY OF ALUMINUM, TITANIUM, ZIRCONIUM, AND PHOSPHORUS 

FROM THE FILTRATE FROM IRON SULPHIDE.

The filtrate.from the iron sulphide obtained according to 9. E. b (p. 

124), containing ammonium tartrate, is evaporated in a large platinum 

dish with 10 to 12 cm. of strong sulphuric acid and heated carefully 

until charring and frothing have continued as far as the capacity of

1 Jour. Am. Chem. Soc., vol. 35, 1913, p. 871. Consult Hostetter, J. C., and Roberts.H. S. 

Jour. Am. Chem. Soc., vol. 41, 1919, p. 1337, for application of the method to the 

determination of iron.

2 Pottery Gaz., vol. 34, 1909, p. 1178; Quantitative inorganic analysis, p. 200, 1913.
MISCELLANEOUS SEPARATIONS OF OXIDES. 127

the dish permits. After cooling 5 cm. of fuming nitric acid is added, 

and when violent reaction has ceased the heat is raised gradually 

until the organic matter is fully oxidized.1 The residue is dissolved 

in water, and the aluminum and phosphorus, together with titanium 

and zirconium, if these are present, are precipitated by ammonia 

according to 8. B. a (p. 106), redissolved, and again precipitated, 

filtered, washed, and weighed. Further separations will then be in 

order by one or another of the procedures described below, the absence 

of rare earths being assumed.

1. A precipitate containing aluminum, titanium, and zirconium 

and free from silicon may be fused with sodium carbonate or sodium 

carbonate and borax (C, below) and the aluminum determined in the 

aqueous extract of the melt, the other components in the insoluble 

residue. (See sections 14 and 15.) But if phosphorus is also present it goes with the aluminum into the extract. Then, when tho 

aluminum is precipitated by ammonia after acidifying with hydro-' 

chloric or nitric acid, phosphorus will accompany the aluminum 

and must be determined separately in the ignited and weighed precipitate of A12 03 and P2 05 . Thus finally the aluminum is found by 

difference. If chromium and vanadium are also present, other modifications must be introduced.

2. A first variant of the foregoing procedure, after destroying the 

ammonium tartrate, is to precipitate titanium and zirconium by " cupferron " (14. C. b, p. 162). Vanadium, if present, will be partly precipitated, phosphorus only slightly.

3. A second variant is to evaporate the ammonium tartrate filtrate 

from the iron sulphide to dryness in a large platinum dish without 

the addition of sulphuric acid, to char the residue and fuse it with 

sodium carbonate and nitrate, extract with water, and filter. Titanium and zirconium are left on the filter as sodium salts, while 

chromium and vanadium are carried into the filtrate as chromate and 

vanadate along with aluminum and phosphorus. The further separation of the last two from chromium and vanadium is outlined under 

18. B (p. 178).

As with the other methods, this is as far as the separation can bo 

carried. The aluminum must still be found by subtracting the P2 05 

(separately determined) from the combined weights of the A12O3 

and P2 05 .

C. DIRECT FUSION OF THE OXIDES OBTAINED UNDER 8 WITH SODIUM 

CARBONATE AND BORAX.

A procedure tried by L. Weiss and H. Kaiser 2 for separating 

aluminum from titanium and iron is applicable probably also when 

phosphorus and zirconium are present. The weighed oxides are

iThornton, W. M., Am. Jour. Sci., 4th scr., vol. 34, 1912, p. 214. 

a Zeitschr. anorg. Chemie. vol. 65, 1910, p. 345.
128 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

fused over the blast with twenty times their weight of a mixture in 

equal parts of sodium carbonate and borax. To the clear fusion is 

added half the former weight of flux, and when this is melted the 

mass is cooled .and let stand for 24 hours in cold water. After filtering, the fusion and extraction are repeated on the residue, if necessary. The authors claim complete separation of aluminum in this 

way. If silicon is present they remove it before the alkali fusion by 

treating the mixed oxides with sulphuric and hydrofluoric acids.

In this treatment phosphorus should accompany the aluminum, 

and zirconium the titanium and iron. Further separations and 

eventual determinations can be made in ways that have been given 

for iron or are to be consulted in the sections on titanium and zirconium.

D. SEPARATION OF ALUMINUM, TITANIUM, AND ZIRCONIUM FROM IRON IN

THE FERROUS STATE.

a. BY PHENYLHYDBAZINE.

A method for the " direct determination of alumina in presence of 

iron, manganese, calcium, and magnesium " is that of Hess and 

Campbell,1 but, as with the methods just considered, it involves 

finally weighing aluminum, phosphorus, titanium, and zirconium 

together. Precipitation is made by phenylhydrazine, after first neutralizing the (preferably chloride) solution by ammonia and reducing 

iron by a saturated solution of ammonium bisulphite. Phenylhydrazine " precipitates aluminum from its solutions quantitatively as the 

hydroxide without a trace of the precipitate being redissolved in excess of the precipitant."

E. T. Alien investigated the method in the Survey laboratory 2 and 

confirmed the above authors' statements in the main, finding, however, 

that two precipitations are needed to free the precipitate entirely 

from iron. " The method is excellently adapted to the separation of 

very small quantities of aluminum, such as a milligram or even less, 

from a large excess of iron, a point of considerable practical importance."

Although such conditions will not be met with in ordinary rock 

analysis, it will not be out of place here to give the treatment as 

slightly modified by Alien :

The volume of the solution may vary, according to the quantity of alumina to 

be precipitated, from 100 to 200 cm.3 It should be heated and reduced by adding 

saturated ammonium bisulphite. From 5 to 20 drops, according to the quantity 

of iron, may be used. If the solution turns deep red (ferric sulphite), it is not 

acid enough, and a few drops of hydrochloric acid should be added, for the sulphite itself does not reduce ferric salts, at least not with rapidity. Now, quickly

iJour. Am. Chem. Soc., vol. 21, 1899, p. 776; Chem. News, vol. 81, 1900, p. 158. 

a Jour. Am. Chem. Soc., vol. 25, 1903, p. 421.
MISCELLANEOUS SEPARATIONS OF OXIDES. 129

bring to neutrality .with ammonia, and then add several drops of dilute hydrochloric acid. If this last operation is done too slowly the oxygen of the air 

helps to form a little ferric hydroxide, which does not always readily dissolve in 

the dilute acid. Finally, add from 1 to 3 cm.3 of phenylhydrazine,1 according to 

the weight of the alumina to be precipitated. If too little has been used, a few 

drops added to the filtrate will disclose the mistake. Stir until the precipitate 

has become sufficiently flaky and allow to settle. The supernatant liquid will 

now be plainly acid to litmus. One need not be disturbed if the precipitate has 

a brownish color, for it is not due to ferric hydroxide but to the coloring matter 

contained by all phenylhydrazine which has not been freshly distilled. When 

the determinations are allowed to stand too long the air increases this oxidation product, and a brown insoluble scum forms on the surface of the liquid and 

on the sides of the vessel, which is rather troublesome to the analyst. Fortunately equilibrium appears to be established in a short time. The vessels need 

not stand more than an hour, at any rate. The precipitate is washed by a solution of phenylhydrazine sulphite made by adding cold saturated sulphurous acid 

to a little phenylhydrazine until the crystalline sulphite first formed dissolves in 

the excess. The solution has an acid reaction. Five to 10 cm.8 of this are used 

in 100 cm." of hot water.

b. BY SODIUM ACETATE.

a. According to Dittrich and Freund. M. Dittrich and S. Freund 2 

found that the separation of titanium and zirconium from iron by 

sodium acetate could be made perfect if the iron was first reduced 

and then kept in the ferrous state. In another paper 3 they apply 

it also to the separation of thorium.

The acid solution of the pyrosulphate fusion of the mixed oxides 

is treated with hydrogen sulphide, to reduce the iron, and filtered. 

The acid is neutralized by adding a solution of sodium carbonate, 

whereby the formation of black ferrous sulphide ser\7 es as an indicator. Then a few drops of dilute sulphuric acid are added and more 

hydrogen sulphide is passed in to complete the reduction of the iron. 

The solution is brought to boiling while a current of carbon dioxide 

is made to pass until every trace of hydrogen sulphide is expelled. 

A concentrated solution of 5 grams of sodium acetate is added, followed by hot water to make a volume of 400 to 500 cm.3 Boiling and 

continued passage of carbon dioxide are kept up for an hour, with 

replacement of the escaping water. The liquid is then cooled while 

the gas current continues. The white precipitate is filtered and 

washed with water charged 'with a little hydrogen sulphide. Precipitate that adheres to the glass is removed by a few drops of concentrated sulphuric acid and a little hydrogen peroxide, precipitated 

by ammonia after destroying the excess of peroxide, and added to

1 The reagent should," of course, be free from inorganic impurities which could disturb 

the results. The author [Alien] found one sample which after persistently giving high 

results was proved to contain tin, which had probably been used in its preparation.

 Zeitschr. auorg. Chemic, vol. 56, 1907, p. 337.

3 Idem, p. 348.

LSI 909° 19 9
130 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

the main portion. The whole is then ashed and-weighed. After 

fusing with pyrosulphate and dissolving in water, any silica that 

may have separated is filtered off and weighed.1 Titanium is then 

determined colorimetrically and zirconium'found by difference. It 

is better, if zirconium is relatively in very small amount, to determine this according to 16. A (p. 173) and the titanium by difference 

or by colorimetry (14. B, p.- 155).

The iron can be precipitated by ammonia in the filtrate after it 

has been oxidized.

The method was applied by Dittrich and Freund in absence of 

aluminum and phosphorus, but in view of the reported success of the 

method which is next described the presence of aluminum may not 

be detrimental. It should be borne in mind, however, that the precipitation of aluminum by sodium acetate as ordinarily done is not 

supposed to afford as perfect a separation of that element as of iron.

P. According to Barrier. P. Barbier 2 successfully applied a very 

similar method to the separation of aluminum from iron in analyzing many minerals, the reducing agent being sodium hyposulphite 

(Na2S2O4 ) instead of sodium bisulphite.

To the hydrochloric acid solution a slight excess of sodium hyposulphite is added until the liquid takes on a reddish tint. A 10 per 

cent solution of sodium hyposulphite is then added, little by little, 

until the red color disappears. The solution is boiled, whereupon 

the aluminum separates as a dense powder entirely free from iron 

and easy to filter and wash. The precipitate and paper are ashed, 

after moistening with nitric acid. If glucinum is present it accompanies the aluminum. Probably titanium and zirconium would be 

precipitated also and could be determined by one dr another of the 

methods given in their respective sections. No analytical data are 

given by Barbier. The reagent is unstable and is subject to contamination, particularly by zinc.

E. SEPARATION OF TITANIUM AND ZIRCONIUM FROM ALUMINUM AND IRON. 

a. ACCORDING TO BASKEEVILLE.

A method devised by C. Baskerville 3 for separating jointly 

titanium and zirconium from aluminum and iron is claimed by 

A. J. Rossi 4 to be the best gravimetric method for the precipitation of titanium and its separation from iron and aluminum. It 

has also given very good results in the laboratory of the Bureau 

of Standards. The method succeeds in hydrochloric but not in

1 If silica is present, however, its recovery is imperfect unless the operation Is conducted as detailed in 9. B. a (p. 110).

2 Bull. Soc. chim., vol. 7, 1910, p. 1027.

3 Jour. Am. Chem. Soc., vol. 16, 1894, pp. 427, 475.

4 Titanium in steel, 1911, p. 38, quoted by B. Neumann and R. K. Murphy in Zeitschr. 

angew. Chemie, vol. 26, 1913, p. 613.
MISCELLANEOUS SEPARATIONS OF OXIDES: ' 131

sulphuric acid solution, and is therefore not directlj applicable to 

the solution of the oxides obtained as described under 9. B. a (p. 116). 

If it is desired to apply this method to that solution after separating 

silica, an ammonia precipitation must be made and the precipitate 

dissolved in hydrochloric acid after filtering and washing.

In the second of his two papers Baskerville, in describing the 

method as applied to zirconium, states that it is necessary to neutralize the solution with ammonia until the precipitate formed no 

longer dissolves on boiling, to effect re-solution of it by two or three 

drops of hydrochloric acid, and to boil for two minutes after adding 

an excess of sulphur dioxide. As the precipitate may contain a little 

iron, it should be dissolved after filtering and reprecipitated as 

before.

If both titanium and zirconium are present, these must be separately determined according to 14. B (p. 155) for titanium and 16. A 

(p. 173) for zirconium. If nothing but the two oxides is present and 

one of these is in great excess over the other, it may suffice to determine directly only the lesser and to obtain the other by difference. 

Phosphorus will also be precipitated if not in excess. Further reference to this method appears under 14. C. c (p. 166).

b. ACCOBDING TO DITTBICH AND FRETJNI).

Of several methods proposed by M. Dittrich and S. Freund,1 by 

which they claim to separate completely titanium and zirconium 

from iron, they regard the one given below as relatively the simplest. 

It presupposes, however, a prior fusion of the mixed oxides with 

potassium hydroxide in a silver crucible, in order to remove aluminum and phosphorus, an operation which involves a probable error 

as pointed out in the next section, F.

The sulphate solution is reduced by hydrogen sulphide, filtered 

into a 750 cm.3 Jena flask provided with a stopper carrying inlet and 

outlet tubes and a separatory funnel. The solution is now neutralized 

with sodium carbonate, the formation of ferrous sulphide serving as 

indicator, a few drops of sulphuric acid are added, and hydrogen 

sulphide is passed in to complete the reduction of the iron. The gaseous reagent is then wholly removed by carbon dioxide at boiling 

heat, whereupon a concentrated solution of 5 to 10 cm.3 of ammonium 

sulphate is allowed to flow in, followed by water, if needed, to make 

the volume 400 to 500 cm.3 . With continued passage of carbon dioxide and renewal of escaping water the solution is now boiled for about 

an hour, then cooled. The white precipitate is filtered and washed 

with hot water slightly charged with hydrogen sulphide. A few 

drops of sulphuric acid and hydrogen peroxide are used to cleanse 

the walls of the flask, and the titanium and zirconium thus dissolved

1 Zeitschr. anorg. Chemie, vol. 56, 1907, p. 337.
132 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

are precipitated by ammonia and added to the main portion, the 

whole being ignited in platinum over the blast to constant weight. 

The oxides are fused with potassium bisulphate; silica, derived from 

the reagents or apparatus, is separated (9. B. a, p. 116); and titanium 

and zirconium are determined, the one colorimetrically, the other by 

difference. In view of the very small amounts of zirconium in rocks 

it is far preferable to find it directly (16. A, p. 173) instead of by 

difference.1

In the filtrate from the oxides Dittrich and Freund precipitate 

iron and manganese by ammonia and hydrogen peroxide.

F. SEPARATION OF ALUMINUM FROM IRON, ETC., BY A FIXED CAUSTIC

ALKALI. 

A favorite practice in some countries of Europe has been to fuse the 

ignited precipitate containing A12 03 , Fe2 03 , TiO2 , P2O5 , etc. or that 

of the A12O3 , TiO2 , P2O5 , etc., after separation of iron by ammonium 

sulphide in tartrate solution with sodium hydroxide in a silver crucible, or to boil the freshly precipitated mixture with a solution of the 

alkali, on the assumption that the oxide of titanium is hereby rendered wholly insoluble and thus separated from the alumina. This, 

however, is in part an error long since pointed out by F. A. Gooch,2 

who showed that pure titanic oxide is markedly soluble under both 

conditions of treatment. Experiments made by me to test the extent 

of this error brought .out the following interesting results:

When 0.045 gram of titanic oxide was fused by itself with sodium 

hydroxide, the clear aqueous extract of the fusion held 0.0031 TiO2 , 

or about 7 per cent, determined colorimetrically. When freshly precipitated and boiled with the alkali, the solubility was less. When 

fused with sodium carbonate but an infinitesimal trace was dissolved, which required strong concentration for its detection. When 

mixed with a large excess of alumina and fused with the caustic 

alkali, the solubility was still very marked, though less than when 

alumina was absent. With a large excess of ferric oxide, with or 

without alumina, no titanium could be detected in the unconcentrated 

filtrate.

It thus appears that fusion with caustic alkali after first removing 

iron involves an error in the gravimetric determination of both 

aluminum and titanium which does not appear if the iron has notbeen removed. The procedure of M. Dittrich 3 involves this error 

and therefore is not described here.

 » The newer method of Dittrich and Freund (Zeitschr. anorg. Chemie, vol. 56, 1907, 

p. 344), by which zirconium is precipitated as the salicylate and ignited to the oxide, may 

find application here.

2 Proc. Am. Acad. Arts and Sci., vol. 12, 1885, p. 436; Bull. U. S. Geol. Survey, No. 27, 

1886, pp. 16, 17. -

3 Anleitung zur Gesteinsanalybe, 1905, pp 9-81.
MISCELLANEOUS SEPARATIONS OF OXIDES. 133. 

G. SEPARATION OF IRON FROM ALUMINUM, ETC., AS VOLATILE CHLORIDE.

F. A. Gooch 1 and some of his students have modified an old 

method for separating iron completely from aluminum, zirconium, 

glucinum, and chromium by volatilizing it as ferric chloride at a 

lower temperature than was formerly thought to be necessary. The 

results they obtained are excellent. Presumably an equally good 

separation from titanium could be effected.

The mixed oxides, put in porcelain boat which is placed in a wide combustion tube heated in a small furnace, are submitted to the action of dry 

hydrochloric acid gas, generated by dropping sulphuric acid upon a mixture 

of strong hydrochloric acid, common salt, and a small amount of manganese 

dioxide. The gas is admitted at one end of the combustion tube and passed 

out at the other through a water trap, while the required temperature, best 

200° to 300°, is maintained by regulating the burners of the furnace. The 

time of action varies somewhat with the condition of the oxide to be volatilized 

and the temperature. Generally an hour's heating at 200° proves sufficient for 

the complete removal of 0.1 gram of iron. At higher temperatures the action 

is more rapid; but the nonvolatile oxide is liable to mechanical loss if the 

volatilization of the iron is too rapid. It is better, therefore, to make use of a 

lower temperature until the volatilization of iron is nearly complete, and then 

to raise the heat for a few minutes to insure the removal of the last traces of 

the volatile chloride.

H. Borck 2 claims to effect a perfect separation of iron from 

aluminum by heating the mixed oxides in a current of hydrochloric 

acid vapor and air.

c 

II. SEPARATION OF IRON FROM TITANIUM BY HYDROGEN PEROXIDE. .

A. Classen's method '3 of separating titanium from iron by hydrogen peroxide succeeds well, according to K. Bornemann and H. 

Schirmeister* when carried out as follows:

To the acid solution containing a considerable excess of hydrogen 

peroxide (the pure article " perhydrol" should be used) a solution 

of potassium hydroxide is added till.the iron is fully precipitated as 

hydroxide. The solution should be cold, and the peroxide should 

always be in excess. The precipitate when settled is filtered and 

washed with cold water containing a little peroxide. In order to 

determine the titanium in the filtrate the excess peroxide is destroyed 

by sulphur dioxide, disappearance of the color of the peroxidizecl 

titanium being the test of its complete reduction. The titanium is 

then precipitated twice by ammonia. The method is said to be 

especially good for small amounts of titanium in company of much 

iron, which in turn is precipitated by ammonia after dissolving in 

acid, filtered, washed, and weighed.

1 Methods in chemical analysis, New York, Tohn Wiley & Sons, 1912.

a Zeitsclii-. ange\v. Cliemie, vol. 25, 1912, p. 719.

3 Bcr. H . > . !>. t-hom. Gesell., vol. 21, 1888, p. 370.

 "Mot;;.}!:-!'. ' vol. 7, 1910, p. 726.
134 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Classen says regarding his method that if aluminum is present it 

is incompletely separated from the iron by the caustic alkali. Further, that when the attempt was made to use ammonia instead of 

a caustic alkali, the aluminum was not all precipitated, and that if 

ammonium carbonate was used no precipitation of aluminum took 

place.

11. MANGANESE, NICKEL, COBALT, COPPER, AND ZINC.

A. DIFFICULTIES IN THE WAY OF A CORRECT GRAVIMETRIC 

DETERMINATION OF MANGANESE.

The gravimetric determination of manganese in small amounts 

seems to be more of a stumbling block to the average chemist than, 

that of almost any other of the frequently occurring elements met 

with in mineral analysis. This is due almost always to incomplete 

prior separation of elements which later suffer coprecipitation with 

the manganese. The error is therefore generally a plus one, and 

often amounts to many times the weight of the manganese actually 

present. The importance of thorough separation of the constituents 

treated of in the foregoing pages is therefore manifest, particularly 

since to the inexperienced analyst very small amounts of manganese 

precipitated in the form of a higher hydroxide may easily mask a 

good deal of alumina or other colorless precipitates.1

i It is for these reasons that Washington deems it better for the novice in rock analysis to make no attempt 

to determine the manganese, but to allow the error from this neglect to distribute itself over the alumina, 

lime, and magnesia. The relative order of this distribution was determined by George Steiger in tho 

Survey laboratory white analyzing a series of carbonate rocks, some of them highly siliceous. The results 

are instructive. Double precipitations were the rule, and iron and aluminum were thrown out by ammonia in slight excess, according to the procedure then followed.

Tests showing distribution of manganese in gravimetric separation*.

No.

957.................

973.................

974.................

975.................

1126................

1128................

1130................

1131................

Partial composition of rock.

A12 03 , 

Fe2O3 .

2.03 

9.35 

4.80 

12.71 

.58 

.98 

3.49 

1.00

CaO.

10.60 

11.84 

50.51 

11.98 

30.54 

29.69 

3.99 

28.04

MgO.

6.30 

2.81 

1.04 

4.30 

20.41 

19.07 

.92 

19.11

MnO by colorimetry.

Total.

0.193 

.311 

.700 

.442 

.281 

.245 

.016 

.574

With 

A1 S03 

Fe2O s (by 

difference).

0.085 

.036 

.301 

.088 

.030 

.019 

.016 

.032

CaO.

0.011 

.023 

.087 

.016 

.030 

.055 

None. 

.101

Mg2P207 .

0.097 

.252 

.312 

.338 

.221 

.171 

None. 

.441

The results in 974 and 1130 particularly show how the manganese once precipitated tends to remain 

with the alumina, presumably by reason of its having become peroxidized.

According to Steiger, the present practice in the Survey follows to a degree that of Washington, 

assuming a method of precipitating aluminum, etc., that does not also precipitate manganese. The procedure is to determine total manganese by colorimetry in a separate portion of the sample and to correct 

the magnesium pyrophosphate for its manganese content by another colorimetric determination. This 

correction is the more permissible because, as the table above shows, the major part of the manganese 

remains in solution until precipitated as phosphate with the magnesium, and the error thus thrown upon 

the alumina and lime is slight. Indication of contamination of ignited calcium oxalate by even very 

little manganese is revealed usually by a brownish discoloration, sometimes by the green color of calcium 

manganate.
MANGANESE, NICKEL, COBALT, COPPER, AND ZINC. 135

If the directions already given have been carefully followed, however, there will be little chance of error due to foreign contamination, by either alumina or magnesia, a sufficiency of ammonium 

salts being a guaranty against the latter. Eegard must be had, however, to the rather remote possibility of the presence of rare earths 

which were not thrown out by the basic-acetate precipitation (see 

footnote, p. 119), for they will appear at this stage.

B. PRECIPITATION OF TUB GROUP AND SEPARATION OF ITS CONSTITUENTS, 

a. TUB AMMONIUM-SULPHIDH METHOD.

a. Its advantages and disadvantages. On the other hand, the 

usual methods of separation of manganese from the alkaline earths 

and magnesia by bromine or ammonium sulphide are imperfect, in 

part by reason of incompleteness, in part because of coprecipitation 

of small amounts of these metals. The former error, though absolutely slight, is probably of more consequence in rock analysis than 

the latter. In regard to completeness of precipitation bromine offers 

no advantage over ammonium sulphide, and the latter has the advantage that by a single operation nickel, cobalt, copper, and zinc, 

if present, are likewise separated from the earth metals and alkalies. 

There need be no fear of overlooking nickel or copper, for under 

the conditions of the precipitation they are not retained in solution. 

It is for this reason chiefly that the ammonium-sulphide method is to 

be preferred. Most of the small amount of manganese that escapes 

precipitation is weighed later with the magnesium as pyrophosphate 

and can be corrected for readily by the colorimetric method described on page 137.

The precipitation of manganese in alkaline solution by hydrogen 

peroxide, as proposed by P. Jannasch and E. v. Cloedt,1 a method 

which appeared to be simple and accurate, besides affording a separation from zinc, was shown by C. Friedheim and E. Briihl 2 to be 

valueless.

(}. Precipitation by ammonium sulphide and separation of manganese and zinc from nickel, cobalt, and copper. Two or three cm.3 

of ammonia are added to the flask containing manganese, the earth 

metals, etc. (8. D. a and b, p. 113), and hydrogen sulphide gas is 

introduced to saturation, whereby manganese, nickel, cobalt, copper, 

zinc, and a small part of the platinum from the dish are precipitated. A second like amount of ammonia is now added. The flask, 

filled to the neck and corked, is set aside for at least 12 hours, and 

preferably 24, or even longer. The precipitate, collected and washed

^eitschr. anorg. Chomie, vol. 10, 1895, p. 405. 

2 Zeitschr. anal. Cbemie, vol. 38, 1899, p. C81.
136 ANALYSIS -OF SILICATE AND CARBONATE ROCKS.

on a small filter with water containing ammonium chloride and 

sulphide, is extracted by hydrogen-sulphide water acidified with 

one-fifth its volume of hydrochloric acid (sp. gr. 1.11), manganese 

and zinc, if present, going into solution.

(For treatment of the ammonium-sulphide filtrate see 12. B, p. 

144.) . '

b. MANGANESE AND ZINC.

The hydrochloric-acid filtrate is evaporated to dryness, ammonium 

salts are destroyed by evaporation with a few drops of sodium-carbonate solution, hydrochloric acid and a drop of sulphurous acid 

are added to decompose excess of carbonate and to dissolve precipitated manganese, and the latter is precipitated at boiling heat by 

sodium carbonate after evaporation of the hydrochloric acid. If 

zinc is present it can be separated from the manganese after weighing. 

For the small quantities of manganese usually found the sodiumcarbonate method of precipitation is to be preferred to that by 

bromine or sodium phosphate, as equally accurate and a time saver.

The manganese is weighed as Mn3O4 and calculated to MnO, or, 

if present in some quantity, it may preferably be weighed as the 

sulphate,1 or, finally, it may be determined colorimetrically with 

much greater certainty, as in C, below, when the amount is within 

the usual limits for rocks. In the last case, in the absence of zinc, 

the hydrochloric-acid solution of the sulphide may be used for the 

colorimetric test, after first evaporating off the hydrochloric acid 

with nitric or sulphuric acid.

C. NICKEL, COBALT, AND COPPER.

The paper containing nickel, cobalt, and copper is incinerated in 

porcelain, the ash is dissolved in a few drops of aqua regia, and the 

solution evaporated with hydrochloric acid; the copper and platinum 

are thrown out warm by hydrogen sulphide, and in the filtrate made 

ammoniacal nickel and cobalt are thrown down by hydrogen sulphide. 

This liquid is then rendered faintly acid by acetic acid and allowed 

to stand. The sulphide precipitate after filtering is burned and 

weighed as oxide its weight being always very small, hardly ever 

over 0.3 or 0.4 mg. which is then tested for cobalt in the borax bead. 

The color of the last drop or two of the hydrochloric-acid solution, 

after decomposing the aqua regia, is a good indication of the presence or absence of nickel and cobalt. It is always well at this point 

to separate by ammonia any traces of iron that may be present, then 

to acidify and treat with hydrogen sulphide as above.

It is somewhat unsafe to consider traces of copper found at this 

stage to belong to the rock jf the evaporations have been conducted,

1 Volhard, J., Ann. Chemie, vol. 198, 1879, p. 329. Gooch, F. A., and Austin,, Martha, 

Am. Jour. Sci., 4th sei1 ., vol. 5, 1898, p. 209 ; Zeitsclir. anorg. Cbomie, vol. 17, 1898, p. 264.
MANGANESE, NICKEL, COBALT, COPPER, AND ZINC. 137

as is usually the case, on a copper water or steam bath, or if water has 

been used which has been boiled in a copper kettle, even if the kettle 

is tinned inside. Therefore, and because of its contamination by a 

little platinum, it is better to determine copper in a separate portion 

if its presence is indicated with certainty. (See 7, p. 106.) This 

warning is particularly to be heeded if copper or brass sieves were 

used in preparing the sample.

C. COLORIMETRIC DETERMINATION OF MANGANESE.

a. PRELIMINARY TREATMENT.

As has been shown above (p. 134), the gravimetric determination of 

manganese is subject to grave error, even when great care is used. 

This is due to a variety of reasons, such as incompleteness of separation from aluminum and iron, incomplete precipitation by ammonium 

sulphide, and contamination by other bodies. Because of the small 

amounts in question these errors may be relatively enormous, and 

they can not be depended on to balance each other. Therefore, it 

would be an advance if the total manganese could be determined in a 

separate portion of the sample, and in the main portion only that part 

which is weighed with the magnesium pyrophosphate, and this only 

as a correction to the magnesia. This course is readily feasible with 

carbonate rocks, which can usually be brought into a fit state in a few 

minutes without a fusion or the separation of silica. With silicate 

rocks more labor is involved, but the determination itself is very 

accurately performed by colorimetry, as in the case of carbonates.

The preliminary treatment consists in decomposing a gram or half 

a gram of the rock powder in a small platinum dish or capacious crucible (placed in the radiator shown in fig. 2, p. 33) with hydrofluoric 

and sulphuric acids till all is disintegrated. The hydrofluoric acid is 

then to be driven off by repeated evaporations with small portions of 

sulphuric acid, after which either sulphuric or nitric acid free from 

chlorine is added, together with water, and as much of the residue is 

brought into solution as possible. What remains insoluble is usually 

barium and calcium sulphates. This is filtered off on a small filter, 

the filtrate is caught in a small beaker or flask, and the manganese 

determined as in the following paragraphs.

b. COLORIMETRIC DETERMINATION OF MANGANESE BY AMMONIUM PERSULPHATE. 1

The use of ammonium persulphate for the colorimetric determination of manganese has the advantage over that by lead peroxide in 

that, unless chlorides happen to be in the solution, no filtration is necessary. Two solutions are needed, one of silver nitrate containing

1 Walters, H. E., Cheni. News, vol. 84, 1901, p. 23f); Proc. Eng. Soc. West. Pennsylvania, 

vol. 17, 1901, p. 257. Based on a suggestion of H. Marshall, Chem. News, vol. 83, 1901, 

p. 73.
138 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

2 grams of the salt to the liter, and one of manganous sulphate or 

nitrate containing the equivalent of 2 mg. of MnO in 10 cm.3 . This 

last can be made conveniently by acidifying a standard permanganate 

solution, reducing it by sulphurous acid, and diluting appropriately. 

A solution of permanganate can be used directly as a color standard 

when very small quantities of manganese are in question. Ammonium persulphate in the solid form is also needed. The commercial 

article needs no purification ordinarily in this case.1

The rock solution must be strongly acid with nitric or sulphuric 

acid and considerably less than 100 cm.3 in bulk unless the manganese 

exceeds 1 milligram in weight. To it is added 10 cm.3 of the silver 

solution for every milligram of metallic manganese, and it is transferred to a graduated flask of size suited to the solution. Should it 

show a turbidity from precipitated silver chloride, the liquid must be 

agitated and then filtered into the flask. About 1 gram of solid ammonium persulphate is now added and the flask is placed on the 

steam bath or hot plate. Very soon the pink color of permanganic 

acid begins to appear and increases rapidly to a maximum. The flask 

may be removed soon after the color begins to show and placed in 

cold water when it is fully developed. If the depth of color is very 

great the solution must be poured into a larger flask. The flask is 

filled with water to the mark and the contents are thoroughly mixed.

According to the depth of color there is now placed in another 

flask of 100 cm.3 or less volume 10 cm.3 , or some multiple of that 

amount, of the manganese solution, so that when both solutions are 

oxidized and the flasks filled the color in the standard shall be more 

intense than in the test solution. This solution is oxidized by the aid 

of silver salt and persulphate in the same manner as the other, cooled, 

filled to the mark, shaken, and poured into a burette. Ten cm.8 is 

drawn off into one of the comparator cylinders shown in figure 5 (p. 

36), and diluted with water from a burette till the color equals that 

of the properly diluted and mixed test solution, a part or all of which 

has been poured into the' companion cylinder. The observations are 

made exactly as given on page 37. If the form of colorimeter depicted in figures 6 or 7 is used, the dilution of the standard solution is, 

of course, unnecessary. Nessler cylinders can be used instead of 

either of the colorimeters described. The results are very exact.

Should, perchance, a brown precipitate form during the oxidation 

of the standard, it will sometimes be necessary to start with a fresh 

portion, but often the error can be remedied by immediate addition 

of more silver salt and continued heating. If this treatment fails 

with the test solution, the precipitate must be brought into solution 

by a little sulphurous acid, more silver salt added, and the oxidation 

repeated with persulphate.

1 See footnote, p. 112.
MANGANESE, NICKEL, COBALT, COPPER, AND ZINC. 139

G. Bertrand 1 operates in nitric acid solution, employs potassium 

instead of ammonium persulphate, and boils the solution to destroj 

an excess of the persulphate. The function of the nitric acid, according to Bertrand, is not only to cause any precipitate of silver peroxide that may form to disappear on boiling, but also to assure complete transformation of the manganese to permanganate.

If the rock carries much iron, it will be well to eliminate the effect 

of the color of the iron by adding to the standard ferric sulphate or 

nitrate in proper proportion. (See p. 160.)

In order to overcome the disturbing effect of chromium, if present, 

M. Dittrich 2 precipitates all the iron and manganese by ammonia 

after oxidizing with persulphate, filters, redissolves the precipitate 

in sulphuric acid with the aid of sulphurous acid or hydrogen peroxide, warms to expel or destroy the excess of either of these, and 

repeats the oxidation with persulphate and silver nitrate.

D. DIRECT TITKATION OF MANGANESE.

F. J. Metzger and L. E. Marrs 3 have developed a method for 

the direct titration of manganese in the presence of other bases, 

which they say is applicable to irons, steels, ores, and slags. It is 

based on the fact that under favorable conditions MnTI1 in hydrofluoric acid solution oxidizes Mn11 to Mnm and is itself reduced to 

Mnm. (See 21. D. b. a, p. 197.) The authors say that if sufficient of 

this acid is present the reaction is quantitative.

My experience with the method as the authors apply it to rocks 

does not bear out their claims for great accuracy, perhaps because of 

the disturbing influence at the.end of the titration of the brown color 

of the manganic salt. Nevertheless, in view of the very positive 

statements made by Metzger and Marrs, their procedure for rocks is 

given below.4

Boil the. sample (5 to 10 grams) with 5 to 15 cm.3 of dilute sulphuric acid (1:2); add 5 to 15 cm.3 of hydrofluoric acid, and boil further until the sample is completely decomposed. Add 5 to 10 cm.3 of 

dilute nitric acid (1:1) and 2 or 3 cm.3 of concentrated sulphuric 

acid. Kemove from the flame and add about 1 gram of ammonium 

persulphate in small portions. When evolution of gas has ceased, 

evaporate until white fumes are evolved, cool, add 50 cm.3 of water, 

boil, and cool again. Transfer to a wax beaker (a ceresin bottle with 

the top cut off), add 5 grams of ammonium fluoride and 25 cm.3 of

1 Ann. chim. appl., vol. 16, 1911, p. 283.

- Z-eitschr. anorg. Chemie, vol. 80, 1913, p. 171. 

»Jour. Ind. Eng. Chemistry, vol. 5, 1913, p. 12:3.

* E. Miiller and P. Koppe (Zeitschr. anorg. Chemie. vol. G8, 1011, p. 160) were the 

originators of the method but rejected the reaction for quantitative use because of the 

disturbing color due to the manganic fluoride.
14.0 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

hydrofluoric acid (making a total volume of about 100 cm.3 ), and 

titrate to a permanent pink color with permanganate (about N/30). 

The value of the permanganate in terms of iron multiplied by O.T868- 

gives the value in terms of manganese, or by 1.016 in terms of MnO.

12. CALCIUM AND STRONTIUM (BARIUM).

A. SEPARATION FROM MAGNESIUM, 

a. GENERAL CONSIDEKATIONS.

Calcium is found in rocks and minerals almost always associated 

with magnesium. If, as is usual, there is no excessive disparity in 

the proportions of the two, the oxalate method of separating the 

calcium from the magnesium can be used directly. Even then, apparently correct results are clue to slight compensating errors. The 

method is less applicable if either metal preponderates very largely 

over the other. When magnesium preponderates greatly the calcium is incompletely precipitated if ammonium oxalate is not used 

in great excess, arid on the other hand there is coprecipitation of 

magnesium oxalate if a great excess of the precipitant is used. If 

calcium is the greatly preponderating metal, much of the little magnesium present is precipitated with it, and the error is not overcome 

wholly by re-solution and reprecipitation. These are but special illustrations of the too little observed rule that in general " when testing 

for minute amounts of impurity, the procedure of first removing the 

main element by precipitation should never be followed." 1 The rule 

is not always applicable, but in most cases it is good practice to 

concentrate the minor component of a mixture in a precipitate that 

carries but a fraction of the major component, and upon this precipitate to apply the methods of separation that serve when the 

relative amounts are not altogether disproportionate. Fortunately, 

most silicate rocks fall in the latter category.

Strontium precipitates with the calcium in the oxalate method.2 

For the behavior of barium see C, page 145.

In the separation of calcium from magnesium by the ammonium 

oxalate method at least two precipitations are essential to the attainment of correct results, not only for complete removal of magnesium 

but of sodium as well, the retention of compounds of the latter element being now well known. This subject has been studied by many 

authors and especially by T. W. Richards, C. T. McCaffrey, and H. 

Bisbee,3 who call attention also to the danger of too long washing

1 Hostetter, J. C.. Jour. Ind. Eng. Chemistry, vol. 6, 1914, p. 392 ; Chem. News, vol. 110, 

1914, p. 155.

2 Confirmed by C. A. Peters, Am. .Tour. Sci., 4th ser., vol. 12, 1901, p. 216.

3 Proc. Am. Acad. Arts and Sci. vol. 36, 1901, p. 375 ; Zeitschr. unorg. Chcmie, vol. 

28, 1901, p. 71.
CALCIUM AND STRONTIUM. 141

with hot water, because of the very appreciable solubility of calcium 

oxalate in it. This is a point that needs greater attention than it 

receives from analysts. A liter of nearly boiling water dissolves 

over 1 eg. of calcium oxalate; at room temperatures about 7 mg. is 

dissolved.

b. SEPARATION WHEN NEITHER CALCIUM NOR MAGNESIUM PREPONDERATES EXCESSIVELY.

The platinum derived from the dish in the silica, evaporation, 

except for the small portion precipitated with the manganese sulphide, is now wholly in the filtrate from the latter (11. B. a. (3, p. 

135). Its separation at this or any other stage is quite unnecessary; 

nor is the removal of ammonium chloride usually demanded, for 

as a rule there is no undue amount present, the first precipitation of 

alumina, etc., having been effected by ammonium or sodium acetate.2 

Therefore, without destroying ammonium sulphide the calcium and 

strontium are thrown out by ammonium oxalate at boiling heat, the 

precipitate, often darkened by deposited platinum sulphide, is ignited 

and dissolved in hydrochloric acid, the solution is boiled-with ammonia to throw out traces of alumina sometimes present, filtered, and 

the calcium and strontium are reprecipitated as before, but in a small 

bulk of solution. For the treatment of the filtrates see section 13, 

Magnesium (p. 148).

For this second precipitation, and whenever a separation as complete as possible is called for by one precipitation, the following 

procedure of Richards and his coworkers is recommended.

The magnesium must.not be in greater concentration than 1/50 

normal. Add to the solution about 10 times the equivalent of ammonium chloride and enough oxalic acid to combine with all the 

calcium. It is advisable to repress the dissociation of the oxalic acid 

in advance by addition of three to four times its equivalent of hydrochloric acid. Add at intervals to the boiling solution, colored by a 

drop of methyl orange, very dilute ammonia, with continuous stirring, until the neutral point is just passed. Half an hour is needed to 

complete this operation. Then add a great excess of ammonium 

oxalate and let the liquid stand for about four hours. Longer standing results in reprecipitation of magnesium oxalate upon the calcium 

salt; with less time precipitation of the calcium is incomplete. Wash 

with water containing a little ammonium oxalate, in which calcium 

oxalate is much less soluble than in pure water. " The filtrate contains all the magnesium except 0.1 to 0.2 per cent, and in the precipitate is all-the calcium with about the same deficit." This quotation 

refers to a first precipitation.

1 If two or three precipitations by ammonia alone are depended on, the second and third 

filtrates are evaporated rapidly to dryness and the ammonium salts removed by ignition.
142 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

C. IGNITION OF THE CALCIUM OXALATE.

The moist precipitate of calcium and strontium oxalates, wrapped 

in the filter paper, is placed in a platinum crucible and heated so as 

to char without inflaming the paper. When the carbon has been 

made to disappear by stronger heat, the crucible is to be coTered and 

blasted with an inclined flame. It is a very mistaken idea that with 

a really good blast it takes long to reach constant weight. Five minutes is ample, ordinarily, for any amount of lime that is likely to be 

met with. For ordinary amounts the heat of a large and good Bunsen burner is in reality sufficient. I was able by it in 50 minutes to 

reduce 3 grams of calcium carbonate to the oxide, or so nearly so that 

the blast afterwards caused a further loss of only 1 mg. This, of 

course, was with the crucible covered. The lime should not be left 

over half an hour in the desiccator before weighing, for it gains 

weight appreciably if left long.

The weighed oxide is transferred to a small flask of 20 cm. capacity, 

dissolved in nitric acid, and evaporated to dryness at 150° to 160°, 

and the separation of strontium from calcium is effected by etheralcohol x as described below, under B.

The weight of the strontia found, deducted from that of the two 

oxides, gives that of the lime.

d. SEPARATION OF LITTLE CALCIUM FROM MUCH MAGNESIUM.

i

a. Preliminary remarks. The procedure given on page 141 is 

applicable to almost all silicate rocks, but the results are affected 

by slight compensating errors, as already pointed out under A. a, 

even when the separation is made under the most carefully regulated 

conditions. If an extremely accurate determination of very little 

calcium in presence of much magnesium is desired, as in the mineral 

magnesite, recourse must be had to successive precipitation of the 

calcium, first as sulphate, then as oxalate.2 Various procedures have 

been proposed, of which perhaps the best review is that by 0. Kallauner and I. Preller.3 They found that direct weighing of the calcium precipitated as sulphate is quite unsatisfactory, but that very 

good results are obtainable by their modification of the sulphate

1 See Fresenius, R., Zeitschr. anal. Chemie, rol. 32, 1893, pp. 189, 312, for the latest 

improvements in this method, in their application to considerable quantities.

2 It is probable that a very good procedure would be to precipitate the calcium and 

magnesium together as phosphate according to 13. A. b. and ft (pp. 149-150), and to 

determine the calcium in the ignited magnesium" pyrophosphate according to 13. C. h. (p. 

152). For this suggestion I am indebted to Dr. James A. Holladay, chief chemist of 

the Electro-Metallurgical Co., Niagara Falls.

3 Chem. Zeitung, vol. 36, 1912, p. 462. A method by A. Cappcl (Kali, rol. 4, 1910, 

p. 77) is based on the precipitation of calcium by sodium bicarbonate in presence of 

ammonium chloride. B. C. Carron (Ann. chim. appl., vol. 17, 1912, p. 127) bases a method 

unsupported by analytical data on the precipitation of calcium as sulphite.
CALCIUM AND STKONTIUM. 143

method of C. Stolberg and that of E. Murmann, followed by precipitation as the oxalate.

(5. Modified Stolberg method. The original Stolberg method l begins with evaporation of a mixture of the chlorides with sulphuric 

acid and complete expulsion of the excess of the acid. The residual 

sulphates are treated with a very little water, so as to form a saturated solution of magnesium sulphate, to which is added a mixtura 

of 10 per cent ethyl alcohol and 90 per cent methyl alcohol, in which 

magnesium sulphate is freely soluble. The wholly insoluble calcium 

sulphate is washed with a mixture of the two alcohols in the proportion 5 to 95.2 The alcohols must be free from basic organic substances, which would precipitate magnesium. G. E. F. Lundell 

found these in one lot of methyl alcohol.

In order to shorten the operation Kallauner and Preller treat a 

mixture of the dry chlorides with the 10-90 alcohol mixture saturated with lithium sulphate (which is readily soluble in the alcohol), 

or they evaporate to dryness a solution of the chlorides with lithium 

sulphate, extract the residue with the alcohol mixture, and proceed 

in either case according to Stolberg until the sulphate is washed. 

They dissolve it then in hydrochloric acid and purify it by precipitation with ammonium oxalate. Needless to say, this latter operation 

should be done in a small volume of liquid.

Y. Mur.man'ri's method* E. Murmann's method presupposes 

knowledge of the amount of calcium present and is limited accordingly.

Add to the chloride solution the requisite amount of sulphuric acid 

to combine with the calcium, evaporate to dryness, digest and wash 

with ethyl alcohol (90 per cent), dissolve the precipitate in hydrochloric acid, and separate the calcium as oxalate from the contaminating magnesium salt.

8. Author's method. Tests made for me by G. E. F. Lundell, in 

order to learn if the separation is really complete in presence of free 

sulphuric acid, as recommended by me in the past (see 13. C. b, p. 152), 

show that with 100 mg. MgO and 1 mg. CaO the precipitation of 

calcium is complete by using a mixture of ethyl alcohol, water, and 

sulphuric acid in the proportion of 90 to 9 to 1 by volume, or one of 

methyl alcohol, ethyl alcohol, and sulphuric acid in the proportion 

of 90 to 10 to 1. With 1,000 mg. MgO and 1 mg. CaO the precipitation of calcium was not complete.

iZeitschr. angew. Chemie, vol. 17, 1903, p. 741.

2 Stolberg found that precipitation of magnesium sulphate from a half-saturated solution by ethyl alcohol ceases only when the alcohol is diluted with at least 40 per cent of 

water, and that calcium sulphate is somewhat soluble in alcohol of 90 per cent strength ; 

hence, that direct separation seems impossible. But a saturated solution of magnesium 

sulphate is not precipitated by methyl alcohol.

3 Zeitschr. anal. Chemie, vol. 49, 1910, p. 688.
144 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

6. SEPARATION OF LITTLE MAGNESIUM FROM MUCH CALCIUM.

J. C. Hostetter 1 draws attention to gross errors current in the 

determination of very little magnesium in presence of much calcium, 

especially in commercial salts of calcium used as reagents, and proposes the following procedure, which, however, is not applicable for 

determining calcium in the same solution:

Ten grams of the calcium salt are brought into solution in water, and the 

solution is made up to 100 cm.3. If acid is used to bring the salt into solution, 

the excess is neutralized with sodium hydroxide, after the expulsion of 

CO2 , S02, etc., by boiling. The calcium oxide made from 0.3 to 0.4 gram of 

calcium carbonate by ignition is now added and the solution heated to boiling; 

the precipitate is filtered off but not washed. The precipitate is dissolved in 

hydrochloric acid and the calcium removed by two precipitations with ammonium oxalate. The filtrates from these two precipitates are combined, and 

the magnesium in the combined filtrate is determined by precipitation as 

ammonium-magnesium phosphate by microcosmic salt.

B. SEPARATION OF STRONTIUM (BARIUM) FROM CALCIUM, 

a. BY ETHER-ALCOHOL.

The thoroughly dried nitrates obtained in A. c are treated with as 

little (seldom over 2 cm.8 ) of a mixture in equal parts of absolute 

alcohol and ether as may be needed to dissolve the calcium salt, solution being hastened by occasional gentle agitation. After standing 

overnight in the corked flask the insoluble matter is collected on the 

smallest possible filter and washed with more of the above mixture of 

alcohol and ether. After drying, a few cubic centimeters of hot water 

is passed through the filter, on which may remain a few tenths of a 

milligram of residue, which does not usually contain any lime or other 

alkaline earth and whose weight is therefore to be deducted from that 

of the lime,-unless it can be shown that it is derived from the glass of 

the little flask in which the nitrates of calcium and strontium were 

evaporated. To the solution of strontium nitrate in a small beaker a 

few drops of sulphuric acid and then its volume of alcohol are added, 

whereby the strontium is precipitated as sulphate, in which form, 

after twelve hours, it is weighed and then tested spectroscopically as 

to freedom from calcium and barium.

b. OTHER METHODS.

Because of the slight solubility of strontium nitrate in amyl alcohol 

the method of Browning 2 does not appear to be adapted to the separation from calcium of the small amounts of strontium met with in 

rocks, though with barium the case is different, since its nitrate, 

according to Browning, is insoluble in absolute amyl alcohol.

i.Tour. Ind. Eng. Chemistry, vol. 6, 1914, p. 392; Chem. News, vol. 110, 1914, p. 155. 

2 Am. Jour. Scl., 3d ser., vol. 43, 1892, pp. 50, 314.
CALCIUM AND STRONTIUM. - - 145

; A method which seems not to have been given rigid test as yet, for 

separating barium and strontium from calcium, is that of S. G. Rawson,1 which is as follows: A nitrate solution of the metals is evaporated until the mass is quite dry. Concentrated nitric acid is added 

in excess, and the mixture is kept well stirred. After settling, the 

precipitate is collected in a Munroe crucible (platinum felted) and 

washed with more of the concentrated acid. Calcium is determined 

in the filtrate after evaporation. The barium and strontium nitrates 

are dissolved in water; the barium is determined as chromate, the 

strontium as sulphate in the filtrate from the barium chromate.

C. BEHAVIOR OF BARIUM.

Barium, after two ammonium-oxalate precipitations, will never be 

found with the ignited calcium and strontium in more than spectroscopic traces, unless originally present in excess of 3 or 4 mg., and 

very often only when in considerable excess.2 If present with them, 

hoAvever, it will be separated with the strontium by ether-alcohol or 

amyl alcohol, and these two must then be treated by the ammoniumchromate method, given below, in order to arrive at the strontium. 

The barium is best estimated in a separate portion.3 (See " Barium," 

15, p. 170.)

D. SEPARATION OP BARIUM FROM STRONTIUM.

Profiting by the experience of R. Fresenius and others, A. Skrabal 

and L. Neustadl 4 have shown in what manner alone a very nearly 

correct separation of barium can be made from calcium and strontium. The following solutions are requisite:

Ammonium'bichromate, 100 grams to the liter.

Ammonium acetate, a, 300 grains, neutralized by ammonia, to the liter.

Ammonium acetate, &, 20 cm.3 of a diluted to 1 liter.

The reaction of the acetate solutions should be alkaline rather than 

acid.

The method for the amounts used by the authors (0.135 gram BaO 

as the chloride and the same of strontium) is as follows:

To the neutral or weakly acid solution is added ammonium acetate 

(10 cm.3 of solution a) in excess. The liquid is brought to boiling and 

while swirled about 5 cm.3 of the bichromate solution is added. 

After settling and cooling the clear liquid is decanted through a filter

1 Jour. Soc. Chem. Industry, vol. 16, 1897, p. 113.

" Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 16, 1894, p. 83; Chem. News, vol. 69, 

1894, p. 147.

3 For the separation and estimation of barium associated with calcium and magnesium, 

by the action of acetylchloride in acetone upon the mixed chlorides, consult F. A. Gooch 

and C. N. Boynton, Am. .Tour. Sci., 4th ser., vol. 31, 1911, p. 212.

4 Zeitschr. anal. Chemie, vol. 44, 1906, p. 742.

131999° 19 10
146 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

and the precipitate washed by decantation with ammonium acetate 

(solution b) till the filtrate is no longer perceptibly colored (100 cm.3 

of wash solution). The beaker is placed under the funnel, the precipitate on the paper dissolved by warm dilute nitric acid, and the 

paper washed. More acid is then added to dissolve the rest of the 

precipitate, followed by ammonia till the precipitate forming again 

no longer redissolves. Ammonium acetate (10 cm.3 of solution a) 

is now poured in, the liquid brought to boiling while kept in swirling 

motion, allowed to cool slowly, and the precipitate is washed by 

decantation with solution Z> of the ammonium acetate. The barium 

chromate is dried and weighed as such after ignition, the filter being 

burned separately.

The strontium may be thrown down from the combined filtrates 

by ammonia and ammonium carbonate, after concentration in presence of a little nitric acid, and weighed as carbonate; or the carbonate may be redissolved, precipitated by sulphuric acid and alcohol, and weighed as sulphate.

It is probable that for the small amounts encountered in rocks a 

single precipitation of the barium by bichromate will suffice, but this 

is not so when any considerable quantities are. to be separated.

E. OTHER METHODS OF DETERMINING CALCIUM AFTER PRECIPITATION AS

OXALATE.

a. PRELIMINARY REMARKS.

Additional methods more or less in vogue for determining the 

calcium after precipitation as oxalate are the volumetric method by 

potassium permanganate and the conversion of the oxalate into carbonate, sulphate, or fluoride. None of these is applicable in rock 

analysis if it is desired to determine the strontium, except the second, 

but apparently any one of them will afford good results if no account 

is to be taken of that element. The methods have not been tested 

in the Survey laboratory, however, though the several gravimetric 

methods have been compared by 0. Brunck,1 who finds that duplicates by any one of them show better agreement than by the oxide 

method. Brief descriptions of them are therefore given below, as 

well as of the volumetric method.

It is to be said, however, regarding Brunck's determination of 

calcium as the oxide, that no such variations as those reported by 

him are ever obtained in the Survey laboratory. Duplicates by that 

method agree as well as his by the other methods. His high and 

varying results by the oxide method are probably to be attributed 

to the employment of a vertical instead of an inclined flame. The 

complete conversion of the oxide to sulphate or to fluoride by treatiZeitschr. anal. Chemie, vol. 45, 1906, p. 77.
CALCIUM AND STRONTIUM. 147

ment with sulphuric or hydrofluoric acid is, in my opinion, based on 

experience with the conversion of lead chloride to sulphate, by no 

means easily brought about. There will always be a tendency, where 

an insoluble compound is at once produced by action of one of the 

acids in question, for some of the original compound to be protected 

from conversion to the salt, even after two or more evaporations 

with fresh portions of acid.

It is further doubtful if the loss in weight of the crucible during 

blast ignition of the lime is really as great as he thinks. It is well 

known that barium oxide attacks platinum strongly when heated in 

contact with it, and it is certain that lime does so to a less but appreciable extent. That it does can be demonstrated readily by dissolving in hydrochloric acid lime that has been blasted in platinum for 

half an hour and precipitating and weighing the dissolved platinum. 

The amount recovered will nearly and sometimes quite equal the loss 

in weight of the crucible itself.

b. VOMJMETKIC METHOD.

The washed oxalate is rinsed into a beaker and the filter is extracted 

with hot dilute sulphuric acid, the filtrate being caught in the beaker. 

It is not permissible to omit this extraction, for simple rinsing with 

water will not extract all of the oxalate held in the pores of the paper. 

More acid is added if necessary, and the contents of the beaker are 

digested at a moderate heat till decomposition can be considered 

complete. The oxalic acid is then titrated warm at about 70° with 

permanganate, which has been standardized against pure Iceland 

spar dissolved in hydrochloric acid and precipitated as the oxalate, 

or, better, against the Bureau of Standards' sodium oxalate.

C. BY WEIGHING AS THE CAKBONATE.

The oxalate is ignited gently to convert it to carbonate and is then 

digested with a few drops of a solution of ammonium carbonate. The 

liquid is evaporated cautiously and the residue ignited gently to just 

visible dull redness and weighed. The treatment with ammonium 

carbonate, etc., is repeated till constant weight is reached.

Cl. BY WEIGHING AS THE SULPHATE.

The strongly ignited oxide is slaked cautiously with water and a 

slight excess of sulphuric acid is added. The liquid is concentrated 

by evaporation and the excess of acid removed in the radiator (fig. 2, 

p. 33). The dry sulphate is then ignited moderately (to dull redness 

for a short time) and weighed, the treatment with acid, etc., being 

repeated to constant weight.
148 ANALYSIS OF SILICATE AND..CARBONATE BOOKS.

6. BY WEIGHING AS THE'jFLUOBIDE. . .

The strongly ignited oxide is slaked with water and covered 

with hydrofluoric acid, the excess of which is removed on the bath 

and the residue ignited for a few moments and weighed. The treatment with acid, etc., is to be repeated till the weight becomes constant. According to Brunck this last method is simpler than the canbonate or sulphate method, and in the hands of the inexperienced 

leads to better results, though he regards the sulphate method as the 

best in experienced hands.

13. MAGNESIUM. 

A. PRECIPITATION.

a. CONDITIONS NECESSARY TOR THE PRODUCTION OF A NORMAL PRECIPITATE.

There are few analytical procedures regarding which so much uncertainty has existed and still exists as that by which magnesium is 

precipitated as the ammonio-phosphate, notwithstanding the enormous mass of detailed work that has been done on the subject. The 

work of H. Neubauer,1 . confirmed in part and supplemented.by F. A. 

Gooch and Martha Austin,2 seemed to clear the ground fairly well. 

Neubauer found that precipitation is complete even in the presence 

of large quantities of salts of ammonium, including the oxalate, but 

that the composition of the precipitate is largely affected by ammonium salts and also by the way in which the precipitation is made. 

The precipitate is also said to be rendered impure if sodium chloride 

is in the solution. Hence the need for a double precipitation. 

Gooch and Austin show that the large amount of ammonia of 0.96 

specific gravity (one-third the original volume of the solution) usually prescribed is not only unnecessary, but, in fact, disadvantageous, 

at least until the precipitate has fully formed. The authors named 

agree that it is only by working under certain conditions absence of 

any large excess of precipitant, of ammoniacal salts, and of ammonia that a precipitate of normal composition is obtainable (see below). From their labors it would seem clear that the common way of 

adding the phosphate precipitant to the ammoniacal solution of the 

magnesium salt is not calculated to produce a precipitate of normal 

composition. The precipitant should be added to the acid solution of 

the magnesium, and ammonia should then be added in slight excess.

The precipitate as ordinarily formed contains an excess of phosphorus, a condition which Neubauer ascribed to admixture of perhaps Mg(NH4 ) 4 (PO4 ) 2 , the result being that when it is ignited in the 

ordinary way the calculated value for magnesium will be high, because of the formation of some metaphosphate. K. Bube,3 however,

1 Zeitschr. angew. Chemie, 1896, p. 435.

3 Am. Jour. Sci., 4th ser., vol. 7, 1899, p. 187 ; Chem. News, vol. 79, 1899, pp. 233, 244, 

and 255 ; Zeitschr. anorg. Chemie, vol. 20, 1899, p. 121. 

3 Zeitschr. anal. Chemie, vol. 49, 1910, p. 587.
. MAGNESIUM. . . 149

seems to have shown that the normal precipitate carries with it ammonium phosphate. In order to overcome the resulting error Neubauer considered it to be absolutely necessary to blast the precipitate 

for half an hour, and after weighing to repeat the blasting for a 

second half hour. If the weight has not changed the phosphate is 

then entirely pyrophosphate, which is quite unaffected by further 

blasting. (See, however, B, p. 150.) The intense heat has volatilized 

the ammonium phosphate or has caused a decomposition of the metaphosphate with volatilization of P2 05, as follows: 2 Mg(P03 ) 2 = 

Mg2P2O7 -f P205« Neubauer worked with the usual excess of ammonia added after the bulk of the precipitate had formed, and it 

remains to be seen whether by precipitating and working according 

to Gooch and Austin the composition of the precipitate is always close 

enough to the ideal MgNH4P04 to obviate the necessity for blasting. 

Gooch and Austin call attention to a modification proposed long 

since by Wolcott Gibbs,1 whereby the phosphorus and magnesium 

salts are first boiled together in neutral solution for a few minutes and 

to the cooled solution ammonia is added. The results are said to be 

remarkably exact, but K. K. Jarvinen 2 reports to the contrary. 

Jiirvinen and numerous .other chemists have published papers upon 

one phase or another of the general subject, and many are the modifications of procedure that have been proposed. They need not be discussed here, for most of them aim at obtaining a precipitate of normal 

or nearly normal composition by making only a single precipitation, 

whereas a repetition is called for in mineral and rock analysis, and 

the proposed procedures do not adapt themselves thereto well, if at 

all. Mention may be made, however, of the latest contributions 

numerous papers by D. Balarew 3 and one by Z. Karaoglanow and 

P. Dimitrow.4 These authors discuss also the conditions under which 

the glowing of magnesium-ammonium phosphate occurs when it is 

being converted to pyrophosphate by ignition, the probable causes 

of the phenomenon and ways of inhibiting it, and the means of 

whitening magnesium pyrophosphate that becomes discolored during 

ignition.

b. PBECIPITATION AND FILTRATION.

a. First precipitation. The first precipitation is made without 

precautions in the ammoniacal filtrate from the first calcium-oxalate 

separation (12. A. b, p. 141) by sodium-hydrogen phosphate 5 (microcosmic salt in indefinite decided excess and with addition of about 

one-fifth the volume of strong ammonia solution at the end. Vigor1 Am. Jour. Sci., 3d ser., vol. 5, 1873, p. 114.

2 Zeitschr. anal. Chemie, vol. 44, 1905, p. 335.

3 Zeitschr. anorg. allg. Chemie, vols. 101-104, 1918-1919.

4 Zeitschr. anal. Chemie, vol. 57, 1918, p. 353.

E The objection that has been made by one writer to the use of this salt instead of 

disodium-hydrogen phosphate Is, so far as my experience teaches, entirely groundless.
150 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

ous stirring hastens formation of the precipitate. It is not necessary 

first to remove ammoniacal salts unless very little magnesium is 

present, and then only in order to hasten precipitation. The facts 

that large quantities of these salts retard precipitation and that the 

composition of the precipitate is affected by them as well as by the 

way in which the precipitation is made are of importance only when 

a single precipitation is to be made or in the final of two or more.

Continued agitation of the liquid by a mechanical stirrer is of advantage in greatly shortening the time of complete precipitation, 

which is in general shorter the greater. ,the"*qiiantity of magnesium 

present.

After standing for at least 4 hours, and for as much as 12 hours 

if the precipitate was slow to form, filter through paper. Wash 

with water to which about one-tenth its volume of strong ammonia 

water has been added. Half a dozen washings suffice after the rinsings from the dish have passed the filter. Filtering and washing are 

done best without much if any suction, but it is well to suck the precipitate dry at the end. , .

(3. Second precipitation. Platinum sulphide usually strongly contaminates the separated phosphate, but this matters not, as it remains 

on the filter when the phosphate is redissolved in hydrochloric acid, 

of which not more than the amount really needed should be used. 

The stirrer must be treated with acid; also, the beaker or dish. The 

solution thus obtained is united with that of the residue from evaporation and ignition of the second filtrate from the calcium oxalate 

(12. A. b, p. 141) and is diluted if necessary. A few drops of sodiumammonium-phosphate solution are now added, and ammonia, drop 

by drop, with constant stirring till in slight excess and the crystalline 

precipitate has formed well. Once formed, .a few cubic centimeters 

more of ammonia is to be added.

The filtering and washing are done on a fresh paper after three 

to six hours, and great care must be exercised to clean the precipitation vessel and the stirrer thoroughly from strongly adhering precipitate by the aid of a " policeman " or feather.

Were it not for the necessity of examining the precipitate for impurities after ignition (C, p. 152) a Gooch filtering crucible could be 

used with advantage instead of a paper filter, provided the asbestos 

felt is well constructed and not of the serpentine variety. A Munroe 

(platinum felted) crucible may be used, but subsequent operations 

are shortened if paper is employed.

B. IGNITION OF THE PRECIPITATE.

The precipitate, wrapped in its moist paper, is dried in a weighed 

platinum crucible, the paper then slowly charred without allowing it 

to ignite, the carbon burned off over a gradually increasing flame,
MAGNESIUM. . . 151

and finally a weak blast applied for a long time in order to insure 

volatilization of any excess of P2 05 over and above that required for 

the pyrophosphate formula. (See A. a, p. 148.) After weighing, the 

heating is repeated as often as may be necessary to bring the phosphate, to a constant weight.

The danger of attack of the platinum crucible by igniting the precipitate in contact with the paper is very slight, though it has happened once or twice in my experience that a crucible has been ruined 

by so doing. Why reduction should have occurred in these cases and 

not in the hundreds of others is not known.

The experience of the Survey chemists was for a time decidedly 

adverse to the blasting of magnesium pyrophosphate as prescribed by 

Neubauer, whether obtained by precipitation of magnesium or of 

phosphate solutions. If the weights were not large the salt fused in 

part or wholly, and when this occurred reduction seemed to be rapid 

and the crucible was rather strongly attacked, as shown by its loss in 

weight after dissolving out the pyrophosphate. Presumably this 

effect was caused by a blast of higher temperature than that employed 

by Neubauer, who is very emphatic in his assertion that neither pure 

pyrophosphate nor crupible suffers the slightest loss when blasted for 

hours. This seems to be true with a blast of but moderate temperature, giving less than 1,100° in the crucible. What effect the presence of slight amounts of foreign phosphates may have in increasing 

the. fusibility of magnesium pyrophosphate is unknown. Jarvinen 

found that his precipitates obtained by the Gibbs method fused 

readily and gave too high results, and further that P2 05 did seem to 

volatilize slowly from Mg2P2 07 over the blast.

The practice of Fresenius and others of moistening the ignited 

pyrophosphate with a drop or two of nitric acid, evaporating, and 

again igniting, in order to insure obtaining a perfectly white precipitate, is open to objection. Chemical changes occur which invite loss 

during the final ignition.1

Still more objectionable is the procedure recommended by several 

authors, to dissolve the precipitate of magnesium-ammonium phosphate in nitric acid, to evaporate the solution in a platinum crucible 

and then to ignite carefully. The objections are that the effect of 

the nitric acid is far more pronounced than when the pyrophosphate 

is treated with a drop or two of nitric acid, and the final result is 

not pure pyrophosphate but a mixture of phosphates, one of which is 

probably a metaphosphate, as it is insoluble, or nearly so, in hydrochloric and nitric acid. However, the procedure affords a most deli1 Campbell, D., Phil. Mag., vol. 24, 1862, p. 380. Luck, E., Zeitschr. anal. Chemle, 

vol. 13, 1874, p. 225. Karaoglanow, Z., and Dimitrow, P., Zeitschr. anal. Chemie, vol. 

57, 1918, p. 353.
152 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

cate test for contamination by manganese, for if it is present a, pink 

color of varying intensity, according to the amount, becomes apparent as the mass approaches dryness.

0. CONTAMINATION BY AND REMOVAL OF BARIUM, CALCIUM, AND

MANGANESE. ' .

a. BARIUM.

Barium phosphate will not contaminate the second magnesian precipitate unless there are notable amounts of barium in the rock, in 

which case it must be removed by sulphuric acid prior to the final 

precipitation of the magnesium.

b. CALCIUM.

Calcium, however, is probably never absent, and must be. determined and allowed for as follows:

a. Preferred method. The ignited pyrophosphate is dissolved in 

a little dilute sulphuric acid and enough absolute alcohol is added to 

make about 90 to 95 per cent of the final volume. After several hours 

the sometimes almost invisible precipitate of calcium sulphate is 

brought onto a small filter and washed free of phosphoric acid with 

alcohol, dried, and dissolved in hot water slightly acidulated with 

hydrochloric acid. After rendering the solution ammoniacal and 

heating, a few crystals of ammonium oxalate are thrown in and the 

heating is continued till a precipitate becomes visible. In a short 

time it may be filtered, ignited, and weighed as calcium oxide. Its 

weight, averaging less than 0.5 mg<, is to be added to that of the lime 

already found and subtracted as tricalcium phosphate (not pyrophosphate) from that of the magnesium pyrophosphate, in order to 

arrive at a truer figure for magnesia. The alcoholic filtrate is to be 

evaporated, ignited to destroy organic matter, and tested for manganese, as under c below.

G. E. F. Lundell has shown (see 12. A. d. 8, p. 143) that this separation is satisfactory with amounts of 100 mg. of MgO and 1 mg. of 

CaO, but that it is incomplete with 1,000 mg. of MgO and 1 mg. 

of CaO.

(3. Alternative method. A less certain way to separate the calcium 

that is in the pyrophosphate, but one which admits of detecting 

small amounts of aluminum and iron that may have escaped precipitation earlier in the analysis, is the following:

To the ignited pyrophosphate dissolved in but slight excess of 

hydrochloric acid is added ammonia to alkalinity, and then acetic 

acid, drop by drop, till the solution, which should measure 10 to 30 

cm.3 and not be hot, clears. It happens now and then that a little 

flocculent matter fails to dissolve. This is to be removed, ignited,
 MAGNESIUM. 153

and subtracted from the original weight if proved to be free from 

magnesium, which it often contains. (See c, below.) It is likely to 

consist in great part or wholly of phosphates of aluminum, iron, 

or manganese, and shows often a reddish color on ignition. If an 

excess of acetic acid has been added, most of this is cautiously removed by ammonia. Then a drop or two of solution of ammonium 

oxalate is added, and the small beaker is set aside for 12 hours if 

necessary. Almost invariably a small precipitate shows itself, which, 

if fine grained and nonadherent to the glass, may be regarded as pure 

calcium oxalate; otherwise it contains or may consist largely of magnesium oxalate. In that case it is to be collected, ignited, redissolved, 

and reprecipitated. This separation, to be satisfactory, requires 

.great care.

C. MANGANESE.

A separation from one another of the iron, aluminum, and manganese which the flocculent precipitate mentioned under the second 

method in b may contain is not worth the trouble, careful prior 

treatment being presupposed. The first two constituents named may 

have been introduced since the original precipitation of the iron and 

aluminum, and their amount in terms of those elements is very small. 

But the amount of manganese it contains may be a sensible proper-. 

tion of the whole of that element if bromine or ammonium persulphate was not used to secure its removal earlier in the analysis. The 

precipitate should therefore be brought into nitric or sulphuric acid 

solution. The solution containing the magnesium is also manganiferous. It is to be evaporated to dryness, the volatile salts expelled 

by ignition, and the residue again evaporated two or three times 

with a few drops of nitric acid, or once with sulphuric acid, to certainly remoye all traces of chlorine, and united with the small 

solution above mentioned. The manganese is now determined colorimetrically, as in 11. C. b (p. 13Y), and its amount added to that 

already found, unless the total has been ascertained from a separate 

portion of the sample. In any case its amount, if significant, is to 

be deducted as pyrophosphate from the gross weight of the magnesium pyrophosphate.

The distribution of the manganese over the alumina, lime, and 

magnesia, when ammonia has been employed for the precipitation 

of the alumina and no attempt has been made to remove the manganese at all, is shown in the table on page 134.

D. LIABILITY TO ERROR IN THE AVERAGE MAGNESIUM DETERMINATION.

Experience has shoAvn that most analysts are prone to make a 

very serious plus error in determining moderate amounts of magnesia, such as are found in limestones and Portland cements. The
154 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

causes of this error will be sufficiently apparent after a careful 

perusal of the foregoing pages. Everyone ought to make the tests 

for foreign contamination just described, if only to convince himself 

of the reality of the error, even after very careful work.

14. TITANIUM. 

A. GENERAL CONSIDERATIONS.

Since the last edition of this work appeared the analytical study 

of titanium has received great attention, not so much from rock 

analysts as from steel-works chemists, with respect to both the ores 

and the metals and alloys derived from them. The same is true to 

a degree of zirconium. As zirconium is a very common though 

minor constituent of rocks and in - many of its chemical characteristics patterns after titanium, no presentation of methods of precipitation and separation of the latter can be made without frequent 

reference to the former, particularly when gravimetric methods are 

considered.

The analyst will welcome suggestions as to the relative values of 

the methods and as to the circumstances under which one is to be 

preferred to another, hence a few are offered in the following paragraphs.

When titanium and zirconium are unaccompanied by ether elements that would be precipitated, it is best to throw them out by 

ammonia. Otherwise, under favorable conditions the colorimetric 

method for titanium is believed to be the best and quickest for such 

amounts as are found in rocks. The favorable conditions referred to 

are absence of large amounts of iron and phosphorus, alkali salts, 

vanadium, and even traces of fluorine. The use of the colorimetric 

method when one or more of these are present in disturbing amount 

introduces so many complications that it is advisable to employ this 

method, whenever possible, only after the titanium has been separated from all interfering elements by one or another of the procedures given under 10. B, D, E (pp. 126-132). Under certain conditions, as in the absence of zirconium, it may suffice to weigh the 

titanium so separated, but generally the determination by color or 

by titration will be necessary. Which course to pursue the analyst 

will soon learn to decide when he has familiarized himself with the 

limitations and advantages of all the methods.

Of gravimetric methods, the Thornton or " cupferron " and the 

Baskerville methods, being much simpler than that of Gooch, seem 

likely to supersede it to a large extent. The interference of zirconium if present in more than traces also limits the usefulness of 

the Gooch method. The older method of precipitation by long boiling of a nearly neutral sulphuric solution need not be considered.
TITANIUM. 155

The volumetric methods have been so perfected that they may be 

regarded as eminently satisfactory in the absence of interfering 

elements. They have the great advantage of being applicable in 

the presence of iron and aluminum and are therefore likely to find 

most extended use in assaying ores and technical products.

In general it will be advisable to employ either the colorimetric 

or a volumetric method as the final test after separating interfering elements. The choice of a procedure will also be influenced by 

the purpose in view. If only the percentage of titanium is sought, 

a method may be acceptable which could not be introduced in a 

scheme for complete analysis.

The above remarks are predicated upon the assumption that it 

is titanium without regard to its state of oxidation that is to be determined. In almost all titaniferous minerals the element is beyond 'doubt in the quadrivalent state, corresponding to the oxide 

Ti02 . There is some reason to believe, however, that it may here 

and there be in the trivalent state, corresponding to the oxide Ti2O3 . 

The proof is fraught with almost unsurmountable difficulty at present, mainly because of the general occurrence of iron. Until we 

know how to ascertain if the element is present in the lower state of 

oxidation it would be premature to try to indicate analytical means 

of differentiating the two states of oxidation; hence the directions 

that follow assume the quadrivalent state.

B. COLORIMETRIC DETERMINATION WITH HYDROGEN PEROXIDE, 

a. PRINCIPLE OF THE METHOD (WELLER'S) 1 AND THE CONDITIONS THAT AFFECT IT.

The colorimetric method consists in comparing the color of a 

known bulk of solution to be tested with that of a standard solution of titanic sulphate, both having been fully oxidized by hydrogen 

peroxide. The strength of the peroxide should be approximately 

measured by titration with permanganate on opening a fresh bottle 

and again after a few weeks, otherwise very serious error may arise 

through its deterioration.

Mere traces of hydrofluoric acid or a fluoride in either the peroxide 

or the titanium solution render this method inexact by partly bleaching the yellow color,2 hence care should be exercised as to the 

character of the peroxide, of which the commercial brands often 

contain fluorine. (For methods of testing see p. 46.) For the same 

reason the peroxide should be free from appreciable traces of phosphoric acid. (See e. Y> P- 161.) The " perhydrol" of Merck is a 

most excellent preparation, though some commercial brands are satisfactory.

1 Ber. Deutsch. chem. Gesell., vol. 15, 1882, p. 2593.

2 Hlllebrand, W. F., Jour. Am. Chem. Soc., vol. 17, 1895, p. 718; Chem. News, vol. 72, 

1895, p. 158 ; Bull. U. S. Geol. Survey No. 167, 1900, p. 56.
156 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

Dunnington 1 has pointed out the necessity for the presence of at 

least 5 per cent of sulphuric acid in solutions which are to be thus 

tested for titanium, in order, as he concluded, to prevent partial reversion to metatitanic acid, which does not give a color with 'hydrogen peroxide. P. Faber 2 believes that failure to get full coloration 

in absence of excess of acid is not due to reversion, but to the presence 

of a weakly coloring basic sulphate of titanium. (See, however, below as to the effect of alkali sulphates.) He showed that the normal 

sulphate suffers loss of acid at moderate temperatures and that even 

in a bisulphate fusion it becomes basic. L. Weiss and H. Kaiser 3 do 

not accept Faber's explanation. Faber 4 explains the bleaching effect 

of phosphoric acid or a phosphate as due to the slow formation of a 

salt of the peroxide. The color can be partly restored by adding 

sulphuric acid.

If iron is present in the rock or mineral to the extent of several 

per cent, its color affects the result. (See e, p. 160.)

In the absence of fluorine the mineral constituents that are likely 

to be present in important amounts in the titanium solution undergoing test do not appear to exert any appreciable effect, according to 

George Steiger,5 but H. E. Merwin ° maintains that alkali sulphates 

bleach markedly unless much sulphuric acid is present. He -gives the 

following data:

Sulphate

(grams).

3

6

Acid

(cm. 8).

I 0.5

\ 2.0 

I 8.0

I 0.4

\ 2.9 

8.0

Bleaching

(per cent).

15

9 

2

21

14 

5

Now, since alkali sulphates are almost always present in the test 

solution as ordinarily prepared (9. C. a. (2, p. 120) in amounts up to or 

exceeding 6 grams, he concludes that all titanium determinations 

hitherto made by colorimetry are too low.

Merwin's statements as to the bleaching effect of alkali sulphates, 

both in presence and absence of fluorine, were confirmed by William 

Blum at the Bureau of Standards in 1909. Blum emphasizes in an 

unpublished memorandum the desirability of the preparation by the 

analyst of diagrams showing the corrections to be applied under his 

working conditions.

1 Jour. Am. Chem. Soc., vol. 13, 1891, p. 210.

2 Chem. Zeitung, vol. 31, 1907, p. 263.

3 Zeitschr. anorg. Chemie, vol. 65, 1910, p. 345. 

4 Zeitschr. anal. Chemie, vol. 46, 1907, p. 277.

5 Jour. Am. Chem. Soc., vol. 30, 1907, p. 219.

6 Am. Jour. Sci., 4th ser., vol. 28, 1909, p. 119.
. : TITANIUM. 157

Merwin also found that the color intensity is increased by increase 

of temperature.

In spite of the above observations the colorimetric method gives 

results that are probably fully equal to those attainable by the best 

gravimetric method and in much less time, for such percentages as 

are found in rocks, clays, and soils, usually under 1 per cent, but 

occasionally rising to 2 or even 3 per cent or more. Normally the 

error should not exceed 2 per cent over a Avide range of concentrations.1

b. PREPARATION OF THE STANDARD.

Potassium titanium fluoride, K2TiF6 , serves best as the starting 

point for the preparation of the standard solution. A quantity of 

this is recrystallized from boiling water one or more times, dried, 

and preserved in a glass-stoppered bottle. Enough of it to make 

one-half to 1 liter of a standard sulphate solution containing as 

nearly as may be 1 gram of Ti02 to the liter, is put into a platinum 

dish and evaporated several times with strong sulphuric acid without bringing to dryness, till the fluorine is completely expelled. The 

residue is then taken up- with water containing enough sulphuric acid 

to make at least 5 per cent of the latter when fully diluted. Two50 to 100 cm.3 portions of the prepared solution are then further 

diluted, boiled, and precipitated with ammonia. The precipitates 

are collected on paper, washed with hot water till free from alkali, 

ignited moist in the filter, blasted, and weighed. Duplicates should 

agree almost exactly. From the averages of the weights found the 

strength of the solution is calculated and the result affixed to the 

bottle containing it. T]he stopper of the bottle should be coated 

with vaseline and the needed quantities of solution should be withdrawn by a pipette, never poured. In a solution so prepared there 

is not enough alkali sulphate to weaken the color when peroxidized.

In making an analysis 5 cm.3 of the standard solution (or 10 if 

the larger amount is needed) is mixed with a sufficiency of hydrogen 

peroxide (2 cm.8 of 3 per cent reagent is ample for 10 cm.3 of the 

standard) and diluted with 5 per cent sulphuric acid in a measuring 

flask to 50 or 100 cm.3 , according to the original volume. Each cubic 

centimeter of the diluted standard will then contain nearly, if not 

exactly, 0.1 mg. of Ti02 .

C. THE TEST SOLUTION.

1. Titanium can be determined most conveniently, as a rule, in 

the solution which has served for the titration of total iron (9. C. a. 

(J, p. 120). The direct use of this solution involves, however, for

:1 Wells, R. C., Jour. Am. Chem. Soc.,'vol. 33, 1911, p. 501; Zeltschr. anorg. Chemie, 

vol. 70, 1911, p. 399.
158 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

accurate work corrections for its iron and alkali sulphate contents, 

and sometimes for vanadium, as given later. The effect of the alkali 

salt can be overcome by an ammonia precipitation, moderate washing 

of the precipitate, and its solution in 5 per cent sulphuric acid.

2. The error arising from the use of alkali sulphates can also 

be avoided by making the determination on some other portion of 

the rock powder than that indicated in the foregoing paragraph. At 

one time it was the practice in the Survey laboratory to combine it 

with the determination of barium, as described in Bulletin 148, by 

decomposing the powder by sulphuric and hydrofluoric acids,1 expelling the latter by repeated evaporations with sulphuric acid, taking 

up with dilute sulphuric acid,2 filtering from barium sulphate, etc., 

and estimating the titanium colorimetrically in the filtrate. The 

expulsion of fluorine must be thorough, or else the titanium result 

will be low7 , as already stated (p. 155), and it is not always easy to 

effect this complete removal, though the time required to do so seems 

to be in no slight degree dependent on the nature of the fluorides to 

be decomposed. Long after every trace of fluorine seems to be gone 

the formation of a crust on the evaporating solution sometimes allows 

an accumulation of enough hydrofluoric-acid gas to become plainly 

manifest to the smell on breaking the crust.3

3. Both the iron and alkali effects are excluded if the determination is made on the precipitate of TiO2 and Zr02 obtained by one 

of the methods given under 10. B, C, D, E (pp. 126-132).

4. The residue from an alkali-carbonate fusion of rock powder, 

which has been obtained as in 15. A (p. 170), can be used conveniently, 

either before or after separation of zirconium, (16. A, p. 173). Prior 

removal of zirconium is to be preferred for the reason that this is 

done in a small volume of solution, and with restricted acidity, 

"whereas the titanium is determined as a rule in a larger volume containing 5 per cent of sulphuric acid. The expulsion of most of this 

acid after determining the titanium, in order to bring the solution to 

the desired smaller volume, takes time, and to neutralize it with ammonia would produce a concentration of sulphate that might be objectionable in the subsequent precipitation of the zirconium. The 

conditions are such as to involve in the titanium determination a

1 It is to be borne in mind that evaporation with hydrofluoric acid alone results in 

loss of titanium by volatilization, but that there is no loss if excess of sulphuric acid is 

also present.

- With acid rocks solution is very complete, and it can be made nearly so with the most 

basic by transference to a small beaker and gentle boiling. The residue thus obtained 

may contain, besides barium sulphate, a little calcium sulphate, zircon, andalusite, topaz, 

and possibly a trace of titanium in some form. It is therefore to be fused thoroughly 

with sodium carbonate, leached with water, fused with potassium pyrosulphate, dissolved in dilute sulphuric acid, filtered, and the filtrate, added to the main one. The 

insoluble matter will now be chiefly barium sulphate, for the further treatment of which 

see 15. A, page 170.

3 See footnote on p. 90 for a procedure to facilitate the removal of fluorine.
TITANIUM. 159

correction for the iron of the rock, whether zirconium is first removed 

or not. If it is removed first, a further correction may have to be 

ntade for the alkali sulphate that results from the addition of the 

sodium phosphate used to precipitate the zirconium and also, possibly, for the phosphoric acid in the rock and that added. However, 

in most cases the amounts of sodium phosphate needed for two precipitations of the zirconium should not produce a sensible error in 

the value found for the titanium. The precaution should never be 

omitted, when determining the titanium here, to combine the two 

filtrates from the zirconium phosphate in order to find all the 

titanium.

The needs of the case or the convenience or preference of the 

analyst after he has acquired experience will determine which of the 

courses outlined in paragraphs 1-4 to pursue in determining titanium 

by colorimetry. Naturally, a procedure is to be preferred which will 

obviate the need for corrections, but in order to secure final conditions 

which satisfy this aim it were folly to run the risk of incurring other 

errors of uncertain and varying magnitude when it is possible, though 

perhaps troublesome, to apply corrections.

Even if no corrections are applied in rock analysis the error in the 

titanium value found is so small as to be of rather slight importance, 

especially if it. is known to be always in one direction. Of course, any 

error incurred involves an equal and opposite one in the value found 

indirectly for alumina.

Cl. THE COLOR COMPARISON.

The sulphate solution containing the titanium, having been evaporated, if necessary, to less than 100 cm.3 , is to be oxidized fully with 

hydrogen peroxide, and, if the color,is less intense than that of the 

standard, is made up to 100 cm.3 with dilute sulphuric acid in a 

measuring flask and mixed; otherwise, in a flask of sufficient size to 

insure that its color shall be less intense. The mixed solution should 

contain at least 5 per cent of the acid. One of the rectangular glasses 

(fig. 5, p. 36) being filled with the solution to be tested, 10 cm.3 of 

the diluted standard is run into the other from a burette, and sulphuric acid of 5 per cent strength is added from a second burette 

until there is no distinction as to color. The temperatures of test 

solution and standard should be alike. A second and a third portion 

of the standard can be run in and diluted and the mean of several 

determinations struck, when a simple calculation gives the percentage 

of TiO2 in the rock, the amounts in the two solutions being directly 

as their volumes, provided acid and interfering substances are present 

in each in like amounts.

If the convenient but expensive Soleil-Duboscq colorimeter is used, 

or the modification of Steiger or Schrener (figs. 6, 7, pp. 38,40), or the
160 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

simple Nessler tubes, it is of course unnecessary to dilute the rock 

solution to the extent above required, should it be stronger than the 

standard. Experience has shown, however, that differences can not 

be estimated sharply in strongly colored solutions,, and that the 

results are much more satisfactory when the color intensity is not 

much, if any, greater than that given by a diluted standard of the 

above concentration that is, 0.1 mg. Ti02 per cubic centimeter.

6. CORRECTION FOR THE COLOE OF FERBIC SULPHATE.

The error introduced by iron in consequence of the yellowish color 

of its sulphate solution, is practically negligible unless its percentage 

is high, say, over 5 per cent. Correction should be applied in one of 

the following ways:

a. By (Mowing for the coloring power of the iron in the test solitr 

tion. The color of ferric sulphate solution can not be matched closely 

by that of one containing titanium peroxide, but tests that have been 

made go to show that the coloring effect of 0.1 gram Fe2O3 in. 100 cm.3 

of 5 per cent sulphuric acid solution is about equal to 0.2 mg. of Ti02 

in 100 cm.3 when oxidized by hydrogen peroxide. This amounts to 

a correction of only 0.02 per cent on 1 gram of rock containing the 

unusual amount of 10 per cent Fe2 03 . The following methods are 

probably more exact with high iron percentages, though not so expeditious: 

P. By addition of iron to the slcmdard. W. A. Noyes x adds to the 

standard solution approximately, as much ferric iron as will give it, 

after the colors are matched, the same iron strength as the test solution. This could not be done with the apparatus depicted in. figs. 

6, 7 (pp. 38,40), though practicable with Nessler tubes. In using the 

Survey colorimeter (fig. 5, p. 36) it would perhaps be best to make first 

an approximate determination of the titanium in order to find the 

final volume of the standard after dilution and then to make an exact 

determination, having added to a fresh portion of the standard the 

requisite amount of iron salt.2 For all practical purposes it would 

probably be sufficient to add the. requisite amount of iron salt in 

solid form to the standard after having diluted it nearly enough to 

match the test solution, and after it has dissolved to proceed with 

the test. But this procedure has the disadvantage that each comparison would necessitate the weighing out of a separate portion of 

iron salt, whereas by the following method the number possible 

would be limited only by the stock of diluted standard and of prepared ferric sulphate solution which serves for its further dilution.

1 Jour. Anal, and Appl. Chem., vol. 5, 1891, p. 39.

2 Ferric-ammonium alum is most convenient for the purpose, but its use introduces an. 

error due to the bleaching effect of the ammonium suiphate it contains. The amount 

of this is, however, so small as to give rise to an error that is probably negligible.
TITANIUM. 161

The amount to be used per cubic centimeter of diluent is calculated 

as f ollows: Let A be the number of cubic centimeters of the test solution, a of the standard used, & of the water needed to dilute the 

standard in the preliminary test, p the weight of iron in terms of 

Fe2O3 in A, and as the weight of iron in terms of Fe2 03 to be contained 

in each cubic centimeter of water used for diluting the standard in

the final tests. Then a? = -^-i p. It will of course be understood Ab ^

that a new test solution req'uires the preparation of a new ir6n solution with which to dilute the standard.

Y. By the use of phosphoric acid. The color of a ferric sulphate 

solution is removed by addition of phosphoric acid. Several observers have, however, noticed that this acid greatly weakens the 

color of a titanium peroxide solution.. This is no objection to its 

employment in titanium colorimetry, provided a corresponding 

amount is also added to the standard that serves for comparison. 

It can be used as the acid or in form of an alkali salt,

A known amount, sufficient to decolorize the iron, is first added 

to the test solution before complete dilution, and the amount to be 

contained in each cubic centimeter of the water used in the final 

dilution of the standard can be found like the iron in (} above.

Both P. Faber,1 in the paper already cited on page 156, and J. H. 

Walton, jr.,2 have experimented with the method and report excellent 

results. Walton gives data showing the effect of increasing amounts 

of phosphoric acid in bleaching the titanium color, from which and 

from corroborative tests made in the Geological Survey laboratory 

it appears that with highly phosphatic minerals and ores their 

phosphorus content must be taken into account. The percentages 

of phosphorus in rocks are too small, even in extreme cases, to affect 

the color of the titanium that may be present when peroxidized.

f. COBEECTION FOR THE EFFECT OF ALKALI SULPHATES.

In order to correct for the bleaching effect of alkali salts, the 

standard may be diluted with alkali sulphate solution in the same 

manner as with ferric iron or phosphoric acid in e, (3 and Y 5 or Merwin's corrections 3 may be applied. These vary with the amounts 

of titanium in the solution, but

in rock analysis, by using 6 grams of pyrosulphate, which is equivalent to 4 

grams of normal sulphate, and 2 grams of acid for the melt containing the 

titanium, and dissolving this in water to which 10 cm.3 of strong sulphuric 

acid has been added, a nearly negligible correction of only 3 per cent need be

1 Chem. Zeitung, vol. 31, 1907, p. 263.

2 Jour. Am. Chem. Soc., vol. 29, 1907, p. 481.

3 Am. Jour. Sci. 4th. ser., vol. 28, 1909, p. 119.

131999° 19 11
162 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

added. If the titanium exceeds 0.02 gram, no correction is required. In case 

the melt is dissolved in 100 cm.3 of 5 per cent sulphuric acid, the titanium 

found if the amount is between 0.002 gram and 0.01 gram is too low by 

approximately 0.0004 gram.

g. CORRECTION FOB THE EFFECT OF VANADIUM.

As vanadium in acid solution gives a color with hydrogen peroxide, a correction for it may have to be made sometimes. It is, 

however, improbable that the amounts «of vanadium occurring in 

rocks are ever sufficient to influence in a disturbing degree the color 

due to the titanium. Should the unexpected case present itself, the 

best procedure would seem to be to precipitate the titanic oxide 

(alone or mixed with other oxides) to fuse with sodium carbonate, 

and, after extracting with water and filtering, to make the color 

determination on the residue brought into sulphuric acid solution.

J. W. Mellor, however, has devised a procedure for the colorimetric determination of titanium in the presence of vanadium. The 

method requires great care and is vitiated by the presence of more 

than traces of iron; hence, as occasion to use it will seldom arise, it 

will suffice to refer to the sources of information that are given in 

the footnote.1

C. GRAVIMETRIC METHODS.

a. GOOCH'S METHOD.

a. Description of the method. When titanium is present in excess 

of 4 to 5 per cent and whenever for any reason it is desired to employ 

a gravimetric method, that of F. A. Gooch 2 was for quite a time 

unequaled, provided zirconium is absent. It is applicable to any 

solution of the rock which is free from silica, and consequently to 

the mixture of oxides obtained according to the main procedures 

described in section 8. With one or two minor modifications introduced by T. M. Chatard 3 it is as follows:

After removing iron as sulphide (9. E, p. 124) the ammonium tartrate is to be destroyed, preferably by Thornton's procedure given 

under 10. B (p. 126), or as follows, according to Gooch:

Potassium permanganate to the extent of two and one-half times 

the weight of the tartaric acid used is made into a strong solution, 

and to the ammoniacal filtrate from the iron sulphide enough sulphuric acid is introduced to leave some excess after all the permanganate has been reduced. After expulsion of hydrogen sulphide by

iTrans. English Ceramic Soc., vol. 12, 1912-1913, p. 33. Mellor, T. W., Quantitative 

inorganic analysis, p. 486 ; Clay and pottery industries, vol. 1, 1014, p. 325.

2 Proc. Am. Acad. Arts and Sci., new ser., vol. 12, 1885, p. 435 ; Bull. U. S. Geol. Survey No. 27, 1886, p. 16; Chem. News, vol. 52, 1885, pp. 55, 68.

3 Am. Chem. Jour., vol. 13, 1891, p. 106; Bull. U. S. Geol. Survey No. 78, 1891, p. 

87 ; Chem. News, vol. 63, 1891, p. 267.
TITANIUM. 163

boiling, the permanganate is added gradually to the hot solution 

contained in a large beaker or flask. A vigorous reaction ensues. 

When a permanent brown precipitate of manganic hydrate appears, 

the tartaric acid has been fully broken up, and the precipitated manganese is to be redissolved by a few drops of ammonium bisulphite or 

of sulphurous acid solution.

Ammonia is then added in slight excess, followed at once by acetic 

acid in considerable excess, and the boiling is continued for a few 

minutes. Thereby the titanium is freed from most of the alumina, 

and from lime and magnesia if they had not been removed earlier, 

also from most of the manganese introduced. The precipitate is filtered and washed with water containing acetic and sulphurous acids, 

then ignited, fused thoroughly with sodium carbonate,1 and leached 

with water to remove phosphoric acid and most of the remaining 

alumina. The residue is again ignited and fused with sodium carbonate. To the cooled melt in the crucible strong sulphuric acid is to be 

added, wherein it dissolves readily by aid of gentle heat. This solution is to be poured into a small volume of cold water and the platinum it contains precipitated by hydrogen sulphide at or near boiling 

temperature. After filtering and cooling, ammonia is added till the 

titanium is just precipitated, and a measured volume, containing a 

known weight of absolute sulphuric acid, is then added just enough 

to redissolve the precipitate. The solution is then made up with 

acetic acid in such amount that the final bulk shall contain from 7 to 

11 per cent of absolute acid, and then enough solid sodium acetate is 

stirred in to more than take up the sulphuric acid introduced. On 

rapidly bringing the liquid to ebullition the titanium is precipitated 

in flocculent and easily filterable condition, and the precipitation is 

complete after a minute's boiling, provided all the prescribed conditions have been followed and zirconium is absent.

The precipitate is washed first with acetic acid of 1 per cent strength 

and then with hot water. After fifteen to twenty minutes' ignition 

over a good burner it is in condition for weighing and will lose no 

more weight over the blast lamp. . For large amounts of titanium a 

repetition of the sodium-carbonate fusion, etc., should be made. The 

actual carrying out of all these operations, when once the method is 

understood, requires much less time than the detailed description 

would indicate.

P. Goocfts method not directly applicable to rocks containing zirconium. Prior to the adoption of the colorimetric method, Gooch's 

was invariably used in the Survey laboratory. Occasional inability 

to secure clean and complete precipitation by it was experienced,

1 This operation will probably free the precipitate from any vanadium that may 

be present, which P. .T. Pope (Trans. Am. lost. Min. Bng., vol. 29, 1899, p. 372) says 

Is carried down with the titanium to some extent.
164 . ANALYSIS OF SILICATE AND CARBONATE BOCKS.

especially with a certain series of rocks rather poor in titanium. 

Long search showed the difficulty to be due to the presence of zirconium, which acts as a marked preventive of the precipitation of 

titanium by boiling in an acetic-acid solution under the conditions of 

the Gooch method.

The above rocks were found to contain up to 0.2 per cent of ZrO2 , 

and this amount was able to prevent precipitation of 0.3 per cent of 

TiO2 . The titanium which came down in excess of this amount did 

not settle out in flocculent condition, as happens when zirconium is 

not present, and it was difficult to filter. After the removal of the 

zirconium, however, in the manner to be hereafter described (16. A, 

p. 173), no difficulty was experienced in precipitating all the titanium 

with the usual ease.

b. THOBNTON'S METHOD.

a. Preliminary remarks. W. M. Thornton,1 in order to obviate the 

need of destroying the tartaric acid that the Gooch method calls 

for and the attendant introduction of a large amount of manganese, 

extended earlier work by himself and I. Bellucci and L. Grassi 2 so 

as to effect a very satisfactory separation of titanium from aluminum 

and phosphorus, after prior separation of iron according to 9. E 

(p. 124), and defined the requisite acidity and volume of the solution. 

His test results are excellent, and it seems as if the method might 

well supersede that of Gooch. Thornton's method has an advantage over Gooch's in that the operations are reduced in number and 

that zirconium is also precipitated quantitatively.3 Applying the 

method to zirconium, Thornton and E. M. Hay den 4 found that 

some phosphorus, if present, is precipitated with the zirconium. 

This observation has been confirmed by G. E. F. Lundell and H. B. 

Knowles at the Bureau of Standards, but they found that although 

in a 5 per cent sulphuric acid solution the error is appreciable, in one 

of 10 per cent strength it is of the order of only half a milligram 

when operating with a decigram or more of ZrO2 and 2 centigrams 

of P2O5 . Hence, considering the very small amount of zirconium 

that is usually encountered in rocks, it seems unnecessary to modify 

the method so as to exclude error from this source alone.

However, Lundell and Knowles found that vanadium is precipitated to a considerable extent in both the quadrivalent and quinquivalent states, more in the latter than in the former, that dissolved 

silica is appreciably precipitated with titanium and zirconium, and

1 Am. Jour. Sci., 4th ser., vol. 37, 1914, p. 407; Chem. News, vol. 110, 1914, p. 5; 

Zeitschr. anorg. Chemie, vol. 87, 1914, p. 375.

2 Gazz. chim. ital., vol. 43, pt. 1, 1913, p. 570.

3 Schroeder, K., Zeitschr. anorg. Chemie, vol. 72, 1911, p. 95

< Am. JQUF. Scl.; 4th ser., vol. 38, 1914, p. 137; Chem. News, vol. 110, 1914, p. 153; 

Zeitschr. anorg. Chemie, vol. 89, 1914, p.. 377.
TITANIUM. 165

that neither boron nor hexavalent uranium is precipitated. The 

procedure of Thornton therefore needs slight modification, as introduced below, in order to care at one stroke for possible errors arising 

from the presence of the interfering elements. According to I/undell 

and Knowles, thorium and cerium are precipitated partially, but 

in rock analysis these may be disregarded.

P. Procedure. To the filtrate from the iron sulphide (9. E, p. 124) 

is added about 40 cm.3 of sulphuric acid (1:1), and the hydrogen 

sulphide thus liberated is boiled out. After cooling to 10° to 15° 

the solution is made up with water to 400 cm.3 and a cold 6 per cent 

solution of "cupferron" (ammonium nitrosophenylhydroxylamine) 

is added slowly, with constant stirring. The beaker is set aside for 

the precipitate to settle, and the supernatant liquid is then tested by 

adding a few drops of the reagent. The formation of a white precipitate indicates that the reagent is in excess, whereas a yellow turbidity shows the precipitation to be incomplete. It is well also to 

test the filtrate. The precipitate is collected on a filter paper, using 

gentle suction, and washed 20 times with cold hydrochloric acid 

(made by diluting 100 cm.3 of acid of specific gravity 1.20 to 1 liter). 

After having been sucked dry at the pump, the precipitate and filter 

are dried completely in a platinum crucible at 110°. With the 

crucible not quite covered by the lid, the ignition is begun with a very 

small flame. After the first violent gush of smoke the heat is raised 

a little, when the destructive distillation will proceed quietly. When 

the carbon is burned off the residue is fused with sodium carbonate, 

the melt extracted with water, the solution filtered, and the insoluble 

matter washed with water containing a little sodium carbonate. 

The contents of the filter are dissolved in sulphuric acid and the precipitation by " cupferron " is repeated. From the finally purified 

and weighed oxides the zirconium can be separated and determined 

according to 16. A (p. 173), and the titanium measured by colorimetry, 

as in 14. B. d (p. 159), or either one can be determined and the other 

found by difference. In the latter case it is better to determine the 

zirconium rather than the titanium, as the former is usually present 

in very small amount and any slight error incurred in determining 

the titanium would throw a large relative error upon the zirconium.

Thornton and Hayden fuse phosphatic materials containing zirconium with sodium carbonate, leach with water, and apply the 

" cupferron " separation to the sulphuric acid solution of the residue.

Thornton's results seem to indicate that alkali salts are carried 

down with titanium (and presumably with zirconium) to a slight 

extent, and Lundell and Knowles have confirmed this indication. 

The error so caused will be very small, indeed, and usually negligible 

in rock analysis. When the contamination is likely to be of moment
166 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

the precipitate should be fused with sodium carbonate, the melt 

extracted with water, the residue washed and dissolved in acid, and 

the precipitation repeated, or preferably, perhaps, the titanium and 

zirconium should be precipitated first by ammonia, filtered, dissolved 

in sulphuric acid, and then precipitated by " cupferron."

James Brown 1 has described modifications of the "cupferron" 

method for separating zirconium, titanium, iron, manganese, 

and aluminum, which he applied to the analysis of zircon and 

baddeleyite.

c. BASKERVILLE'S METHOD.

The excellent method of Charles Baskerville for separating titanium and zirconium from iron and aluminum has been referred to 

in section 10, under E. a (p. 130). Baskerville says in the first of 

his papers:

If a neutralized solution of titanium and iron chlorides of not too great dilution be boiled with an excess of sulphur dioxide, the iron becomes deoxidized 

at once and a white flocculent precipitate of titanium separates out.

The method can be applied to a hydrochloric acid solution of one 

or more of the oxides obtained according to section 8 (p. 106). It 

has not been determined whether sulphur dioxide is necessary when 

iron is absent, but probably it is not, although it may assist to keep 

aluminum in solution. Phosphorus will accompany the titanium and 

zirconium if present, but can be removed by fusing the ignited precipitate with sodium carbonate and extracting with water. Either 

titanium or zirconium, or both, can then be determined in the insoluble salts, after filtering, by methods described above and also under 

"Zirconium" (p. 172) and "Phosphorus" (p. 177).

Cl. METHOD OF DITTRICH AND FREUND.

A method proposed by M. Dittrich and S. Freund has been 

described under 10 E. b (p. 131). In view of the required absence 

of aluminum, its use is restricted.

D. VOLUMETRIC METHODS.

a. .GENERAL CONSIDERATIONS.

Many writers have proposed or worked upon the development of 

volumetric methods for titanium, all based upon reduction of the 

titanium to the trivalent state. The probable reason why these 

methods did not receive at once extended recognition lies in the difficulty and uncertainty that attached to the procedure employed for 

effecting reduction and preventing premature reoxidation of the 

reduced titanium. The difficulty was overcome as to sulphate solu1 Jour. Am. Chem. Soc., vol. 39, 1917, p. 2358.
TITANIUM. 167

tions by passing the hot solution through a Jones reductor into a flask 

connected with a suction pump and kept filled with carbon dioxide, or 

into a solution of ferric sulphate in such a manner as to prevent all 

contact with air that is, by having the tip of the reductor long 

enough to reach beneath the surface of a solution of ferric sulphate 

in the receiving flask with which the reductor is connected. Which of 

these procedures to adopt depends upon the particular volumetric 

method that is to be used. Presumably the use of the reductor is 

permissible with methods that call for a hydrochloric acid solution 

of titanium.

P. W. and E. B. Shinier l were the first to use the reductor in determining titanium. They avoided contact of the titanous solution 

with air by keeping the flask full of carbon dioxide, and recommended 

an exceptionally long (36-inch) and very narrow (f-inch bore) reductor tube, filled with amalgamated zinc granules of sizes that pass 

a sieve of 10 meshes to the linear inch and remain on one of 20 meshes. 

Other workers have found that the ordinary and shorter form of 

reductor gives entire satisfaction, even without using carbon dioxide, 

when a titration method is to be used which permits collecting the 

titanous solution in one of ferric sulphate. It is only necessary that 

the tip of the reductor be made long enough to discharge the titanous 

solution beneath the surface of the ferric sulphate solution in the 

receiving flask.

The titanous and ferric salts react at once, with formation of ferrous sulphate equivalent to the titanium.

The volumetric methods have the great advantage that in general 

they are applicable in the presence of iron and aluminum. They can 

be used to best advantage in rock analysis on the ignited and weighed 

precipitate of the oxides of iron, aluminum, etc., or on the titanium 

that has been separated from the mixture in a more or less pure state 

by a gravimetric method. The only interfering elements likely to be 

present are vanadium and chromium, which can be removed by making a fusion with sodium carbonate and extracting the alkali chromate and vanadate with water.

In the following sections reference is made, as a rule, only to the 

later papers on the several subjects. Suffice it to mention, among 

earlier authors, F. Pisani,2 F. W. Hinrichsen,8 and H. D. Newton.4 

Hinrichsen reduced in hydrochloric acid .with a magnesium-zinc 

alloy (50-50) and titrated with ferric chloride solution.

For rock and mineral analysis it is probable that methods c and d, 

described below, will be found more convenient than method b.

1 Eighth Internal Cong. Appl. Chemistry, 1912, vol. 1, p. 445.

2 Compt. Rend., vol. 59, 1864, p. 298.

3 Chem. Zeitung, vol. 31, 1907, p. 738.

* Am. Jour. Sci. 4th ser., vol. 25, 1908, p. 130.
168 ANALYSIS OF SILICATE AND CARBONATE HOCKS.

. b. METHYLENE BL1TE METHOD. . .

Eva Hibbert 1 applied to the determination of titanium a volumetric method which had been worked out earlier by E. Knecht 2 for 

another purpose. B. Neumann and R. K. Murphy, 3 seemingly unaware of Hibbert's work, developed an essentially identical method. 

Oxidation of titanous chloride in an atmosphere of carbon dioxide 

by means of a standardized solution of methylene blue is the basis 

of the method. Knecht and Hibbert use a solution containing 

about 2 grams of methylene blue to the liter; Neumann and Murphy 

use one containing 3.9 or 7.8 grams, corresponding to 1 and 2 mg. of 

Ti respectively. The appearance of a blue color indicates complete 

oxidation of the titanium even in the presence of ferrous iron, which 

is not oxidized by methylene blue. The titanous solution is formed 

from the titanic by reduction with zinc and hydrochloric acid. The 

authors carry out the reduction in a flask, but a better way would 

seem to be to pass the titanic solution through a zinc reductor (see a, 

above) into a receiver filled with carbon dioxide.

The titration can be conducted hot in a strong hydrochloric acid 

solution. The end point is not sharp in nitric or sulphuric solutions. The method is applicable in the presence of silica, iron, and 

other basic metals, also of antimony, arsenic, and phosphorus, but 

molybdenum, vanadium, tungsten, chromium, and tin interfere.

The standardization of the methylene blue solution is made 

against a " commercial" titanous chloride solution, of which the 

titanium content must be determined by a gravimetric method or by 

titration with a standard solution of ferric alum. (See c, below.)

C. FERRIC ALUM METHOD.

A method quite equal to the foregoing, according to Knecht,4 and 

likewise applicable in the presence of silica, iron, and aluminum, is 

that of G. Gallo,5 based on the oxidation of titanous chloride by 

ferric alum in the presence of potassium thiocyanate as indicator. 

Knecht's titrating solution contains 14 grams of ferric alum and 

5 cm.3 of concentrated sulphuric acid in a liter and is standardized 

by permanganate, after reduction, or by titanous chloride.

The titanium-bearing material (according to Knecht), after being 

brought into hydrochloric acid solution, is first reduced by zinc and 

then titrated cold with the ferric alum solution.

iJour. Soc. Chem. Industry., vol. 28, 1909, p. 189.. See also Knecht, E., and Hibbert, 

E., New reduction methods in volumetric analysis, London, Longmans, Green & Co., 1910. 

2 Jour. Dyers and Col., vol. 21, 1905, p. 5. 

3 Zeitschr. angew. Chemie, vol. .26, pt. 1, 1913, p. 613. 

'Idem, p. 734. 

6 Atti Accad. Lincei, vol. 16, pt. 1, 1907, p. 325.
TITANIUM. ; 169

The Shimers (see a, above) say that when the reduction is effected 

in the long zinc reductor " the time required for complete reduction 

need not be more than 15 minutes." They proceed as follows:

The reductor is first washed out with hot dilute sulphuric acid, 

whereby the zinc is heated and the reduction is made more effective. 

The receiving flask is then filled with carbon dioxide, whereupon the 

reductor is connected and the hot sulphuric solution of iron and 

titanium is drawn through it, but not faster than by rapid dropping. Several portions of hot water containing a little sulphuric 

acid are passed through the reductor and then carbon dioxide is 

again introduced rapidly. Finally, when cool, at least 5 cm.3 of a 

saturated solution of. potassium thiocyanate is added and the titration with ferric alum is carried out. The end reaction is rather slow, 

and the solution must be added until a brownish color remains for 

at least a minute. With large quantities of iron the solution must 

be put twice, through the reductor.

Cl. PERMANGANATE METHOD.

The Shimers also titrate both iron and titanium with permanganate 

after reducing as described in the last paragraph, and in the same 

solution determine either the iron alone by permanganate after reducing the iron with hydrogen sulphide, boiling out the excess of the 

latter and cooling in an atmosphere of carbon dioxide (see 9. c, p. 119) 

or the titanium as in c, above.

This method has been used satisfactorily by the Shimers in cooperative analyses of the steels and irons that are issued by the Bureau 

of Standards as standards for analysis.

If titanium is the only reducible substance present, the operation 

is simpler, and it is preferable to let the reduced solution enter the 

receiving flask under the surface of a ferric sulphate solution. (See 

a, above.) In this case it is advantageous to add syrupy phosphoric 

acid to the ferric solution in order to obtain a sharper end point in 

the permanganate titration. This mixture may be prepared in advance by dissolving the sulphate and phosphoric acid in water in the 

proportion of 100 grams of the sulphate and 150 cm. 3 of the acid in a 

liter. The procedure as communicated .by James A.. Holladay, of 

the Electro-Metallurgical Co., is essentially as follows:

A reductor of the ordinary type having been washed out with 

dilute (2.5 per cent) sulphuric acid and water, the receiver is charged 

with 10 cm.3 of the prepared ferric solution, the reductor is inserted 

into the flask so that its tip enters the liquid, and connection is made 

with the suction pump. The stopcock of the reductor is then opened 

arid there are poured, in order, into the funnel of the reductor the 

following solutions: 100 cm.3 of warm sulphuric acid (2.5 per cent),
170 ANALYSIS OF SILICATE AND CARBONATE ROCKS,

the warm titanium solution (about 50 cm.3 in volume and containing 

10 per cent of sulphuric acid), 200 cm. 3 of the dilute sulphuric acid, 

and 50 cm.3 of water. The funnel of the reductor should be allowed 

at no time to become empty and the stopcock should be closed while 

some of the water still remains above the zinc.

A blank is run in the same way, except that 50 cm.3 of 10 per cent 

sulphuric acid is substituted for the titanium solution. The permanganate should be standardized against sodium oxalate, such as is 

furnished by the Bureau of Standards.

15. BARIUM (ZIRCONIUM, RARE EARTHS, TOTAL SULPHUR, CHROMIUM).

The five constituents barium, zirconium, rare earths, total sulphur, 

and chromium can be determined with great economy of time and 

labor in the same portion of rock powder, of which a 2-gram portion 

should be used, though if vanadium is to be looked for it will be 

best to determine it and chromium in a different portion (20. C, 

p. 185). It has been said (12. C, p. 145) that only in very exceptional 

cases will barium be found with the calcium and strontium after 

two or possibly three precipitations of the latter as oxalate, since 

it passes into the filtrates with the magnesium, whence it may 

be obtained as sulphate after removal of ammoniacal salts. Addition of some alcohol insures also the simultaneous recovery of traces 

of strontium if the rocks are very rich in it; but it is unsafe to 

regard the amount of barium thus separated from the magnesium 

as representing the total amount in the rock. It will almost always 

be found lower than the truth, probably for the reason that there are 

opportunities during the analysis for slight losses.

A. THE GENERAL METHOD.

Decomposition is effected by fusing the 2-gram portion" with sulphur-free sodium carbonate and an amount of niter insufficient to 

injure the crucible (0.5 to 1 gram), first over the Bunsen flame, then 

over the inclined blast, the crucible being fitted snugly into a hole 

in a disk of platinum foil or asbestos board (fig. 3, p. 34) to prevent 

access of sulphur from the gas flame. In case sulphur is not to be 

regarded, the niter and disk are omitted. After thorough disintegration of the melt in water, to which a drop or two of methyl or 

ethyl alcohol has been added for the purpose of reducing manganate, 

the solution is filtrated and the residue washed with a very dilute 

solution of sodium carbonate free from bicarbonate. This is to 

prevent turbid washings. A yellow color in the filtrate indicates 

chromium.

After reduction of the manganate by alcohol the filtrate contains 

silica, alumina, and all the other acid constituents except titanium,
BARIUM. . 171

also a very little iron, but the separation of these from the remaining 

constituents is not always quantitative, never so as to silica and 

alumina. The proportions of these two which go into the aqueous 

extract vary greatly according to their relative proportions in the 

original material and the amounts and character of the bases other 

than alumina. For instance, with alkali feldspars* much of each 

dissolves, but with pure kaolinite very little of either. With most 

rocks both filtrate and residue contain large amounts of both.

(For the further treatment of the filtrate see " Sulphur," 26. C, 

p. 231, and " Chromium," 19. B, p. 182.)

The residue is washed from the paper into a small beaker without 

removing the filter from the funnel and is digested with little more 

than enough warm.dilute sulphuric acid to effect solution of all soluble constituents (stronger acid may be used and in larger aniQimt if 

barium only is sought). If zirconium is to be determined, the amount 

of acid used at this stage and later should be measured, so as to permit control of the concentration given under 16. A. b (p. 173). A 

few drops of sulphurous acid are-added at the same time to effect 

solution of the brown hydroxide of manganese. There will remain 

undissolved more or less residue. Care must be taken not to digest so 

long with acid as to cause gelatinization of the dissolved silica. The 

liquid is passed through the original filter and collected in an Erlenmeyer flask of 100 to 150 cm.3 . The paper with its contents after 

washing is ignited, evaporated with hydrofluoric and sulphuric acids 

together, and the final residue taken up with a little hot dilute sulphuric acid. All the barium will remain undissolved, besides some 

of the strontium and perhaps a good deal of calcium. This is collected on a small filter and the filtrate added to the former one, which 

now contains all the zirconium and rare earths. (For its further 

treatment see 16. A, p. 173, and 17. A, p. 176.)

The residue last obtained is ignited and fused with sodium carbonate, leached with water, and the residue dissolved off the filter by 

a few drops of hydrochloric acid, from which solution the barium is 

thrown out by a large excess of sulphuric acid. A single solution of 

the ignited barium sulphate in concentrated sulphuric acid and reprecipitation by water suffices to remove traces of calcium which might 

contaminate it if the rock was one rich in calcium, and even strontium 

is seldom retained by it in quantity sufficient to give concern. Should 

this be the case, however, which will occur when the SrO and BaO are 

together in the rock in, roughly speaking, 0.2 and 0.4 per cent, respectively, the only satisfactory way is to convert the sulphates into 

chlorides and to apply to the mixture the ammonium-chromate method 

of separation (12. D, p. 145),
172 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Barium and strontium sulphates can be brought into a condition 

for testing spectroscopically by reducing for a very few moments the 

whole or part of the precipitate on a platinum wire in the luminous tip 

of a Bunsen burner, then moistening with hydrochloric acid and testing in the usual manner. This test should not be omitted.

The procedure outlined in the foregoing paragraphs for the determination of barium in silicate rocks and its separation from calcium 

and strontium is the one which long experience has shown to be best 

adapted for securing the most satisfactory results with a minimum 

expenditure of time.1 Even where no attempt is made to separate 

contaminating traces of strontium and barium one from the other, 

the error is usually of no great consequence, for an absolute error of 

even 25 per cent in a substance constituting only 0.1 or 0.2 per cent of 

a rock is ordinarily of small moment compared with the ability to 

certify to its presence with approximate correctness.

With such small amounts of barium as are usually found in rocks 

it is doubtful if Mar's method 2 for the separation of barium from 

calcium and magnesium by the solvent action of concentrated hydrochloric acid mixed with 10 per cent of ether on the chlorides could be 

conveniently applied here, although for larger amounts the method 

would seem to be accurate and easily executed. Moreover, it would 

probably not entirely remove contaminating strontium, and hence 

offers no advantage,

B. THE METHOD WITHOUT REGARD TO ZIRCONIUM AND SULPHUR.

If zirco°nium and sulphur are not to be looked for, the simplest 

procedure is to decompose the powder by sulphuric and hydrofluoric 

acids (see 14. B. c. 2, p. 158, under " Titanium ") and to complete the 

purification of the barium sulphate thus obtained in the manner described in the fourth paragraph of A, above.

16. ZIRCONIUM.

Zirconium is seldom looked for by chemists, though shown by the 

microscope to be one of the most constant rock constituents, usually 

in the form of zircon, in which occurrence its amount can be approximately judged and a chemical test rendered almost unnecessary; but 

sometimes it occurs in other minerals, and is then unrecognizable 

under the microscope. In most exceptional cases it may be present 

up to a few per cent of the rock, rarely reaches 0.2 per cent, and is 

usually much less than 0.1 per cent.

1 For details consult Hillebrand, W. F., Tour. Am. Chem. Soc., vol. 16, 1894, p. 83 ; 

Chem. News, vol. 69, 1894, p. 147.

2 Am. Jour. Sci., 3d ser., vol. 43, 1892, p. 521.
- ZIRCONIUM. - 173

A. AUTHOR'S METHOD.

a. PRELIMINARY REMARKS.

For its detection and estimation in such cases, or whenever a search 

for it seems called for, the following procedure, resulting from an 

attempt to use a method of G. H. Bailey,1 has been devised, which 

serves, when carried out with care, to detect with certainty the merest 

trace 0.02 per cent, for instance in 1 gram. The precipitant is a 

soluble orthophosphate.

The preliminary treatment of the rock powder has been fully given 

under " Barium" (15. A, p. 170), where the separation from barium 

has been described and also the concentration of the zirconia in a 

small amount of dilute sulphuric solution.

In earlier editions of this work the statement was made that the 

precipitation should be made in a solution containing only a small 

amount of sulphuric acid, probably not much more than 1 per cent. 

George Steiger 2 has shown, however, that precipitation is complete 

in presence of as much as 3 per cent of the acid, and more recently P. 

Nicolardot and A. Eeglade 3 have found that it is complete with even 

20 per cent of acid (by weight). This higher acidity has the advantage of preventing contamination of the precipitate by titanium, iron, 

and chromium. According to Nicolardot and Reglade separation 

from aluminum is complete with 10 per cent of acid.

G. E. F. Lundell, in studying the method at the Bureau of Standards, found that the composition of the precipitate is affected by the 

amount of precipitant used and by the manner of washing. With 

not less than 10 times the theoretical amount of precipitant the composition is uniformly such, after washing with ammonium nitrate 

solution, that on ignition it yields Zr2P2O7 , containing 46.3 per cent 

of ZrO2 . With less precipitant the composition is variable, although 

precipitation is complete if twice the theoretical amount is used. 

Lundell found also that washing with pure water extracts phosphorus. 

Nicolardot and Eeglade used in their tests 1 gram of ammonium 

phosphate, which they prefer to sodium phosphate, although the 

latter precipitates zirconium completely.

b. PROCEDURE.

To the solution, which should be in a small flask or beaker and 

contain about 20 per cent by weight of sulphuric acid, is added 

hydrogen peroxide to oxidize the titanium and then at least ten 

times the theoretical amount of a soluble alkali orthophosphate in

1 .Tour. Chem. Soc., vol. 49, 18S6, pp. 149, 481.

" .Tour. Washington Acad. Sci., vol. 8, 1918, p. 637.

3 Compt. Rend., vol. 168, 1919, p. 348.
174 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

water solution. The ammonium, salt is preferred. Ordinarily 1 

gram of the precipitant may be used. The solution is then kept 

tepid for 2 hours. If the solution bleaches after a time more, 

hydrogen peroxide should be added. Under these circumstances the 

zirconium is thrown out as phosphate and collects as a flocculent 

precipitate. If it can be assumed to be free from titanium and iron 

the precipitate may be filtered, washed thoroughly with water containing ammonium nitrate (5 per cent), ignited, and weighed as 

Zr2P2 07 (46.3 per cent Zr02 ). For the amounts of zirconium met 

with in rocks the phosphate may be ignited without special precautions, but if the amount is large, such as is obtained with ores of 

zirconium, marked decrepitation occurs, which makes it necessary 

to ignite up to a certain point in a tightly covered crucible. Even 

then slight loss may be suffered. (For the treatment of the filtrate 

see "Rare-earth metals," 17. A, p. 176.)

If there is reason to think that the precipitate is not pure it is 

collected on a filter, ignited, fused with sodium carbonate, and 

leached with water. The insoluble matter collected on a filter is 

washed, ignited, and fused with potassium or sodium pyrosulphate. 

The melt is dissolved in sulphuric acid of 20 per cent strength, a 

little hydrogen peroxide is added, and the precipitation with alkali 

phosphate is repeated. Naturally the volume of the solution should 

be gaged by the amount of the zirconium. For most rocks it need 

not exceed 20 cm.3 Titanium is now almost never present, and the 

zirconium soon appears as a colorless flocculent precipitate in a fit 

condition to be collected and weighed as phosphate.

If there is doubt of the precipitate having the normal composition, especially if large, or if the qualitative identification of zirconium is desired, the following procedure is in order. Fuse with 

sodium carbonate, leach, ignite, fuse with pyrosulphate, reprecipitate by ammonia, and weigh as Zr02. Certainty as to its identity 

can be had by again bringing it into solution, precipitating by ammonia, dissolving in hydrochloric acid,-evaporating to a drop or two, 

and testing with turmeric paper or by a microchemical reaction. 

With the very smallest amounts no color can be obtained by this 

turmeric-paper test, which, however, responds readily to as little as 

1 mg. of dioxide and with proper care for as small an amount as. 

0.3 mg. (H. N. Stokes). No element other than thorium is ever 

likely to contaminate the zirconium thus precipitated.

The above-described method is applicable to the separation of 

zirconium, if present, in the mixture of it and titanium obtained by 

the methods of Thornton (14. C. b, p. 164), of Baskerville (14. C. c, 

p. 166, and B, below), and of Dittrich and Freund (14. C. d, p. 166).
ZIRCONIUM. 175

In Bailey's experiments the precipitation was not made by addition of a phosphate but is said to be due solely to the hydrogen 

peroxide, the precipitate being a hydrated peroxide, Zr2 05 , or Zr03 .1 

My own efforts as well as those of others to secure a precipitate in 

acid solutions of zirconium sulphate by hydrogen peroxide alone 

have been unsuccessful, except in very concentrated solutions and 

with 30 per cent peroxide. The ability to obtain the zirconium free 

from phosphoric acid would certainly be a great improvement on the 

method described above.

B. OTHER METHODS.

G. Streit and B. Franz 2 claimed to secure complete separation of 

titanium from iron and zirconium by boiling the neutralized solutions of the sulphates with a large excess (50 per cent) of acetic acid. 

The method has been recommended from time to time, but without 

any data showing its value. The single separation made by Streit 

and Franz was far from perfect.

J. T. Davis 3 separated zirconium sharply from aluminum, though 

not from iron, by precipitation as an oxyiodate in a boiling neutralized solution of chlorides, but the method has not been studied 

further.

C. Baskerville 4 proposed a method for the separation of zirconium 

from iron and aluminum similar to his method for the separation of 

titanium from those elements (14. C. c, p. 166). It is based on the 

precipitability of zirconium by boiling the neutralized chloride solution for two minutes in presence of sulphurous acid, and seems to be 

excellent. As titanium is always present and is quantitatively 

thrown down also, the two would have to be separated by hydrogen 

peroxide and a soluble phosphate. No tests as to the availability of 

the method for separating the small amounts met with in rock analysis have been made, but M. Dittrich and S. Freund have used it successfully in slight modification for larger amounts (14. C. d, p. 166), 

and have also devised a method for the direct separation of zirconium 

from titanium by precipitation with ammonium salicylate.5

The ".cupferron" method of Thornton, as given under "Titanium" (14. C. b, p. 164), can be used also for the precipitation of 

zirconium alone or in company with titanium, but how accurate it is 

for the final determination of the very small amounts that occur in 

rocks is still to be ascertained.

J. D. Ferguson ° determines zirconium in ores and alloys by precipitation with either phenylhydrazine (see 10. D. a, p. 128) in hydro1 Chem. News, vol. 60, 1889, p. 6.

- .Tour, prakt. Chemie, vol. 108, 1869, p. 65.

:'Arn. Chem. Jour., vol. 11, 1889, p. 27.

4 Jour. Am. Cbem. Soc., vol. 16, 1894, p. 475 ; Cbern. News, vol. 70, 1894, p. 57.

c Zeitschr. anorg. Chemie, vol. 56, 1907, p. 344.

"Bug. and Min. Jour., vol. 106, 1918, p. 793.
176 ANALYSIS OF SILICATE AND CAKBONATE BOCKS.

chloric acid solution or with sodium phosphate in sulphuric acid 

solution (see A, above) and defines carefully the procedure in each 

method. He finds that results by the two methods agree well. He 

seems to have worked under conditions giving a precipitate of uniform composition by the phosphate method but takes no account of 

titanium in the phenylhydrazine method. If the ores he worked 

with held no titanium the last factor does not enter.

17. RARE-EARTH METALS OTHER THAN ZIRCONIUM.

If it is necessary to look for rare earths other than zirconia, the 

following procedures will prove satisfactory and not at all difficult.1

A. USUAL METHOD.

The filtrate from the zirconium phosphate (16. A, p. 173) or, if zirconium is not to be determined, the earlier solution (15. A, p. 170) is 

treated with excess of potassium hydroxide to precipitate the rare 

earths and ferric and titanic oxides, while retaining the silica and 

alumina in solution. After settling, the liquid is decanted and the 

precipitate is washed once or twice by decantation and slightly on 

the filter. The precipitate is washed from the paper into a small 

platinum dish, treated with hydrofluoric acid, and the liquid evaporated nearly to dryness. A little water with a few drops of hydrofluoric acid is added and the insoluble rare-earth fluorides (crude) 

are collected on a small filter held by a perforated platinum or rubber 

cone and washed with water acidified with the same acid. The precipitate is washed into a small platinum dish and evaporated to dryness with sulphuric acid, the paper being burned and added before 

expulsion of the acid. The sulphates are dissolved in dilute hydrochloric acid, the rare-earth hydroxides precipitated by ammonia, redissolved in hydrochloric acid, the solution evaporated to dryness, 

and the residue heated with a few drops of a solution of oxalic acid. 

Anything that may be present except the rare earths dissolves readily, 

these remaining as insoluble oxalates. If there is a doubt as to the 

complete separation of the alkaline earths the ignited oxalates may 

be dissolved in hydrochloric or nitric acid; precipitated by ammonia, 

redissolved in whichever one of the acids may have been used, the 

solution evaporated to dryness, the oxalates reprecipitated, ignited, 

and the resulting oxides weighed.

1 M. Dittrich (Ber. Deutsch. chem. Gesell., vol. 41, 1908, p. 4373) calls attention to 

the fact that ferric, aluminum, and chromic, as well as uranic compounds prevent 

precipitation of cerium and presumably other rare-earth metals as oxalate, unless a very 

large excess of the precipitant is used, but that with such excess precipitation is complete. Salts of these metals even dissolve cerium oxalate, but excess of oxalic acid or 

ammonium oxalate throws it out again. This behavior need hardly be considered in 

the procedures here given.
PHOSPHORUS. 177

The amounts are too small to permit separation into further 

groups, but the presence of cerium can be readily shown if a strongyellow color develops on heating the ignited oxides with strong 

sulphuric acid.

B. ALTERNATIVE METHOD.

, The rock powder is thoroughly decomposed by several partial 

evaporations with hydrofluoric acid, the transparent precipitate of 

silico-fluorides and of the fluorides of all earth metals except zirconium is collected on a platinum cone, washed with water acidulated 

by hydrofluoric acid, washed back into the dish or crucible, and 

evaporated with enough sulphuric acid to expel all fluorine. The 

filter is burned and the ash added. By careful heating the excess of 

sulphuric acid is removed and the sulphates are taken up by dilute 

hydrochloric acid. The rare earths, with perhaps some alumina, are 

then precipitated by ammonia, washed, redissolved in hydrochloric 

acid, and evaporated to dryness, then taken up with water and a 

drop of hydrochloric acid, and only enough ammonium acetate to 

neutralize the latter added, followed by oxalic acid (not ammonium 

oxalate, which would fail to precipitate thorium). In. this way as 

little as 0.03 per cent of rare earths has been found when working 

on not more than 2 grams of material.

18. PHOSPHORUS.

A. PRELIMINARY REMARKS.

It is sometimes possible to extract all phosphorus from a rock by 

simple digestion with nitric acid, but not always; hence the necessity 

for resorting to one of the longer methods of extraction detailed 

below. Whatever method is used great care is required in order to 

obtain accurate results.

Unless the utmost economy of material is called for it is unadvisable to determine the phosphorus in the mixture of oxides obtained 

as described in section 8, but an independent portion of the rock 

sample should be used. Furthermore, phosphorus should never be 

determined in any solution that has been obtained from a fusion with 

< alkali bisulphate or pyrosulphate, or after fuming with sulphuric 

acid, because these operations cause a loss of P2 05 (see second paragraph under 9. A, p. 115), either by volatilization (as metaphosphoric 

acid) or by reversion to metaphosphoric acid without volatilizing. 

In the latter event the subsequent treatment of the solution may not 

effect its complete retransformation to the orthophospha'te state, 

in which alone is the ordinary precipitation by'magnesia mixture 

applicable.

131999° 19 12
178 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

B._PROCEDURE WHEN MATERIAL IS AMPLE, 

a. WASHINGTON'S METHOD OF PRELIMINARY TREATMENT.

About 1 gram of rock powder is decomposed in a platinum dish or 

capacious crucible with dilute nitric and hydrofluoric acids. When 

all gritty particles have disappeared the solution is evaporated to 

dryness and reevaporated with nitric acid two or three times to 

decompose fluorides and silicofluorides to a considerable extent.1 The 

residue is treated on the bath with dilute nitric acid and eventually 

filtered from any undissolved matter. This last should be for precaution's sake always ignited, fused with a little sodium carbonate, 

extracted with water, and the extract acidified with nitric acid and 

added to the main solution. (For further treatment see c, below.)

b. ALTERNATIVE METHOD OF PRELIMINARY TREATMENT.

Fuse with sodium carbonate, separate silica by a single evaporation 

with nitric acid, treat the ignited silica with hydrofluoric and nitric 

acids, evaporate to expel hydrofluoric acid, repeat the evaporation 

with nitric acid alone two or three times, bring the small residue into 

solution by boiling with nitric acid and add it to the main portion.

C. SUBSEQUENT TREATMENT.

Add to the solution obtained in a or b ammonium nitrate and 

molybdate solution as ordinarily prescribed, and allow to stand at a 

temperature of not over 40° for 12 'hours, or until it is certain that 

precipitation is complete.

The precipitate is filtered on paper and washed with water containing 5 per cent ammonium nitrate and 1 per cent nitric acid, after 

which it is transferred by a jet of water to a small beaker, which is 

then placed under the funnel containing the filter paper. The paper 

is washed with dilute ammonia water and two or three times with 

pure water. If the ammonia is insufficient to dissolve the whole of 

the yellow precipitate in the beaker, more ammonia is added, and if 

a clear solution does not result the liquid is passed through the same 

filter in order to collect the insoluble matter.

The turbidity often observed on dissolving the precipitated and x 

washed phosphomolybdate in ammonia is due to a compound of 

phosphorus. If the addition of a small fragment of a crystal of 

citric or tartaric acid fails to dissolve it, this should always be fused 

with sodium carbonate, extracted with water, and the filtrate otherwise treated as above, in order to obtain the phosphorus in it.

1 The method as originally described in Washington's " Manual of the chemical analysis 

of rocks " has been modified by Washington and by me independently to the extent of 

doing away with the filtration of the precipitate of silicofluorides and fluorides before 

proceeding with the evaporation.
»:*- :' .. PHOSPHORUS. X>- - 179

Hydrochloric acid is added to the ammoniacal filtrate until the 

yellow precipitate begins to reappear and does not redissolve quickly, 

and then a slight excess of magnesia mixture. Ammonia is now 

added slowly with continuous stirring until the precipitation of magnesium-ammonium phosphate has been largely accomplished. About 

one-fifth the volume of strong ammonia solution is then added, and 

after a little further stirring the beaker is set aside for some hours. 

The precipitate is then collected on a paper filter and washed with 

ammonia solution of about 2.5 to 3 per cent strength (roughly, 1 

volume strong ammonia water to 9 volumes water).

If a reprecipitation is necessary, which will seldom be the case in 

rock analysis, the first precipitate of magnesium-ammonium phosphate is'not collected on a filter, but the supernatant liquid is decanted through the filter which is later to be used, the precipitate 

in the beaker is dissolved in a little hydrochloric acid, a drop or 

two of magnesia mixture is added, then ammonia, and the final precipitation is made as at first. (For ignition, etc., of the precipitate, 

see this subject under "Magnesium," 13. B, p. 150.)

Vanadium, if present, is not only precipitated with phosphorus by 

the molybdate reagent, but it renders the precipitation of the phosphorus incomplete. Further, the mixed precipitate is affected differently by wash solutions'than the pure phosphomolybdate. J. R. 

Cain and J. C. Hostetter 1 devised a method for.the determination 

of vanadium in steels which is based on the complete precipitation 

of vanadium \vith a large excess of phosphorus. An orange color of 

the phosphomolybdate betrays the presence of vanadium. However, in rocks the vanadium content is so low that ordinarily its 

effect may be disregarded. If the unexpected case should present 

itself works on steel analysis should be consulted, in particular a 

paper by J. R. Cain and F. H. Tucker,2 who effect perfect separation 

of the phosphorus after reducing the vanadium in a particular 

manner.

C. PROCEDURE WHEN MATERIAL IS SCANTY.

The following procedure admits of determining in the same portion not only phosphorus but also barium, iron, vanadium, chromium, and titanium, the last two either colorimetrically or gravimetrically, and is in large part extracted from a paper by T. M. 

Chatard.8

1 Tech. Paper Bur. Standards No. 8, 1913 ; Jour. Ind. Eng. Chemistry, vol. 4, 1912, p. 

250.

2 Tech. Paper Bur. Standards No. 24, 1913; Jour. Ind. Eng. Chemistry, vol. 5, 1913,

p. 647.

3 Am. Chem. Jour., vol. 13, 1891, p. 106; Bull. U. S. Geol. Survey No. 78, 1891, p. 87; 

Chem. News, vol. 63, 1891, p. 267.
180 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Silica is removed by hydrofluoric and sulphuric acids, excess of 

fluorine expelled 1 (6 A. a, footnote, p. 90), the residue brought into 

solution as far as possible with sulphuric or hydrochloric acid and 

hot water, filtered, the residue ignited, fused with sodium carbonate, 

dissolved in hydrochloric acid, and the solution, after precipitation 

of barium, added to the main one, which is now precipitated by 

ammonia to get rid of the magnesium salts usually present, and thus 

insure a cleaner subsequent fusion with sodium carbonate.

The precipitated A12 03 , P205 , Cr2 03 , Fe2 03 , Zr02 , and Ti02 are 

dissolved in hot hydrochloric acid and filtered into a large platinum 

crucible, the filter is burned and added, the solution evaporated to 

pastiness, a little water added to dissolve the salts, and dry sodium 

carbonate added in portions and stirred in thoroughly to prevent 

lumpiness in the fusion to follow, which is continued for half an 

hour. Addition of sodium nitrate is not necessary.

The fused mass is boiled out with water and filtered and the insoluble matter is washed with very dilute sodium-carbonate solution. 

In the residue iron and titanium can be determined by the methods 

already described.2 In the filtrate chromium can be determined 

colorimetrically if present in sufficient amount to give a pronounced 

color. (See 19. B, p. 182.) Afterward, or immediately if the chromium is not to be thus estimated, enough ammonium nitrate is added 

to react with all the carbonate, and the solution is digested on the bath 

till most of the ammonium carbonate is gone. Nearly if not quite all 

alumina is thus thrown out, carrying with it all the phosphorus. 

The precipitate is washed with dilute ammonium-nitrate solution till 

the yellow color wholly disappears, after which it is dissolved in 

nitric acid and the phosphorus thrown out by molybdate solution. 

The filtrate from the aluminum and phosphorus, containing chromium and most of the vanadium, can be treated as detailed in the 

following sections.

Tests made by G. E. F. Lundellat the Bureau of Standards have 

shown, that some of the vanadium is precipitated with the aluminum. 

Perhaps a second precipitation would reduce the amount to a negligible quantity.

19. CHROMIUM.

If vanadium is absent, or nearly so, as it is likely to be in those 

highly magnesian rocks (peridotites) which usually carry a good 

deal of chromium, the following separation and gravimetric method 

for chromium gives good and concordant results, but in the presence

3 The expulsion of fluorine should be made without excessive volatilization of sulphuric acid, so as to avoid loss of P205. (See 9. A, p. 116.)

2 See 9. C. b, pp. 122-123, concerning recovery of a small amount of iron that may have 

passed into the alkaline filtrate.
CHROMIUM. 181

of vanadium, and it is best generally to assume its presence, the 

colorimetric method should always be adopted.

A. GRAVIMETRIC METHODS, 

a. AUTHOR'S METHOD.

Having obtained chromium in solution as chromate and free from 

all else but a little alumina, as at the conclusion of the preceding 

section on phosphorus, proceed as follows:

Concentrate if necessary and add fresh ammonium sulphide, or 

introduce hydrogen sulphide. The chromium is reduced, and appears as a precipitate of sesquioxide mixed with the rest of the 

alumina. This precipitate is now treated, according to H. Baubigny,1 

by dissolving in nitric acid, evaporating nearly to dryness arid 

heating with strong nitric acid and potassium chlorate, finally evaporating to dryness to get rid of the acid. Oxidation is complete and 

very speedy. On dilution with cold water, sodium bicarbonate is 

added in slight excess, and after two or three hours the precipitated 

alumina is filtered off. From the filtrate the chromium is then 

^thrown out by fresh ammonium sulphide, redissolved, reprecipitated 

to free from alkali, and weighed.

b. JAKOB'S METHOD.

W. Jakob 2 recommends the following method for the precipitation of aluminum (and evidently of ferric iron, titanium, zirconium, 

and manganese) and its separation from chromium. To the hydrochloric-acid solution containing the equivalent of 0.1 to 0.2 gram of 

A12O3 and 20 to 100 cm.3 in volume, in an Erlenmeyer flask of 100 

to 300 cm.3 capacity, is added drop by drop a freshly prepared solution of sodium hydroxide (about 5 per cent strength) till the aluminum hydroxide formed redissolves. 'Avoid an excess. The solution 

is then boiled, and saturated bromine water is added, drop by drop 

at first in order not to lower the temperature of the solution too 

much and so'produce a slimy precipitate. Toward the end the bromine may be added faster until the solution remains red. The excess bromine is then boiled out, the liquid is filtered, and the precipitate is washed with hot water. Precipitate adhering to the glass is 

loosened by a little nitric acid and reprecipitated by ammonia. 

Some chromium is carried down with the aluminum but can be 

removed, after decanting, by boiling for a few minutes with water 

containing ammonium nitrate and ammonia. It is possible that a

1 Bull. Soc. chim., new ser., vol. 42, 1884, p. 291; Chem. News, vol. 50, 1885, p. 18. . 

3 Zeitscbr. anal. Chemie, vol. 52, 1913, p. 651. , .
182 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

little aluminum may be reclissolved by this treatment. The combined precipitates are ignited and weighed.

The chromium can be determined in the filtrate by applying the: 

treatment given under a, above.

Magnesium and zinc, if present, are partly precipitated with the 

aluminum. Jakob claims that small amounts of these can be removed by the treatment with ammonium nitrate and ammonia. In 

the presence of sulphates and borates the method is unsatisfactory.

B. COLORIMETRIC METHOD.

For the colorimetric method, which is very accurate and by far the 

quickest method 1 for determining chromium in rocks and pres where 

the amount does not exceed a few per cent, there is needed the aqueous extract of a sodium-carbonate fusion of the rock, (as obtained, 

for instance, in the manner explained under " Phosphorus," C, p. 179, 

or under A, above) in order to compare its color with that of a 

standard solution.

a. Preparation and strength of standard solution. This standard 

solution is made by dissolving 0.25525 gram or double that amount 

of pure potassium monochromate in 1 liter of water made alkaline 

by a little sodium carbonate. Each cubic centimeter then corre-0 

sponds to 0.1 or 0.2 mg. of chromic oxide (Cr2 03 ), in which condition chromium is usually reported in rocks and ores. It is probably 

inadmissible to increase the strength of the standard much above 

the higher of the figures given.

P. Preparation of the test solution. Before filtering the aqueous 

extract of the sodium-carbonate fusion a few drops of alcohol (ethyl 

or methyl) are added to destroy the color of sodium manganate. If 

the yellow color of the filtrate is very faint, concentration by evaporation will strengthen it, and less than 2 mg. of chromic oxide in-1 

gram of rock can then be determined exactly. For smaller amounts 

it is best to employ from 3 to 5 grams of powder and then to concentrate the chromium by precipitation by mercurous nitrate, as detailed in the next section under " Vanadium " (20. C, p. 185); otherwise it may be difficult or impossible, because "of the large amount of 

alkali carbonate present, to obtain a filtrate of sufficient]y small 

bulk to show a decided color.

If niter has been used in the fusion and the crucible has been at all 

attacked by it, a yellow coloration of the filtrate may be due to dissolved platinum, but neither the proportion of niter nor the temperai Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 20, 1898, p. 454 ; Chem. News, vol. 78, 

1898, pp. 227, 239 ; Bull. U. S. Geol. Survey No. 167, 1900, p. 37. First applied by L. de 

Koningh (Nederl. Tyds. voor Pharm., Chem. en Tox., 1889) for the estimation of chromium in foodstuffs.
CHROMIUM. 183

ture of the blast should ever be high enough to permit the crucible to 

be attacked. A passing yellowish coloration of the filtrate, due to 

this or some other cause,1 is not to be ascribed to chromium.

If it is desired to use the solution obtained as in either A. a or A. b, 

above, there will be no need to add alcohol, for manganese is absent.

Y. Comparison of colors. The final solution is transferred to a 

graduated flask, which is then filled to the mark with water. The 

flask should be of such size that the color of the oxidized solution 

shall be weaker than that of the standard chromium solution. Definite amounts of the latter are then diluted with water from a burette 

until of the same strength as the test solution, exactly as described 

on page 37. For very minute amounts it may be necessary to use 

Nessler tubes, as in ammonia estimations, instead of the glasses and 

apparatus there described and depicted.

As with colorimetric methods in general, this one gives better 

results with small than with large percentages of chromium, yet it 

can be applied in the latter cases with satisfactory results by making 

a larger number of consecutive comparisons with the same solution.2

C. COMPARATIVE DATA.

A few comparisons between colorimetric and gravimetric determinations of chromium are here given to show the order of agreement, 

the former having been made several months and even years after 

the latter. I 

Percentage determinations of chromium

Gravimetric.

Trace.

0.05

.14

.08

. Trace.

None.

None.

Colorimetric.

0.018

.051

.12

.083

.013

.0086

.0067

The outcome was somewhat surprising, for it was hardly to be 

expected that the long and laborious quantitative separations should 

have resulted so well. It should be mentioned that for the gravimetric tests but 1 or 2 grams at most were used, which accounts for 

the reported absence of chromium in two instances, this report being 

based on the lack of color in the aqueous extract of the alkali fusion 

after removal of manganese.

1 Consult McBride, R. S., and Scherrer, J. A., Jour. Am. Chem. Soc., vol. 39, 1917, p. 

928.

2 D. W. Horn has studied the " Variable sensitiveness in the colorinietry of chromium." 

See Am. Chem. Jour., vol. 35, 1906, p. 253; vol. 36, 1906, p. 196.
184 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

20. VANADIUM (CHROMIUM) AND MOLYBDENUM.

A. DISTRIBUTION OF VANADIUM AND MOLYBDENUM.

The wide distribution of vanadium throughout the earth's crust 

has been clearly established in recent years (see pp. 22-23), not only 

in ores and in coals, but in clays, limestones, sandstones, and igneous rocks.1 I have shown that vanadium occurs in appreciable 

amounts in the more basic igneous and metamorphic rocks up to 

0.08 per cent or more of V2O3 , but that it seems to be absent or nearly 

so from the highly siliceous rocks. Some of their ferric aluminous silicate constituents carry still higher percentages up to 0.13 

per cent V2Q3 in a biotite separated from a pyroxenic gneiss. Molybdenum, on the other hand, appears to be confined in quantities susceptible of detection to the more siliceous rocks, and except perhaps 

in rare instances is not present in them in quantitatively determinable amount when operating on 5 grams of material. Hence the quantitative search for vanadium will usually be limited to rocks with 

less than 60 per cent of silica. The search for it even then will 

perhaps not often warrant the necessary expenditure of time, but in 

this connection it is to be remembered that neglect to determine it introduces an error in the figures for both ferrous and ferric oxides, 

which in extreme cases may be of considerable moment. (See 9. C. b, 

p. 121; 21. D. c. 0, p. 202.)

B. CONDITION OF VANADIUM IN ROCKS.

The connection below and elsewhere mentioned of vanadium with 

the ferric aluminous silicates of rocks, taken in connection with the 

existence of the mineral roscoelite, classed as a vanadium mica, indicates that the vanadium corresponds in condition to aluminum and 

ferric iron, and that it is to be regarded as replacing one or both of 

these elements. Hence it should be reported as V2O3 and not as V2O5 .

What its condition may be in matter of secondary origin, like clays, 

limestones, sandstones, coals, and ores of iron, is yet open to discussion. It was my opinion at one time that it should be regarded as in 

the pentavalent state (V-jOg), but my work on certain remarkable 

vanadiferous sandstones 2 of western Colorado, in which it unquestionably occurs as trivalent vanadium (V2O3 ), has led to a decided 

unsettling of this view. It is proper to recall that C. Czudnowicz,3 

because of the extreme difficulty in completely extracting it from iron 

ores by an alkali-carbonate fusion and because of the easy reducibility of vanadic acid by ferrous salts, under the conditions in which 

brown iron ores are supposed to form, considered the vanadium in

1 Hillebrand, W. F. Distribution and quantitative occurrence of vanadium and molybdenum in rocks of the United States: Am. Jour. Sci., 4th ser., vol. 6, 1898, p. 209; 

Chem. News, vol. 78, 1898, p.. 216; Bull. U. S. Geol. Survey No. 167, 1900, p. 49.

2 Hillebrand, W. F., and .Ransome, F. L., Am. Jour. Sci., 4th ser., vol. 10, 1900, p. 

120; Bull. U. S: Geol. Survey No. 262, 1905, p. 9.

3 Poggendorff's Annalen, vol. 120, 1863, p. 20.
VANADIUM. . 1-85

such ores to be in a lower condition of oxidation (V2 03 ). 0. Lindemann's contrary conclusion * with regard to certain iron ores, because 

the vanadium was extracted as V2O5 by sodium-carbonate fusion 

without niter, is not valid, since this would probably be the case even 

if it existed in the ore as V2O3 .

c. AUTHOR'S METHOD.

a. DESCRIPTION OF THE METHOD.

In the following method there is nothing absolutely novel except 

that chromium and vanadium, when together, need not be separated, 

but are determined, the former colorimetrically, as already described 

(19. B, p. 182), the latter volumetrically, in the same solution.2

Five grams weight of the rock is thoroughly fused over the blast 

with 20 of sodium carbonate and 3 of sodium nitrate. After extracting with water and reducing manganese with alcohol it is probably 

quite unnecessary, if the fusion has been thorough, to remelt the 

residue as above, though for some magnetites and other ores containing larger amounts of vanadium than the generality of rocks this may 

be necessary, as Edo Claassen has shown.3 The aqueous extract is next 

nearly neutralized by nitric acid, the amount to be used having been 

ascertained conveniently by a blank test with exactly 20 grams of 

Bodium carbonate, etc., and the solution is evaporated to approximate 

dryness. Care should be taken to avoid overrunning neutrality, because of the reducing action of the nitrous acid set free from the 

nitrite produced during fusion, but when chromium is present it has 

been my experience that some of this will invariably be retained by 

the precipitated silica and alumina, though only in one case have I 

observed a retention of vanadium, it being then large. The use.of 

ammonium nitrate, instead of nitric acid, for converting the sodium 

carbonate into nitrate does not seem to lessen the amount of chromium 

retained by the silica and alumina.

As a precautionary measure, therefore, and always when chromium 

is to be determined also, the silica and alumina precipitate should be 

evaporated with hydrofluoric and sulphuric acids, the residue fused 

with a little sodium carbonate, and the aqueous extract again nearly 

neutralized with nitric acid and boiled for a few moments, the filtrate 

being added to the main one.

Mercurous nitrate is now added to the cold alkaline solution in 

some quantity, so as to obtain a precipitate of considerable bulk, containing, besides mercurous carbonate, chromium, vanadium, molybdenum, tungsten, phosphorus, and arsenic, should all happen to be in 

the rock. The mercurous carbonate serves to counteract any acidity

1 Dissertation, Jena, 1878, through Zeitschr. anal. Chemie, vol. 18, 1879, p. 99. 

' 2 Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 20, 1898, p. 461; Chem. News, vol. 

78, 1898, p. 295; Bull. U. S. Geol. Survey No. 167, 1900, p. 44. 

s Am. Chem. Jour., vol. 8, 1886, p. 437.
186 ANALYSIS OF SILICATE'AND CARBONATE ROCKS.

resulting from the decomposition of the mercurous nitrate. Precipitating in a slightly alkaline instead of a neutral solution Tenders 

the addition of precipitated mercuric oxide unnecessary for correct^ 

ing this acidity. If the alkalinity, as shown by the formation of an 

unduly large precipitate, should have been too great, it may be 

reduced by careful addition of nitric acid until an added drop of 

mercurous nitrate no longer produces a cloud.

After heating and filtering, the precipitate is ignited in a platinum 

crucible after drying and removing from the paper to obviate any 

chance of loss of molybdenum and of injury to the crucible by reduction of arsenic. The residue is fused with a very little sodium carbonate, leached with water, and the solution, if colored yellow, filtered 

into a graduated flask of 25 cm.3 or more capacity. The chromium is 

then determined accurately in a few minutes by comparing with a 

standard alkaline solution of potassium monochromate (19. B,p. 182). 

Then, or earlier in absence of chromium, sulphuric acid is added in 

slight excess, and molybdenum and arsenic, together with occasional 

traces of platinum, are precipitated by hydrogen sulphide, preferably 

in a small pressure bottle.1 If the color of the precipitate indicates 

absence of arsenic the filter with its contents is ignited carefully in 

porcelain, and the delicate sulphuric-acid test for molybdenum is 

applied as follows: The molybdenum compound is heated in porcelain 

with a single drop of strong sulphuric acid till the acid is nearly volatilized. On cooling the appearance of a beautiful blue color is proof 

of the presence of molybdenum. 

The filtrate, in bulk from' 25 to 100 cm.3 , is boiled to expel hydrogen sulphide, and titrated at a temperature of 70° to 80° with a 

very dilute solution of permanganate, representing about 1 nig. of 

V2 05 per cubic centimeter, as calculated from the iron strength of the 

permanganate, one molecule of V2O5 being indicated for each one of 

tFe2O3 . One or two checks are always to be made by reducing again 

by means of a current of sulphur-dioxide gas, boiling this out again,2 

and repeating the titration. The latter results are apt to be a very 

little lower than 'the first and are to be taken as the correct ones.

The cause of the difference was attributed to extraction of oxidizable matter from the paper, and this view has been confirmed by R. S.

1 From a sulphuric solution the separation of platinum and molybdenum by hydrogen 

sulphide is much more rapid and satisfactory than from a hydrochloric solution.

^ The direct use of a solution of sulphur dioxide or of an alkali sulphite is inadmissible 

unless these have been freshly prepared, for after a lapse of time they contain other, 

oxidizable bodies than sulphurous acid or a sulphite. The sulphur dioxide is best obtained 

as wanted by heating a flask containing a solution of sulphur dioxide, or of a sulphite to 

which sulphuric acid has been added.

The expulsion of the last trace of sulphur dioxide is said to be accomplished more 

effectively by boiling with simultaneous passage of a rapid current of carbon dioxide for 

a few minutes at the last than by boiling alone. Because of the small amount of air 

carried with it, long passage of the gas is said to result in slight oxidation of, the 

vanadium (Manasse, O., Ann. Chem. u. Pharm., vol. 240, 1887, p. 23; Zeitschr. anal. 

Chemie, vol. 32, 1893, p. 225.)
. - . :..... VANADIUM. . ... 187

McBride and J. A. Scherrer 1 in work undertaken at my suggestion at 

the Bureau of Standards. These authors found that the effect could 

be eliminated almost wholly by first passing as little as 25 cm.3 of 

water through the paper arid completely with a larger amount. The 

use of a platinum-felted perforated (Munroe) crucible should also 

eliminate the error.

b. CONFIKMATOBY QUALITATIVE TESTS.

In case the volume of permanganate used is so small as to make 

doubtful the presence of vanadium, it is necessary to apply a qualitative test, which is best made as follows: The solution is evaporated 

and heated to expel excess of sulphuric acid, the residue is taken up 

with 2 or 3 cm. 3 of water and a few drops of dilute nitric acid, and a 

couple of drops of hydrogen peroxide are added. A characteristic 

brownish tint indicates vanadium. Unless the greater part of the free 

sulphuric acid has been removed the appearance of this color is sometimes not immediate and pronounced, hence the above precaution. 

It is also necessary that the nitric acid shall be in considerable excess, 

since in a neutral or only faintly acid solution the color does not 

appear strongly.

The above is a surer test to apply than the following: Reduce the 

bulk to about 10 cm.3 , add ammonia in excess, and introduce hydrogen 

sulphide to saturation. The beautiful cherry-red color of vanadium 

in ammonium-sulphide solution is much more intense than that 

caused by hydrogen peroxide in acid solution, but the action of 

ammonia is to precipitate part or all of the vanadium with the chromium or aluminum that may be present or with the manganese used 

in titrating, and ammonium sulphide is unable to extract the vanadium wholly from these combinations. Usually, however, the solution will show some coloration, and addition of an acid precipitates 

brown vanadium sulphide, which can be collected, ignited, and 

further tested if desired.

C. APPLICATION OF THE METHOD IN PEESENCE OF BELATIVELY MUCH CHEOMIUM.

The application of the method in its foregoing simplest form is 

subject to one limitation the chromium must not be present above a 

certain moderate amount. This limitation is due to the considerable 

amount of permanganate then required to produce a clear transition 

tint when titrating in a hot solution, as is advisable with vanadium. 

In a cold solution of chromic sulphate much less permanganate is 

needed to. produce the peculiar blackish tint without a shade of green, 

which affords a sure indication of e,xcess of permanganate, but in a 

5 hot and especially a boiling solution the oxidation of the chromium 

itself takes place so rapidly that a very large excess of the reagent

1 Jour. Am. Chera. Soc., vol. 39, 1917, p. 928.
188 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

may be added before a pronounced end reaction is obtained. Nevertheless, fairly satisfactory determinations of as little as 1 or 2 mg. 

of vanadium pentoxide can be made in presence of as much as 30 mg. 

of chromic oxide. To accomplish this it is only necessary to apply a 

simple correction obtained by adding permanganate to a like bulk of 

equally hot chromic sulphate solution containing approximately the 

same^ amount of chromium.

C. H. Eidsdale x titrated the cold solution to avoid oxidation of 

chromium and obtained accurate results, but in my experience the 

end reaction is then uncertain.

The following tables contain the results of a considerable number 

of tests, those in Table 2 being tabulated separately in order to show 

the degree of accuracy attainable with a large excess of chromium by 

applying the correction mentioned above and also the amount of 

this correction:

TABLE 1. Tests for vanadium in the presence of chromium.

No.

1

2

3

4

5

6

7

Chromic 

oxide.

Milligrams.

1

1

1.5

2

3

3

3.5

Vanadium 

pentoxide.

Milligrams.

9.37

.94

5.25

5.62

4.68

5.62

18.74

Vanadium 

pentoxide 

found.

Milligrams.

9.22

1.04

.98

5.49

5.43

5.5

5.5

 4. 78

4.78

4.83

5.58

5.58

18.89

Error.

Milligram.

-0.15

+ .10

+ .04

+ .24

+ .19

- .12

- .12

+ .10

+ .10.

+ .15

- .04

- .04

+ .15

No.

7

8

9

10

It

12

13

14

15

Chromic 

oxide.

Milligrams.

3.5

6

6

6

10

10

10

25

87.5

Vanadium 

pentoxide.

Milligrams.

18.74

5.6

4.68

5.62

5.62

23.52

46.85

23.52

23.52

Vanadium 

pentoxide 

found.

Milligrams.

18.97 e:i

4.78

5.58

5.58-

23.81

23.71

46.98

47.20

23.65

23.75

23.71

Error.

Milligram.

+0.23

.+ .50

+ .10

- .04

- .04

+ .29

+ .19

+ .13

+ .35

+ .13

+ .23

+ .19

TABLE 2. Application of correction for larger amounts of chromium, obtained 

by adding potassium permanganate to an equal bulk of solution containing 

a like amount of chromic sulphate.

No.

16

17

18

19

20

21

Chromic 

oxide.

Milligrams.

20

20

20

30

30

62

Vanadium 

pentoxide.

Milligrams.

0.94

1.87

18.74

1.87

1.87

46.85

Vanadium pentoxide

found.

Uncorrected.

Milligrams.

1.59

2.69

2.39

2.59

19.4

19.3

19.3

2.99

2.79

2.79

2.69

2.69

2.69

2.89

2.89

2.79

48.90

Corrected.

Milligrams.

0.99

2.09

1.79

1.99

18.73

18.63

18.63

2.14

1.94

1.94

1.84

1.84

1.79

2.09

2.09

1.99

47.60

Error.

Milligram.

+0.05

+ .22

- .08

. + .12

- .01

- .11

 .11

+ .27

+ .07

+ .07

- .03

- .03

- .08

+ .22

+ .22

+ .12

+ .75

Volume of solution.

50 to 100 cm.'

50 to 100 cm.a 

50 to 100 cm."

About 100 cm.8

200 cm.a

200cm.s

1 Jour. Soc. Chem. Industry, vol. 7, 1888, p. 73.
FEKROUS IRON. 189

111 spite of the fact that the correction in most of the trials of this 

last table represents a large proportion of the permanganate used, 

the results must be considered satisfactory in view of the small 

amount of vanadium present, and they show that the method in competent hands after a little experience affords trustworthy figures.

The method of T. Fischer x digestion of the precipitated lead salts 

with a strong solution of potassium carbonate appears to offer the 

long-needed satisfactory quantitative separation of arsenic, phosphorus, chromium, tungsten, and molybdenum from vanadium, the 

normal lead metavanadate remaining quite unattacked, according to 

Fischer, while the .other lead salts are wholly decomposed, but the 

applicability of this method to the separation of the minute amounts 

often found in rocks and ores has not been tested. The object has 

been in the present case to reach satisfactory results with the greatest 

expedition, and when chromium is not present in considerable amount 

this is accomplished.

Fortunately chromium is almost never a prominent constituent of 

clays, coals, iron ores, and those rocks in which vanadium has thus far 

been reported, for although it is usually certain of the most basic of 

the silicate rocks that are highest in chromium as the peridotites 

yet in these, so far as present experience teaches, vanadium is lacking, 

a fact doubtless connected with the simultaneous absence from them 

of ferric aluminous silicates.

D. COLORIMETRIC METHOD FOR VANADIUM.

In the paper already cited 2 the possibility of a colorimetric method 

for vanadium, based on its behavior toward hydrogen peroxide, was 

suggested. L. Maillard 3 has since developed such a method, though 

it has not been tested in the Survey laboratory.

21. FERROUS IRON. o

A. OXIDATION OF FERROUS IRON IN MINERALS BY GRINDING PREPARATION OF SAMPLE.

As already pointed out under 3. C (p. 60), the effect of grinding 

in air is to lower the FeO and increase the Fe2O3 in a mineral powder 

that contains FeO.4 Of the latter 20 to 30 per cent or more may 

thus be caused to disappear by grinding steadily for two hours. 

Attempts to prevent this chemical change by grinding under water, 

alcohol, and carbon tetrachloride have been partly successful, buts 

not enough so to permit the substitution in general practice of one

1 Inaugural dissertation, Rostock, 1894.

~ I-Iillebrand, W. F., Jour. Am. Chem. Soc., vol. 20, 1898, p. 461; Chem. News, vol. 

78, 1898, p. 295 ; Bull. U. S. Geol. Survey No. 167, 1.900, p. 44.

3 Bull. Soc. chim., .vol. 23, 1900, p. 559.

* Cf. Mauzelius, R., Sveriges Geol. Umlersokning, Arsbok I, No. 3, 1907 ; Hillebrand, 

W. F., Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120 ; and Chem. News, vol. 98, 1908, pp. 

205, 215.
190 ANALYSIS OP SILJCATE^AND CARBONATE ROCKS.

of these media for air. Grinding in a wholly inert atmosphere, such 

as nitrogen (not carbon dioxide, which I find seems to. form car? 

bonates), might be successful in preventing oxidation in large part, 

if not wholly, but is quite impracticable for general work. That,it 

would not prevent taking up both loosely and firmly held water-on. 

subsequent contact of the powder with the air is certain, as such 

absorption is due to increased surface exposure. From the fact 

that oxidation is greatly lessened by grinding under one of the abovenamed liquids, even though the powder be then exposed to air, it 

follows that increased surface exposure is not the dominant factor 

in promoting oxidation, but probably local heating as the grains are 

fractured and rubbed under the pestle. The effect seems to be 

influenced also by the hardness of the iron minerals and those associated with them, and perhaps still more by the chemical nature of 

the iron-bearing molecules themselves.

The following table contains some selected and typical data, taken 

from the paper already cited,1 that show the effect on the FeO content of grinding different rocks under different conditions and also 

the comparative merits of the Pratt and Cooke methods of determining ferrous iron:

Effect of grinding on the ferrous-iron content of rock powders.

Material and maximum 

size cf grain of bulk 

sample.

Diabasic norite or gabbro. .

Altered basaltic greenstone, 0.18 mm.

Quartz diorite, 0.11 mm. . .

Altered basaltic rock, O.is 

mm.

Conditions of grinding.

No.

la 

Ib

1C

Id

2a 

2b 

2c 

2d 

2e

3a 

3b

3c 

3d

3e

4a 

4b

5a 

5b

ea 

6b 

7a 

7b 

7c 

7d

8a 

8b 

8c 

8cl

Grams.

Unground. 

4 

4

4

Unground. 

4 

4 

4 

4

Unground. 

4

4 

4

4

Unground. 

4

Unground . 

4

Unground. 

4 

Unground. 

4 

4 

4

Unground. 

4 

4 

(?)

Time (min1 utes).

30 

30

120

120 

120 

140 

120

20

60 

30

120

50

120

120

120 

30 

120

120 

30

(?)

Medium.

Abs. ale. 

Air.

Air.

Abs. ale. 

CC14 . 

H2 0. 

Air.

Abs. ale.

CCli. 

Air.

Air.

Air.

Air.

Air.

Abs. ale. 

Air. 

Air.

Abs. ale. 

Air. 

Air.

FeO (per cent) .

Pratt method.

7.03,7.07,7.09,7.11 

7.09,7.12,7.14 

7.01.7.07,7.08,7.16, 

7.18,7.23 

6.84,6.90

3.65,3.65 

3.47,3.49 

3.30,3.37 

3.40,3.43 

3.28,3.36,3.40

13.55, 13.35 

13.00,13.10,13.11, 

13.16,13.19 

12.88. 12.93 

12.91, 12.93, 13.06, 

13.07 

12.59, 12.66

3.32,3.34 

3.09

6.68 

3.64

2.58 

1.67 

2.08,2.09 

2.01,2.01 

2.04,2.07 

1.47,1.47

8.33,8.34 

8.11,8.14 

8.23 

5.74

Cooke 

method.

3.55,3.52 

3.40,3.49 

3.25,3.30 

3.36,3.38 

3.29,3.38

13.54 

13.11

13.06, 13.07

Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120 ; Chem, News, vol. QS, 1908, pp. 205, 215,
' - ' .. FERROUS IRON. 191

The experiments carried out by me show several things: (1) Although comparatively brief grinding (15 to 30 minutes) in air 

and long grinding under alcohol do not, as a rule, yield powders 

that are markedly oxidized (sometimes almost no oxidation seems 

to have taken place), this is not always so; hence grinding under one 

or the other of these media can not be recommended as a practice 

to follow at all times. The data for short and long grinding in the 

same enveloping medium are not strictly comparable, as the former 

was done by hand, the latter by a more effective mechanical process. 

(2) Alcohol, in spite of its greater solvent power for oxygen, seems 

to be a little more effective in preventing oxidation than water. It 

has the further advantage that it can be removed more quickly afterward. (3) Of the organic media employed alcohol seems to be 

more efficacious than carbon tetrachloride. (4) The effect of the 

presence of refractory iron-bearing minerals (garnet and others) is 

indicated by the rather wide variations in duplicate determinations, 

as shown under 1 and 3 of the table, when the material is not in a 

fine state of division. (5) The agreement that can be expected in 

duplicate determinations by either the Pratt or the Cooke method 

is excellent with fine powders or with coarse powders that yield 

readily to attack by hydrofluoric acid. (6) Inasmuch as powders 

so fine as to pass sieves of- 30 and even 60 meshes to the linear centimeter often show much less than 0.1 per cent of moisture if hydrous 

alteration products are absent it is reasonable to conclude that in 

their preparation there has been occasioned relatively as little oxidation, of ferrous iron as absorption of moisture, on the assumption 

that the small amount of water found results from the increased 

surface exposure due to crushing and is not inherent. Therefore if 

the powder is completely decomposed by hydrofluoric acid it is safe 

to assume that a determination of ferrous iron in it carried out with 

proper precautions will give a result close to the truth when other 

disturbing factors are not in evidence. (7) With different minerals 

very different degrees of oxidation are brought about under like conditions from a few per cent (Id) up to about 45 per cent (5b) of 

the FeO after several hours' grinding and it is not always the mineral that might a priori be regarded as most oxiclizable that shows 

most oxidation. (See paper cited.) Further, a soft or tough mineral undergoes greater oxidation if ground with a hard one than by 

itself alone.

It is plain that nearly all mineral analyses which have been made 

in the past ,are affected by more or less serious errors in respect not 

only to the oxides of iron but also to water, the error being greater 

the further the comminution of the sample was carried. Very many 

analyses show ferric iron in minerals that should apparently contain
192 ANALYSIS OF SILICATE AND CARBONATE ROCKS.;

none and small amounts of water for which there seems to be no 

place in any probable formula. These are discordances for which a 

simple and in most cases probable explanation is now offered. A 

revision of much past analytical work, particularly that relating to 

iron minerals, is called for, but before it can be properly done adequate provision must be made to avoid the old errors. In the paragraphs following are set forth the procedures that seem best adapted 

to attain this end in the light of present experience. Much routine 

and experimental work, must, however, yet be done before rules to 

fit all cases can be formulated. It is perhaps advisable to add here, 

in order to prevent misconception, that the errors in past work are 

not as a rule to be assumed equal to those in the above table that 

resulted from grinding for two hours or more, for few, if any, 

analysts have made it a rule to grind for such a length of time.

The mineral powder that has been prepared by crushing without 

grinding (3. B, p. 57) serves as the starting point. If trial shows 

that gentle boiling of it for 20 minutes with hydrofluoric acid leaves 

no residue or but little, this sample is to be used directly for the 

ferrous iron determination. If the residue is considerable, a weighed 

portion (0.5 to 1.0 gram) of the sample is to be ground with absolute alcohol in a large agate mortar only long enough to yield a 

powder that will leave little or no residue.' The alcohol is then to be 

allowed to evaporate spontaneously, and when the last trace has

' disappeared the powder is to be transferred to a platinum crucible of 

80 to 100 cm.3 capacity, the powder which may adhere to the mortar 

and pestle being also transferred by the aid of a fine jet of hot water. 

The! subsequent operations are given under the respective methods (D, 

below), which are those involving decomposition by hydrofluoric 

acid. The Mitscherlich method (C, below) requires in almost every 

case a very fine powder. For this and other reasons that method 

finds little application. For the same reason the modifications of the 

hydrofluoric acid method that require a powder of considerable fineness (D. d. (i, f, 8) will be less applied than the one (D. d. a) which 

permits the use of a relatively coarse powder. If a very fine powder 

must be employed, there seems to be no way known at present of correcting for whatever oxidation may have taken place during grinding. 

It will be preferable in such cases to grind under alcohol a small 

weighed portion of' the coarse sample, instead of grinding a large 

portion and taking from this an aliquot part, the reason being that 

in the latter case separate determinations of both loosely and firmly 

held water must be made in order to be able to correct the FeO found 

for the considerable weight of water taken up during grinding (4. B,

 p. 69).
FEKBOUS IRON. 193

B. COMPARISON OF SEALED-TUBE AND HYDROFLUORIC-ACID METHODS 

COMPARATIVE WORTHLESSNESS OF THE FORMER IN ROCK ANALYSIS.

No point in rock analysis has been the cause of greater solicitude 

to the chemist, and especially to the mineralogist and petrographer, 

than the determination of iron in ferrous condition. The sealed-tube 

or Mitscherlich method with sulphuric acid, for a long time the 

only available one, is in theory perfect, since complete exclusion of 

oxygen is easily attainable. Its earliest recognized defect lies in the 

inability to secure always complete decomposition of the iron-bearing 

minerals, and even to ascertain, oftentimes, whether or not the 

decomposition has been complete. The addition of hydrofluoric 

acid to the sulphuric in the tube, in order to insure this breaking up, 

is to be regarded as of very doubtful utility in most cases, since the 

glass may be so strongly attacked as to add an appreciable amount 

of iron to the solution, and the hydrofluoric acid may have exhausted 

itself in attacking the glass before the more refractory minerals 

succumb. Nevertheless, if decomposition can be effected by sulphuric acid alone the results obtained are sharp and concordant; 

but they are in rock analysis usually higher than when made by 

any of the modifications of the hydrofluoric-acid method now so 

extensively practiced. This difference is not very marked with rocks 

containing but 1 or 2 per cent of ferrous iron, but it increases with 

rising percentage to such an extent that where the sealed-tube method 

will show 12 per cent ferrous oxide the other may indicate no more 

than 10 per cent. This is a fact of which I have long been cognizant, 

but it seems not to have been known to chemists or petrographers at 

large, though E. A. Wulfing 1 noticed this difference in certain 

analyses without appreciating its significance. Experiments with 

soluble iron salts of known composition, like ferrous sulphate and 

ferrous-ammonium sulphate, throw no light on the subject, for both 

methods give with them the same sharp and accurate results.

The key to the problem was discovered by L. L. de Koninck 2 a 

good many years ago but remained unknown to the chemical world 

by reason of its obscure medium of publication until rediscovered 

by H. N. Stokes in the Survey laboratory during an investigation on 

the action of ferric salts on pyrite and other sulphides.3 That 

oxidation of the sulphide and reduction of the ferric salt hereby 

takes place was also recognized by J. H. L. Vogt,4 but not the ease 

with which the change takes place and the completeness of the 

oxidation of the pyrite, not only- of its iron but of the greater part 

of the sulphur as well. Pure pyrite itself is attacked with extreme

1 Ber. Deutsch. chem. Gesell., vol. 32, 1899, p. 2217, footnote.

2 Ann. Soc. ge"ol. Belgique, vol. 10, 1882-83, p. 1.01; Zeitschr. anorg. Chemie, vol. 

2G, 1901, p. 123.

3 Bull. U. S. Geol. Survey No. 186, 1901; Am. Jour. Sci., 4th ser., vol. 12, 1901, p. 414. 

* Zeitsclir. prakt. Geologic, 1899, pp. 250-251.

131999° 19 13
194 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

slowness by boiling dilute sulphuric and hydrofluoric acids, either 

alone or mixed, but the moment a ferric salt is introduced the case is 

altogether different.

The complete solution to the problem was afforded by the observation made in the Survey laboratory that rocks with hardly an exception and many minerals carry pyrite or pyrrhotite, or both, often in 

considerable amount, often in traces only. Sulphur can almost 

always be detected in 2 grams of rock powder.

Experiment has shown (D. c. a, p. 201) that with the amounts of sulphides usually found in igneous rocks their effect on the estimation 

of ferrous iron by the hydrofluoric-acid method at atmospheric 

pressure and boiling heat is negligible, though by increasing the 

amount of sulphide the effect becomes more and more apparent, 

because of the greater surface of pyrite exposed to the action of the 

ferric iron of the rock.

Under the conditions of the Mitscherlich method, on the other 

hand a temperature of 150 to 200°, and even higher, high pressure, 

much longer time of action, and impossibility of escape of any hydrogen sulphide that may be formed the sulphur of the sulphides 

becomes nearly if not fully oxidized to sulphuric acid at the expense 

of the ferric iron in the rock, with the production of an equivalent 

amount of ferrous iron in addition to that resulting from the sulphide 

itself.

Let us now see what the effect of these traces of sulphides when 

fully oxidized amounts to. One atom of sulphur (32) requires for its 

complete conversion to trioxide the oxygen of three molecules of 

ferric oxide (480), which then becomes 6 molecules of ferrous oxide 

(432). In other words, 0.01 per cent of sulphur may cause the ferrous 

oxide to appear too high by 0.135 per cent, and 0.10 per cent of sulphur may bring about an error of 1.35 per cent in ferrous oxide. The 

case is still worse if the sulphur is set free as hydrogen sulphide from 

a soluble sulphide, for then the above percentages of sulphur produce 

errors of 0.18 and 1.8 per cent, respectively, in the ferrous oxide 

determination.

The error caused by sulphides tends to become greater the more 

there is present of either or both sulphide and ferric salt. Now, the 

highly ferruginous rocks usually carry more ferric iron than the less 

ferruginous ones, and they are often relatively high in pyrite and 

pyrrhotite; hence the increasing discrepancy between the results by 

the two methods as the iron contents of the rocks rise is fully in 

accord with the above explanation. 1

1 For details of experiments showing the worthlessness of the Mitscherlich method for 

rocks and minerals which contain even a trace of free sulphur or sulphides, see Hillebrahd, 

W. P., and Stokes, : H; N., Relative value of the Mitscherlich and hydrofluoric acid methods 

for ferrous-iron determinations: Jour. Am. Chem. Soc., vol. 22, 1900, p. 625; and 

Zeitschr. anorg. Chemie, vol. 25, 1900, p. 326.
FERROUS IRON. 195

Of course carbonaceous matter will, under the conditions of the 

Mitscherlich method, likewise reduce sulphuric acid ai^d cause the 

determination of ferrous iron to be fault}*".

Notwithstanding the fact that the Mitscherlich method has thus 

been discredited in its general applicability to rocks and minerals, 

it is still probably the best with those which are totally free from 

sulphides and wholly decomposable. Hence the conditions under 

which success can best be achieved by it are set forth in the following paragraphs.

C. THE MODIFIED MITSCHERLICH METHOD.

a. Strength of acid. The method in its original and usual application calls for a mixture of 3 parts of sulphuric acid and 1 of water 

by weight, or about 3 to 2 by volume, though a still stronger acid is 

sometimes used. In some cases, however, perhaps in most, much 

better decomposition of the silicates is effected by reversing the proportions of water and acid, or at any rate by diluting considerably 

beyond the above proportion. Hereby the separation of salts difficultly soluble in the stronger acid is avoided and the actual solvent 

effect on the minerals seems to be in no wise diminished.

(3. Filling, sealing, and heating of the tube. The very finely powdered mineral having been introduced into a tube of resistant glass 

free from ferrous iron, the open end is drawn out, so as to leave a 

funnel for the introduction of the acid. A very little water is then 

introduced and carefully heated to boiling for a moment to expel 

all air from the powder. The diluted acid which has just been 

boiled down from a state of greater dilution in order to have it free 

from air is then poured in until the tube is about three-fourths 

filled. Carbon dioxide free from hydrogen sulphide is then introduced, from a generator which has been in active operation for some 

time, through a narrow glass tube drawn out of the same kind of 

glass as that of which the decomposing tube consists. In a few 

moments the air is expelled, and the small tube is then sealed into 

the large one over the blast lamp without interrupting the gas current until the very last instant, when to prolong it would perhaps 

cause a blowing out of the softened glass. The interruption of the 

current at the proper moment is easily effected by the pressure of the 

thumb and finger holding the small tube at the point where it enters 

the rubber tube leading from the gas generator. No breakage in 

the oven ever occurs as a consequence of thus fusing one tube into 

the other.

The heating is done in a bomb oven at any desired temperature 

up to, say, 200°, and continued at intervals until examination by aid
196 ANALYSIS OF SILICATE. AND CARBONATE ROCKS.

of a low-power lens shows that decomposition is complete or has 

progressed as far as can be hoped for. By inclosing the glass in an 

outer tube of strong steel, properly capped 1 and containing a little 

ether or benzine to equalize the pressure on both sides of the glass, 

the temperature can be elevated far beyond what is otherwise permissible, and the decomposition will then doubtless be more complete 

with refractory silicates.

f. Reason for introducing gas and sealing as above directed. The 

usual practice in employing the above method has been to expel air 

 before sealing by introducing a few crystals or lumps of an alkali 

carbonate or bicarbonate, the gas set free on their contact with the 

acid being supposed to effectively expel all air. That this is not 

accomplished the following series of comparative results, long since 

published elsewhere,2 fully shows. The material used was the oxide 

of uranium U308, requiring by theory 32.07 per. cent of U02. 

Operating as just described on from 0.3 to 0.5 gram, the results were

31.06, 31.07, 29.72, 29.33, 29.89, 30.69,

whereas after filling the tube with gas from a generator there was 

found

32.11, 31.90, 32.15, 32.12, 32.06, 32.17, 32.28,

the average error of the former series being 1.78 per cent. The percentage error would, of course, be reduced by increasing the weight 

of mineral operated on. An average error equal to the above when 

employing 1 gram of ferrous minerals would make the percentage 

for FeO about 0.3 per cent too low. While the absolute error might 

be the same in all cases, the relative error would increase with minerals low in ferrous iron.

D. THE HYDROFLTJOKIC-ACID METHOD.

a. PRINCIPLE OF THE METHOD.

The hydrofluoric-acid method consists simply in securing complete 

decomposition of the powder in absence of air by means of hydrofluoric acid in presence of sulphuric acid, and titrating the ferrous 

iron in the resulting solution. It is the one which has been used almost exclusively in the Survey laboratories. The form of apparatus 

employed for a long time was the original one devised by J. P. Cooke 3 

(fig. 19, p. 205). But the method as ordinarily carried out is subject to

1 Ullman, C., Zeitschr. angew. Chemie, 1893, p. 274; Zeitschr. anal. Chemie, vol. 33, 

1894, p. 582.

2 Bull. U. S. Geol. Survey No. 78, 1891, p. 50 ; Chem. News, vol. 64, 1891, p. 232.

3 Am. Jour. Sci., 2d ser., vol. 44, 1867, p. 347.
FERROUS IRON. 197

two defects of opposite sign but unequal value, the second and greater 

of which long remained unsuspected. 1

It is possible to titrate ferrous iron in presence of sulphuric acid 

and as much as 5 to 7 cm. 3 of 40 per cent hydrofluoric acid in a total 

volume of 200 to 400 cm.® almost if not quite as exactly as in sulphuric acid alone, provided the iron solution is diluted with air-free 

water and the titration is made immediately after adding the 

hydrofluoric acid and with all possible dispatch. This condition 

can not be fulfilled in practice, because the mineral must be in 

contact with the acid for a long time in the apparatus commonly 

employed, and it seems to be almost impossible to prevent some 

oxidation during this period.

b. DEFECTS OF THE METHOD.

a. Oxidizability of divalent manganese by permanganate in the 

presence of hydrofluoric acid. Manganic fluoride in dilute solutions 

is hardly at all dissociated, wherein it differs from manganic sulphate. 

The entering of the manganic ion as fast as formed into the undissociated state or into a complex ion 2 explains the fact that in the presence 

of hydrofluoric acid divalent manganese is oxidized readily by permanganate, whereby a sharp end reaction is rendered unattainable 

in the presence of much hydrofluoric acid, say over 7 cm.3 of 40 per 

cent acid. It is easy to obtain a transitory pink color throughout the 

liquid, but this disappears rapidly, the more rapidly the greater the 

amount of hydrofluoric acid or of manganous salt present. The 

oxiclizer can be added by the cubic centimeter to solutions already 

containing manganous sulphate in presence of hydrofluoric acid 

without producing a more than passing pink color. The solution, 

however, takes on in ever-increasing intensity the red-brown color 

characteristic of manganic salts. Hence the decolorization due to this 

cause is much more pronounced in the case of rocks high in ferrous 

iron than in that of those low in this constituent, because of the 

greater amount of manganous salt resulting from reduction of a 

correspondingly larger amount of permanganate, and is also greater 

with increasing hydrofluoric acid. In presence of but little ferrous 

iron, up to say, 2 centigrams, and 5 to 7 cm.3 of hydrofluoric acid the 

color produced by a drop of permanganate lasts some time, but is very 

evanescent as the ferrous iron, and consequently the manganous salt 

formed, increases.

1 It is not clear what, if any, bearing certain observations of E. Deussen. (Monatsh. 

Chemie, vol. 28, 1907, p. 163) may have on the method. He claims that dissolving 

ferric oxide in hydrofluoric acid involves partial reduction of the iron with formation of 

both ferrous iron and hydrogen peroxide : 2Fe2O3 + 8HF = Fe3F8 + FeO + 3H20 + H2O2. The 

experiments described on the following pages do not indicate such action, at least in presence of sulphuric acid.

-'Miiller, E., and Koppe, P., Zeitschr. anorg. Chemie, vol. 68, 1911, p. 160.
198 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

E. Deussen,1 on the basis of but a few tests, ascribes the extra consumption of permanganate to some obscure action of iron and seeks 

to counteract it by the addition of manganous sulphate. In both 

these assumptions he is, however, certainly in error,2 as shown (1) 

by the fact that the addition of a drop or two of the oxidizer to a 

solution of ferric sulphate in even a large amount of hydrofluoric 

acid produces a very stable coloration, which is destroyed by the 

addition of manganous sulphate, and (2) by the above-mentioned 

very evident partial reoxidation of the reduced manganese. This 

last, the oxidation of divalent manganese by permanganate in the 

presence of hydrofluoric acid, can be effected with the greatest ease 

in the entire absence of ferric iron.

M. Dittrich and A. Leonhard,3 on the basis of numerous series 

of unconvincing tests, ascribed the indefinite end point to the effect 

of Ti2O3 . They slighted or ignored the demonstrated fact that in 

hydrofluoric acid solution divalent manganese is oxidized by permanganate, even quantitatively under proper conditions (11. D, 

p. 139), and that the simultaneous existence of trivalent titanium 

and trivalent iron in acid solution is not in accord with observation, 

for the former is oxidized easily by the "latter, the reaction being 

used as the basis for titrating trivalent iron (9. D, p. 123). Hence, 

even if trivalent titanium occurs in some rock-forming minerals, 

it would be converted on solution to the quadrivalent state at the 

expense of ferric, iron, and the ultimate titration by permanganate 

would involve only ferrous iron. Further, it is a fact that when 

much ferrous iron is titrated permanganate can be added without 

the attainment of a definite end point in amount far exceeding that 

which the titanium (if present as Ti2O3 ) would require.

Numerous tests have been made to ascertain the error due to oxidation of the manganese under conditions similar in respect to the 

amounts of iron involved to those encountered in rock analysis. 

Increasing amounts of hydrofluoric acid were added to fixed amounts 

of ferrous sulphate and sulphuric acid and the titration was made 

with the least possible expenditure of time. With not more than 7 cm. 3 

of 40 per cent hydrofluoric acid a very slight tendency was observed 

toward high results, but in most cases the results were identical with 

those obtained in the presence of sulphuric acid alone. As the 

amount of hydrofluoric acid was increased to 10 cm. 3 a perceptible 

increase was noticed, which became markedly greater with 15 cm. 3 

of the acid, amounting in this case to about 0.2 cm.3 in the average on 

a normal consumption of 20 cm.3 of permanganate of 0.0032 FeO

1 Zeitschr. anorg. Chemie, vol. 44, 1905, p. 425. See also Monatsh. Chemie, vol. 28, 

1007, p. 163.

2 This statement is confirmed by the work of O. L. Barnebey (Jour. Am. Chem. Soc.; 

vol. 37, 1915, p. 1481).

3 Zeitschr. anorg. Chemie, vol. 74, 1912, p. 21.
FERROUS IRON. 199

titer. The personal factor enters here, G. Steiger having found 

slightly greater differences, but it is possible that they resulted from 

his titrating in more concentrated solutions, for with greater dilutions the differences are unquestionably less, according to experiments of my own.

Hence, after decomposition of the rock, removal of the excess of 

hydrofluoric acid is called for if the best results are to be expected. 

To a certain extent Treadwell's apparatus accomplishes this, but, as 

the experiments show, its complete expulsion is unnecessary.

A distinct contribution to the subject was made when 0. L. 

Barnebey 1 investigated the effect of a large number of proposed 

preventives and found that boric acid is the most effective of all. 

When added, either as solid or in solution, it renders the fluorine 

inactive by formation of fluorboric acid (HBF4 ), "which does not 

dissociate appreciably to yield hydrofluoric acid in the presence of 

boric acid."

P. Extreme oxidizabiUty of divalent iron ~by free oxygen in the 

presence of hydrofluoric acid or a fluoride. In comparing two series 

of results obtained with the Cooke apparatus, using a solution of 

ferrous sulphate in sulphuric acid alone in the one and in sulphuric 

acid with hydrofluoric acid in the other, a minus error was in all 

cases observed when the latter acid was present. An observation 

made by E. Peters,2 but not applied by him to the present case, explains this. Ferric fluoride, like the corresponding manganic salt, 

is almost undissociated in solution, whereas the sulphate undergoes 

considerable dissociation, and in this state counteracts, to a great 

extent, the tendency of any ferrous iron present to become oxidized 

by free oxygen. Hence the slow oxidation of divalent iron by air 

in sulphuric-acid solution and its very rapid oxidation in the presence of hydrofluoric acid. While a sulphuric solution of ferrous 

sulphate exposed to the air in an open dish will hardly change in 

strength during an hour, a similar solution to which hydrofluoric 

acid has been added will suffer a large measure of oxidation in a 

quarter of the time. The change in titer becomes pronounced after 

a few minutes.

In the experiments with the Cooke apparatus referred to, the 

minus error should amount to not more than 0.1 to 0.2 cm.3 of permanganate, on a normal consumption of 20 cm.3 or 0.5 to 1 per cent 

of the iron, but it may be considerably greater if the utmost care is 

not taken to employ carbon dioxide as free as possible from air and to 

exclude most carefully .the entrance otherwise of air into the apparatus. It will also be greater the higher the concentration, within 

certain limits, of the solution during titration.

1 Jour. Am. Chem. Soc., vol. 37, 1915, p. 1481.

3 Zeitschr. physikal. Chemie, vol. 26, 1898, p. 193. . :
200 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

With a view to lessening the error, if possible, the mode of operating was varied by doing away with carbon dioxide, except at the 

start, shutting it off as soon as the bath was in active ebullition, and 

transferring the crucible direct from the hot bath to the titration vessel. The results were, if anything, a trifle better. As the employment 

of either the Cooke, Barnebey, or Treadwell apparatus involves long 

contact of the mineral with the acids, and as the experiments last 

mentioned were favorable in their results, it seemed as if the simple 

method of J. H. Pratt 1 might be modified in the same sense. He 

avoided the use of all apparatus other than a capacious platinum 

crucible fitted with a perforated cover for the introduction of carbon 

dioxide, in which he boiled the mineral powder with sulphuric and 

hydrofluoric acids, the decomposition being greatly hastened by the 

active movement and higher temperature and usually completed in 

five to ten minutes. The modification consists in doing away altogether with carbon dioxide, except at the start, and depending on the 

steam of the boiling iron solution to exclude air, a modification 

which Pratt himself tried with rather considerable minus errors, resulting perhaps from his having a smaller crucible at command than 

the method really demands. With a crucible of 100 cm.3 capacity, 

the following results with ferrous sulphate show what are' the possibilities of the method:

Ferrous-iron determinations ~by the modified Pratt method. 

[Strength, of permanganate 0.0032 FeO per cm.8 ]

Time of 

boiling.

Minulcs.

10

10

10

10

10

10

10

10

Permanganate 

used.

cm. 3

4.9 1.8

5.0

4.9

9.6

9.6

9.6

19.2

Normal 

consumption of permanganate.

cm. 3

4.8

4.8

4.8

4.8

9.6

9.6

9.6

19.2

Time of 

boiiing.

Minutca.

10

10

15

15

15

20'20

Permanganate 

used.

cm.'

19.4

19.3

19.25

19.1

19.3

. 19.2

19.3

Normal 

consumption of permanganate.

cm 3

19.2

19.2

19.2

19.2

19.2

19.2

19.2

These results leave little, if anything, to be desired. They show 

either normal values or a slight plus error instead of the invariable 

negative one of all previous determinations. The method was tested 

during two years in comparison with that of Cooke with favorable 

results, a few of which are shown in the table under A, page 190. It is 

the method employed by me in preference, not only because of its 

simplicity and quickness, but also because with it a coarser powder 

can be decomposed than with either the Cooke, the Barnebey, or the 

Treadwell method. However, as the exigencies of the FeO deter1 Am. Jour. Sci., 3d sen, vol. 48, 1894, p. 149.
FERROUS IRON. 201

mination are now known to demand a powder as coarse as possible, 

a longer treatment has to be given than was called for by the fine 

powders used by Pratt.1

C. INFLUENCE OF SULPHIDES, VANADIUM, AND CARBONACEOUS MATTER ON THE DETERMINATION OF FEHKOUS IRON BY THE HYDBOFLUORIC-ACID METHOD.

A dark color of the insoluble fluorides and silicofluorides may be 

due to pyrite, graphite, or carbonaceous matter. The first of these 

affects the result but little, the second probably not at all, and they 

can be distinguished by their behavior toward nitric acid. Organic 

matter, of course, renders impossible the determination of ferrous 

iron.

a. Sulphides. Pyrite, in the quantities usually met with in igneous 

rocks, is probably without serious effect on the ferrous-iron determination by any of the hydrofluoric-acid methods. This sulphide is very 

resistant toward attack in the absence of oxygen, as is shown by the 

fact that if present in any quantity it can be recognized readily in the 

residue after titration. In any case it is impossible to allow for an 

error introduced by its possible decomposition, and the result of titration must count as ferrous iron. In the case of soluble sulphides two 

sources of error are introduced that of reduction of ferric iron by 

hydrogen sulphide evolved, and that due to the ferrous iron which the 

sulphides themselves may contain, especially if pyrrhotite is present. 

The first of these is perhaps negligible, for most of the hydrogen 

sulphide would probably be expelled without reducing iron. The 

second is approximately measurable if it is known that pyrrhotite is 

the only soluble sulphide present, and its amount has been ascertained by determining the hydrogen sulphide set free on boiling with 

hydrochloric acid in a current of carbon dioxide. In this case a.correction is to be applied to the result of titration for total ferrous iron. 

(See also 26. C. b, p. 233, under " Sulphur.")

In order to obtain quantitative data regarding the effect of pyrite 

on the ferrous-iron determination by the hydrofluoric-acid method the 

following tests were made: Part of a fine crystal of pyrite was powdered rather finely and boiled with dilute sulphuric acid, which extracted considerable ferrous iron, derived presumably from admixed 

or intergrown pyrrhotite, as a second boiling with fresh acid gave a 

negative test for ferrous iron. After washing by decantation with 

water, followed by alcohol and ether, the powder was dried and 

further pulverized. A quarter of a gram of it when treated with 

hydrofluoric and sulphuric acids in a large crucible by the Cooke

1 M. Dittrich (Ber. Deutsch. chem. Gesell., vol. 44, 1911, p. 990) facilitates the attack 

of refractory minerals by adding half a gram of not too finely ground quartz (not precipitated silica). The effect Is to separate the mineral grains and prevent caking on 

the bottom of the crucible, thus exposing them to more offuctive action of the acid.
202 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

method for ferrous iron, then rapidly filtered through a very large 

perforated platinum cone fitted with filter paper, required but 2 

drops of a permanganate solution representing only 0.0032 gram 

FeO to the cubic centimeter.

However, as H. N. Stokes found * that the oxidizing effect of ferric 

salts on pyrite and other sulphides is vastly greater than seems to 

have been suspected (see pp. 193-194), the following tests were made 

in order to ascertain the probable error due to this action under the 

conditions prevailing in rock analysis: Successive portions of 1 gram 

each of a hornblende schist, free from sulphur and carrying 10.09 

per cent FeO as the mean of several determinations and 4.00 per cent 

Fe2O3 , were mixed in a large 100 cm.3 platinum crucible with 0.02, 

0.025, and 0.10 gram, respectively, of the above purified pyrite 

powder, and treated with hydrofluoric and sulphuric acids by the 

Cooke method, the water bath being at boiling heat for one hour. 

The cooled contents of the crucible were poured into a platinum dish 

containing water and titrated rapidly nearly to an end. Then, in 

order to get rid of the pyrite, which would obscure the end reaction 

by its reducing effect on the permanganate, the solution was filtered 

as above and in the clear filtrate the titration was carried to completion. The results were iO.02, 10.16, and 10.70. Inasmuch as the 

smallest of these three charges of pyrite was several times greater 

than what may be considered an unusually high amount for an 

igneous rock, it is very evident that for all practical purposes the influence of pyrite on the ferrous determination by the Cooke method 

is negligible. At the same time it is to be borne in mind that with 

increased content in ferric iron an increased amount of pyrite will 

be attacked, and that the extent of this attack is influenced by the 

degree of fineness of the pyrite powder, which itself undergoes 

oxidation during grinding.

(3. Vanadium. If vanadium, when present, exists in the trivalent 

condition, it affects with an error varying with its amount the result of titration for ferrous iron. If the amount of the trivalent 

vanadium is known, a correction can be applied as follows: One 

molecule of V2O3 (150.8) in oxidizing to V2O5 requires as much 

oxygen as four molecules of FeO (288) when oxidized to Fe2O3 . 

The proportion, 150.8:288: : V2 03 present: 0, therefore gives the 

figure to be deducted from the uncorrected value for FeO. That this 

correction is very needful with many of the basic rocks becomes evident at once from the following perhaps extreme example:

Found 2.50 per cent apparent FeO in a rock containing .13 per cent V2OS. 

Deduct .25 per cent FeO equivalent in its action on KMnO* to .13 V2O3 . 

Leaving 2.25 per cent FeO corrected.

1 Bull. U. S. Geol. Survey No. 186, 1901; Am. Jour. Sci., 4th ser., vol. 12, 1901, p. 414.
FERROUS IRON. 203

Found 5.00 per cent apparent total iron as FeOs in the same rock. 

Deduct .14 per cent Fe20s corresponding to .13 per cent V2 03 . 

Leaving 4.86 per cent corrected total iron as Fe2O3 . 

Deduct 2.50 per cent Fe-Os equivalent to 2.25 per cent FeO. 

Leaving 2.36 per cent Fe2 03 in the rock.

Failure to correct for the vanadium in both cases would have made 

the figures for FeO and Fe2 03 , respectively, 2.50 and 2.22 instead of 

2.25 and 2.36 as shown above.

Y. Carbonaceous matter. As said before (c, p. 201), matter-of 

organic origin other than graphitic carbon renders the results of the 

ferrous-iron determination altogether unreliable.

Cl. THE METHOD IN ITS VARIOUS MODIFICATIONS.

a. According to Pratt (modified}. One-half to 1 gram of the 

coarsest powder 1 that can be used successfully is placed in a platinum crucible of 80 to 100 cm.3 capacity with a little air-free water 

and about 10 cm.3 of dilute sulphuric acid (1 acid to 3 water by volume). If the rock contains carbonates there will be effervescence1 , 

hence the acid must be added cautiously and the cover placed on till 

the action is over. There need be no fear of oxidation of ferrous 

iron at this stage, should any go into solution. Air-free hot water 

is now added till the crucible is at least half full; the crucible with 

cover on is placed on a triangle well down over a lamp turned low and 

protected from drafts. The air in the crucible is displaced rapidly 

by carbon dioxide entering beneath the lid slightly raised on one 

side. In a few seconds the liquid boils, but before allowing this to 

happen the gas current is stopped and the well-fitting lid lowered. 

Then from a small platinum crucible a measured quantity of strong 

hydrofluoric acid (5 to 7 cm.3 ) is poured in with one hand, while the 

other draws the lid a little to one side. A Second of time suffices. 

The lid is replaced, the flame is increased for a few moments with 

great caution not to allow boiling over, and the moment steam is 

1 seen to issue around the lid it is again lowered to a point that causes 

steady ebullition without danger of loss. Steam should issue continually for five, ten, or as many minutes as may be deemed necesr 

sary or allowable. Then the crucible, still covered, is transferred 

with the tongs shown in figure 1 (p. 32) to the titration vessel, which 

may be of glass (containing a cold saturated solution of boric acid * 

in freshty boiled water with an excess of the solid acid and a few 

cubic centimeters of sulphuric acid) and which is already under the 

'burette; the contents of the crucible are poured in quickly with the

1 The fineness of grinding will depend on the nature of the rock. Most granite rocks 

require but moderately fine grinding, those high in ferruginous and refractory minerals 

generally, as tourmaline, need to be very fine.

2 Barnebey, O. L., Jour. Am. Chem. Soc., vol. 37, 1915, p. 1481.
204 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

rinsings, and permanganate is run in rapidly till the first pink blush 

appears throughout the whole liquid.

Even without boric acid and with little iron the color will last 

some time, but with increasing amounts of iron, as also with, increasing amounts of hydrofluoric acid, it fades with ever greater rapidity. 

In making a duplicate determination it is well to run in . a little 

less than the calculated amount of permanganate before introducing 

the contents of the crucible.

The method should be tested first by the novice with ferrous-sulphate solution that has been standardized without hydrofluoric acid. 

It is important not to prolong the boiling unduly, for salts not easily 

soluble will separate, and as the temperature rises the oxidizing action 

of the concentrating sulphuric acid comes into play.

If an unattacked residue shows after titrating, this should be allowed to settle completely, then freed from the liquid by a decantation with water, once repeated. It is now transferred by a jet of 

water to a small agate mortar, allowed to settle again, freed from 

most of the water by decantation, ground for a few minutes under 

the water that remains, and washed back into the large crucible. The 

treatment with hydrofluoric and sulphuric "acids, in smaller amounts 

and for a shorter time than at first, is then to be repeated. The succeeding titration can be made in the .crucible itself after quickly 

filling this nearly full of cold air-free water. Usually decomposition 

will now be complete; if not, the various operations are to be repeated. 

In the very short time required for grinding the residues under water 

no appreciable oxidation of ferrous iron need be feared.

The directions given by Pratt 1 with reference to the treatment of 

a possible undissolved residue of very refractory minerals must be 

understood as applying only to homogeneous minerals and not to 

rocks, where the relations of ferrous and ferric iron in the undecomposed portion are certainly different from those in the part dissolved.

P. According to Cooke. 2 The apparatus, as shown in figure 19, 

consists of a small water bath of a single opening and covered with a 

glass funnel the stem of which has been cut off near the flare, resting 

in a troughlike depression of the specially made cover. Into this 

trough water constantly drops from a tubulated bottle, thus securing 

a perfect water joint and serving to keep the bath full by overflowing 

on the inside. For the more perfect exclusion of air it is best to use 

water that has been freshly boiled. Through a small metal pipe carbonic-acid gas flows into the bath under the cover, but above the surface of the water, and rising through notches in the edge of the opening of the cover fills the funnel and crucible., (See footnote 1 to 9. 

C. a, p. 120.)

1 Am. Jour. Scl., 3d ser., vol. 48, 1894, p. 150. 

= Iclem, 2d ser., vol. 44, 1867, p. 347.
FERROUS IRON. 205

One-half to 1 gram of the powder is treated exactly as in a until 

any carbonates that may be present cease to effervesce. The cover 

of the crucible is rinsed if need be and the open crucible at once 

placed in the opening of the bath, the funnel put in place, the gas 

current started, as also the flow of water from the reservoir, and the 

lamp under the bath already full of water is lit. As soon as it can

FiauitK 19. Cooke's apparatus for ferrous-iron determination.

be safely assumed that the air in both funnel and crucible has been 

displaced a measured volume of strong hydrofluoric acid (5,to 7 

cm.3 ) is poured into the crucible through a funnel of platinum or 

rubber and a platinum stirring rod is inserted through the stem of 

the glass funnel into the crucible. In the absence of a suitable 

funnel for the acid, the glass may be momentarily raised for the 

introduction of the acid, but not before the crucible has become 

filled with carbon dioxide.
206 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

When steam issues strongly from the funnel, the gas current from 

the generator is stopped and the apparatus left to itself for an hour, 

except for occasional stirring of the powder. When no gritty matter 

can be felt longer or when experience tells that decomposition must 

be complete, the gas current is turned on again, the lamp extinguished, and the water flow increased to the capacity of the outlet 

tube from the bath. In 15 minutes the crucible and contents should 

be cool. The rod is then removed and placed in the titration vessel 

and the titration made as in a. Until the 'operator has became experienced a duplicate determination should invariably be made. It 

is to be noted that the crucible is always much fuller at the end of 

the heating than when first placed on the bath, because of condensation of steam.

Instead of allowing the crucible to cool in a current of carbon 

dioxide, it may be transferred at once to the titration dish and permanganate run in as above directed. If carefully done, the experiments already referred to seem to show that the results by this variation of the method may be a trifle better than those obtained after 

cooling.

Those inexperienced with -the method in either variation should 

not fail to test it first with solution of ferrous sulphate that has been 

standardized without hydrofluoric acid, and in practice duplicate 

determinations should be made if possible.

Y. According to Barnebey. 0. L. Barnebey 1 has described a 

simplified form of the Cooke apparatus. In an 8-inch porcelain 

dish are placed some glass beads and a 5-inch" porcelain desiccator 

plate having under-supports. On the plate is a suitable support of 

glass or porcelain to hold in place the platinum dish in which the 

decomposition of the sample is effected. Over the plate is placed 

a 6-inch funnel like that for the Cooke apparatus. This extends 

far enough down to form a trap when a suitable liquid is poured into 

the outer dish. For the determination of ferrous iron Barnebey 

uses as the liquid a solution of phosphoric acid (1:2). This serves 

not only as a trap but also to furnish steam for expelling and excluding air from the funnel and inner dish. The bath is heated by 

a direct flame or by a hot plate. If needed air-free water can be 

added to replace that which evaporates, by the aid of a platinum 

rod. Reference to the description of the Cooke apparatus renders 

further explanation unnecessary.

Of course, the absence of provision for introducing carbon dioxide 

makes it necessary to transfer the hot solution of the sample to the 

titration vessel, and the need of a fine powder is a serious objection, 

as with the Cooke apparatus. The latter has the advantage over

1 Jour. Am. Chem. Soc., vol. 38, 1916, p. 374.
ALKALIES. 207

Barnebey's modification that the introduced carbon dioxide effects 

more rapid expulsion of the air in the decomposition vessel than 

is possible by the aid of steam alone.

8. According to Treadwell. F. P. Treadwell 1 used a paraffin 

bath in which was supported a lead box having a lead cover provided 

with two openings, one at the side for introducing carbon dioxide, 

the other in the center for the escape of steam and the insertion of 

a stirring rod. In the box the small dish containing the sample 

rested on a support, under the central opening.

Although the chief object of this device was, by raising the temperature to 120° at the end of the experiment, to remove the excess of 

hydrofluoric acid and thus avoid one source of error in the titration, 

it may be said, so far as my own limited experience with it goes, 

that the expulsion of the acid is by no means perfect and that the 

long duration of the experiment (about two hours) renders it likely 

that lower results will be obtained than with the procedures already 

described, especially the'procedure given under a.

E. UNCERTAINTIES OF THE FERROUS-IRON DETERMINATION.

From the foregoing it is apparent that despite the utmost care in 

practical manipulation, the exact determination of ferrous iron in 

rocks is one fraught with, extraordinary difficulties and uncertainties. 

Only in the absence of decomposable sulphides a-nd carbonaceous 

matter and when the amount and condition of vanadium are known 

and relatively coarse powders can be used, is it permissible to regard 

the result as fairly above suspicion.

22. ALKALIES.

A. THE J. LAWRENCE SMITH METHOD.

a. ITS ADVANTAGES. :

The various methods of getting at the alkalies in soluble silicates 

differ more in the mode of attack of the mineral powder and in the 

immediately subsequent treatment than in the final stages. With 

very few exceptions, since the early days of the Survey's existence all 

alkali determinations have been made by the method of J. Lawrence 

Smith,2 which is far more convenient than and fully as accurate as 

those in which decomposition is effected by hydrofluoric and sulphuric acids, or by bismuth, lead, or boric oxides. One of its chief 

advantages is the entire elimination of magnesia at the start.

1 Ktirzes Lehrbuch der analytischen Chemle, 6th ed., 1913, vol. 2, p. 425.

2 Am. Jour. Sci. 2d ser., vol. 50, 1871,. p. 269; Am. Chemist, vol. 1, 1871; Annalen 

Chem. und Pharm., vol. 159, 1871, p. 82.
208 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

b. BEAGENTS AND APPARATUS.

Decomposition of the powder is effected by heating it with its 

own weight of ammonium chloride and eight times as much precipitated calcium carbonate.

The ammonium chloride used must be purified, preferably by sublimation, or made by neutralizing pure ammonia by pure hydrochloric 

acid, and the calcium carbonate is obtained best from pure calcite by 

solution and precipitation. However obtained, this last is rarely 

free from alkalies, which must be estimated once for all in a blank 

test in order to apply a correction. Eight grams of the carbonate 

will yield usually from 0.0012 to 0.0016 gram of alkali chlorides, 

almost entirely the sodium salt, but the amount has been brought 

down to half the above by very long washing. This correction may 

be admitted at once to be a defect of the method, but it is one easily 

applied with safety. It is not at all certain that all the alkali found 

in the blank test comes from the carbonate. Much hot water is used 

for the analysis and a hot-water bottle, even of the best glass, will 

afford weighable amounts of alkali.

The ignition may be made in a covered crucible of ordinary shape 

and of about 20 to 30 cm.3 capacity, heated to-full redness for not 

more than two-fifths of its height, but the heat has to be kept so low 

in this case to avoid loss by volatilization that perfect decomposition 

is not always assured.1 Hence, to avoid waste of time in very fine 

grinding, the form of crucible with cap originally advocated by 

Smith is very much to be preferred, since it permits, when set at an 

angle through an opening in the side of a fire-clay cylinder, the application of the full heat of two burners, and perfect decomposition 

invariably results without the need of extraordinary care in grinding. The crucible used in the Survey laboratory (fig. 20) for onehalf gram of rock powder and 4 grams of calcium carbonate is 8 cm. 

long, 1.8 cm. wide at the mouth, and 1.5 cm. at the bottom. For 

double the amounts or more the dimensions are 8 cm., 2.5 cm., and 

2.2 cm. The weights are 25 and 40 grams.

C. TREATMENT OF THE MINERAL POWDER.

Perfectly satisfactory v results are to be obtained with but half a 

gram of rock powder. This is weighed out, ground fine in a large 

agate mortar, mixed with its own weight of sublimed ammonium

1 R. L. Steinlen (Chem. Zeitung, vol. 29, 1905, p. 364) describes a simple cooler for 

the lid of an ordinary crucible to obviate this difficulty. B. W. Morley (private communication) uses with good effect as a lid a closely fitting small platinum dish filled 

with cold water. Th. Boring (Zeitschr. anal. Chemie, vol. 49, 1910, p. 158) in a careful 

test of the method found that an ordinary crucible gave excellent results if it was set 

in a hole in asbestos board. After the preliminary gentle heating the full heat of a 

Teclu burner could be applied without loss of alkali. E. Wilke-DOrfurt confirms this finding (Zeitschr. anal. Chemie, vol. 51, 1912, p. 755).
ALKALIES. 209

chloride, and the two are ground together thoroughly. Then nearly 

all of 4 grams of calcium carbonate is added and the grinding continued till a thorough mixing has resulted. The contents of the mortar are transferred to the long crucible, the rest of the carbonate being used for rinsing off mortar and pestle. The crucible is then 

capped and placed in an inclined position in a clay cylinder (fig. 20) 

or through a hole in a piece of stout asbestos board clamped in a vertical position, and heated for about ten minutes by a low flame placed 

at considerable distance beneath. As soon as the odor of ammonia 

is no longer perceptible the nearly 

full flame of two Bunsen burners 

is substituted, and continued for 40 

to 50 minutes. The sintered cake 1 

detaches readily from the crucible 

as a rule; if not, it is softened up 

in a few minutes by hot water and 

digested in a dish until thoroughly 

disintegrated. It is first washed by 

decantation, and any lumps are 

broken up by a pestle, then thrown 

on the filter and well washed with 

hot water. The residue should dissolve completely in hydrochloric 

acid without showing the least trace 

of unattacked mineral, not even of 

quartz, though sometimes a few 

black particles of iron ores will dissolve but slowly.

Inasmuch as J. W. Mellor 2 and 

M. Dittrich 3 report 0.1 to 0.2 per 

cent of the alkali, and M. F. Connor 4 

even more, as not recovered by one 

treatment according to Smith, it 

may be necessary when the alkali 

content is considerable to dry and 

reheat the extracted mass with 

calcium carbonate and ammonium 

chloride and to add the second extract to the first. The unfavorable 

results reported may have been due to an insufficient temperature.

1 To avoid the formation of a melted cake with silicates high in iron it is advisable to 

increase the proportion of calcium carbonate. In order to lessen the chance of adhesion 

to the bottom W. T. Schaller, of the Survey laboratory, finds it well to place a layer 

of calcium carbonate at the bottom of the crucible before introducing the mixture. George 

Steiger finds that the slacking- of the cake is aided by using but 1 or 2 cm.3 of water 

at first.

2 Quantitative inorganic analysis, pp. 225, 247.

a Neues Jahrb., 1903, vol. 2, p. 69.

4 Cong. geol. internal., 12« sess., Canada, 1913, p. 885.

131999° 19 14

FIGURE 20. The J. Lawrence Smith 

crucible for alkali determinations. 

For dimensions see text.
210 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

E. Makinen 1 uses calcium chloride (melted and kept in a wellstoppered bottle) instead of the mixture of calcium carbonate and 

ammonium chloride and claims to get with it a slightly more perfect attack in consequence of the fusion which accompanies its use. 

Faturally the flux must be tested for an alkali content.

d. SEPARATION OF CALCIUM AND SULPHURIC ACID.

All but a trifling amount of the calcium is separated at boiling heat 

in a large platinum dish by double precipitation by ammonia and 

ammonium carbonate. The combined filtrates are evaporated to 

dryness and the ammonium salts are carefully driven off (B, p. 33). 

From the aqueous solution of the residue but a few cubic centimeters in bulk the rest of the calcium is thrown out by ammonia 

and ammonium oxalate, the last being more effective than the carbonate. The filtrate, caught in an untared platinum crucible or 

small dish, is evaporated to dryness and gently ignited; the residue 

is moistened with hydrochloric acid to decompose any alkali carbonate that may have been formed by action of the ammonium oxalate during ignition, again evaporated, ignited very gently, and 

weighed. On solution in water a few tenths of a milligram of fixed 

residue is invariably left, which should be collected, ignited, and 

weighed in the same crucible or dish in order to arrive at the weight 

of the chlorides.

If the rock contains sulphur, this will be found in part with the 

chlorides as sulphate. Therefore, if the sulphur is at all considerable in amount it must be removed by a drop of barium chloride 

before the final precipitation of the calcium. The excess of barium 

is removed by ammonium carbonate and the last of the calcium by 

ammonium oxalate, as above. If the sulphur is not thus removed, 

the weight of the chlorides will be slightly in excess, and there is 

danger, if not certainty, of the potassium chloroplatinate carrying 

sodium sulphate. A faint reaction for sulphate can usually be 

obtained, anyway, if the evaporations have been made on a water 

bath heated by gas.

6. PRECIPITATION OF POTASSIUM.

To the solution of the chlorides in a small porcelain dish 2 there 

is added sufficient chlorplatinic acid solution (containing 10 per cent 

of platinum) to react with both the sodium and potassium. The 

dilution should be such that when heated on the water bath any 

precipitate that may form redissolves wholly. This is to prevent

1 Zeitschr. anorg. Chemie, vol. 74, 1912, p. 74.

2 Preferred to platinum because of the possibility, under certain rare and ill-understood 

conditions, of the formation of an insoluble platinous compound, probably by reaction 

between the platinum of the dish and that of the salt. (See also Bolm, P., Zeitschr. 

aual. Chemie, vol. 38, 1899, p. 349.)
ALKALIES. 211

occlusion of mother liquor in a mass of crystals suddenly formed. 

Evaporation is then carried on till the residue solidifies on cooling. 

It is then drenched with alcohol x of 80 per cent strength, filtered by 

decantation through a very small filter, and washed by decantation 

with alcohol of the same strength. The precipitate is not brought 

onto the filter more than can be avoided. Dish and filter are then 

dried for a few minutes to remove adhering alcohol, the contents of 

the former are transferred to a weighed platinum crucible or very 

small dish, and what still adheres to the porcelain is washed through 

the filter with hot water into the weighed receptacle. This is now 

placed on the steam bath and afterward heated for a short time to 

135° in an air bath. It is very important to cover the dish at first 

in the air bath, for decrepitation with resultant loss sometimes takes 

place if this is not done. With rocks low in potash drying at 100° 

suffices fully to expel all water. The factor used for reduction of 

K2PtCl6 to 2KC1 is 0.307 and of 2KC1 to K2 0, 0.632. It does not 

seem necessary with the relatively small amounts of potassium in 

rocks to make use in place of the first of these of the slightly different empirical factor given in some textbooks, a factor based on the 

analysis of commercial potassium salts. If thought desirable the 

potassium chlorplatinate can be tested spectroscopically for caesium 

and rubidium.

f. SODIUM AND LITHIUM.

If it is desired to check the sodium, ordinarily determined by difference, this can be done readily by evaporation of the alcoholic 

filtrate from the potassium chlorplatinate, reduction of the platinum by hydrogen or otherwise as mentioned in the footnote,2 filtra1 The claim of H. Precht (Zeitschr. anal. Chemie, vol. 18, 1879, p. 513) that absolute 

alcohol is preferable, especially if evaporation has been carried to dehydration of the 

sodium salt, has been disputed by A. Atterberg and seems to have been conclusively 

disproved by J. Morozewicz (Anzeig. Akad. Wiss, Krakau, 1906, p. 796). According to 

Morozewicz, absolute alcohol partly decomposes Na2PtCle with formation of NaCl, which 

goes to increase the weight of the K2PtClo. A further advantage of the weaker alcohol 

lies in the fact that no more chlorplatinic acid than the amount theoretically required 

to convert both sodium and potassium to chlorplatinates need be used. In cases calling 

for the highest degree of accuracy Precht's solubility coefficient for K2PtCl8 In 80 per cent 

alcohol can be used, namely, 1: 26400. H. Fresenius and P. H. M.-P. Brinton (Zeitschr. 

anal. Chemie, vol. 50, 1911, p. 21) after extended study adhere to the use of alcohol of 

80 per cent strength.

- When haste is not an object, this way of Bunsen's for removing platinum from the 

chlorides of the alkalies is by far the neatest and most satisfactory. The small flask 

containing the solution is placed in a water bath and attached to a hydrogen generator. 

After expelling all air the flask is closed, without breaking connection with the generator, 

and left to itself, except for occasional light shaking up, till reduction is accomplished. 

A more expeditious and very satisfactory reduction is effected by evaporating the solution to dryness with metallic mercury, then heating to expulsion of the excess of 

mercury and of its chloride. E. Sonstadt (Jour. Chem. Soc., vol. 67, 1895,-p. 984) thus 

reduces potassium cblorplatinate in order to weigh its platinum. M. Horsch (Compt. 

Rend., vol. 168, 1919, p. 167) effects reduction by heating the solution jn a platinum 

dish on the steam bath with 2 to 3 cm. 8 of alcohol. Contact with metallic platinum is 

essential. The deposit is adherent to the dish.
212 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

tion, evaporation, and weighing of the sodium chloride. A check 

made in this way should agree with the determination by difference 

within half a milligram on the weight of the chloride. Lithium may 

then be tested for by the spectroscope, or in case no direct weighing 

of the sodium chloride is made, the evaporated alcoholic solution 

may be examined directly. Lithium is almost invariably present, 

but almost never in amount to warrant quantitative estimation. 

Should it be so, however, the very excellent Gooch method (summarized below) of separation by amyl alcohol is to be followed. In 

rock analysis there need be no fear of enough lithium falling with the 

potassium to cause any concern.

If ammonium carbonate alone has been relied on to separate all 

calcium (see d, p. 210) the few tenths of a miligram of calcium chloride that escaped precipitation should be separated now from the 

sodium and the proper correction made.

a. Gooctts method 1 for separating lithium. Gooch thus describes 

his method for separating lithium:

To the concentrated solution of the chlorides amyl alcohol is added and heat is 

applied, gently at first, to avoid danger of bumping, until the water disappearing from solution and the point of ebullition rising and becoming constant for 

some minutes at a temperature which is approximately that at which the alcohol 

boils by itself, the chlorides of sodium and potassium are deposited and lithium 

chloride is dehydrated and taken into solution. At this stage in the operation 

the liquid is cooled and a drop or two of strong hydrochloric acid added to 

reconvert traces of lithium hydrate in the deposit, and the boiling continued 

until the alcohol is again free from water. If the amount of lithium chloride 

present is small, it will now be found in solution and the chlorides of sodium 

and potassium will be in the residue, excepting the traces, for which correction 

will be made subsequently. If, however, the weight of lithium chloride present 

exceeds 10 or 20 mg., it is advisable at this point, though not absolutely essential to the attainment of fairly correct results, to decant the liquid from the 

residue, Wash the latter a little with anhydrous amyl alcohol, dissolve in a few 

drops of water, and repeat the separation by boiling again in amyl alcohol. For 

washing, amyl alcohol, previousy dehydrated by boiling, is to be used, and the 

filtrates are to be measured apart from the washings. In filtering it is best 

to make use of the perforated crucible and asbestos felt, and apply gentle pressure. The crucible and residue are ready for the balance after drying for a 

few minutes directly over a flame turned low. The weight of insoluble chlorides 

actually obtained in this manner is to be corrected by the addition of 0.00041 

gram for every 10 cm.3 of amyl alcohol in the filtrate, exclusive of washings, if 

the insoluble salt is entirely sodium chloride, 0.00051 gram for every 10 cm.3 if 

potassium chloride constitutes the residue, and, if both sodium and potassium 

chlorides are present, 0.00092 gram; but * * * the entire correction may 

in any case be kept within very narrow limits if due care be given to the reduction of the volume of residual alcohol before filtration. The filtrate and washings are evaporated to dryness, treated with sulphuric acid, the excess of the

* Proc. Am. Acad. Arts and Sci., 1886, p. 177; Bull. U. S. Geol. Survey No. 42, 1887, 

pp. 85-86; Chem. News, vol. 55, 1887, pp. 18, 29, 40, 56, 78 ; Am. Chem. Jour., vol. 9, 

1887, p. 33. Consult also Skinner, W. W., and Collins, W. D., Bull. Bur. Chemistry No. 

153, 1912.
ALKALIES. 213

latter driven off, and the residue ignited to fusion and weighed. From the 

weight thus found the subtraction of 0.0005 gram is to be made if sodium 

chloride constitutes the precipitate, 0.00059 gram if potassium chloride alone is 

present in the residue, and 0.00109 gram if both these chlorides are present, 

for every 10 cm.3 of filtrate, exclusive of washings.

Amyl alcohol is not costly, the manipulations of the process are easy, and 

the only objectionable feature the development of the fumes of amyl alcohol 

is one which is insignificant when good ventilation is available.

The process has been used for some months frequently and successfully, by 

others as well as by myself, for the estimation of lithium in waters and 

minerals.

B. PRELIMINARY TREATMENT BY OTHER METHODS.

It may happen, for lack of sufficient material in the case of silicate minerals decomposable by hydrochloric acid, that it is necessary 

to determine the alkali as well "as other bases and silica and titanium 

oxide in the same portion of the sample after all of these have been 

separated by methods which exclude the use of alkali reagents. 

Then the question of a suitable method for separating magnesium 

becomes important. Because of its cumbersomeness and possible 

sources of error the old barium-hydroxide method is not to be recommended in comparison with the methods that follow.

a. THE MERCURIC OXIDE METHOD.

The mercuric oxide method of Zimmermann, whereby the magnesia is precipitated from solution of the chlorides by moist, freshly 

precipitated, and alkali-free mercuric oxide, can give satisfactory 

results. The oxide is added in excess to the solution in a platinum 

crucible and evaporated to dryness. Then the mercuric chloride 

and most or all of the excess of oxide are expelled by cautious heating. On leaching with water the magnesia remains on the filter. 

With more than 1 per cent of magnesia the operation must be 

repeated (Dittrich).

b. THE AMMONIUM CARBONATE METHOD.

The once favored method of precipitating the magnesium by neutral ammonium carbonate in concentrated solution has been again 

recommended.1 The magnesium solution must be as strongly concentrated as possible, and a great excess of ammonium carbonate 

solution must be used. A voluminous precipitate forms, which dissolves on vigorous, stirring if enough of the precipitant is used. 

After a time a ciystalline precipitate falls a double carbonate of

1 Wiilfing, E. A., Ber. Deutsch. chem. Gesell., vol. 32, 1899, p. 2214. The neutral 

carbonate is prepared by dissolving 230 grams of ammonium carbonate in 180 cm.3 of 

ammonia of 0.92 specific gravity and enough water to make 1 liter. This is sometimes 

called Schaffgotsch's solution.
214 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

magnesium and ammonium which is insoluble in the concentrated 

solution of ammonium carbonate. Allow to stand for six to twentyfour hours. Wash with the concentrated ammonium carbonate 

solution. It is no exercise of undue caution to redissoive and reprecipitate, to make sure of getting all alkali in the filtrate, especially 

potassium.

F. A. Gooch and E. A. Eddy 1 find that, when carried out as 

directed above by Wiilfing, precipitation of the magnesium is incomplete, but that this defect can be remedied by addition of alcohol. 

Of several procedures devised they prefer the following as most 

convenient for the proportions of salts they used, namely, about 

0.15 gram MgO and 0.1 to 0.2 gram alkali chlorides.

A solution is first prepared by saturating with ammonium carbonate a mixture in the proportions by volume 'of 18 cm. 3 ammonia solution [density 0.92?], 80 cm. 8 water and 90 cm.3 absolute alcohol. The 

solution containing the chlorides of magnesium and the alkalies is 

brought to a volume of about 50 cm.3 and an equal amount of absolute alcohol is added. Precipitation is made by addition of 50 cm.3 

of the prepared reagent and the mixture is allowed to stand 20 

minutes, with stirring for 5 minutes. If the amount of alkali salts 

originally present is small, the precipitate may be collected on asbestos 

in a perforated crucible and washed with the precipitant. When the 

amount of alkali salt originally present is large, the precipitate may 

be freed from traces of the alkali salt by pouring off the supernatant 

liquid through the prepared asbestos filter, dissolving the precipitate, 

and precipitating ammonium-magnesium carbonate as at first. If it 

is desired to determine the magnesium as well as the alkalies, the precipitate of carbonate freed from alkalies is ignited and the residual 

magnesium oxide weighed.

C. THE AMYL ALCOHOL METHOD.

Under certain circumstances, notably in the absence of lithium, the 

method of Gooch developed by Riggs 2 may be satisfactory. It is 

similar to that of Gooch for separating lithium from sodium and 

potassium chlorides by amyl alcohol, and involves the same solubility corrections for the alkali chlorides above noted (A. f. a, p. 212) 

in the description of Gooch's method.

C. DIRECT SEPARATION OF POTASSIUM BY SODIUM COBALTINITRITE.

It may happen sometimes that of the alkalies present the percentage of potassium alone is desired. In this case use may be made of

1 Am. Jour. Sci., 4th ser., vol. 25, 1908, p. 444; Chem. News, vol. 97, 1908, p. 280.

2 Am. Jour. Sci., 3d ser., vol. 44, 1892, p. 103.
ALKALIES. 215

the cobaltinitrite method, which afforded W. Autenrieth 1 results that 

are in good agreement with those obtained by the J. Lawrence Smith 

method.

a. PREPARATION OF THE REAGENT.

Crystallized cobalt nitrate (30 grams) is dissolved in 60 cm.3 of 

water. To the solution is added 100 cm.3 of a saturated solution of 

sodium nitrite (corresponding to 50 grams of NaNO2 ) and 10 cm. 3 

of glacial acetic acid. Effervescence, with escape of nitric oxide, 

ensues and the color changes to dark yellow-brown. Some potassium 

cobaltinitrite usually separates, which, after one to two days, is filtered 

off. The reagent undergoes hardly any decomposition in three to 

four weeks if kept in a dark bottle. It is still available if a few drops, 

when added to 5 cm. 3 of water containing one drop of 10 per cent 

KC1 solution, cause almost immediately a yellow precipitation.

b. APPLICATION OF THE METHOD.

The mineral powder (1 to 3 grams) is decomposed with hydrofluoric and sulphuric acids, the excess of the sulphuric acid is volatilized, the dry residue is ground and digested with. 30 to 40 cm.3 of 

water. To the solution, contained in a capacious beaker of Pyrex or 

Jena glass (or in a platinum dish), is added 10 cm.3 of a saturated 

solution of potassium-free sodium acetate 2 and the mixture is boiled 

for from 10 to 15 minutes. The precipitate of basic acetates is 

filtered and washed a few times with hot water. The filtrate is 

evaporated to a bulk of 15 to 20 cm.3 , then, according to the amount 

of potassium present, 5 to 10 cm.3 of the cobalt reagent is added, and 

after stirring the liquid is let stand for 24 hours, cold. The yellow 

precipitate is filtered, washed with cold water containing a little of 

the reagent, and dried at 100°. As it is not free from sodium, it is 

useless to- weigh it in this condition, and it is treated therefore as in 

a or (3 below.

E. C. Haff and E. H. Schwartz * treat the filtrate obtained after 

attack according to Lawrence Smith, as follows:

An excess of acetic acid (5 to 10 cm.3 ) is added and evaporated till 

the odor of the acid is no longer perceptible. The residue is taken 

up with a little hot water, from 10 to 15 cm. 3 of the cobalt reagent 

is added, and the solution is evaporated to a pasty consistency. 

After cooling, cold water (30 cm.3 ) is poured upon the residue, with 

care to wash the sides of the dish well. The solution is filtered and 

washed with water, which should be cold.

1 Centralbl. Mineralogie, 1908, p. 513.

2 Five grams dissolved in water should give no yellow precipitate with the cobalt 

reagent after 24 hours.

3 Jour. Ind. Eng. Chemistry, vol. 9, 1917, p. 785.
216 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

The further treatment differs according as the potassium is to be 

weighed as chlorplatinate or as perchlorate.

a. Determination as chlorplatinate. The precipitate is removed 

from the paper, which is ashed in a platinum crucible; the precipitate 

is then added and heated to dull redness for a few minutes. The 

resulting alkali nitrites are extracted with hot water, filtered from 

the cobalt oxide, evaporated to dryness with strong hydrochloric acid, 

and the potassium is determined as in A. e, p. 210.

P. Determination as perchlorate. The yellow precipitate is transferred as far as possible to a small porcelain dish, the paper is ashed 

and its aqueous extract is added to the contents of the dish. To this 

is then added, drop by drop, a few cubic centimeters of hydrochloric acid (sp. gr. 1.124), the blue solution is evaporated to complete dryness and treated with 5 to 6 cm.3 of perchloric acid (sp. gr. 

1.124) free from sulphuric acid. The solution is evaporated to dryness, treated again with 6 cm.3 of perchloric acid, again evaporated 

to dryness, and finally heated over a free flame till copious vapors of 

perchloric acid come off. There must be complete conversion of the 

salts to perchlorates, and ammonium salts must be absent. The residue is then extracted with 10 cm.3 of absolute alcohol containing 0.2 

per cent of perchloric acid and allowed to stand for some minutes. 

The clear solution is filtered through a platinum-felted crucible without disturbing the precipitate, which is transferred and washed with 

absolute alcohol saturated with potassium perchlorate 1 and containing 0.2 per cent of perchloric acid, dried at 120° to 130°, and weighed. 

It is not considered necessary to wash finally with alcohol and ether 

in order to remove the very small amount of wash liquid that adheres to the precipitate.

As applied when sodium is present the procedure is somewhat different. In that case the precipitate is transferred to the crucible 

by means of the filtrate,2 washed once or twice with the alcoholic solution of perchloric acid, redissolved and reprecipitated, and finally 

washed with the alcoholic solution of perchlorate and perchloric 

acid.

1 Davis, W. A., Jour. Agr. Sci., vol. 5, 1912, p. 52. Thin, R. G., and dimming, A. C., 

Jour. Chem. Soc., vol. 107, pt. 1, 1915, p. 361. Baxter, G. P., and Kobayashi, M., Jour. 

Am. Chem. Soc., vol. 39, 1917, p. 249. The earlier directions, to use alcohol containing 

only perchloric acid, involve too great a solubility loss. Thin and Cumming prepare the 

solution by shaking up the alcohol and perchlorate for 10 minutes and pouring off the 

clear liquid. Baxter and Kobayashi use alcohol saturated at 0° and wash at the same 

temperature. The solution must be prepared shortly before use.

2 Gooch, F. A., and Blake, G. R., Am. Jour. Sci., 4th ser., vol. 44, 1917, p. 381
ANALYSIS OF SILICATE AND CARBONATE BOCKS. 217 

23. CARBON DIOXIDE, CARBON.

A. QUALITATIVE TEST FOR CARBON DIOXIDE.

In the preliminary qualitative! test for carbon dioxide, it must be 

remembered that while calcite gives off its carbon dioxide on treatment with cold acid, dolomite and siderite do not, and hence warming 

should not be omitted; otherwise a few tenths per cent of carbon 

dioxide can be overlooked. Moreover, the powder should first be 

agitated with a little hot water, to remove all inclosed air which might 

otherwise be mistaken for carbon dioxide. In order not to overlook 

traces the test should be made in a test tube, first boiling the powder 

with a little water, then cooling, and adding dilute hydrochloric 

acid. If effervescence is immediate the presence of calcite is assured; 

if escape of bubbles takes place only on warming the carbonate is 

not calcite. In order to make sure of the reaction it may be necessary to use a pocket lens, holding the test tube in an inclined position 

and looking down in order better to see the minute bubbles as they 

stream up along the upper glass wall. It is, of course, important not 

to mistake escaping hydrogen sulphide for carbon dioxide.

B. QUANTITATIVE TEST FOR CARBON DIOXIDE.

For the quantitative determination of carbon dioxide an apparatus 

permanently set up is used, of which several forms have been described by different writers.1 The one depicted in figure 21 is a 

compact arrangement long used in the Survey laboratory.

The rock powder (1 to 5 grams) is boiled with dilute hydrochloric 

acid in a small Erlenmeyer flask attached to an upward-inclined condenser, whence, after passing through a drying system calcium 

chloride, anhydrous copper sulphate to retain hydrogen sulphide 

from decomposable sulphides and any hydrochloric acid that may 

pass over, then calcium chloride again the carbon dioxide is caught 

by absorption tubes filled with soda lime followed by calcium chloride. Of course, arrangement is made for a current of air free 

from carbon'dioxide with which to sweep out the apparatus before 

and after the determination and for a slow current during its continuance. The results are very accurate and the determination can 

be carried out quickly.

The manipulations are as follows: Hot water is poured upon the 

powder in the flask; this is attached to the condenser, and a current 

of air free from carbon dioxide is forced through the whole system, 

except the weighed absorption tubes, until the original air has been

1 For a simple and convenient form, see Treadwell's " Quantitative analysis," 4th 

American ed., p. 381.
218 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

displaced, the observation bulbs E being attached directly to the 

drying system B. Then the stopcock in the separatory funnel is 

closed, the funnel is half filled with hydrochloric acid (1:1), the 

rubber stopper of the funnel is replaced, the absorption tubes are 

inserted between B and E, and the acid is allowed to flow into the

FIGURE 21. Compact form of apparatus for determination of carbon dioxide. A, Protective calcium chloride tube, frequently refilled, to retain most of the moisture from 

the condenser. B, Double U-tube, filled iu the center with pumice impregnated with 

anhydrous copper sulphate and at both ends with calcium chloride. C and D, Absorption tubes, C and one-third of D containing soda lime, followed in D by calcium 

chloride. C needs to be refilled before the soda lime in D has absorbed much if any 

carbon dioxide, D then requires only occasional refilling, but it will not do to use it

. indefinitely, since the calcium chloride in it becomes less and less effective a? it takes 

up the water set free from the soda lime in C during its conversion to carbonate. E, 

Observation bulbs containing sulphuric acid to show the rate of gas flow.

flask, slowly if there is much carbon dioxide, rapidly if there is 

but little. When effervescence diminishes in the former case, at once 

in the latter, the lamp is lighted and the flow of water through the 

condenser started. The flame is kept low, so as to have steady but 

quiet ebullition, and the gas current is not interrupted, although
CARBON DIOXIDE, CARBON. 219

'reduced to a slow rate. With much carbon dioxide the rate of absorption is noted very readily by holding the hand to the soda-lime 

tubes, which become hot or warm where absorption is taking place. 

A sufficient time having .elapsed, the flame is extinguished and the 

air current increased. When cool the tubes C and D are weighed 

after remaining some time in the balance case.

The soda lime must be porous, not hard and unabsorptive like that 

sometimes used for the combustion of nitrogenous organic substances 

and should contain 2 per cent of water for the most effective absorption of carbon dioxide.

For the simultaneous determination of carbonates and the carbon 

of carbonaceous matter see C, below.

It has been shown already under "Water" (5. C. h, p. 89) how in 

case of need, as because of paucity of material, the determination of 

carbon dioxide can be combined with that of water by fusion with 

lead chromate, provided that free carbon or organic matter is absent. 

Soda -lime absorption tubes then follow the calcium chloride tube in 

carrying out the determinations there referred to.

L. H. Borgstrom1 calls attention to the difficulty of decomposing by 

hydrochloric acid some minerals that contain carbon dioxide, especially certain scapolites. When these are present he adds to the 

hydrochloric acid 30 cm.3 of a mixture of 1 part strong hydrofluoric 

acid and 4 parts water. He recommends also to pass hydrochloric 

acid gas through the calcium chloride in the tubes B before use, in 

order to neutralize any alkalinity it may have and so prevent retention of some of the carbon dioxide by it.

C. CARBOoST.

Fusion with lead chromate is commonly resorted to in order to 

determine the carbon of graphite or carbonaceous matter in rocks 

and ores, though boiling in presence of sulphuric and chromic acids 

can be made to yield good results.

If carbonates are at the same time present they can be determined as in B (p. 217) , and by a second determination, as just referred 

to, the total carbon in both forms can be found as CO2 , whence that 

of the graphite is derived by difference. Or, according to G. T. 

Morgan,2 the carbonates are first decomposed as in B by orthophosphoric instead of hydrochloric acid, whereupon chromic acid 

is added and the carbon oxidized and determined as C02 .

A. C. Fieldner, W. A. Selvig, and G. B. Taylor,3 in a recent paper, 

describe a procedure for determining the carbon and hydrogen of 

combustible matter in shales, clays, and limestones, which seems to

r. anal. Chemie, vol. 53, 1914, p. 685. 

2 Jour. Chem. Soc., vol. 85, 1904, p. 1001. 

8 Bur. Mines Tech. Paper 212, 1919.
220 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

afford results as satisfactory as could be expected. It does not take 

account of volatile components of the combustible matter that might 

be driven off in the preliminary treatment of the rock.

24. CHLORINE.

A. CONDITION IN ROCKS.

Chlorine may exist in rocks in a water-soluble condition, in minerals that are decomposed by nitric acid, and in those not attacked 

by this acid. In the first form it doubtless exists as infiltrated 

sodium chloride or as original inclusions in one or more of the constituent minerals; in the second in minerals of the sodalite group 

and sometimes apatite; in the last chiefly in the scapolites. Where 

a qualitative test shows the water-soluble form to be present in determinable amount, it must be extracted separately and the amount 

found deducted from the total as determined in a second portion. 

Sometimes it may be possible to use the extracted material for the 

determination of the rest of the chlorine.

B. DETERMINATION OF WATER-SOLUBLE CHLORINE.

A suitable amount, which may be several grams, of the powder is 

extracted with water. Very often the filtrate is turbid, a condition 

which may sometimes be prevented by using double filters or by 

adding some chlorine-free salt, like sodium nitrate, to the wash 

water. If the filtrate remains persistently cloudy the precipitation 

of silver chloride may be proceeded with as usual, after acidifying 

with nitric acid. It is best to let the precipitate settle over night in 

order to obtain a clear filtrate on the morrow. It is collected on a 

small filter, washed with water acidified with nitric acid, dried, and 

ignited in a very small porcelain crucible without allowing the paper, 

to burst into flame. Most of the chloride will be reduced to metal. 

On disappearance of all carbon a drop of nitric acid is added and 

evaporated, then similarly a drop of hydrochloric acid, and the. crucible heated gently, but not to fusion of the silver chloride, and 

weighed. The chloride is then dissolved in a few drops of warm 

ammonia water and separated by filtration from the siliceous matter, 

which latter is ignited and weighed in order to get the weight of the 

chloride.

This method of procedure is permissible even when the original 

aqueous extract was quite clear, though the operation then stops with 

the weighing of the chloride. Or, if very small in quantity, the dry 

paper with its contents is wound up in a tared platinum wire and 

carefully ignited after Bunsen's manner. The increased weight of 

the wire is due to the metallic silver of the chloride which has alloyed 

with the platinum.
CHLORINE. 221 

C. DETERMINATION OF ACID-SOLUBLE CHLORINE.

a. BY NITRIC ACID.

If nitric acid will decompose the chlorine-bearing minerals, or if 

it is desired to distinguish between the chlorine in soluble and in 

insoluble minerals, the rock powder may be boiled for a few minutes with dilute chlorine-free nitric acid. The acid should be very 

dilute in order to cause no loss of chlorine, and the boiling should 

be as brief as possible for the same reason and also to prevent 

gelatinization of the silica from soluble silicates. Acid as dilute 

as 1:40 will decompose apatite readily and probably the minerals 

of the sodalite group, but it is doubtful if anything like this dilution is called for.

The filtrate does not require evaporation for the removal of dissolved silica but may be precipitated at once with silver nitrate. 

The precipitate is treated as in B, or if at all appreciable in amount 

may be collected on a Gooch crucible.

b. BY NITRIC AND HYDROFLUORIC ACIDS.

In many cases in order to obtain all the chlorine it is sufficient to 

attack the powder (which must be much finer usually than the coarse 

bulk sample) by chlorine-free hydrofluoric and nitric acids in the 

cold, with occasional stirring, and after filtering through paper fitted 

into a rubber funnel or large platinum cone to throw down the 

chlorine by silver nitrate. The presence of nitric acid is necessary, 

since in its absence ferrous iron in presence of fluorine reduces silver 

nitrate with deposition of crystallized silver. It may be advisable 

to redissolve the chloride on the filter in ammonia and to reprecipitate by nitric acid and a drop of silver nitrate. It seems difficult to obtain in the market hydrofluoric acid free from a trace of 

hydrochloric.

D. DETERMINATION OF CHLORINE BY ALKALI FUSION.

Chiefly because of the difficulty just mentioned, in order to make 

sure of getting all the chlorine, it is best to fuse with chlorine-free 

sodium-potassium carbonate, or even sodium carbonate alone, first 

over the .full burner, then for a moment or two over the blast, to 

leach with water, acidify in the cold with nitric acid, and precipitate by silver nitrate without preliminary separation of silica. After 

icidification in the cold, except in a very concentrated solution, no 

precipitation of silica need be feared. The treatment of the precipitate will be as in B or C, according to its amount and freedom 

from contamination.
222 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

25. FLUORINE (SILICA IN PRESENCE OF FLUORINE). 

A. GENERAL REMARKS.

There is no direct qualitative test which will reveal with certainty 

the presence of fluorine in rocks. Heating the powder before the 

blowpipe with sodium metaphosphate on a curved piece of platinum 

foil inserted into one end of a narrow glass tube, or in a bulb tube, 

and noting the presence or absence of etching on the glass where 

water from the flame condenses, after the tube has been dried, is not 

to be relied on in all cases. Although in some rocks as little as 0.1 

per cent of fluorine can be detected thus with ease, in rocks of another class much larger amounts may fail to show.

The same is true of the direct quantitative methods. Here the 

result is almost certain to be low and may even be negative when 

fluorine is present. Those who have given most attention to the subject therefore seem to favor indirect determination, for which only 

the method given under C, below, is known. Indeed, it is the only 

one that can be depended upon for fluorine in rocks. However, the 

preliminary attack of the rock and the subsequent treatment, up 

to a certain point, are alike for both methods, and as one may be used 

as a check upon the other both will be described in detail.

For the reason that most of the fluorine minerals occurring in 

rocks are attacked but partly, if a-t all, by strong hot sulphuric acid, 

none of the methods depending on the volatilization of silicon fluoride can be used. There is the further reason that even with decomposable fluorides it is impossible to obtain quantitative results in 

presence of amorphous silica or silicates.1 Only with quartz powder or feldspar is volatilization perfect. The method to follow is 

that of Berzelius, which, though not difficult, requires great attention to details and even then affords low results. (See B. a. 7 for 

causes of error.) It admits of the determination of silica at the 

same time and is in fact the only method available for silica in 

fluorides.

B. DIRECT QUANTITATIVE DETERMINATION OF FLUORINE. 

a. METHOD OF BERZELIUS.

a. Procedure. Two grams of the rock powder is fused with four or 

five parts of sodium-potassium carbonate free from fluorine, avoiding 

the use of a blast if possible. For minerals rich in fluorine and low in 

silica it may be necessary to add pure silica before fusing in order to 

effect complete decomposition of thefluoride, just as with the alkalineearth phosphates. But probably this will never be required in ordinary rock analysis. To the aqueous extract, containing the fluorine and 

usually much of the silica besides other bodies, several grams. of

1 Sec Daniel, K., Zeitschr. anorg. Chemie, vol. 38, 1904, pp. 257-306.
FLUORINE. 223

ammonium carbonate is added, the liquid is digested at a gentle heat 

(40°) for some time, and on cooling more carbonate is. introduced.1 

After twelve hours the precipitate is collected and washed with water 

containing ammonium carbonate. From the filtrate the excess of the 

latter is expelled by evaporating nearly to dryness and the somewhat 

diluted solution is brought toward neutrality as follows, according to 

the directions of Treadwell. A few drops of phenolphthalein are 

added, then nitric acid (not hydrochloric in this case, see below) till 

the red color disappears. The solution is now boiled, the color reappearing, to be again discharged by acid on cooling. These operations 

are repeated till it requires but 1 to 1.5 cm.3 of 2 N acid to discharge 

the color. There is now added 1 to 2 cm.3 of an ammoniacal solution 

of zinc oxide,2 and the liquid is boiled till the ammonia is wholly expelled. The precipitate, containing the last of the silica and some 

phosphorus, in addition to that thrown down with alumina by 

ammonium carbonate, is separated and washed with water.

The above-prescribed use of nitric instead of hydrochloric acid for 

neutralizing is necessitated by the fact that phosphorus, which is 

almost invariably present, and chromium, must still be removed, and 

this can be done only from a nitric solution, as follows: To the still 

alkaline solution silver nitrate is added in excess, whereby phosphate, 

chromate, chloride if chlorine is present, and carbonate of silver are 

precipitated. The last serves to correct any acidity resulting from 

the reaction between the alkaline phosphate and the silver salt, thus 

producing the neutral solution needed fpr complete precipitation of 

the phosphate and chromate. After slight heating and filtering, 'the 

excess of silver is removed by sodium chloride and 1 cm.8 of 2 N sodium-carbonate solution is added to the filtrate, which is then boiled 

in a dish of good size with a large excess of calcium-chloride solution. 

At this stage there must be no ammoniacal salts in solution, otherwise 

calcium fluoride may be held up. The precipitate consists of a mix1 The use of ammonium nitrate or chloride, instead of carbonate, for throwing out 

the silica and alumina is not to be recommended because of loss of fluorine on. subsequent 

evaporation (H. Rose).

2 Made by precipitating pure zinc chloride solution with potassium hydroxide,, filtering, 

washing, and dissolving the precipitate in ammonia. Or, more simply, by dissolving zinc 

oxide in ammonium carbonate solution. If the rocks are very basic, it may happen that 

the amount of silica in the alkaline solution of the fusion is so small that ammonium 

carbonate may be dispensed with for its precipitation and the zinc oxide solution added 

at once, after neutralizing as above.

Instead of the ammoniacal zinc oxide solution F. Seemann (Zeitschr. anal. Chemie, vol. 

44, 1905, p. 343), advocates using the Schaffgotsch solution (p. 213, footnote) in which 

has been dissolved in the cold 20 grams of freshly precipitated mercuric oxide to the 

liter. For every 0.2 gram of dissolved silica 100 cm. 8 of this reagent is to be used. 

The solution is then. to be evaporated to complete dryness, the residue taken up with 

water, filtered and washed, the filtrate again neutralized with hydrochloric acid [nitric in 

rock analysis W. F. H.], and again evaporated to remove the last of the silica. Where 

silica is to be determined at this stage this reagent has the advantage over the zinc 

solution that direct ignition of the precipitates (under a good draft hood) yields at once 

silica. Its use is manifestly allowable in rock analysis only after the alumina has first 

been separated by ammonium carbonate.
224 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

ture of calcium carbonate and fluoride, the former serving to aid 

filtration of the latter. The precipitate is collected on paper and 

washed with hot water, dried, and ignited separately from the filter 

as far as possible. If the dish used for the precipitation was of platinum, it is not necessary to cleanse it from adhering precipitate, but 

the contents of the filter are washed back into the dish, the liquid in 

this is evaporated away, the ash of the filter added, and the dish 

heated over a free flame to faint redness for a few moments.

Dilute acetic acid is now poured upon the gently ignited mixture in small quantities at a time and in amount slightly in excess 

of that needed to dissolve the calcium carbonate. When visible 

action ceases, the liquid is evaporated to dryness and the residue 

taken up with hot water and a drop of acetic acid, filtered, dried, 

and ignited gently.

The amount of fluoride obtained from rocks being usually very 

small, a single treatment as above suffices, but for the larger amounts 

obtained from fluorine minerals a second and even third treatment 

with acetic acid may be needed, filtering and igniting after each. 

S. L. Penfield and J. C. Minor x found in such cases that if a great excess of acetic acid is used at the start the results are lower than by the 

repeated treatment. For considerable amounts, when the loss 

between two treatments is reduced to not more than half a miligram, 

F. P. Treadwell and A. A. Koch 2 take the next to the last weight as 

correct.

P. Testing of the calciu/fri fliwride. The well-washed and gently ignited calcium fluoride finally obtained in the course of 

this method should be converted to sulphate as a check on its 

purity, and at the same time as a qualitative test to ascertain if 

it really is calcium fluoride by the characteristic odor of the 

gas given off. Should fluorine be found, and the weight of sulphate not correspond to that of the fluoride, the sulphate should be 

dissolved in hot nitric acid and tested for phosphorus by ammonium 

molybdate solution. If phosphate is absent the impurity may have 

been silica or calcium silicate which of these it would be difficult to 

decide. In the former case the fluorine might be safely deduced 

from the weight of the sulphate, but not in the latter. If the rock were 

rich in sulphur it might happen that calcium sulphate would be 

thrown down with the fluoride, but this should be removed by thorough washing. If not, and it were certainly the only impurity 

present, the fluorine could be calculated, after conversion of the 

fluoride into sulphate, by the formula

CaS04 -CaF2 :2F ::& a:x

1 Am. Jour. Sci., 3d ser., vol. 47, 1894, p. 389. 

"Zeitschr. anal. Chemie, vol. 43, 1904, p. 469.
FLUOKINE. . 225

in which b is the weight of the sulphate and a that of the impure 

fluoride.

It is an exceptional case when there is exact agreement between 

the weight of fluoride and sulphate, and with the small amounts 

 usually met in rocks the error may be an appreciable one in percentage of fluorine, though of no great significance otherwise.

Y. Accuracy of the method. It is evident from the above that 

if the greatest care is not taken to prevent any kind of contamination of the weighed fluoride the error in the small amounts in 

question may be very great. If phosphate were present it would 

not do to apply the check by conversion to sulphate, because the 

evaporation with sulphuric acid and following ignition would 

volatilize metaphosphoric acid.

There is another source of error due to the solubility of the fluoride 

itself, in water and acetic acid. F. P. Treadwell and A. A. Koch* 

have investigated the solvent effect of these and some other reagents. 

They find that it is possible to detect additional fluorine by repeating the precipitation with calcium chloride in presence of sodium 

carbonate, and that the total errors are such that for 5 mg. CaF2 

or less the results are much too low, though the qualitative detection 

still can be made in 100 cm.3 of solution with only 0.0009 gram CaF2 , 

notwithstanding the fact that the quantitative tests had seemed to 

indicate that the loss would be about 0.0015 gram CaF2 for every 

100 cm.3 , including wash water. It thus appears that with 1 gram 

of sample amounts of less than 0.04 to 0.05 per cent of fluorine will 

escape observation entirely.

A source of error not generally known arises whenever calcium 

fluoride is ignited in contact with paper. Fluorine escapes to a slight 

extent and is replaced by oxygen, this reaction being doubtless due 

to the action of water vapor and not to oxygen of the air.

F. Seeman 2 subjected all the known methods of determining 

fluorine to extended examination, using calcium fluoride as his test 

material, and declares the Berzelius method to be far inferior to those 

based on volatilization of the fluorine as silicon fluoride, by reason of 

great and varying losses, the causes of which he was unable to satisfactorily trace. He was unable to recover by it more than about 87 

to 89 per cent of the fluorine. My tests, confirmed by other workers, 

do not support his very unfavorable results. I was able repeatedly 

to regain 95 to 98 per cent of the fluorine. To do so requires, however, re-fusion of the residue left after leaching the alkali-carbonate 

melt, including in the same re-fusion the silica precipitated by

iZeitschr. anal. Chemie, vol. 43, 1904, p. 469. 

2 Idem, vol. 44, 1905, p. 343.

131999° 19 15
226 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

ammonium carbonate and ammoniacal zinc oxide, the treatment of the 

filtrate from the precipitate of calcium carbonate and calcium fluoride with additional sodium, carbonate and calcium chloride, and 

the reevaporation of the acetic acid solutions of the precipitated 

calcium carbonate.

b. DETERMINATION OF SILICA IN THE METHOD OF BERZELITJS.

The several precipitates obtained by ammonium carbonate and 

zinc oxide, together with the residue from the original alkali fusion, 

are dissolved as far as may be in hydrochloric acid, the papers ignited and their ashes added, and silica is separated by the processes 

detailed in section 6 (p. 89). These may be greatly simplified, if 

bases are not likewise to 15e determined, by evaporating the first 

filtrate from the silica with much sulphuric acid as in 9. B. a (p. 117) 

in order to recover the silica which that filtrate always contains. Of 

course, the determination of silica is not made if it was necessary to 

add silica when making the original fusion of the rock.

C. OTHER DIRECT METHODS FOR FLUORINE.

Many methods have been devised for the ultimate determination 

of fluorine in minerals that are decomposed by concentrated sulphuric acid fluorides and fluophosphates which it is unnecessary 

to describe here. All of them depend upon first expelling the fluorine with special precautions, either as silicon fluoride or hydrofluoric acid.

Other methods, devised for fluorides soluble in water, are perhaps 

applicable to the solution obtained as described in a. a, from which 

all silicon, aluminum, and phosphorus have been removed, but the 

same defect that applies to the Berzelius method affects them also, 

namely, a certain solubility of the precipitate in the precipitating 

solution. Of these may be mentioned (1) the method of G. Starck,1 

in which the fluorine is thrown down as lead chlorofluoride, PbCIF; 

(2) that of F. Pisani,2 modified by J. G. Dinwiddie,3 the precipitation being made by calcium sulphate with a resulting mixture of 

calcium sulphate and fluoride; and (3) that of F. A. Gooch and 

M. Kobayashi,4 the precipitating agent being thorium nitrate.

An excellent digest of the methods for determining fluorine is 

that given by C. K. Wagner and W. H. Koss.5

1 Zeitschr. anorg. Chemie, vol. 70, 1911, p. 173.

"Compt. Rend., vol. 162, 1916, p. 791.

3 Am. Jour. Sci., 4th ser., vol. 42, 1916, p. 464.

* Idem, vol. 45,. 1918, p. 370.

5 Jour. Ind. Eng. Chemistry, vol. 9, 1917, p. 1116.
FLUORINE. 227

C. INDIRECT QUANTITATIVE DETERMINATION OF FLUORINE, 

a. STEIGER'S METHOD.

George Steiger devised in the laboratory of the Geological Survey 

an indirect method x for the determination of fluorine that has met 

with much favor, although it is not suited for large amounts.

It is based on the well-known fact that the presence of fluorine has a powerful 

bleaching effect on the yellow color which is produced by the oxidizing of a 

titanium solution with hydrogen peroxide. A solution of definite volume is 

made containing the fluorine to be estimated, also having a known amount of 

titanium present; this is compared in a colorimeter with a second solution containing an equivalent amount of titanium per cubic centimeter, and the bleaching effect recorded. From the extent of this bleaching, the percentage of 

fluorine can be calculated.

Although the results obtained are not so accurate as those given by many 

methods for the estimation of other elements, yet considering the difficulty of 

the fluorine determination, and .the time and labor required by methods now 

in use, the present one may well be employed, where small quantities of fluorine 

are to be determined. The operations require not only less skill to carry out 

but are fewer in number and take much less time.

Traces of fluorine amounting to several hundredths of 1 per cent are easily 

detected, and an approximation to the quantity can be made. In amounts up 

to a few tenths of a per cent this method seems to be more reliable, and if 

not more than 2 per cent is present, the results compare favorably in accuracy 

with the standard methods. It is hardly to be expected, however, to find a 

colorimetric method using only a few milligrams of the material to be determined that will compare in accuracy with the gravimetric methods using much 

larger quantities, where considerable percentages of fluorine are concerned.

Sodium salts in large amount make the observed reading for the 

titanium somewhat low 2 but not enough to affect the results seriously. 

Silica in amounts up to 0.1 gram has but little effect, and by the 

treatment employed its amount is reduced to at most 2 or 3 centigrams. Alumina, which exerts a marked effect, even .in small quantities, is readily removed by the preliminary treatment. Phosphoric 

acid, which bleaches like fluorine, does not interfere unless present 

in larger amounts than are likely to be encountered in rock analysis.

b. MERWIN'S MODIFICATION OF STEIGER'S METHOD.

a. Introductory remarks. Merwin, in the paper just cited, not 

only defined the effect of alkali salts but showed that the concentration of the acid as well as the temperature affects the color of titanium solutions peroxidized by hydrogen peroxide. The salts cause 

bleaching, while addition of acid counteracts this effect to a considerable degree. Merwin's statements were confirmed by tests made

1 Jour. Am. Chem. Soc., vol. 30, 1908, p. 219.

2 Merwin, H. E., Am. Jour. Sci., 4th sen, vol. 28, 1908, p. 119. Steiger observed a 

contrary effect, which was probably due to failure to control the acidity of the solution.
228 ANALYSIS OF SILICATE AND CABBONATE ROCKS.

at my instigation by William Blum at the Bureau of Standards. 

Steiger's. observations as to the effect of compounds other than 

alkali salts are in general accord with those of Merwin. Blum 

further observed that with little acid present the color of the standard and of the bleached test solution can not be matched under certain 

conditions. This was so, for instance, with 3 milligrams fluorine and 

2 per cent sulphuric acid, but with 10 per cent acid a fairly satisfactory comparison was possible with as much as 5 milligrams 

fluorine.

Merwin gave formulas for computing fluorine in the presence of 

known amounts of alkali sulphates and acid and modified accordingly the previous methods of getting the fluorine into final solution. 

He now uses the following procedure, which is taken in part from 

the paper cited and in part from advance information which he 

will soon publish.

/3. Procedure. Two grams of rock powder are fused with 8 grams of mixed 

sodium and potassium carbonates and the fusion is taken up with hot water. 

When leached, and without the necessity for filtering, there are added 3 or 4 

grams of powdered ammonium carbonate. The mixture is warmed for a few 

minutes and then heated on the water bath till the ammonium carbonate is 

destroyed and the bulk of the liquid is small. In this way the silica, which 

otherwise might render the final solution turbid, is thrown down, together with 

the disturbing alumina and ferric oxide. The destruction of the ammonium 

carbonate is necessary because ammonium sulphate bleaches the final solution. 

After filtering there is added to the filtrate which should not exceed 75 cm.8 in 

volume 3 or 4 cm.3 of hydrogen peroxide, and then cautiously 10 cm.3 of 

standard titanium solution 1 (containing 0.01 gram Ti02 ). Including the acid 

in the titanium solution, about 3.5 cm.3 of strong sulphuric acid are required 

to be added to neutralize the alkali carbonates. As soon as neutrality is 

reached the solution acquires a light orange color. Neutrality is tested by 

adding a little sodium carbonate solution to discharge the color, and then a 

drop or two of acid to restore it. The further treatment depends upon the 

amount of fluorine expected and the type of colorimeter used. The amount of 

acid to be added to the neutralized solution depends upon the amount of 

fluorine present. Therefore, add first 3 cm.3 of concentrated sulphuric acid 

and make the solution up to 100 cm.3 at a temperature of about 22° and 

compare at the same temperature with a 100 cm.3 solution containing 0.01 gram 

Ti02, 4 cm.3 of H2 02 and about 3 cm.3 of concentrated sulphuric acid. The 

fluorine content of the test solution can then be read off on the curves in figure 

22.2 If the ratio is greater than about 0.40 the amount of fluorine can be read 

off accurately. For smaller ratios (more fluorine) more acid should be added 

to the test solution, a new color comparison made, and a new reading taken 

from the chart.8 The chart is made on the assumption that the alkali sulphate

1 The hydrogen peroxide prevents the precipitation of the titanium by the alkali 

carbonate.

2 This chart was prepared recently for me by Dr. Merwin. It was made from new 

and more accurate data than the former, covering a larger range, but it gives essentially 

the same fluorine values as the formulas previously mentioned.

3 For certain forms of colorimeter a correction corresponding to the increased volume 

of the test solution must be made.
FLUORINE. 229

corresponds to 8 grams of the half-and-half mixture of potassium and sodium 

carbonates, or 7 grams of sodium carbonate, used in the fusion. The chart 

shows, on the zero line of fluorine, the average color ratio for 8 grams of carbonates. The carbonates used for the fusion should be tested in the same way 

as the filtered solution for the fluorine test. These ratios will probably not 

differ more than 0.03 from

Color Ratio 

.90 .so .70 .60 .50 .40 .30

.OO4 

.008

5*12

1

0)

.§.016 

O

^,020 

.024 

r»o«

\

^

\

~-~~ 

\

X

"-- 

^

\

---

\

\

\

V

\

^

X

\\

s^

\

\

\

\

X

V \

\

\

\

I2\

X.\

\

\

\

\

s

\

#

\3

those on the chart. This difference represents about 0.5 

milligram of fluorine, which 

is about the limit of accuracy of the method for 

amounts of fluorine below 

0.006 gram. At about 0.025 

gram this limit is about 

0.002 gram.

It is very evident 

that the analyst must 

take into account the 

amounts of alkali salts 

and of acid and must 

always take his readings 

at about the same temperature. Anyone who 

has frequent occasion to 

determine fluorine i n 

this indirect way should 

prepare diagrams indicating the corrections to 

be made under his own 

conditions of operation.

L. A. Steinkonig 1 has 

determined the fluorine 

in a number of soils by a 

slight modification of 

the Merwin procedure as 

given in Bulletin 422. 

The amounts found were 

as high as 0.05 per cent. 

The'method as used " is not delicate enough to indicate with certainty 

the presence of 0.01 per cent of fluorine," but even so it is a great 

advance over the gravimetric method for such small quantities.

iJour. Ind. Eng. Chemistry, vol.. 11, 1919, p. 463.

FIGURE 22. Merwin's diagram for

ratio= ^*A- °l-stan-d9-r<1 S0lut-i21>. 

depth of test solution

fluorine. Color 

Each solution is

peroxidized and made up to 100 cm.3 and contains 

0.01 gram of Ti02 . The test solution contains the 

number of cubic centimeters of concentrated sulphuric acid indicated by the numbers near the 

curves, and the amounts of fluorine shown, besides 

sulphates equivalent to 4 grams each of sodium and 

potassium carbonates. The standard solution contains an indefinite amount of acid between 3 and 5 

cm. 8. The chart was made at 22°, but it is not significantly different at any temperature between 19° 

and 25° if both solutions are at the same temperature. If the test solution is 5° wanner than the 

standard the curves are displaced toward the left 

hand about 0.02 for 12 cm.3 of acid, and 0.01 for 

3 cm.3 of acid. The total color of the solutions is 

not significantly affected by 10 per cent change of 

water content.
230 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

26. SULPHUR. 

A. DETERMINATION OF THE CONDITION OF SULPHUR IN ROCKS.

Before proceeding to the determination of sulphur, when present, 

its condition should be ascertained, both by microscopic identification 

of the sulphur-bearing minerals, when this is possible, and by qualitative tests. The importance of a microscopic examination can not 

be too strongly emphasized, for it may give the analyst most useful 

information.

Evolution of hydrogen sulphide on boiling with diluted hydrochloric acid is evidence of a soluble sulphide, usually pyrrhotite, 

but possibly lazurite. Extraction of magnetic particles reacting for 

sulphur shows pyrrhotite to have been in part at least the source of 

the hydrogen sulphide. A reaction for sulphuric acid in. the filtered 

solution indicates a soluble sulphate, usually a silicate sulphate, 

noselite, or hauynite. If the residue, when well washed and treated 

with aqua regia or hydrochloric acid and bromine, gives more sulphuric acid, the probable presence of pyrite is shown. Should this 

solution likewise show arsenic, the sulphide1 may be arsenopyrite, 

which, however, is found very rarely if ever in igneous rocks.

It is most uncommon to find any sulphur in rocks in the ordinary 

simple sulphate condition, except sometimes water-soluble traces, 

even when considerable pyrite is in evidence. The barium of fresh 

and even moderately decomposed rocks is apparently always in 

silicates and not in combination with sulphur.

B. QUANTITATIVE METHOD GENERAL DISCUSSION.

The literature on the determination of sulphur as barium sulphate is very voluminous, and it is only within a comparatively few 

years that the difficulties attending even an approximately exact 

determination have become well recognized. Most of the researches 

made have had to do with the determination of sulphur under conditions where the precipitate of barium sulphate was large, as in the 

commercially important mineral pyrite. In such cases it is only 

when the precipitation is made under well-defined conditions that 

the result is good, and then through compensation of considerable 

plus and minus errors.

These errors have been attributed to a variety of causes, and 

various explanations have been offered to account for them. They 

are referred to in some detail in previous editions of -this work. 

Suffice it to say that they result from occlusion in some manner of 

chlorine, of alkali metals, and of the ammonium radical and the 

formation of sulphate compounds that lose sulphur trioxide on 

ignition. There is no method of treatment that will eliminate en-
SULPHUR. 231

tirely all these disturbing factors. In the footnote 1 are listed papers 

that may be consulted with profit on various phases of the general 

subject. Particularly useful are those of Alien and Johnston and 

Johnston and Adams.

In general there should be present the least amount of free hydrochloric acid that will prevent hydrolysis of salts in the hot solution, 

for the acid has marked solvent effect on barium sulphate. Nitric acid 

should be avoided or removed by evaporation with hydrochloric acid. 

The barium chloride solution used as precipitant should be of not over 

10 per cent strength and should be delivered slowly and in fine drops, 

if much sulphur is present, into the nearly boiling solution. The 

precipitate then will be well crystallized and contain a minimum of 

chlorine, whereas with rapid precipitation its amount may be several 

milligrams per gram of precipitate.

When pure sulphuric acid is ^precipitated by barium chloride, the 

problem is relatively simple because of the absence of soluble salts; 

hence in mineral analysis it is desirable to avoid an alkali fusion 

whenever possible, but it must not be overlooked that direct treatment of the mineral with hydrochloric acid or oxidizing agents will 

extract certain amounts of salts, one or another of which may be 

fatal to the attainment of acceptable results.2

In rocks sulphur is not often present in large amounts, hence 

special precautions in making the precipitation or special purification of the barium sulphate are hardly ever necessary, especially as 

the precipitation is usually made in the absence of iron.

C. QUANTITATIVE DETERMINATION IN ROCKS, 

a. TOTAL SULPHUB.

Although sometimes the sulphur of sulphides may be extracted 

wholty with aqua regia or some other powerful oxidizer, in the

iHulett, G. A., and Duschak, L. H., Zeitschr. anorg. Chemie, vol. 40, 1904, p. 196. 

Lunge, G., and Stierlln, R., Zeitschr. angew. Chemie, vol. 18, 1905, p. 1921. Lung°e, G., 

Rept. Eighth Internat. Cong. Appl. Chemistry, Rome, 1906, p. 399. Hlntz, C., and Weber, 

H., Zeitschr. anal. Chemie, vol. 45, 1906, p. 31. Folin, 0., Jour. Biol. Chemistry, vol. 

1, 1906, p. 131. Van't Kruys, M. J., Chem. Weekblad, vol. 6, 1909, p. 735; Zeitschr. 

anal. Chemie, vol. 49, 1910, p. 393. Alien, E. T., and Johnston, J., Jour. Am. Chem. 

Soc., vol. 32, 1910, p. 588. Alien, E. T., and Johnston, J., Jour. Ind. Eng. Chemistry, 

vol. 2, 1910, p. 196; Chem. News, vol. 101, 1910, pp. 257, 267 ; Zeitschr. anorg. Chemie, 

vol. 69, 1910, p. 102. Johnston, J., and Adams, L. H., Jour. Am. Chem. Soc., vol. 33, 

1911, p. 829; Chem. News, vol. 105, 1912, pp. 162, 173, 183. Huybrechts, M., Bull. 

Soc. chlm. Belgique, vol. 24, 1911, p. 177. Smoot, A. M., Eng. and Min. Jour., vol. 94, 

1913, p. 412. Smith, G. McP., Jour. Am. Chem. Soc., vol. 39, 1917, p. 1152. Wlnkler, 

L. W., Zeitschr. angew. Chemie, vol. 30, 1917, pp. 251, 259, 281. Karaoglanow, Z., 

Zeitschr. anal. Chemie, vol. 56, 1917, pp. 225, 417, 561; vol. 57, 1918, pp. 77, 113.

2 Smoot (op. cit.) In analyzing pyrite eliminates Iron and other heavy metals by electrolysis, using a mercury cathode for collecting the metals. The solution then carries 

practically only free sulphuric acid, from which the sulphate radical can be precipitated 

with less error than when Iron, alkali, or ammonium salts are present. The device has 

been used under other conditions to separate elements that do not lend themselves to effective separation when together.
232 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

wet way, this is not always so.^ Therefore it is generally better by far 

to fuse with sulphur-free sodium carbonate and a little niter over the 

Bunsen burner, and for a. few moments over the blast, using throughout the heating the arrangement shown in figure 3 (p. 34), in order to 

exclude access of sulphur from the flame gases. This determination 

may be combined very conveniently with that of barium, titanium, 

zirconium, and rare earths (p. 170). After thorough disintegration 

of the fusion in water, to which a drop or two of alcohol has been 

added for the purpose of reducing and precipitating any manganese 

dissolved as manganate, the solution is filtered and the residue washed 

with a dilute solution of sodium carbonate. In the filtrate (100 to 250 

cm.3 in bulk) the sulphur is precipitated at boiling heat or on the 

steam bath by barium chloride in excess, after slightly acidifying in 

the cold by hydrochloric acid. Evaporation to dryness first with acid, 

in order to eliminate silica, is needless, for in the above bulk of solution there will almost never be the least separation of silica with the 

barium sulphate.1 It is well that this is so, for evaporation on a bath 

heated by gas, in order to remove silica, would involve in many cases 

an error fully equal to the sulphur present, by contamination from 

the sulphur of the gas burned. With a steam bath this difficulty does 

not present itself. Should there be fear of a trace of silica being 

present, it can be removed by a drop of hydrofluoric and sulphuric 

acids before weighing the barium sulphate.

In order to reduce greatly the error caused by the presence of 

sodium chloride resulting from the sodium carbonate used in the 

fusion, W. A. Turner 2 reduces the solution to a small volume (25 

cm.3 ), saturates it with hydrochloric acid gas, or adds concentrated 

hydrochloric acid (five times the volume of the solution concentrated 

to 10 cm.3 ), filters through a Gooch crucible, washes with strong 

hydrochloric acid, evaporates the filtrate, filters again if need be, and 

precipitates with barium chloride. This seems to be an excellent 

suggestion.

Errors due to the solvent action on the barium sulphate of hydrochloric acid or of ammonium or fixed salts in the solution can 

usually be corrected by evaporating the filtrate from the bariurn sulphate, destroying or expelling ammonium salts if present, treating 

the residue with water slightly acidified with hydrochloric acid, and

irThe results of C. W. Stoddart (Jotir. Am. Chem. Soc., vol. 24, 1902, p. 852) show, 

in the determination of sulphur in. coals by the Eschka method, often higher sulphur 

when silica is not removed by evaporation in the usual way, but this is contrary to all my 

experience in silicate work, where duplicates agree usually exactly, and if they differ 

are as likely to be high by one way as by the other. The explanation, may be that 

Stoddart acidified his solutions hot or used too strong an acid and had some silica precipitated.

2 Am. Jour. Sci., 4th ser., vol. 38, 1914, p. 41; Zeitschr. anorg. Chemie, vol. 88, 1914, 

p. 412 ; Chem. News, vol. Ill, 1915, p. 100.
SULPHITE. 233

collecting arid purifying the barium sulphate that may be left undissolved.

B. FRACTIONAL DETERMINATION.

When sulphur is present in more than one condition it is usually 

desirable to know the respective amounts, hence fractional determinations must be made.

If traces of sulphates soluble in water are present, they can be 

removed by extraction with boiling water.

For the quantitative extraction, of the sulphur of all soluble sulphates, simple boiling with hydrochloric acid suffices, which should 

be done in an atmosphere of carbonic acid if pyrites or other oxidizable sulphides are present, and should be finished as quickly as 

possible in order to minimize the error resulting from oxidation to 

sulphuric acid of the sulphur of sulphides, if present, by any ferric 

salts that may have been dissolved.

If soluble sulphates and sulphides as well as insoluble sulphates 

and sulphides are present together, the sulphur of the first is found 

in solution after extraction by hydrochloric acid in a carbon-dioxide 

atmosphere, and that of the decomposable sulphides by collecting the 

hydrogen sulphide evolved.1 Then in the residue the sulphur of the 

insoluble sulphides can be determined after suitable oxidation, and 

in the resulting residue that of the insoluble sulphates after fusing 

with sodium carbonate. The sulphur of the insoluble sulphates can, 

however, be calculated by subtracting the barium sulphate equivalent 

of the preceding fractional determinations from that found for the 

total sulphur.

The error involved in the above estimation of the sulphur of 

soluble sulphides, due to the possible reducing effect of hydrogen 

sulphide on ferric salts, is probably negligible. Most of the hydrogen sulphide would be expelled before any such action could take 

place and probably before the ferric salts were largely attacked, but 

of course the small proportion of sulphur set free as such from 

pyrrhotite would escape estimation and introduce further uncertainty. In general, it would be safe enough to assume the composition Fe7 S8 for pyrrhotite.

Obviously, such a procedure as that given above is open to many 

errors, especially with the more complex mixtures, and however 

carefully all these separate determinations may be carried out, the 

final figures for ferrous and ferric oxides can hardly be regarded as 

more than approximations when much sulphide is present. (See 

21, D. c. a, p. 201).

1 With pyrrhotite a small fraction of its sulphur one-eighth If the formula Fe7S8 Is 

adopted Is liberated as free sulphur and not as hydrogen sulphide.
234 ANALYSIS OF SILICATE AND CARBONATE HOCKS.

27. BORON. 

A. GENERAL REMARKS.

No doubt boron occurs occasionally in rocks in amounts superior 

to those of some of the other constituents that are habitually determined. But the lack of precision of the methods that are at all 

applicable to mineral substances not directly soluble in acids other 

than hydrofluoric acid is accountable for the fact that no one has 

ever sought to apply these methods to rocks, unless boron was supposed to be present in appreciable amount. When this condition is 

fulfilled it is customary to fuse with an alkali carbonate and then 

apply in one of its numerous modifications the Rosenbladt-Gooch 

method. In the footnote below x are given the most important' 

references that relate to the development of this method and its 

application to refractory minerals.

The method depends on expelling the boron as methyl ester by 

distillation with methyl alcohol from an acid solution, collecting 

the ester in some suitable manner and then determining the boron 

gravimetrically or volumetrically. For simple borates, especially 

the soluble ones, the method gives satisfaction when all needful 

precautions are carefully observed, and that it may do so also with 

refractory borosilicates has been shown by several workers, most

irrh. Rosenbladt (Zeitschr. anal. Chemie, vol. 26, 1887, p. 21) used magnesia for 

binding the boron, while F. A. Gooch (Proc. Am. Acad. Arts and Sci., 1886, p. 167; Bull. 

U. S. Geol. Survey No. 42, 1887, p. 64; Chem. News, vol. 55, 1887, p. 7) preferred lime as 

more active and reliable. Gooch and L. C Jones have later (Am. Jour. Sci., 4th ser., 

vol. 7, 1899, p. 34; Chem. News, vol. 79, 1899, pp. 99, 111) upheld the use of lime and 

proposed as a convenient though perhaps not quite so perfect substitute, sodium tungstate 

containing an excess of tungstic oxide. In this article they likewise indicate the precautions now used to insure complete collection and retention of the boron.

For a useful modification in the way of collecting the boric ether in ammonia before 

bringing in contact with the lime, see S. L. Penfleld and E. S. Sperry (Am. Jour. Sci., 

3d ser., vol. 34, 1887, p. 222) ; also H. Moissan (Compt. Rend., vol. 116, 1893, p. 1087; 

Bull. Soc. chim., vol. 12, 1894, p. 955), who modifies the Gooch distilling apparatus in 

certain respects.

G. W. Sargent (Jour. Am. Chem. Soc., vol. 21, 1899, p. 858) obtained satisfactory 

results with tourmaline by collecting the boron in sodium-hydroxide solution, neutralizing 

the alkali with hydrochloric acid by the aid of methyl orange, then, titrating the freed 

boric acid by sodium hydroxide in presence of glycerin, using phenolphthalein as indicator 

(method of Thompson, Jour. Soc. Chem. Ind., vol. 12, 1893, p. 432).

Later contributions to the application of this method are by R. J. Manning and W. R. 

Lang (Jour. Soc. Chem. Ind., vol. 25, 1906, p. 396), who determine the boron in the 

distillate gravimetrically as the barium salt Ba(BOs) 2, and by Wilson H. Low (Jour. Am. 

Chem. Soc., vol. 28, 1906, p. 807), who modifies the distillation feature, with much 

apparent advantage, by the addition of dry granulated calcium chloride and perfects 

the turmeric-paper qualitative test. This author titrates the distillate in presence of 

glycerin. W. H. Chapin (Jour. Am. Chem. Soc., vol. 30, 1908, p. 1691) applies the Low 

method successfully with slight modifications to borosilicates but prefers mannite to 

glycerin. E. T. Wherry (Jour. Am. Chem. Soc., vol. 30, 1908, p. 1687) devised a method 

for refractory boron minerals that yielded him results comparing favorably with those 

of Chapin, the same samples being used. It depends on separating aluminum and iron 

by means of calcium carbonate in a special manner, after making an alkali fusion, and 

titrating the filtrate directly in presence of mannite. The aluminum and iron must, 

however, be redissolved and reprecipitated one or more times.
BORON. - ' 235

recently by Chapin. Before Chapin's work it was considered necessary 

to extract with water the alkaline fusion of a mineral and to treat 

the extract for the boron. The wide divergence of results obtained 

by different chemists, even between duplicate results by the same 

analyst, is probably referable to the employment of only a single 

fusion and extraction, for it has been shown by S. L. Penfield 

and H. W. Foote,1 by G. W. Sargent,2 and by W. E. Ford 3 

that these operations must be repeated. A decided advance seems 

to have been scored by Chapin, who shows that aluminum and iron 

need not be removed but that the carbonate melt may be dissolved 

directly in acid without prejudice to the accuracy of the method as 

carried out by him. Furthermore, the presence of chlorine, even of 

fluorine, does not seem to be detrimental. Possibly his procedure 

may yet prove applicable to rocks as well as to boron minerals.

Mainly in the hope of stimulating search for boron in rocks the 

Chapin procedure is given in detail below.

B. DISTILLATION METHOD AS MODIFIED BY CHAPIN.

\ 

a. REAGENTS. *

1. Paranitrophenol. One gram dissolved in 75 cm. 8 of neutral 

ethyl alcohol and made up to 100 cm.3 with water.

2. Phenolphthalein. One gram dissolved in 100 cm.3 of ethyl alcohol and made up to 200 cm.3 with water.

3. Hydrochloric acid, 0.1 normal. The water should be boiled 

to remove carbonic acid.

4. Hydrochloric acid, 1.1 strength. A dropping bulb should be 

filled with this acid when it is needed in accurate small amounts.

5. Sodium hydroxide, 0.5 and 0.1 normal. These should be standardized as follows: Fuse pure boric acid in a platinum dish. While 

still warm break the melt up and place the fragments quickly in a 

weighing tube. Dissolve 1.75 grams in 250 cm.3 of hot, recently 

boiled water, cool, and dilute the solution to 500 cm.3 This solution 

is 0.1 normal that is, in presence of mannite or glycerol 1 cm.3 is 

neutralized to the phenolphthalein end point by 1 cm.3 of 0.1 normal sodium hydroxide.

In standardizing the sodium hydroxide against this solution both 

indicators ^should be used, so that the end may be the same as that 

seen in actual titration. Follow exactly the directions given under 

b, below, for the final titration, only assuming that the boric acid 

solution is exactly neutral to paranitrophenol that is, free from

1 Am. Jour. Sci. 4th ser., vol. 7, 1899, p. 97.

2 Jour. Am. Chem. Soc., vol. 21, 1899, p. 858.

3 Am. Jour. Sci., 4th ser., vol. 14, 1903, p. 195.
236 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

mineral acid. When yodium hydroxide is standardized in this way 

the small amount of carbonate present does no harm.

6. Mannite. This is preferable to glycerol, for it requires no 

special preparation, does not materially increase the bulk of the solution to be titrated, and gives an equally sharp end point.

°7. Methyl alcohol. This should be distilled over lime after it has 

been heated for some hours in contact with the lime under a reflux 

condenser. The more nearly anhydrous the alcohol is the better.

8. Calcium chloride. This should be granular, anhydrous, and 

free from boron.

b. APPARATUS.

The main set up of the apparatus required is shown in figure 23.

C. PROCEDURE.

Chapin used not more than half a gram of mineral powder for 

even very small amounts of boron, and not less unless the percentage exceeded 10. When the percentage is high it is best to so limit 

the weight of the sample that the amount of B2O3 shall not exceed 0.1 

gram. If a flux is used it should be weighed to within a milligram 

or two; then the amount of acid required to take up the melt can 

be measured out at once and there is no danger of using too great 

an excess.

If the mineral is soluble in hydrochloric acid, transfer 1 gram 

of it to the flask B, without letting any adhere to the neck, and treat 

with not more than 5 cm.3 of 1:1 hydrochloric acid. Heat gently 

on a water bath until solution is complete.

If the mineral is not soluble, add to it exactly six times its weight 

of sodium carbonate or of an equimolecular- mixture of sodium and 

potassium carbonates, mix, and fuse in the usual manner. Without 

removing from the crucible, decompose the melt with 1:1 hydrochloric acid in calculated amount added by degrees. While this is 

being done the crucible should rest in a casserole, and the lid should 

be kept in place as much as possible. Toward the end it may be 

necessary to heat a little, but care should be taken not to boil, for 

boric acid would be lost with the steam. Pour the solution into the 

flask B and rinse the crucible with a very little water.

Then add pure anhydrous calcium chloride, using about 1 gram 

for each cubic centimeter of solution and running it through a paper 

funnel to keep the neck of the flask clean. Twirl the flask a little 

to allow the chloride to take up the water, connect it with the rest 

of the apparatus, raise the casserole beneath it until the flask rests 

in the water but does not touch the bottom, and then begin the distillation of the alcohol from flask A, taking care that the open end
BOEOF. 237

of the capillary "boiling tube" is free from alcohol and that the 

U tube attached to the receiver is trapped with water.

The decomposition flask, B, is not heated until about 25 cm.3 of 

alcohol has condensed in it. After that the water bath is heated by

FIGURE 23. Distilling apparatus for boron.

A. Flask of 500 cm. 3 capacity for methyl alcohol, having a U tube containing a little 

mercury as a safety trap, and a capillary " boiling tube" 3 ram. in bore, the 

bore closed at 1 cm. from the lower end.

B. Flask of 250 cm. 3 capacity, supported in a casserole of water but not touching the 

bottom. The outlet tube of B should be not less than 12.cm. in vertical height 

and of rather wide bore. The end inside the flask should be jagged to allow 

condensed liquid to drop back instead of jumping up the tube.

C. Glass condenser, 40 cm. long, of tubing 3 cm, wide.

D. Receiving flask of 250 cm. 3 capacity. Two or three of these flasks should be at 

hand, with necks of the same size, so that the receiver can be changed without 

interrupting the distillation. The small U tube attached contains a little water 

to prevent the escape of any uncondensed methyl borate.

.E. (Not shown.) A second glass condenser like C, connected on the one side to a 

flask exactly like B, which, however, has a stopper with only one hole and 

rests completely within a large bath. The flask carries also a " boiling tube." 

On the other side is a receiver like D, but without the U trap. This apparatus 

is used for distilling off the alcohol after the preliminary titration.

F. (Not shown.) Filter pump. At the end of the side tube is an elbow tube connected 

to a rubber stopper with two holes and of a size to fit the flask mentioned in 

connection with E. The second hole of the stopper is closed by a glass plug, 

which can be withdrawn to break the vacuum. Midway between pump and 

stopper is a small safety bottle, to prevent the tap water from sucking back into 

the flask.

a small flame and the flask thus kept hot enough to prevent further 

condensation of alcohol. The distillation should not be so rapid 

as to permit escape of methyl borate from the system.
238 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

When a distillate of about 100 cnv3 has collected the receiver is 

exchanged for a fresh one and the collection of a second distillate 

is proceeded with. The contents of the trap tube are added to the 

first receiver, and a preliminary titration is made as follows: Add 

a few drops of paranitrophenol solution and run in the standard 

sodium hydroxide until the indicator shows that the free mineral acid 

is neutralized. Next, add 1 cm.3 of the phenolphthalein solution 

and continue the titration until the color of that indicator begins 

to appear. The end point will not be sharp, but the amount of 

alkali used between the two end points indicates approximately the 

amount of boric acid in the distillate. If the mineral is likely to 

contain more than 3 or 4 per cent of B2O3 use the 0.5 normal solution, the object being to keep the distillate as free from water as 

possible and thus facilitate the dehydration later on.

After completing the titration add to the distillate twice as much 

alkali as was used between the two end points, transfer the distillate to the second distilling apparatus, and boil off the alcohol. 

The addition of the indicated amount of alkali prevents loss of 

boron by converting unstable NaBO2 to stable Na3BO3 .

In the meantime the second distillate of 100 cm.3 will have collected. Unless the alcohol contained water or insufficient calcium 

chloride was used, this second distillate will contain the remainder 

of the boron. Therefore, before removing the receiver stop the distillation. Treat the second distillate exactly like the first and then 

add it to the first.

If the amount of alkali used for titrating the second distillate is 

less than 0.1 cm. 3 of the 0.1 normal solution the distillation may be 

regarded as complete.

When the liquid from which the alcohol is being distilled no 

longer boils in the steam bath, remove it to a casserole, rinsing the 

flask once or twice with water, and heat over a direct flame, rotating the casserole while doing so, until the little remaining alcohol 

has been boiled out. The residue should now^be small about 25 

cm.3 if 0.1 normal alkali was used and much less if 0.5. If the 

volume is less than 25 cm.3 make up to that extent.

Return the solution to the flask and add drop by drop with constant twirling 1:1 hydrochloric acid from a dropping bulb, until the 

color of both indicators is discharged, taking care not to add a drop 

too much. Now put in the "boiling tube," heat the flask in the 

steam bath for a minute or two, then attach to the filter pump and 

boil under reduced pressure until the liquid is nearly cold and only 

an occasional bubble appears. All carbon dioxide being thus removed, break the vacuum, cool if necessary under the tap, and proceed to the final titration.
BORON. 239

First neutralize the excess of hydrochloric acid by running in 

carefully 0.5 normal sodium hydroxide until the yellow of paranitrophenol just appears. Bring back to acid reaction with 0.1 

normal hydrochloric acid and then to the appearance of a faint 

yellow with 0.1 normal alkali. The solution is now exactly neutral, 

as the indicator itself shows this color in a neutral solution. Make 

sure that the end point is reached exactly. One drop of 0.1 normal 

acid should discharge the color entirely.

Now add 1 gram of mannite, read the burette, and continue titrating to the end point for phenolphthalein. Add another gram of mannite, and if this causes a disappearence of the end color add more 

alkali until it reappears.

The number of cubic centimeters of alkali used multiplied by its 

equivalent in terms of E2 08 gives the amount of the latter contained 

in the solution. If the solution of alkali is exactly 0.1 normal this 

equivalent is 0.0035.

The changes of color that take place during the titration need mention. When the mannite (or glycerol) is added to the solution the 

yellow color due to the paranitrophenol disappears at once. This is 

due to the fact that the combination of these reagents with the boric 

acid forms an acid of sufficient strength to affect the indicators, although boric acid alone does not. As the titration proceeds the color 

reappears and grows stronger, becoming very intense just before the 

phenolphthalein end point appears. The latter will be noticed as a 

faint brownish tinge, and then another drop of the 0.1 normal alkali 

changes it to an intense brownish red, which is the real end point.

Compared with the time required for gravimetric determinations 

that necessary to carry out this method is not excessive. After apparatus and reagents are ready a series of four determinations may be 

run easily in eight hours.

E. T. Alien and E. G. Zies* tested the Chapin method very fully 

in its application to the determination of boron in glasses and regard it as far superior to other methods, even though it is subject to 

a slight but very uniform correction of 1 milligram or less, to be determined by a blank run. The correction seems to be due always in 

part to a boron content of the reagents used and in part to a titration 

error. The fact that such correction is unavoidable makes the method 

of uncertain value for determining the very small amounts of boron 

that rocks may be presumed to carry, but the constancy of results is so 

great that a consistent excess found over what the blank affords is 

strong evidence that boron is actually present.

Alien and Zies found the method to be affected appreciably by relatively large amounts of arsenious acid but not by arsenic acid. The

1 Jour. Am. Ceramic Soc.,' vol. 1, 1918, p. 739. ''
240 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

effect of the former can be eliminated by converting it to arsenic 

acid by oxidizing with hydrogen peroxide after making the solution 

distinctly alkaline with sodium hydroxide.

Alien and Zies also found that relatively large amounts of fluorides 

affect the accuracy of the method but do not seriously impair its usefulness for ordinary work.

C. QUALITATIVE TESTS FOR BORON.

The detection of very small amounts of boron in rocks is not 

a simple test. E. T. Wherry and W. H. Chapin 1 found the limit 

of sensibility of the direct flame test to be 0.2 per cent. The test 

is made by mixing the mineral powder with potassium bisulphate 

and calcium* fluoride and introducing it on a clean platinum wire 

into the nonluminous Bunsen burner flame. A green color imparted to the flame, appearing only as evanescent flashes toward the 

lower limit of sensitiveness, is indicative of boron if no other elements are present that might give a green color.

Applied to distillates as obtained under B, above, the color imparted to the flame of burning alcohol by its boric ester affords a 

much more delicate test, as shown by" C. Mannich and H. Priess,2 

V. Lenher and J. S. C. Wells,3 and others.

The turmeric paper test as carried out by W. H. Low 4 gave 

Wherry and Chapin a distinct positive test for boron in a mineral 

carrying 0.08 per cent B2 03 . Low's procedure is as follows: In the 

boric solution acidified with hydrochloric acid and contained in a 

shallow dish (not glass of the boro-silicate type) is placed a piece 

of turmeric paper. The solution is then evaporated to complete 

dryness in a desiccator. Boron imparts a pinkish-red color to the 

paper if no interfering element, such as titanium, or too much hydrochloric acid, is present. The test is not applicable directly to the 

solution of a mineral, but only to distillates obtained as described 

under B, above.

The turmeric test is the most delicate of all when made with the 

precautions taken by G. Bertrand and H. Agulhon,5 for which reference must be made to the original publications. These authors applied the tests for amounts of boric oxide ranging from 0.1 milligram 

down to 0.0005 milligram. Specially prepared reagents must be used. 

E. T. Alien and E. G. Zies 6 have used the method with success. The 

basis of the test is the length of coloration imparted to small strips

'.Tour. Am. Chem. Soc., vol. 30, 1908, p. 1684.

2 Chem. Zeitung, vol. 32, 1908, p. 314.

3 Jour. Am. Chem. Soc., vol. 21, 1899, p. 417.

4 Idem, vol. 28, 1906, p. 807.

"Compt. Rend., vol. 157, 1913, p. 1433; Bull. Soc. chim., vol. 7, 1910, pp. 90, 125; 

vol. 13, 1913, p. 398. 

6 Op. cit.
CERTAIN CONSTITUENTS IN MINUTE TRACES. 241

of turmeric paper dipping into like volumes of the test solution 

and of several standard solutions contained in small graduates. 

The solutions drawn up by capillarity evaporate at the exposed 

ends of the strips, and after some hours these appear colored 

for different lengths according to the amounts of boron present 

in the different solutions. With a sufficient number of standard 

solutions the test yields fairly accurate quantitative results. Application of ammonia turns the color blue.

28. CERTAIN CONSTITUENTS IN MINUTE TRACES.

If, as sometimes may happen, the problem is presented of examining rocks for traces of gold, silver, and other elements which are not 

ordinarily looked for, as in, F. Sandberger's investigations bearing on 

the origin of the metalliferous contents of veins, large weights of 

material must be taken, up to 50 grams or more. This involves the 

use, also, of large quantities of reagents, the purity of which must 

be looked to with the utmost care. Special directions to meet such 

cases can not then be given here, nor even a complete reference list 

of the scanty and scattered literature on this subject. Sandberger's 

own writings deal but little with its analytical side, and from its inaccessibility in the Washington libraries I am as yet unacquainted 

with the report by H. von Foullon,1 "Ueber den Gang und die 

Ausfuhrung der chemischen Untersuchung," following Sandberger's 

own paper 2 in the general report "Untersuchungen der Nebengesteine der Pribramer Gange." I have published a few data as to 

gold, silver, lead, zinc, etc.,3 in S. F. Emmons's report on "The 

geology and mining industry of Leadville;" J. S. Curtis,4 in his report on " The silver-lead deposits of Eureka, Nev.," has given his 

method of assaying rocks for traces of gold and silver; in volume 7 

of the Eeports of the Missouri Geological Survey, page 740, are to 

be found the methods used by James D. Eobertson for the determination of lead, zinc, and copper in silicate and carbonate rocks of 

Missouri. The earlier work of J. G. Forchhammer 5 and L. Dieulaf ait,6 the latter of whom examined many hundreds of Archean rocks,

»Jahrb. der Bergakad. Leoben u. Pribram, 1887, p. 363.

2 From Sandberger's report it appears that the rocks were treated successively with 

water, acetic acid, boiling dilute hydrochloric acid for two days, and finally hydrofluoric acid, the several extracts and final residue of fluorides (and pyrite) being separately examined for heavy metals. The products of distillation were also examined. 

A striking fact observed in all cases was the complete insolubility of the pyrite, even 

after the severe treatment mentioned. This speaks strongly In favor of the correctness 

of ferrous iron, estimations in silicates by the hydrofluoric and sulphuric acid method 

 when pyrite is present unaccompanied by other sulphides. (See 21. D. c. a, p. 201.) "'

3 Mon. U. S. Geol. Survey, vol. 12, 1886, Appendix B, pp. 592-596.

"Idem, vol. 7, 1884, pp. 120-138.

B Poggendorff's Annalen, vol. 96, 1865, p. 60.

'Annales chim. phys., vols. 15, 17, 18, 21, 1878-1880.

131999° 19 16
242 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

was of a qualitative nature. More recent papers on the dissemination and determination of traces of gold are those of J; R. Don i and 

L. Wagoner. 2

29. THE GASES AND VAPORS EXPELLED BY HEAT.

That rocks and minerals evolve large quantities of gases and vapors 

when heated is a well-recognized fact. Numerous analyses have 

shown that the volatile products usually comprise hydrogen and carbon dioxide as preponderating constituents, with carbon monoxide, methane, nitrogen, hydrogen sulphide, etc., in smaller amounts. 

The total volume may be many times that of the solid. To a certain 

extent, sometimes a large extent, especially as to carbon dioxide, the 

source of these is entrapped fluid inclusions, whose origin was contemporaneous with that of the containing minerals. A further portion 

may have been held dissolved in the rocks, particularly in those not 

wholly crystallized. But from the experiments of some recent investigators, especially Morris W. Travers,3 A. Gautier,4 K. Hiittner,5 

and R. T. Chamberlin,6 it is very evident that the gases are often 

produced by chemical changes resulting from the heat used for their 

expulsion. Thus, hydrogen may be due to reduction of water by 

minerals susceptible of oxidation at high temperatures, as ferrous 

silicates; the carbon monoxide to reduction of carbon dioxide in a 

like manner or by the hydrogen formed by the first reaction; the 

methane might arise from interaction between water and traces of 

metallic carbides, etc.7

Free oxygen is not reported as one of the evolved gases, and from 

the nature of the case it should hardly be expected.

Nitrogen, though found in but small relative amount in the free 

state, is comparatively abundant and easily detectable as ammonia or 

ammonium salts in certain classes of rocks and long since was thus 

recognized. H. Kose8 says that pitchstone gives off ammoniacal 

water on heating; A. Delesse 9 found ammonia in rocks, and A. Gautier 

later made quantitative tests; H. Erdmann 10 found that ammonia was

1 Trans. Am. Inst. Min. Eng., vol. 27, 1897, p. 664.

* Idem, vol. 31, 1901, p. 808.

a Proc. Roy. Soc., vol. 64, 1899, p. 130.

* Compt. Rend., vol. 131, 1900, p. 647; vol. 132, 1901, pp. 58, 189 ; vol. 136, 1903, p. 16; 

Annales chlm. phys., 7th ser., vol. 22, 1901, p. 97; Annales des mines, 10th ser., vol. 9, 

1906, p. 316. .

B Zeitschr. anorg. Chemie, vol. 43, 1905, p. 8.

0 The gases in rocks, Carnegie Inst. Washington, 1908. This is a very complete discussion of the subject, supplemented by a mass of experimental data.

7 For the methods of collecting and analyzing such gaseous mixtures consult Travers, 

M. W., The experimental study of gases; the above-cited papers of Gautier; and Moureu, 

Charles, Compt. Rend., vol. 142, 1906, p. 44.

8 Quantitative Analyse, Finkener ed., p. 673.

D Annales des mines, vol. 18, 1860, p. 151.

10 Ber. Deutsch. chem. Gesell., vol. 29. 1896, p. 1710.
GASES AND VAPOKS EXPELLED BY HEAT. 243

obtained by acting on various minerals of ancient igneous rocks with 

a caustic alkali; C. Luedeking and H. A. Wheeler 1 found ammonium 

sulphate in a barite from Missouri, the presence of which I was able 

to confirm.

It has been noted in this laboratory on three separate occasions 

when series of ores, roofing slates, and eruptive rocks were analyzed, 

that ammonia, either in the form of chloride or sulphate, or even as 

free ammonia, was given off on heating. Its. appearance was not limited to one or a few specimens of a series but seemed to be characteristic of all and to be afforded by the unbroken rock as well as by the 

powdered sample. The precise conditions under which the specimens were collected not being known, it is impossible to affirm positively that the ammonia may not have been due to recent organic contamination of some sort, especially in the case of the slates, but it is 

believed that a more critical collection of material will not alter the 

general result. Its amount was sometimes readily determinable by 

Nesslerization, being as high as 0.04 per cent in some slates. Carbonaceous organic matter was absent from most of these, but doubtless existed in them in their early history. In their case the ammonia 

was evolved as such, in part, at least, and imparted a strong alkaline 

reaction to the water in the upper part of the tube. The presence of 

sulphides, fluorides, or chlorides in the rock might cause the ammonia 

to appear as a sublimate of sulphate, fluoride, or chloride. It has 

been suggested that ammonia might result from the action of water 

on metallic nitrides, O. Silvestri 2 having observed a nitride of iron 

on a lava from Etna.

30. SPECIAL OPERATIONS.

The problem presents itself often of ascertaining the composition 

o'f that portion of a rock powder which is soluble in special reagents 

or in a reagent of a particular concentration. No precise directions 

can be formulated to meet such cases. The procedure must vary 

with the character of the constituents of the rock and with the object 

which it is sought to attain, and only in exceptional cases can a separation of this kind be sharp. Much depends on the degree of fineness 

of the powder and on the length of time it is exposed to the action 

of the reagent.

A. DETECTION OF NEPHELINE IN PRESENCE OF OLIVINE.

For confirmation of the microscopic diagnosis, L. V. Pirsson 3 has 

indicated a means of detecting nepheline in presence of olivine, as 

in nepheline basalts, based on the very ready solubility of nepheline,

1 Am. Jour. Sci., 3d ser., vol. 42, 1891, p. 495.

2 Gazz. chim. ital., vol. 5, 1875, p. 301.

3 Am. Jour. Sci., 4th ser., vol. 2, 1896, p. 142.
244 ANALYSIS OF SILICATE AND 'CARBONATE BOCKS.

as compared with olivine, when boiled for but one minute with a sufficiency of very dilute nitric acid (1:40). Gelatinization of the filtrate 

on evaporation is taken as evidence of the presence of nepheline. If 

olivine is present in quantity, however, this test must not be accepted 

at once as final, for some if not all olivines are much more soluble in 

nitric acid of the above strength than Pirsson was led to believe 

from his original tests. If, therefore, oh evaporation of the filtrate, 

much iron is indicated, the gelatinization may be due to olivine alone 

or in part, and then the quantitative relation of silica to iron plus 

magnesium should be ascertained. It must be borne in mind also 

that any other very soluble silicates present will be more or less 

affected, and that apatite is largely or wholly dissolved. It is possible 

that still more dilute nitric or perhaps some other acid may exert a 

slighter solvent action on olivine without being appreciably less effective in dissolving nepheline, etc. In combination with a quantitative 

analysis of the extract the method is perhaps susceptible of a wider 

application than the particular case for which it was first used. It is 

well worth further study.

B. DETERMINATION OF " SOLUBLE " SILICA.

Very often in treatment by acids silica is separated in gelatinous 

or granular form mixed with the unattacked minerals, and it becomes necessary to remove or estimate this silica, or else to discriminate between soluble and insoluble silica already existing together. 

Usually a boiling solution of sodium carbonate has been employed 

for this purpose, though the caustic alkalies have found advocates.

G. Lunge and C. Millberg 1 have shown conclusively that quartz 

is not nearly so insoluble in solutions of the caustic alkalies as has 

been supposed, but that given a sufficient degree of subdivision it can 

be brought wholly into solution; that it is impossible to secure correct separation of quartz and opaline silica by the use of either caustic 

or carbonated alkalies; and that digestion on the water bath for fifteen minutes with 5 per cent solution of sodium carbonate is the only 

way to secure exact separation of unignited precipitated silica from 

quartz, and then only when the finest flour has been removed by 

levigation. The authors say:

If, however, no more of such flour is present than is produced in the ordinary operations of powdering and sifting through cloth of the finest mesh, the 

error arising from the above-mentioned treatment is so slight that it can 

generally be neglected; it reaches 0.1 to, at the most, 0.2 per cent of the total 

silica, by which amount the quartz will appear too low, the amorphous silica 

too high.

The above authors also show, however, that the solvent action of 

the caustic alkalies on quartz becomes very apparent only when the

1 Zeitschr. angew. Chemie, 1897, pp. 393, 425.
SPECIAL OPERATIONS. 245

material has been reduced to such an utterly impalpable degree of 

fineness as is practically never reached in the preparation of samples 

for' rock analysis. For this reason I have no hesitation in recommending the employment of a dilute solution of sodium hydroxide 

when the silica separated by acid from one of several mineral constituents of a rock is to be estimated. Even when dilution is considerable, solution is almost immediate, and as soon as this is accomplished the point being known by the change in appearance 

of the residue the solution should be diluted with cold water and 

filtered at once. The difficulty met with in filtration may often be 

overcome by faintly acidifying, which has the added advantage of 

at once arresting any further action of the alkali. If the dilution 

is sufficient no separation of silica results from so doing. Very 

dilute acid should also be used for washing. Lunge, when using 

sodium carbonate, washes with hot carbonate solution to which alcohol has been added, thus obtaining clear filtrates.

B. Sjollema 1 regards diethylamine as suitable for the separation 

of amorphous silica from quartz and silicates in soils. He found 

that a 33 per cent boiling aqueous solution of the reagent dissolved 

0.65 gram of amorphous silica practically wholly after eight hours' 

action and a 16 per cent t solution within 1 per cent, whereas the 

solubility of quartz powder was only 1.2 per cent after two days.

1 Jour, landw. Chemie. vol. 50, 1902, p. 371; abstracts in Jour. Chem. Soc., vol. 84, 

1903, p. 241; Analyst, vol. 28, 1903, p. 123; Chem. Zeitung, Rep., 1903, p. 21.
CARBONATE ROCK ANALYSIS.

III. INTRODUCTION. 

31. QUALITATIVE COMPARISON OF CARBONATE AND SILICATE ROCKS.

The analysis of an ideally pure carbonate of any one metal is of 

great simplicity. The carbonates met with in nature occasionally 

approach but probably never fully reach this condition of purity, as 

when we find them in the form of well-crystallized mineral species, 

like calcite, magnesite, siderite, and cerusite. Even in such cases it 

is usually true that the crystals either contain included foreign matter to a slight extent or are composed of more than one carbonate in 

isomorphous mixture, and then the separation of the different metals 

may demand considerable skill and time. The great carbonate formations of the earth's crust are never of this simple character, however ; even the most dazzling white marble contains other ingredients 

than calcium carbonate, and the degree of admixture may vary from 

almost nothing up to that indefinite pokit beyond which the rocks 

are not classified as limestones or dolomites, but rather as calcareous 

shales, calcareous sandstones, etc.

The matters other than carbonates which these rocks may contain 

are in the main original constituents, having been introduced at the 

time the carbonates were themselves deposited. They may consist 

of the detritus of earlier geologic formations in the form of sand or 

clay that has undergone little or no alteration in the subsequent passage of time, besides carbonaceous matter derived from the marine 

life existing during their formation. But besides these there may 

be found secondary minerals that have resulted from chemical 

transformation in the mass of the accumulated sediments, either with 

or without the powerful aid of dynamic forces like long-continued 

movements of the crust or the intrusion of hot igneous rocks. The 

metamorphism, produced by these last agencies is often of a most 

profound character and may result in the production of a great variety of minerals altogether foreign to the original sediments. The 

metamorphism may have been accompanied by the introduction and 

incorporation of new material, but even in the contrary case all the 

chemical constituents of the original detrital foreign matter have 

necessarily become a part of the carbonate rock. These constituents 

are furthermore" necessarily those common to silicate rocks of the 

earth's crust, hence the carbonate rocks differ qualitatively in no 

246
QUALITATIVE COMPARISON OF CARBONATE AND SILICATE BOCKS. 247

essential respect from their silicate associates except as to the more 

common occurrence of carbonaceous matter; and a complete analysis 

of one of them involves most of the determinations and separations 

described in, the first part of this work. The analytical procedure 

differs, however, in some respects, owing to the great preponderance 

in most cases of components easily soluble in the common mineral 

acids, which either renders it unnecessary to use an alkaline flux 

or enables the analyst to reduce its amount very materially, thereby 

simplifying subsequent operations. The analysis is further simplified by the occurrence in reduced amounts, as a rule, of those elements 

which most complicate the analysis of a silicate rock. Only in the 

very purest carbonate rocks are some of them nearly or entirely 

lacking, as silicon, aluminum, and the alkalies, but the minor constituents zirconium, barium, and strontium are often not present in 

readily determinable amount.

In the following pages the descriptions will apply especially to 

those large deposits of carbonate materials denominated limestones, 

magnesian or dolomitic limestones, and dolomites, many of which 

are of great and growing economic importance. For the purpose of 

the analyst an exact definition of these terms is of minor significance. 

Indeed, among geologists there has been no uniform rule for the 

delimitation of these rocks, and any rule made must be purely 

arbitrary, since there is absolutely no break in the series between 

limestones and dolomites. The last name applies strictly only to the 

equiatomic double salt of calcium and magnesium, CaMg(C08 ) 2 , 

and by some it is held that this should be its only application. On 

the other hand, the opposite extreme has been 'approached by those 

who contend that all limestones with as much as 1 or 2 per cent 

of magnesium carbonate should be classed as dolomites. According 

to H. Kies 1 the most prevalent practice among geologists seems to 

be to call all limestones with from 5 to 18 per cent of magnesium 

carbonate magnesian limestones and the rest limestones or dolomites, according as their magnesium-carbonate contents lie below or 

above these limits. Some, however, while subscribing to the above 

definition of magnesian limestones, would and do call those rocks 

with from 20 per cent of magnesium carbonate up to the dolomitic 

ratio dolomitic limestones. F. W. Pfaff 2 calls limestones with 11 

to 46 per cent of MgCO3 dolomites, since these are common, while 

those with 7 to 11 per cent he says are very rare, if indeed they occur 

at all.

It has seldom been considered necessary to analyze the carbonate 

rocks with any great attention to detail. The majority of analyses

1 Bull. New York State Mus. No. 44, 1901, p. 644. 

"Neues Jahrb., Bell. Band 23, 1907, p. 529.
248 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

have been made with reference to their technical utilization and with 

determination of only the more important constituents. In such 

cases it has been a common practice to omit direct determination of 

the carbon dioxide and either to calculate its supposed amount on 

the basis of the total lime and magnesia found or to regard the loss 

on ignition as representing the carbon dioxide. The portion insoluble in hydrochloric acid has been frequently stated as silica. Any 

iron that may have been determined has been reported as Fe2O3 , 

water and carbonaceous matter have been overlooked entirely or neglected, as also titanium, phosphorus, and the rarer constituents, and 

sulphur has been reported almost uniformly as SO3 . Such practice 

has repeatedly involved very gross errors of omission as well as of 

commission, which, though of little moment in many cases from the 

commercial point of view, detract much from the value of all these 

analyses in the eyes of the geologist intent on gaining an exact 

knowledge of an important formation and of the possible sources 

of metallic ore deposits of economic value, whether these last are 

residual soils resulting from the subaerial decomposition of limestone 

formations or whether they are deposits of the ores of lead, zinc, 

vanadium, etc., that have been formed, beneath the surface by the 

agency of circulating waters.

32. MINERAL COMPOSITION OF CARBONATE ROCKS.

The chief mineral compounds entering into the make-up of the 

carbonate rocks are of course calcium carbonate for the limestones 

proper, with the double carbonate, the mineral dolomite, in increasing proportions through the magnesian limestones and dolomites; 

but it is the exception to find them free from other carbonates as 

essential components, chiefly those of iron and manganese, which are 

usually in isomorphous combination with the constituents of one or 

the other of the above minerals. The proportion of these is far less 

than that of the others but sometimes aggregates several per cent. 

When they predominate the rock is no longer a limestone but becomes 

an ore of iron or manganese.

Neglect to take account of these minor carbonate constituents is a 

frequent source of error in the statement of analyses, where it is very 

common to find reported as carbonates only calcium and magnesium, 

and perhaps a considerable amount of iron as Fe2O3 and manganese 

as one of its higher oxides, although it is practically certain that 

these must have existed in large part as ferrous and manganous carbonate. A careful determination of the carbon dioxide will often 

tell whether this is so or not, for it will perhaps be found in excess 

of that required for lime and magnesia. A negative result, how-
MINERAL COMPOSITION OF CARBONATE ROCKS. 249

ever, is not to be taken as proof of the absence of iron or manganese 

carbonate or both, for very often a small portion of the magnesia 

may be in silicate combination, or in some formations there may be a 

little gypsum to claim a portion of the lime. This last is not likely 

to be the case in the average hard rock that is used for the manufacture of cement. In such the sulphur often reported as S03 is 

likely to come from iron pyrites and perhaps to a limited extent at 

times from carbonaceous matter. Hence it is easy to see that except 

in absence of iron and manganese it is not possible to ascertain the 

exact proportions of calcium and magnesium carbonates, and in some 

of the excepted cases it is possible only after separate analyses of the 

parts soluble and insoluble in dilute acid have been made.

The commonest sulphide in limestone formations is pyrite, though 

often its presence is obscured by, its extremely fine state of division 

or by carbonaceous matter. In the metamorphosed limestones, 

especially those altered by intruded igneous bodies, other sulphides, 

as sphalerite and galena, are not uncommon, and these and still 

other sulphides may form important ore bodies or again give rise 

by oxidation to equally or even more valuable ores of a different sort. 

The strongly metamorphosed siliceous limestones, however, are seldom subjected to chemical analysis, especially for commercial 

purposes.

The siliceous components may be of the most varied character. 

Their names alone might fill a page. Suffice it to mention for the 

metamorphosed rocks garnet, vesuvianite, wollastonite, tremolite, 

diopside, the scapolites, tourmaline, apatite, and silica in the form of 

chert. Cherty limestones are extremely common, and their silica was 

doubtless introduced during metamorphism. The chief siliceous 

components of unmetamorphosed limestone rocks are, as said before, 

sand and a clay. The latter particularly, since it is a clay, carries 

water, and this fact is usually overlooked in ordinary analyses. The 

analytical statements may show no water, though clayey matter is 

present to a large extent. The sand may be largely or altogether 

quartz, or it may be composed in part of such other minerals as are 

commonly found in sands, like mica, garnet, and zircon. The latter 

may often be detected, even in the less siliceous and clayey limestones, by dissolving large amounts in hydrochloric or acetic acid 

and subjecting the residue to microscopic examination, after burning 

off obscuring carbonaceous matter, if necessary. The unignited 

residue will, needless to say, contain the pyrite of the rock and any 

other sulphides not attacked by dilute acid. In some nonsiliceous 

rocks it may even consist to a considerable extent of iron oxide, 

probably in most cases one of the hydrated oxides, but perhaps often 

hematite. The presence of such a constituent in a limestone is
250 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

occasionally indicated by a reddish cast of color in the fresh rock, 

provided there is not enough carbonaceous matter to obscure it. The 

existence of a ferric oxide is not always incompatible with the simultaneous presence of this carbonaceous matter.

A purple color may be due, as in some slates, to admixture of a 

ferric oxide or hydroxide with carbonaceous matter, while to the 

latter component are due the gray and black colors often encountered. The color of greenish sedimentary limestones may be caused 

by certain minerals of the mica family, as the chlorites.

The condition of phosphorus when it occurs in only minute 

amounts is not determinable with certainty. Doubtless it may be 

found sometimes in traces in the form of heavy phosphates like 

monazite and xenotime in the insoluble residues, and again it is held by 

iron and aluminum, but in the highly phosphatic rocks its usual form 

is overwhelmingly that of phosphorite or apatite, which may in fact 

become the predominating constituent.

It is known from my analyses that vanadium is a regular though 

very minor constituent of limestones as well as of sandstones and 

igneous rocks generally. Tests on 100-gram lots of a great limestone 

formation in northwestern Mexico show that it at least carries 

molybdenum as well as vanadium, and also nickel. Nothing is known 

with certainty regarding the mode of combination of these elements 

in limestones, though it is quite possible, as to the vanadium at least, 

that it was an original ingredient of the aluminous silicates of the 

clayey matter, and that nickel, zinc, and lead when present are mainly 

in the form of carbonate or sulphide.

Carbonaceous matter has been alluded to .frequently as a common 

constituent of secondary importance. It is absent from the white 

marbles and some colored decorative stones but forms an appreciable 

percentage of other limestones in extreme cases.

Some kinds of bituminous limestone are characterized by a fetid 

odor when struck or abraded. This is perhaps due in most cases to 

hydrogen sulphide, either original or resulting from decomposition 

of organic matter. The presence of hydrogen sulphide is sometimes 

unmistakable, and B. J. Harrington determined its amount at about 

> 0.02 per cent in the form of liquid inclusions in a fetid calcite from 

Canada.

The above remarks do not exhaust the subject of the mineral composition of limestone rocks, this term being used here and elsewhere 

in its generic sense to include the magnesian varieties. They may 

serve as a sufficient guide, however, to chemists undertaking the 

analysis of these rocks. Ignorance of the minor mineral components 

has been a prolific source of error in these analyses.
ANALYSIS OF SILICATE AND CARBONATE ROCKS. 251

33. BEHAVIOR TOWARD DIFFERENT REAGENTS AS A MEANS OF DISTINGUISHING

DIFFERENT CARBONATES.

Although for the analyst provided with laboratory facilities it is 

usually of little importance to possess other means for identifying 

qualitatively the different varieties of carbonate rocks than the conventional methods of qualitative analysis, some of the rapid methods 

for so doing may serve a most useful purpose at times, especially in 

the field, where transport of bulky apparatus and quantities of liquid 

reagents is difficult or impossible.

A. DIFFERING SOLUBILITY IN TARTARIC AND CITRIC ACIDS AND IN ACID

POTASSIUM SULPHATE.

This subject, touched on now and then by earlier writers, was first 

studied by H. C. Bolton,1 and many of his results were long afterward confirmed by J. W. Richards and N. S. Powell.2 Solid organic 

acids like citric and tartaric were found to be Avell adapted for distinguishing between many carbonate minerals by the difference in 

the degree of action on them. Potassium acid sulphate had been used 

earlier to some extent by E. Jannettaz,3 and Richards and Powell 

give data as to this reagent for carbonates. It will suffice here to 

refer to the originals, especially Bolton's papers, where will be found 

data as to the solubility of a great variety of minerals in the abovenamed solvents as well as in others of inorganic nature.

B. DISTINGUISHING CALCITE FROM ARAGONITE.

In preceding editions of this work reference was made to chemical 

methods for distinguishing qualitatively calcite from aragonite. 

Since then other methods have been proposed. In the opinion of 

J. Johnston, H. E. Merwin, and E. D. Williamson 4 these tests used 

alone are indecisive, "particularly so where they would be most 

useful, namely, for the characterization of fine-grained material 

which may carry something that interferes with the test." Hence 

their description is omitted from the present volume. Optical 

methods in experienced hands are more trustworthy.

C. DISTINGUISHING BETWEEN CALCITE AND DOLOMITE.

It must be understood that magnesian and dolomitic limestones 

represent, as a rule, mixtures of the double carbonate dolomite with

1 Ann. New York Acad. Sci., vol. 1, 1877-1880, pp. 1, 153 ; vol. 2, p. 1; Froc. Am. Assoc. 

Adv. Sci., vol. 31, 1883, p. 271; Chem. News, vols. 36, 37, 38, 43, 47, 1877-1883 ; Rept. 

Brit. Assoc. Adv. Sci., 1880, p. 506; Mineralog. Mag., vol. 4, 1880-81, p. 181; Ber. 

Deutsch. chem. Gesell., vol. 13, 1880, p. 726.

3 Jour. Am. Chem. Soc., vol. 22, 1900, p. 117.

3 Compt. Rend., vol. 77, 1873, p. 838 ; vol. 78, 1874, p. 852.

* Am. Jour. Sci., 4th ser., vol. 41, 1916, p. 473. This article contains a summary of 

the literature upon the subject.
252 ANALYSIS or SILICATE AND CARBONATE BOCKS.

calcite, and not of calcite Avith magnesite. Calcite is easily soluble 

in dilute hydrochloric and acetic acids; dolomite and magnesite are 

nearly insoluble. Hence calcite effervesces strongly with these acids, 

even in lump form, while dolomite shows little or no effervescence. 

An easy means is thus afforded for distinguishing the two. Dolomitic limestones are also but feebly attacked, according to their content in calcite, so that in powder form it is not difficult to make a fair 

separation of calcite from dolomite and magnesite, but not from 

magnesian hydrocarbonates, which last, however, are never essential 

components of the great carbonate formations.

The behavior toward heat alone is sometimes useful as a distinguishing test, for dolomite loses its carbon dioxide so easily that the 

powder is violently projected from the crucible if the heat is not very 

cautiously applied, whereas calcite can be strongly heated at the 

start without danger of loss of solid matter.

J. Lemberg 1 found that calcite responds by the formation of a 

violet color in its powder when treated with a solution of aluminum 

chloride and hematoxylin (extract of logwood) but that dolomite 

remains unaffected. The solution is prepared by dissolving 4 parts 

of dry aluminum chloride in 60 parts of water, adding 6 parts of 

logwood, and boiling for 25 minutes with replacement of the escaping 

water. The deep-violet solution is then filtered.

Coarsely powdered Iceland spar and Carrara marble became violet 

after 5 to 10 minutes immersion and subsequent removal of the 

adhering solution with water. In the powder of a dolomitic limestone 

the calcite grains were easily distinguishable from those of dolomite 

by this means. It is not advisable to prolong the treatment unnecessarily, for after 20 minutes the dolomite surfaces may show occasional pale-blue spots. The reaction is caused by precipitation upon 

the calcite of aluminum hydroxide, which forms, with the coloring 

matter, a lake.

F. Hinden 2 finds that limestone (calcite) at room temperature 

gives carbon dioxide with 10 per cent solution of ferric chloride, but 

dolomite does so only on warming. A second reagent mentioned by 

him is copper sulphate solution, from which basic copper carbonate 

is separated by calcite, but is not by dolomite!

It is not known if objections similar to those mentioned in the foregoing section B, apply to the procedures of Lemberg and Hinden. 

The possibility, however, should be borne in mind.

1 Zeitschr. Deutsch. geol. Gesell., vol. 40, 1888, p. 357.

2 Verb. Naturforsch. Gesell. Basel, vol. 15, 1905, p. 1.
IV. REFINED METHODS OF ANALYSIS.

34. SILICA, ITS SEPARATION FROM ALUMINA, ETC.

A. METHODS OF DECOMPOSING THE ROCK.

Few limestones are so pure that they leave no residue on treatment 

with hydrochloric acid. The residue may consist of quartz, clay, or 

other silicates, carbonaceous matter, pyrite, etc., and the mode of 

attack employed will depend on the amount of insoluble matter, 

and whether or not it is desired to know its composition separately 

from that of the soluble portion.

a. WHEN THE INORGANIC RESIDUE IS TO BE SEPARATELY ANALYZED.

A gram of the rock powder is moistened with water and dissolved 

in dilute hydrochloric acid (or acetic, if the former acid is likely to 

act appreciably on the silicates) in a covered beaker till all effervescence ceases. Moderate heat is needed if the effervescence is so 

weak as to indicate a rock of dolomitic character. The solution is 

filtred through a 7-cm. filter and the residue washed with water, or 

hot dilute hydrochloric acid should gypsum be present and the silicates 

resistant. The paper, with its contents, is ignited moist in platinum 

(blast needed only if the amount is considerable), and after weighing 

it is fused with sodium carbonate and analyzed like a silicate rock 

(6. A. d, pp. 94 et seq.). If it contains hydrous minerals the original 

water content of the residue is best determined by a separate test on a 

fresh portion of the sample and not by drying and weighing on a 

counterpoised filter and then igniting. The weight of water found 

should be added to that of the ignited residue in order to get the 

true weight of the insoluble matter.

If the ignited residue is wholly quartz, or is very insignificant in 

amount, it may be treated at once with a drop* of sulphuric acid and a 

few drops of hydrofluoric acid, and the acids removed in the radiator 

shown in figure 2 (p. 33). If then a slight residue still is visible, it is 

well to repeat the treatment with acids and evaporation, for it can not 

be too insistently pointed out that quartz resists the action of hydrofluoric acid far more than many silicates, and several evaporations 

may be needed to volatilize the crystallized mineral unless it has first 

been reduced to a most impalpable state of division. When the weight 

after exposure for a few minutes to the full burner heat no longer 

changes, the loss represents silica. If a slight residue still shows

253
254 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

(it is most likely to be mainly alumina), the subsequently obtained 

precipitate of alumina, etc., is added to it and ignited in the same 

crucible. The filtrate is best treated as in 35. A. a, page 257.

If the original residue is small, and accurate knowledge of its composition is desired, several grams of the rock may be dissolved. In 

this case the whole filtrate from the insoluble matter is best treated 

for dissolved iron, aluminum, and manganese as in 35. A. a, page 257, 

but then only an aliquot part of the subsequent filtrate should be 

used for the determination of calcium and magnesium.

In case the filtrate from the residue is colored perceptibly by dissolved organic matter, a condition that may arise occasionally, this 

organic matter must be effectually destroyed before proceeding to the 

precipitation of iron and aluminum, for otherwise incomplete precipitation of one or both will be the result. The complete removal 

of this disturbing material can not always be effected by ordinary 

oxidizing agents, but only by evaporation and heating to its carbonization point. In doing this it .is necessary, in order to avoid possible loss of iron as chloride, to evaporate with nitric acid to dryness 

a couple of times and then to heat over a free flame gently till the 

desired result is achieved. If this seems undesirable for any reason, 

it may be better to start with a fresh portion of the limestone and to 

treat it by one of the methods given under b, below, for the bulk 

analysis.

b. WHEN THE INORGANIC RESIDUE IS NOT TO BE SEPARATELY ANALYZED.

The usual case does not involve separate analysis of the inorganic 

residue. As said above, the residue may consist of clay or other silicates, carbonaceous matter, pyrite, etc., with or without quartz. 

There are two ways open to render the noncombustible part of this 

soluble.

a. By solution in acid after strong ignition. Solution in acid after 

strong ignition is the best method to employ if the ratio of insoluble 

to soluble compounds is not less than that in an argillaceous limestone 

which is directly suite^fl for burning to Portland cement that is to 

say, if the silica does not much exceed 15 per cent and the oxides of 

iron, aluminum, and titanium together are not in excess of 6 per 

cent. The exact allowable limits have not yet been determined, nor is 

it known what the proportions may be in dolomites and dolomitic 

limestones. This is a subject for further investigation.

Limestones, however, in which the above percentages of silica, 

alumina, etc., are not exceeded may be converted in 10 to 15 minutes 

by a good blast capable of giving an effective temperature of 1,100° 

to 1,200° to a product that is wholly soluble in hydrochloric acid, 

provided the rock was first reduced to a very fine powder.
SILICA. 255

A gram of the powder is heated in a covered platinum crucible 

by an inclined blast. If a limestone, the flame may be applied at 

once, as a rule, without fear of loss, or after short exposure to a full 

Bunsen flame. Highly magnesian limestones, if this method is applicable to them, must, however, be heated with the greatest caution, 

for their temperature of decomposition is far below that of limestones, and violent projection of material often begins far short of 

visible redness.

The strong heating is usually stopped after 10 or 15 minutes, 

when the shrunken product may have the appearance of a sintered 

or even clinkered mass that detaches for the most part readily from 

the crucible.1 It is transferred to a beaker or evaporating dish and 

moistened with water. The crucible is then cleaned with hydrochloric 

acid (1 :1), and the contents are poured into the beaker or dish. By 

gentle heat and cautious pressure with the flattened tip of a rod the 

lump or lumps are caused to disintegrate and pass largely into 

solution in a few minutes. A certain amount of silica may remain 

imdissolved in a flocculent state, but this is of no moment. When 

all grit has disappeared, the liquid, if in a beaker, is washed into a 

dish and evaporated to dryness. If solution was made directly in 

the dish the volume of liquid need not exceed a few cubic centimeters 

and the evaporation takes but a short time. A much smaller dish 

is allowable than in the case of wholly siliceous minerals, because of 

the small bulk of solution and the entire absence of added fixed salts.

(3. By solution in acid after heating with sodium carbonate. When 

the siliceous components are in such amount as not to permit the 

formation of a wholly soluble product by strong ignition, it is necessary to mix sodium carbonate with the powder and decompose the 

silicates by its aid over the blast lamp. This procedure may be 

adopted with all siliceous limestones if desired. The amount of flux 

to- be used is but a fraction of that needed for a silicate analysis. 

One-fourth to one-half gram for 1 gram of limestone suffices,2 for 

the lime formed by ignition is itself a powerful flux, and it is quite 

unnecessary to have here a liquid fusion. A sintering suffices. This 

proportion holds also for highly magnesian limestones and for 

cement rocks containing as little as 50 per cent of lime.8

1 The changes that take place during the Ignition comprise loss of all carbon dioxide, 

water, and carbonaceous matter; oxidation of all pyrite, with retention of the whole of 

the sulphur as calcium sulphate. Prolonged heating will gradually expel all the sulphur trloxlde from the calcium sulphate and later the alkalies, which can be wholly 

volatilized in an hour or less by a powerful blast. With an inclined blast the alkalies 

condense in part on the under side of the lid as a soluble and powerfully alkaline 

deposit, sometimes weighing several milligrams, but in the time above set no loss of alkali 

appears to occur.

2 Shimer, P. W., in Meade, R. K., The chemist's pocket manual, p. 162. 

8 Personal communication from R. K. Meade.
256 ANALYSIS OF SILICATE AND CARBONATE EOCKS. 

B. SEPARATION OF SILICA.

In this connection the remarks under 6. B. a. (J (p. 99) should be 

carefully read.

Because of the absence of large amounts of alkali salt and of 

much silica the evaporation of the hydrochloric acid solution obtained 

in A. a and b. a and @, takes little time as compared with a silicate 

analysis. When dry, or nearly so, on the steam bath, the dish may 

be placed in an air bath or (covered) on a platinum triangle resting 

on a hot plate, and heated to 200° for an hour if a limestone is under 

treatment, but for a highly magnesian limestone the temperature 

should not exceed 120°, according to J. P. Gilbert,1 because of 

recombination of silica and magnesia, with subsequent re-solution 

of the silica when acid is added.

Bertram Blount claims 2 that by heating to 200° in this manner the 

silica is completely separated by a single treatment, but I have not 

found it so, though the amounts going into solution-on subsequent 

addition of acid are small, seldom over 2 or 3 milligrams. Therefore, 

for exact work.with silica present to the amount of 2 to 4 per cent and 

over, that already rendered insoluble should be filtered off and the 

solution again evaporated. With this end in view the dry mass is 

drenched with strong hydrochloric acid and allowed to stand for a 

few minutes, then as much water is added and the dish covered and 

placed on the bath for 10 minutes. Instead of strong acid that of 

half strength may be used and the heating begun at once. The silica 

is then separated by filtration on a filter of suitable size, washed 

thoroughly with dilute acid and then twice with cold water. The 

filtrate is evaporated again to dryness, the residue extracted with 

hydrochloric acid as before, but with allowance of only a few minutes' time and the solution filtered once more through a second and 

smaller paper. The two papers with their contents are slowly dried, 

charred, and ignited in platinum, finally over the blast for 10 minutes. The weighed silica is to be corrected for foreign matter by 

evaporating with 5 cm.3 of hydrofluoric acid and one or two drops 

of sulphuric acid, as directed in 6. B. c (p. 103). The residue obtained after ignition is almost always considerably less than that 

found in analyzing a silicate rock, and an ignition of a minute or 

two over a full burner, after expulsion of the sulphuric acid, is in 

almost all cases sufficient. The composition of this residue is similar qualitatively to that derived from silicate rocks. It should 

never contain calcium or magnesium but consists mainly of alumina, 

with a little ferric, titanic, and phosphoric oxides. It is preserved, 

and the subsequently obtained precipitate of these oxides is added 

to it and ignited in the same crucible.

1 Tech. Quart., vol. 3, 1890, p. 61; abstract in Zeitschr. anal. Chemie, vol. 29, 1890, p. 688.

2 Jour. Soc. Chem. Ind., vol. 21, 1902, p. 1217.
ANALYSIS OF SILICATE AND CARBONATE KOCKS. 257

35. ALUMINUM, TOTAL IRON, TITANIUM (SILICA, MANGANESE); PRECIPITATION 

IN COMPANY WITH PHOSPHORUS.1

The next steps differ widely according to the relative amounts of 

iron, aluminum, etc., taken collectively, and according as it is the 

intention to precipitate manganese with these or after separation 

from them. The individual preferences of experienced analysts will 

often differ as to the selection of the particular method, and it is not 

intended here to prescribe definitely the course that anyone should 

follow. Nor in the following paragraphs are all methods of separation that may be capable of affording good results noticed. There 

are some that seem promising but that have not yet been studied 

sufficiently in the Survey laboratory, nor in fact elsewhere, to justify 

description. A method that may be well adapted to a certain combination of elements may be valueless if to that combination a single 

other.element is added; or it may be that the possible disturbing influence of that element has not yet been ascertained.

A. PRECIPITATION OF ALUMINUM, IRON, ETC.

a. COLLECTIVE PRECIPITATION OF ALUMINUM, IRON, MANGANESE, TITANIUM, AND 

PHOSPHORUS BY AMMONIUM SULPHIDE.

If aluminum, iron, manganese, titanium, and phosphorus collectively represent 2 or 3 per cent or less of the rock, the filtrate from 

the silica (34. B, p. 256), reduced in bulk if need be, is put into a 

flask of 150 cm.3 capacity with enough hydrochloric acid to prevent 

precipitation of magnesium when made ammoniacal. This last is a 

most important point. Ammonia free from carbonate is then added 

to strong alkalinity and hydrogen sulphide is introduced to saturation, followed by a fresh addition of ammonia equal to the excess 

first used. Boiled water is then poured in till well up in the neck, 

the cork is inserted, and the flask is set aside for 12 to 24 hours. Its 

contents are then collected on a filter of small size (7 cm.) and washed 

with water containing a little ammonium sulphide and chloride. 

Precipitation is not absolute as to one or more of the constituents of 

the separated mixture, but the amounts recoverable from the filtrate 

are usually very minute. (For treatment of the filtrate, see 38, p. 262.)

The paper and its contents, having been washed with ammonium 

chloride, may be safely charred and ignited as they are, in the crucible containing the residue left after volatilizing the silica. The final 

weight after ignition in full contact with air, followed by application of the inclined blast 'for not over 5 minutes, represents A12 08, 

Fe,O3 , Mn;j O4 , TiO2 , and P2 05 . (For the separation of these, see C, 

p. 259.)_____________________________________

1 See also section 8, p. 106. 

131999° 19 17
258 ANALYSIS OF SILICATE AND OAEBONATE ROCKS.

This method is inapplicable for phosphatic limestones containing 

insufficient aluminum 'to more than combine with the phosphorus, ~f or 

then calcium phosphate would be precipitated also. In such case 

method b or c would apply if the iron and aluminum together more 

than sufficed to carry down the phosphorus, but in .general it would 

be necessary to add a known amount of pure iron oxidized to the 

ferric state, then to precipitate by ammonia or the basic-acetate 

process, and to deduct the added iron oxide from the weight obtained.

b. PKECIPITATION OF ALUMINUM, IKON, TITANIUM, AND PHOSPHOBUS BY AMMONIA.

The filtrate from silica is boiled in a beaker of good glass, with 

addition of a few drops of bromine water or two or three drops of 

strong nitric acid, till all trace of bromine or chlorine is gone. Then 

hydrochloric acid is added, if not already present, in amount sufficient 

to prevent precipitation of magnesium when rendered ammoniacal. 

A few drops of methyl red solution are added and the liquid (100 

to 200 cm. 3 in volume) is heated just to boiling. Neutralization is 

then brought about by means of ammonia (dilute toward the end) 

until the color of the solution changes to a distinct yellow. It is 

then boiled for 1 or 2 minutes, allowed to settle, filtered, then at 

once washed two or three times with hot ammonium chloride solution (2 per cent), and sucked dry. (Consult 8. B. a. £, p. 107.) 

The precipitate is then redissolved in hot and moderately strong' 

hydrochloric acid, the solution is boiled to drive out the trace of 

chlorine derived from solution of any precipitated manganese dioxide, and the precipitation is repeated one or more times just as described, according to the amount of manganese in the rock. Macerated 

filter paper is added before the last precipitation if the oxides are 

in large amount. The final precipitate is washed with water containing a little ammonium chloride. (For treatment of the filtrate, 

see B, below.)

The precipitate is ignited moist in the crucible containing the 

residue from volatilization of the silica by hydrofluoric acid, and 

the combined weights increased by traces subsequently recovered 

(B, below) represent all iron as Fe2O3 , A12O3 , TiO2 , and P2O5 . (For 

separation of the ignited oxides, see C, p. 259.)

C. PRECIPITATION OF ALUMINUM, IRON, TITANIUM, A1STD PHOSPHOBUS BY THE BASICACETATE METHOD.

The basic-acetate method of separation is less employed in limestone analysis than in that of silicate rocks, by reason of the relatively smaller amounts of those elements that precipitate in the basicacetate process, and hence of their more ready separation by ammonia from appreciable quantities of manganese. (For its application, see 8. B. b. (3, p. 130, giving due regard to the smaller amounts of 

iron, etc., involved in the case of limestones.)
ALUMINUM. 259

B. TREATMENT Or THE FILTRATES PROM ALUMINA, ETC.

The combined filtrates obtained in A. b (or c), above, which, besides all the calcium and magnesium, will contain the manganese and 

usually traces of aluminum and even iron, are evaporated to a small 

volume in platinum with the addition of a few drops of ammonia 

from time to time, and any precipitate that separates is collected. 

This is washed a little, redissolved in hydrochloric acid (with addition of a drop or two of sulphurous acid if its color indicates precipitation of some manganese), and reprecipitated by ammonia at 

boiling heat in a very small beaker. If need be the precipitation 

is to be again repeated, but this will seldom be the case. A first 

precipitation is, however, called for in order to separate a little calcium carbonate that may have precipitated during the evaporation 

of the original ammoniacal filtrate. The alumina and perhaps trace 

of iron oxide thus obtained are added to that already found (A. b 

or c, p. 258). (For treatment of the filtrate, see 36, p. 260.)

C. SOLUTION AND SEPARATION OF THE OXIDES OBTAINED IN A AND B.

The same course is followed, whether method a, b, or c under A 

(pp. 257-258) has been employed for precipitating aluminum, iron, 

etc. According to the weight of the ignited oxides, these are fused 

with from one to several grams of potassium or preferably sodium 

pyrosulphate * in the covered crucible over a low flame. By using 

pyrosulphate instead of acid sulphate the time of fusion is greatly 

shortened, especially when the oxides are in a finely divided state, as 

after precipitation in presence of macerated filter paper.

When decomposition is complete the cooled melt is dissolved in hot 

dilute sulphuric acid, the solution is transferred to a capacious platinum dish and evaporated as far as practicable on the bath. Strong 

sulphuric acid is cautiously added, and evaporation is continued over 

a radiator, or on a sand bath, or by aid of a free flame applied with 

care to prevent spattering, till fumes of acid appear freely. When 

cool, the melt should be rather pasty and not hard and dry. It is 

dissolved by the aid of heat in a moderate amount of water, and the 

solution is allowed to digest for 10 to 15 minutes on the bath. A few 

flocks of silica will then generally be apparent at the bottom of the 

dish. Whether visible or not, the solution is passed through a 7-cm. 

filter, which is then washed with hot water till free from salts.

a. SILICA (BARIUM).

The paper with the silica is ignited, weighed, and then treated with 

a drop of sulphuric acid and a few drops of hydrofluoric acid and the 

crucible, after ignition, is again weighed. The loss represents silica 

that escaped earlier separation, and its amount is to be added to that 

already found. _______________ 

1 For its preparation see p, 46.
260 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

If a final residue is reddish, it is to be brought into solution by a 

little pyrosulphate and its solution, if clear, added to the main filtrate 

containing the mass of the iron. If not clear, the turbidity may be 

clue to a trace of barium sulphate, which should of course be separated and deducted from the weight of the alumina plus other oxides.

b. IRON.

In this solution the iron is to be determined by potassium permanganate after reduction by hydrogen sulphide, exactly as detailed 

under 9. C. a (p. 119). The amount of vanadium present is, so far as 

known, always so small as to make it unnecessary to follow the procedure under 9. C. b (p. 121).

C. TITANIUM.

After titration of the iron the solution is treated exactly as prescribed under 9. C. a. 0 (p. 120), and the titanium is determined 

colorimetrically (p. 155).

d. ALUMINUM.

The aluminum is determined by difference after subtracting the 

weights of iron and titanium oxides found as above, and also the 

phosphoric oxide found in a separate portion of the sample (39, p. 

263), and further the manganoso-manganic oxide, if this had intentionally been precipitated along with the iron and aluminum as in 

A. a (p. 257). (For the discussion of the relative merits of 'this 

indirect and the direct methods for arriving at the aluminum, see 9. 

A, p. 115, and 10. A, p. 126.)

36. MANGANESE.

A.-IN THE FILTRATES FROM 35. B.

The filtrates containing the calcium, magnesium, and manganese 

are caught in a flask of about 150 cm.3 capacity, 2 cm.3 of ammonia 

is added, and hydrogen-sulphide gas is introduced to saturation, 

then additional ammonia is added to equal that just prescribed. The 

flask is stoppered and set aside for 12 to 24 hours, the precipitate 

(perhaps colored dark by a little platinum, iron, or other heavy-metal 

sulphide 1 ) is collected on a 7-cm. filter and washed with a dilute 

solution of ammonium chloride carrying a little ammonium sulphide.2 (For treatment of the filtrate, see 37, p. 261.)

1 More than a negligible trace of iron should not appear at this point. If, however, the 

organic matter of the limestone is at all soluble in acids and the method of direct 

solution has been employed, it may very well happen that some iron (aluminum likewise) 

will fail of precipitation by ammonia. The former will then appear at this stage. Hence, 

prior ignition of the limestone is imperative in such cases.

2 This is best prepared by considerably overneutralizing a little hydrochloric acid in 

a small beaker, and then adding hydrogen sulphide water or introducing hydrogen sulphide 

gas for a few moments, aud further diluting if need be.
COPPER, NICKEL, COBALT, LEAD, ETC. 261

If the manganese is not to be determined in a separate portion of 

the rock, the flask is then cleaned from possibly adhering sulphide 

with a solution of half-strength hydrochloric acid diluted with five 

times its volume of hydrogen sulphide water, which is then passed 

through the filter in order to dissolve the manganese sulphide. The 

filtrate is treated exactly as under 11. B. b (p. 136), if the gravimetric 

method of determination is chosen. In view of the relatively enormous errors affecting this method when small amounts are in question 

(see 11. A, p. 134), it is far safer to evaporate the hydrochloric acid 

solution with nitric or sulphuric acid, till no trace of chlorine is left, 

and to apply the colorimetric method (11. C. b, p. 137).

If the manganese is to be determined in a separate portion, the sulphide precipitate is .discarded; indeed, if it is known that but a few 

hundredths of 1 per cent are present, its separation at this stage may 

be altogether omitted.

B. SEPARATE DETERMINATION OF MANGANESE.

Small amounts of manganese are always determined best by colorimetry, and then with greatest accuracy in a separate portion of 

the sample. This, if wholly soluble in acid, is to be dissolved by 

dilute nitric acid free from hydrochloric acid, the solution filtered 

if necessary, and further treated, in whole or in an aliquot part, as 

in 11. C. b (p. 137). If not altogether soluble in acid or if the solution is colored by organic matter, it is best to heat the powder with 

half its weight of sodium carbonate (itself free from manganese) 

over a strong blast, to digest the cooled mass with nitric acid till 

any residue that may remain is entirely colorless, to filter into a 

suitable-sized flask, and to determine as in 11. C. b (p. 137).

37. COPPER, NICKEL, COBALT, LEAD, ZINC, RARE EARTHS, CHROMIUM, VANADIUM,

MOLYBDENUM.

It is commonly useless to look for copper, nickel, cobalt, lead, zinc, 

rare earths, chromium, -vanadium, or molybdenum in a sample so 

small as that taken for the general analysis. To detect these from 50 

to 500 grams of material will be required, which should be dissolved 

in hydrochloric acid and the residue separated by filtration. If it is 

desired to examine this residue, it is analyzed separately, after 

fusion with sodium carbonate and leaching with water. Chromium, 

vanadium, and molybdenum will then be found in the filtrate, 

.the other metals in the residue. The former can be determined according to 20 (p. 184); the latter by the usual methods.

For the hydrochloric acid solution, which will contain the above 

.elements mainly or wholly, the treatment given under 35. A. a
262 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

(p. 257), is probably best adapted, and the following outline may 

serve as a guide:

The precipitate produced by ammonium sulphide is to be dissolved, the copper and perhaps some molybdenum precipitated by 

hydrogen sulphide, the filtrate oxidized and evaporated to dryness, 

and the residue boiled with a solution of oxalic acid. The rare 

.earths, perhaps contaminated by silica, will be thrown out and are to 

be washed with dilute oxalic acid solution, ignited, treated with sulphuric and hydrofluoric acids, redissolved, and reprecipitated in 

neutral or nearly neutral solution by oxalic acid, ignited, and 

weighed. They can then be tested as to their character by methods 

to be found in special treatises on the rare earths. The filtrates are 

freed from oxalic acid by evaporation and gentle ignition and the 

residue is redissolved and tested for nickel, cobalt, zinc, chromium, 

vanadium, and motybdenum by approved methods. It must not be 

forgotten that the filtrate from the original precipitation by ammonium sulphide may hold most of the vanadium and molybdenum, and 

perhaps nickel, which are to be recovered by acidifying with dilute 

acetic acid.

Vanadium may usually be found and determined with sufficient 

accuracy in 5 grams of the limestone by fusing with sodium carbonate and further treating as in 20. C (p. 185).

38. CALCIUM, STRONTIUM, BARIUM, MAGNESIUM (MANGANESE). 

A. ORDINARY PROCEDURES.

The nitrate obtained in 35. A. a (p. 257), or 36. A (p. 260), is 

treated for the most part as in silicate analysis (pp. 135-153).

With dolomitic limestones and dolomites it will be usually impossible to obtain a correction by the method given in 13. C. b. (i (p. 152) 

for the small amount of calcium, with the magnesium pyrophosphate. 

The first of the methods there given (a) is to be followed.

The accurate determination of barium in a limestone is more difficult than in a silicate rock. It is perhaps best to recover it, if present, 

from the filtrates from the calcium oxalate, after evaporating them 

and expelling ammonium salts, by taking up the' residue in as little 

hydrochloric acid as possible and, without filtering, adding a few 

drops of sulphuric acid and allowing to stand for several hours. The 

washed and ignited precipitate is evaporated with a drop of sulphuric 

acid and a few drops of hydrofluoric acid to remove silica, the final 

residue is dissolved by a little Tiot strong sulphuric acid, and the resulting solution poured into a few cubic centimeters of cold water, the 

crucible being well rinsed with cold water by the aid of a feather or 

"policeman." If a precipitate now appears it is barium sulphate, 

which is collected and weighed in the customary manner.
PHOSPHORUS. 263

To the filtrate is added enough hydrochloric acid to prevent pre^ 

cipitation of magnesium when rendered amnioniacal. Ammonia in 

slight excess is added and the solution is boiled for some -minutes in a 

platinum dish. There will probably appear a very slight precipitate 

containing aluminum hydroxide, which is to be redissolred and reprecipitated. In the filtrate the magnesium is precipitated, together 

with any manganese that may be present, in the manner elsewhere 

detailed (13. A, p. 148).

IS. SEPARATION OF LITTLE CALCIUM FROM MUCH MAGNESIUM MAGNESITB

ANALYSIS.

In section 12, under A. -d (p. 142) are given procedures which appear 

 to be the best for separating little calcium from much magnesium, as 

these occur in the commercially important mineral magnesite and its 

product of calcination. A method of F. Himdeshagen l has been condemned by Kallauner and Preller.2 but in the light of what is said in 

section 12. A. d, the'practiced analyst may perhaps be able to adapt 

the procedure to the complete analysis of magnesite or of any mineral 

that carries a great deal of magnesium .and very little calcium.

39. PHOSPHORUS.

In determining phosphorus the rock is dissolved in dilute nitric 

acicl, the solution filtered, the residue fused with a little sodium 

carbonate, and its nitric acid solution added to the other.

Or, if the rock is rather argillaceous, the powder may be mixed 

with half its weight of sodium carbonate and strongly blasted. The 

nitric acid solution of the mass is then evaporated to dryness to 

remove most of the silica, which is collected on a filter, washed, 

ignited, and evaporated with hydrofluoric and nitric acids. The 

evaporation with nitric acid alone is repeated once or twice to expel 

the fluorine, and the residue is dissolved finally in nitric acid and its 

solution added to the former.

To the solution obtained in either of the above ways ammonium 

molybdate solution is added, and the precipitate is treated by one 

of the approved methods.

In limestones very low in phosphorus it may be deemed desirable 

to concentrate the pliosphorus from a considerable weight of sample. 

F. Hinden 3 suggests the following way to do this:

To the nitric acid solution add ammonia until the liquid becomes 

slightly turbid. (Add a few drops of ferric chloride solution if

1 Zeitschr. offerntliche Chetnie, vol. 15, 1909, -p. 85.

2 Chem. Zeitung, vol. 36, 1912, p. 462.

3 Zeitschr. anal. Chemie, vol. 54, 1915, p. 214.
264 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

iron and aluminum are absent.) Then add half a gram of pure 

precipitated calcium carbonate and boil for five minutes. Filter, 

dissolve the precipitate in dilute nitric acid, and precipitate the 

phosphorus as phosphomolybdate.

40. FERROUS IRON.

The presence of carbonaceous matter in limestones renders the exact 

or even approximate determination of ferrous iron often impossible. 

Nevertheless, even in its presence acceptable results are sometimes 

obtainable if there is not much of such matter and if it does not give 

with acid a colored solution. But even then it is only the soluble 

iron, existing chiefly if not wholly as carbonate, that is determinable. 

Occasionally limestones show films of manganese peroxide, which 

likewise interferes with the determination.

A. IN THE ABSENCE OF CARBONACEOUS MATTER, 

a. FERROUS IRON SOLUBLE IN SULPHURIC ACID.

The powder, 1 gram to several grams, is introduced into a stout flask 

of about 200 to 250 cm.3 capacity and boiled with a little water till 

all air is expelled. While still boiling, dilute sulphuric acid is added, 

a little at a time, till effervescence ceases, and then a further amount.- 

Calcium sulphate precipitates, but the iron will remain in solution. 

The flame is then removed and a stopper tightly inserted, through 

which passes a small stopcock funnel. When cool or nearly so, cold 

water is poured into the funnel, the cock cautiously opened, and the 

water "drawn into the flask, more water being poured into the funnel 

as fast as it empties, till the solution amounts to 100 or 150 cm.3 

Such precaution to exclude air is hardly necessary in most cases, 

however, for in presence of sulphuric acid the oxidation of ferrous 

iron is exceedingly slow. It is ordinarily quite sufficient to equalize 

the internal and external pressures by opening the cock, removing 

the stopper, and pouring in cold water. The flask is then brought 

under a burette containing dilute permanganate solution and the 

iron titrated without delay. With a carbonate which is wholly decomposable without the aid of heat, solution may be accomplished 

in a flask filled with carbon dioxide, using cold acid, whereby the 

danger of attack of silicates is lessened if these are present. If the 

preference is for the potassium-bichromate method of titration, 

hydrochloric acid may be used instead of sulphuric, in absence of 

manganese peroxide. In this case there is, of course, no separation 

of an insoluble calcium salt, a fact which renders easier the-subse-
ALKALIES. 265

quent determination of the iron in any insoluble residue the rock 

may yield. The ferrous iron thus found is mostly, if not altogether, 

that existing as carbonate.

b. FERROUS IRON IN THE INSOLUBLE RESIDUE.

The titrated solution is filtered through a medium-sized hardened 

filter, the insoluble matter collected thereon and washed with water. 

The contents of the paper are rinsed into a capacious platinum crucible, the water mostly evaporated, and in the residue the ferrous iron 

is determined as in 21. D. d (p. 203).

The total ferrous oxide found in a and b, when calculated to ferric 

oxide and subtracted from the total iron in the same state, gives the 

ferric oxide in the rock. If separate analyses have been made of the 

parts soluble and insoluble in dilute acid, similar calculations applied 

to the iron derived from the two portions will give the ferric oxide 

in each.

C. TOTAL FERROUS IRON.

If separate determinations are not desired, water is poured upon 

the powder in a capacious platinum crucible, dilute sulphuric acid is 

slowly added till effervescence ceases, then the crucible is placed in 

one of the forms of apparatus described in 21. D. d (p. 203), together 

with 5 cm.3 of hydrofluoric acid, the decomposition of the silicates 

is effected in an atmosphere of carbon dioxide, and the titration is 

made as there directed.

B. IN THE PRESENCE OF CARBONACEOUS MATTER.

Decomposition is effected in a flask by dilute sulphuric acid in an 

atmosphere of carbon dioxide. With limestones and active agitation 

no heat need be used, but with dolomites it will be necessary. The 

solution is then filtered quickly through asbestos (in an atmosphere 

of carbon dioxide if much iron is present), the residue and filter 

washed a few times, and the filtrate titrated at once with permanganate. If it is colored by organic matter, the result may be in error.

As in 40. A. a (p. 264), hydrochloric acid and titration by dichromate may be used in the absence of manganese peroxide. In either 

case it is important to allow the acid to act no longer than is necessary and to filter quickly. A determination of the ferrous iron in th 

insoluble matter is usually not worth attempting, because of the 

admixed'organic matter.

41. ALKALIES.

The alkalies in carbonate rocks are, of course, constituents of the 

siliceous components. As these are usually subordinate, it is advis-
ANALYSIS OF SILICATE AND CARBONATE ROCKS.

-able to operate on not less than 1 gram of the powder, and the J. Lawrence Smith .method is to be followed in nearly all its details (22, 

p. 207). Because of the presence of a large amount of calcium carbonate in the rock it might seem that addition of precipitated carbonate would be needless. That it is not, however, appears to have 

been shown by experiments made with and without its addition. A 

little more alkali was obtained in the former case, a result that is 

probably due to more effective reaction of the finely divided artificial 

carbonate than of the crystalline natural carbonate with the ammonium chloride. One-half the usual amount of precipitated carbonate 

will suffice.

42. CARBON DIOXIDE, OARBON (WATER).

A. DETERMINATION OF CARBON DIOXIDE.

The determination of carbon dioxide is made precisely as under 

23. B (p. 217). If the absorption tubes have a height of about 10 

cm. and a diameter of 1.2 cm. the first one will need refilling after 

every second analysis. For this reason Liebig or Geissler bulbs containing potash solution may be preferred.

B. DETERMINATION OF CARBON OF CARBONACEOUS MATTER. 1

The character of the carbonaceous matter in limestones has not 

been made the subject of study, so far as known to me, but it seems 

reasonable to assume that it resembles coaly matter rather than the 

indefinite humus. Although on solution of the rock in dilute acids 

the odor of the escaping gas is sometimes indicative of volatile 

organic, substances, the amount thus escaping can never be more than 

a small fraction of the total. If the rocks are boiled with acid the 

filtrate may be somewhat colored, but if care is taken to use dilute 

acid and to filter as soon as its action on the carbonates is over, little 

or no organic matter is likely to pass into solution. Hence, in all 

such cases the following method for the determination of its carbon 

is indicated, provided sulphides are practically absent:

Treat 1 to 10 grams of the rock with dilute hydrochloric acid till 

the carbonate constituents are surely decomposed, filter through an 

asbestos plug filling a constriction in a glass combustion tube, wash 

thoroughly with water, dry, and burn the carbonaceous matter over 

an ordinary burner in an air or oxygen current, collecting the escaping water in a calcium-chloride tube and the carbon dioxide in one

1 Since this text was written a paper has appeared upon the determination of combustible matter in silicate and carbonate rocks which takes account of the hydrogen as 

well as to« carbon of the organic matter. (Fieldner, A, C., Selvig, W. A., and Taylor, 

G. B., Tech. Paper Bur. Mines No. 212, 1919.)
CHLORINE. . 267

filled with soda lime. The combustion need occupy but'a few 

minutes as a rule.

If the rock is free from hydrous minerals, if the asbestos likewise 

yields no water on ignition, and if the asbestos and its load have been 

thoroughly dried, from the gain in weight of the calcium chloride 

tube the hydrogen of the organic matter may be calculated. These 

conditions will, however, seldom be fulfilled, so that only the carbon 

has to be considered. In fact, it is quite useless, ordinarily, to attempt 

to determine the organic matter as such, either directly or by calculation. One must perforce be content with knowing its contained 

carbon.

C. SIMULTANEOUS DETERMINATION OF AVATER AND OF TOTAL CARBON.

In presence of sulphides or soluble organic matter the following 

method will sometimes answer for the simultaneous determination 

of water and of the carbon of carbonates and organic matter.

. Ignite in a current of air 1 gram of the rock in a tube of very hard 

glass, or in the tubulated crucible of Gooch (fig. 16, p. 85), collecting 

the water and the carbon dioxide as in B. The sulphur of sulphides 

will be retained as calcium sulphate. It is necessary for the success of 

this operation that the temperature be sufficient to drive out all carbon dioxide from the carbonates, but insufficient to decompose calcium sulphate. The water found represents that in the minerals of 

the rocks as well as that derived from the hydrogen of the organic 

matter.

A separate determination of the carbon dioxide (see A, p. 266) 

gives the data for calculating the carbon of the organic matter.

According to G. T. Morgan 1 the two conditions of carbon can be 

determined successively on the same portion of sample by first finding 

the carbon dioxide as in A, but with substitution of orthophosphoric 

for hydrochloric acid, and then, after weighing and replacing the 

absorption tubes, adding chromic acid and renewing the boiling to 

oxidize the organic matter and liberate its carbon as CO2 .

43. CHLORINE.

Several grams of the rock is dissolved in the cold, or with as low 

a heat as may be, in dilute nitric acid free from chlorine, the solution 

is filtered, silver nitrate added, and the precipitate collected and 

treated as.usual. (See 24, A, B, and C, pp. 220-221.)

If the rock is likely to contain chlorine-bearing silicates, it is decomposed with its own weight or less of chlorine-free sodium carbonate in a platinum crucible over the burner or moderate blast without undue prolongation of the heating. The mass is extracted with 

_____________________\ ____________,________ 

1 Jour. Chein. Soc., vol. 85, 1904, p. 1001.
268 ANALYSIS OF SILICATE AND. CARBONATE ROCKS.

hot water and the filtrate acidified with cold dilute nitric acid, or it 

may be decomposed directly with the acid and the solutions filtered. 

The further treatment is as above given.

44. FLUORINE.

As with silicate rocks, an exact determination of fluorine in carbonate rocks is difficult if not impossible with our present methods, 

and little or nothing has been done along this line.

Because of the great preponderance of lime, direct fusion with 

sodium potassium carbonate and silica is of somewhat doubtful 

practicability. Probably the following treatment will afford the 

best results:

Dissolve the powder in dilute acetic acid, as far as this may be 

possible without boiling, and filter. To the filtrate add a solution of 

sodium carbonate till in some slight excess, boil, and treat the precipitate of calcium carbonate and possible fluoride as described on page 

224. Most of the fluorine that may have been dissolved by the acetic 

acid will thus be found. The siliceous matter insoluble in acetic acid 

is fused with sodium-potassium carbonate.and further treated as in 

25. B. a (p. 222).

45. SULPHUR.

A. TESTS AS TO ITS CONDITION; DETERMINATION OF SULPHATE SULPHUR.

In very many, perhaps most, carbonate rocks any sulphur present 

is chiefly if not wholly in the sulphide condition, and then usually 

as pyrite. In what condition it may be is readily ascertainable. If 

moistened lead-acetate paper is blackened when held over the mouth 

of a test tube in which some of the rock powder is being boiled with 

dilute hydrochloric acid, a soluble sulphide is indicated, but it is 

seldom more than a negligible trace. If the filtrate after approximate neutralization with ammonia gives a precipitate with, barium 

chloride there is sulphate present. If the total sulphur obtained 

as in B, below, is in excess of that in the sulphate -and soluble-sulphide states, the difference may safely be calculated to iron disulphide.

In the presence of much sulphide and also of sulphate sulphur the 

extraction of the latter should be made in an atmosphere of carbon 

dioxide, but usually this precaution is quite unnecessary. For details of the determination of sulphur consult section 26 (p. 230).

B. DETERMINATION OF TOTAL SULPHUR, 

a. METHODS OF CONVERTING SULPHIDES TO SULPHATES.

a. By ignition withcmd flutv. In a rock that is not heavily charged 

with sulphides the following method of my own has afforded excel-
WATER. 269

lent results, even in the presence of 1 per cent of organic matter, 

though its range of application has not been ascertained:

The platinum crucible containing 1 or 2 grams of the rock powder 

is placed in the perforated disk (fig. 3, p. 34) and exposed to the heat 

of a burner for fifteen minutes or to that of an inclined and moderate 

blast for ten minutes. So far as present experience teaches, it is not 

at all necessary to begin with a gentle heat. All sulphide sulphur is 

oxidized and retained by the lime as sulphate without any loss by; 

volatilization, all organic matter is removed, and the silicates are 

rendered soluble in acid if they are not in excess. (See 34 A. b. a, 

p. 254.)

[3. By ignition with sodium carbonate. From 1 to 2 grams of 

powder is mixed with half the weight of sulphur-free sodium carbonate in a platinum crucible and heated in the perforated disk, as 

in a. It is not probable that the addition of niter is called for, even 

when a good deal of carbonaceous matter is present. Since not 

enough flux is used to produce more than a sintering, the air entering the crucible after the bulk of the carbon dioxide has passed off 

effects very speedy oxidation in the porous mass.

With highly impure limestones it may be necessary to increase 

the amount of flux and to use a little niter as well.

b. TREATMENT AFTER IGNITION.

The ignited mass obtained in a. a or (i will usually separate easily 

from the crucible. It is transferred to a small beaker and covered 

with water. The crucible is cleansed with dilute hydrochloric acid 

and the solution poured into the beaker. More acid is added till 

decomposition is complete in the cold or on gently warming. The 

solution is then filtered, diluted if need be to 150 or 200 cm. 3 , brought 

to boiling or simply placed on the steam bath, barium chloride added, 

and. the precipitated sulphate collected in due time and weighed as 

usual.

Evaporation to dryness to separate the dissolved silica is quite 

unnecessary. After decomposition with "acid the solution should 

never be permitted to gelatinize, and it needs but little practice on 

the part of the operator to insure unfailing success in preventing this. 

If it should happen, however, it is generally best to begin over, but 

the difficulty may be overcome if but little free acid is present by 

dissolving the gelatinized silica in sulphur-free fixed alkali and 

reacidifying in the cold with hydrochloric acid.

46. WATER. 

A. HYGROSCOPIC WATER.

From one to several grams of the air-dry powder is heated in a 

current of air dried by calcium chloride in a glass tube at 100° to
270 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

105° and the escaping water is collected in a calcium chloride tube, 

or the air may be dried by sulphuric acid and the water collected in 

sulphuric acid. This direct determination of the water is certain 

to give a higher and more correct result than that obtained by drying in a crucible at the above temperature.

B. FIRMLY HELD WATER.

Combined water may be determined ordinarily on the air-dry 

sample by heating in a tube of combustion glass and collecting the 

water in a calcium chloride tube with the above-mentioned precautions. Or the powder may be mixed with dry sodium carbonate and 

heated in>the apparatus of Gooch (5. C. f, p. 85). From the result 

thus found the separately determined hygroscopic water is to be deducted. It is to be remembered that tlie result will be in error by 

the amount of water afforded by the hydrogen of any organic matter 

there may be in the limestone.
V, CONDENSED ANALYSIS.

For many purposes, especially those with a technical end in view, a 

highly refined or detailed analysis is not called for. The analyses of 

this kind that .are now made vastly exceed in number those demanding the kind of work provided for in many of the sections of Part IV. 

To meet the needs of those having work of this kind to do, a procedure is here given in brief that covers the important constituents 

of limestones. The operations are generally given without explanations. Those who seek reasons for one or another procedure or defails of manipulations are referred to the corresponding sections of 

Part IV.

47. DECOMPOSITION AND SOLUTION.

If the substance is convertible by blasting into a condition wholly 

decomposable by hydrochloric acid, 0.5 to 1 gram of the fine powder 

is strongly ignited in a covered platinum, crucible over the blast for 

15 minutes, or longer if the blast is not very powerful.

If the material is very impure, 0.5 to 1 gram is to be mixed with 

half its weight of pure sodium carbonate and ignited over the burner 

and blast till well sintered together.

The ignited material obtained in either of the above ways is transferred to an evaporating dish, preferably of platinum, and moistened 

with a few cubic centimeters of water. The crucible is cleaned with 

dilute hydrochloric acid, the solution poured into the dish, which is to 

be kept covered if sodium carbonate was used, and more acid added. 

Solution of the mass may be aided by gentle pressure with the flattened end of a glass rod. The solution is then evaporated to dr^yness on the steam bath. It will do no harm with limestones low in 

magnesium to hasten dehydration of the silica by placing the dish 

with its dry contents in an air bath at an elevated temperature or 

on a triangle resting on a hot plate at 200° for an hour or less.

48. SILICA.

The residue is treated with 5 to 10 cm.8 of strong hydrochloric 

acid, which is then diluted to half strength, or upon the residue may 

be poured at once a larger volume of acid of half strength. The dish 

is then covered and digestion allowed to go on for 10 minutes on the 

bath, after which the solution is passed through a 7-cm. paper and 

the silica washed with water, cold at first .and hot later, or with hot 

dilute hydrochloric acid at first, followed by a little hot water. 

The filtrate is again evaporated to dryness, this time only on the 

steam bath, after which the residue is digested with acid as before, 

bnt in smaller amount, and the second portion, of usually dark-col271
272 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

ored silica, is collected on another small paper. The filter papers 

with their contents are slowly charred in a platinum crucible, then 

ignited, first over the burner, finally over the blast for 5 to 15 

minutes, according to the amount of the silica. If the blast is weak, 

a second application of it should follow the first weighing. The 

finally weighed silica is moistened with water, and two drops of sulphuric acid and. 5 to 10 cm.3 of pure hydrofluoric acid are added, 

the crucible is placed in a radiator (fig. 2, p. 33), and the liquid 

wholly evaporated. The- residue is blasted for a minute and in due 

time weighed. It is better not to make this correction if it is not intended to separate and determine also the silica always accompanying the iron and aluminum oxides, for the reason that with the 

small amount of silica in limestones the nonvolatile residue compensates more or less for the silica remaining in solution after the 

second evaporation; but it should never be omitted if this latter correction is contemplated.

49. ALUMINUM, IRON, ETC.

The filtrate, which need not exceed 100 cm.3 in bulk with fairly 

.pure limestones, is brought to boiling in a beaker, or preferably in 

platinum, and made alkaline with ammonia after adding a few cubic 

centimeters of bromine water, and if need be enough hydrochloric 

acid to insure a total of 10 to 15 cm. 3 of strong acid. The ammonia 

should not be in such excess as to require long boiling to expel the 

most of it, nor is the expulsion of the whole of it necessary or indeed 

desirable. As soon as the precipitate settles, the solution is passed 

through a filter of suitable size and the precipitate is washed a few 

times with hot water and sucked fairly dry. It is redissolved in hot 

hydrochloric acid and precipitated again by ammonia in presence of 

bromine, but with less ammonium chloride and in a smaller bulk of 

solution. If the filter is still in good condition, it is used also for 

this precipitate, which is washed with hot water and sucked dry at 

the pump. With high iron and magnesium the precipitation may 

well be repeated.1

The re-solution of the first precipitate may be made with nitric 

acid, if thought desirable. Its use involves very little washing of the 

second precipitate. To reduce the amount of aluminum passing into 

the filtrate, the precipitated oxides may be washed with water containing in the liter 20 cm.3 of nitric acid that has been neutralized 

with ammonia.

The paper containing the final precipitate is placed in a platinum 

crucible, slowly charred, then ignited over a gradually increased 

flame, and finally over the blast for two to five minutes. The weight

1 Although the above is essentially the accepted procedure in commercial work, it 

would be better, and consume no more if as much time if the precipitation procedure 

given under 35. A. b (p. 258) were followed.
CONDENSED ANALYSIS. 273

found represents the oxides of ferric iron, aluminum, titanium, phosphorus, and manganese, the last presumably Mn3O4 .

The iron, titanium, and silica in the ignited oxides are determined, 

after fusion with potassium or sodium pyrosulphate, exactly as 

detailed in 35. C (p. 259). The phosphorus and manganese having 

been determined in different portions (39, p. 263, and 36. B, p. 261), 

the aluminum oxide is found by subtracting all these oxides from 

the original weight of the mixture. Often the percentage reported 

as alumina includes in reality the titanium, phosphorus, and some 

of the manganese, where no 'attempt has been made to separately 

determine these.

50. CALCIUM.

The combined filtrates from the iron, aluminum, etc., are concentrated if need be to a bulk of 200 to 250 cm.3 , with occasional addition of a few drops of ammonia. If a slight precipitate separates, 

it is collected on a small filter, washed with water, redissolved in 

hydrochloric acid, and reprecipitated by ammonia. It is added to 

and treated with the main quantity of iron and aluminum oxides, 

and the filtrates are combined. To them is added while boiling 

40 cm.3 (for 1 gram of sample; 20 cm. 3 if but half a gram is under 

analysis) of a saturated solution of ammonium oxalate, and the boiling is continued until the precipitated calcium oxalate assumes a 

well-defined granular form. It is then allowed to stand for an hour, 

filtered, and washed a few times with hot water. The precipitate 

and filter are ignited in platinum till the oxalate is converted to 

oxide, which is redissolved in hydrochloric acid and the solution 

made up to 100 cm.3 Ammonia is added in slight excess to the 

boiling solution and also ammonium oxalate to reprecipitate the lime. 

After an hour the oxalate is collected, washed a few times with 

small amounts of hot water, ignited over the blast, and weighed as 

the oxide.

Instead of igniting and weighing as oxide it is permissible to dissolve the oxalate in sulphuric acid, taking care to extract the filter 

thoroughly with hot dilute acid, and to titrate the solution with permanganate.

51. MAGNESIUM.

To the combined filtrates from the calcium precipitations are 

added sodium-ammonium phosphate solution in excess and, when the 

precipitate has formed after vigorous stirring, ammonia in considerable excess. After several hours, 12 or 15 if the precipitate is 

verjr slight, the solution is filtered, and the precipitate is redissolved in hydrochloric acid and reprecipitated by ammonia in moderate excess and a drop of the phosphate precipitant in the usual 

131990° 19 IS
274 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

manner. After two hours the precipitate is filtered on paper or on 

a Gooch filter, ignited, and weighed as pyrophospEate.

52. ALKALIES.

See 41r p. 2:65.

S3. CARBON DIOXIDE. 

See 42, p. 266.

54. SULPHUR. 

See 45,. p. 268.

55. WATER. 

'See 46, p. 269.

56. IGNITION LOSS.

The determination of ignition loss has little significance, though 

it affords a more or less correct indication of the proportion of carbonates in the rock. As it is a determination commonly made in 

commercial laboratories, some space will be devoted to it.

Loss on ignition with carbonate rocks represents, as with those of 

a silicate nature, the algebraic sum of a number of chemical changes 

involving both losses and gains, and its amount will depend largely 

on the temperature employed. At the temperature of a moderate 

blast, with crucible covered, carbon dioxide, water, and carbonaceous matter escape wholly. Sulphides are oxidized to sulphates and 

all the sulphur is retained as sulphate by the calcium. With a powerful blast the sulphate is decomposed gradually, with eventual loss of 

-the entire sulphur. At this point the alkalies begin to escape as 

oxides, the potassium relatively faster than the sodium, and they 

may be found in part condensed on the lid of the crucible. If the 

heating is long continued they can be wholly volatilized. As a 

small offset to these losses the iron of pyrite and the iron and manganese of ferrous and manganous carbonates take up oxygen and 

unite with the lime. By proper control of the temperature it is 

not difficult to prevent loss of sulphur and alkalies, and this is the 

object to be sought in making the determination.

From 0.5 to 1 gram of the powder is placed in a platinum crucible 

of 20 to 25 grams weight, the crucible is inserted to three-fifths of 

its depth in a perforated platinum disk or asbestos board (fig. 3, 

p. 34), and an inclined blast flame of considerable intensity is caused 

to play against the bottom of the covered crucible for 15 or 20 minutes. A repetition of the heating for five minutes will usually cause 

little or no further loss. Duplicate determinations should agree within 0.2 per cent, and after the operator becomes skilled probably within 

0.1 per cent. A muffle can be substituted for the blast'. In my experiments the crucibles occupied a position 2 inches inside the closed door of 

the muffle. It is, however, important that each operator should ascertain just what the proper conditions may be for his particular blast or 

muffle. They are right if after the ignition he finds exactly the whole 

of the sulphur in the ignited powder in the sulphate state.
INDEX.

A* Page. 

Abrasion of crusher 58-59 

of mortar 63 

Absorption tubes, use of, in water

determination 79-80 

Acids, quality of 45 

Acknowledgments to those aiding 17 

Adams, B. Q., acknowledgment to 17, 64

(footnote) 

Adams, L. H., and Johnstou, J.,

cited __ 55 (footnote), 231 

Agulhon, H., and Bertrand. G., cited-, 240 

Alkali bisulphates, reagents 46 

pyrosulphates, reagents, advantages and disadvantages of- 116 (footnote) 

Alkalies, determination of- 207-216,

265,274 

figure showing apparatus for

determination of-__ 209

Alien, E. T., cited_______ 63,128

Alien, E. T., and Day, A. L., cited 70-71

pycnometer method of______ 55-57

Alien, E. T.,' and Johnston, J., cited- 231

(footnote)

Alien, E. T., and Zies, E. G., cited. 239, 240 

Aluminum, concealment of by manganese __ _ 134 

direct determination of____ 126-130 

ignition of precipitate of oxide

of ____________ 114 

precipitation of, with iron,

titanium, etc __ 106-113, 

257-258, 272-273 

recovery of, after separation of

iron as sulphide 1-26-127 

from filtrates- __ 113-114,259 

separation of, from iron and

other elements- 127-133,273 

Aluminum chloride, volatilization of- 108

(footnote)

Ammonia, occurrence of, in rocks 243 

Ammonia reagent, preparation of 45 

Ammonium chloride reagent, quality

of____________ 4,6 

preparation of___ _ 107 

Ammonium oxalate reagent, quality

of_________ 46 

Ammonium persulphate reagent,

purification of- 112 (footnote) 

Analysis, allowable error in_____ 30 

completeness and thoroughness

of, importance of _ 18-24, 

48^9

crushing of rock for_______ 57-60 

diversity of, for same rock __ 20-21 

employment of air-dry powder

for 71

Page.

Analysis, grinding rock for_____ 60-63 

neglect of certain factors in,

consequence of-___ 22

preparation of sample for___ 57-63

quantity of sample required for_ 25,

48-49,57,64

statement of___________ 31 

time required for_________ 32 

See also Carbonate rocks;

Silicate rocks.

Analysis, qualitative_________ 41 

Apparatus, glassware and porcelain,

quality of_______ 42 

Appliances and Apparatus, descriptions and figures of_ 33-41 

Aragonite, tests for.1_________ 251 

Arsenopyrite, evidence as to presence of, in rocks____ 230 

Atterberg, A., cited____ 211 (footnote) 

Auraniuni, substitute for platinum_ 44 

Austin, M., and Gooch, P. A., cited 136 

(footnote), 148,149 

Autenrieth, W., cited_________ 215

B.

Bailey, G. H., cited________ 173,175 

Balarew, D., cited__________ 149 

Barbier, P., method of, for separation 

of iron from aluminum - _______ 130 

Barium, determination of______ 146,' 

170-172, 259, 262

ignited silica, free from__ 104-105 

occurrence of, in rocks. 22, 28, 230 

recovery of, from alumina precipitate 118 

from magnesium pyrophosphate________._ 152 

separation of, from calcium__ 144 

from calcium and mag-

 nesium-- _ W5(footnote) 

from strontium_____ 145

Barium sulphate, spectroscopic testing of- 172 

Barnebey, 0. L., method of, for ferrous - iron determination ___ 206 

cited ______ 198 (footnote),

199, 203 (footnote)

Baskerville, C., method of, in determination of titanium- 130, 

131,166 

in determination of zirconium 130,

131,175

Baubigny, H., method of, in determination of chromium- 181 

Bauer, Th., cited _ 103(footnote)

275
276 INDEX.

Page. 

Baxter, G. P., and Kobayashi, M.,

cited_____ 216 (footnote) 

Bayly, R. G. W., cited____ 77 

Bechi, E., cited__ __ 22 

Bellucci, I, and Grassi, L., cited 164 

Bemmelen, J. M. van, cited 65 (footnote) 

Berger, C. W., 'and Hulett, G. A.,

cited_____ 102(footnote) 

Bertrand, G., cited____ 139 

Bertrand, G., and Agulhon, H., qualitative test of, for

boron___ 240 

Berzelius, J. J., method of, for

fluorine________ 222-225 

Beutell, A., and Blaschke, K.,

cited______ 65(footnote) 

Bisbee, H., McCaffrey, C. T., and

Richards, T. W., cited- 140, 

141

Blair, A. A., crucible tongs of 33 

Blake, G. R., and Gooch, F. A.,

cited______ 216(footnote) 

Blaschke, K., and Beutell, A., cited 65

(footnote). 

Blast, temperature of, test of 103

(footnote).

Bloor, W. R., cited________ 105 

Blount, B., cited__________ 102, 256 

Blum, W., cited_____ 107,108,156,228 

Bogitch, F., and Le Chatelier, H.,

cited __ 49 (footnote) 

Bolm, F., cited________ 210(footnote) 

Bolton, H. C., cited__________ 251 

Borck, I-L, cited _ 133 

basic acetate method of- 110(footnote) 

Borgstrom, L. H., cited 219 

Boric oxide, fusion with 92-93 

Boric oxide reagent, preparation of 92 

Bornemann, E., cited 80 (footnote) 

Bornemann, K., and Schirmeister,

H., cited _____ 133

Boron, determination of_ 234-241

apparatus for determination of- 237

occurrence of, in rocks_ 29

qualitative tests for____ __ 240

Boynton, C. N., and Gooch, F. A.,

cited______ 145 (footnote) 

Bravo, J. J.,. cited_______ 27 (footnote) 

Bray, W. C., and others, citedl 41 

Brinton, P. H. Me. P., and Fresenius,

H., cited 211((footnote) 

Brown, James, cited__ -166 

Browning, P. E., cited__ 144 

Briihl, E., and Friedheini, C., cited_ 135 

Brunck, O., cited___________ 146,148 

basic acetate method of- 111 (footnote) 

Brush, G. J., method of, in water

determination 77 

Bube, K, cited__________-__ 148 

Buckley, E. R., method of, for porosity determination- 51, 52, 53 

Bunsen, R., cited__ 71, 98, 211 (footnote) 

Burgess, G. K., and Sale, P. D.,

cited __" 44 (footnote) 

Burgess, G. K., and Waltenberg, R.

G., cited 44 (footnote)

C. Page.

Cain, J. R., and Hostetter, J. C.,

cited ________ 179

Cain, J. R., and Tucker, F. H., cited 179

Calcite, tests for_______ 217,251-252

Calcium, determination of____ 140-144,

146-148, 262-263, 273

ignition of oxalate of______ 142

precipitability of, by ammonium

persulphate __ 111 

removal of, from magnesium

pyrophosphate __ 152-153 

in alkali determination__ .236 

separation of, from magnesium _______ 140-144,263 

separation of strontium from 145-146 

Calcium chloride reagent, deterioration of__________ 80 

Calcium fluoride, testing of precipitate of__________ 250 

Calcium oxalate, solubility of__ 140-141 

Cameron, A., cited _____ 98 

Campbell, D., cited ___ 151 (footnote) 

Campbell, E. D., and Hess, W. H.,

cited __________. 128 

Cappel, A., cited- _ 142(footnote) 

Carbon, determination of __ 219, 266-267 

effect of, on. ferrous-iron determination __ 201, 203, 207, 265 

occurrence of, in rocks____ 219, 250 

Carbonate rocks, analysis of___ 246-274 

analysis of, defects of, as usually

made _________ 247-248 

condensed forms of___ 271-274 

detailed methods of___ 253-270 

causes of color of-_______ 250 

ignition loss of__________ 274 

importance of_-____ _ 15 

impurities in__________ 249-250 

methods of decomposing- 253-255, 271 

mineral composition of__L_ 248-250 

qualitative composition of silicate rocks and___ 246-248 

qualitative tests of ____ 251-252 

Carbonates, qualitative tests of 251-252 

relative solubility of, in certain

reagents ________ 251 

Carbon dioxide, determination of__

217-219, 274 

figure showing apparatus for de- .

termination of_ 218 

inclusions of, in rocks___ _ 242 

Carbon monoxide, evolution of, on

heating rocks 242 

Carnot, A., cited _ __ 122 

Carron, E. C., cited 142 (footnote) 

Cathrein, A., cited_ _ _ 124(footnote) 

Cavaignac, H., cited- _ 90 (footnote) 

Ceramic clays, determination of iron

in_____________ 126

Cerium, detection of . 177

occurrence of, in piedmontite_ 109

(footnote)

in rocks-___'___________ 25,26 

Cerium oxalate, solubility of, in certain salts ____ 176(footnote)
INDEX. 277

Page.

Chalcopyrite, occurrence of, in rocks. 28 

Chamberlin, R. T., cited_____ _ 242 

Chapin, W. H., cited__ 234(footnote), 235 

method of, for boron ____ 235-240 

Chapin, W. H., and Wherry, E. T.,

cited 240 

Chatard, T. M., cited_______ 162,179 

drying oven of, description and

figure of 82 

Chlorine, condition of, in rocks _- 220 

determination of_____ 220-221, 267 

occurrence of. in rocks_____ 29 

Chromium, comparison of colorimetric and gravimetric 

methods for ___ 183 

determination of ___ 170-172, 

180-183, 184, 261 

colorimetric________ 182-183 

gravimetric_ _ 181-182 ( 

occurrence of, in rocks___ 26,189 

precipitation of, with aluminum,

etc. _________ 106-110 

Citric acid, relative solubility of carbonates inr _ 251 

Claasen, E., cited__ ______ 185

Clarke, F. W., cited__________ 22 

Classcn, A., cited_________ 46 

method of, for separation of iron

from titanium _____ 133 

Cloedt, E. v., and Jannasch, P.,

cited__ ________ 135

Cobalt, detection of_________ 136, 261 

determination of_______ _ 136 

occurrence of, in rocks_____ 27 

separation of, from manganese

and zinc _____ 135-136 

Coblentz, W. W., cited ___ 66 (footnote) 

Collins, W. D., and Skinner. W. W., 

; cited __ __ 212 (footnote) 

Colorimeters, description of, and

figures showing 35-41 

Colorimetric methods, for determination of chromium__ 182-183 

for determination of manganese ________ 137-139 

of titanium ________ 155-162 

of vanadium 157 

comparison of colorimetric and 

gravimetric methods 

for determination of 

chromium _ __ 183 

Columbium, occurrence of, in rocks. 25, 30 

Connor, F. M., cited_________ 115, 209 

Contamination of sample by agate 63-64 

by steel 59, 60 

Cooke, J. P., method of, for determination of ferrousiron ______ 196, 204-205 

method of, apparatus for, figure

showing ________ 205

Coppadoro, A., cited- _ 119 (footnote)

Copper, determination of______ 137, 261

occurrence of, in rocks______ 27

separation of 135,136

Cramer, E., and Seger, H., cited 53

Cross, W., and others, cited 49

Pago. 

Crucible, disk for, description and

figure of 35 

tongs for, description and figure

of_____________ 33 

Crucibles, platinum, loss of weight

of 102 (footnote), 

116 (footnote)

Crushing, methods of . 57-60 

Crystal water. See Water. 

Gumming, A. C., and Thin, R. G.,

cited- 216 (footnote) 

Curtis, J. S., cited___________ 241 

Czudnowitz, C., cited____ __ 184

D.

Daniel, K., cited 222 (footnote) 

Daudt, H. W., cited __ 10.8 (footnote) 

Davis, J. T., cited___________ 175 

Davis, W. A., cited_____ 210 (footnote) 

Davy, Humphrey, cited___ 92 (footnote) 

Day, A. L., and Alien, E. T., cited 70-71 

pycnometer method of, for specific gravity_______- 5.5-57 

Dehydrating agents 73-74 

Dehydration, effect of, on physical

properties 69 

Delesse, A., cited _______ 242 

Desiccators, use of °__ 73 

Determinations, importance of order

of_____________ 48

Deussen, E., cited___ 117 (footnote), 197

(footnote), 198

Deville, H. Ste C., cited________ 22 

Dieulafait, L., cited- 22\ 24 (footnote), 241 

Dimitrow, P., and Karaoglanow, Z.,

cited_ 149,151 (footnote) 

Dinwiddie, J. G., cited________'. 226 

Disk, perforated, for crucibles, description and figure of_ 35 

Dittrich, M., cited 30, 71, 73, 79, 94,109, 

115, 132, 139, 176 (footnote), 201 (footnote), 209 

Dittrich, M., and Eitel, W., method 

of, for water determination _ 84 

Dittrich, M., and Freund, S., methods 

of, in separation of 

titanium and zirconium 

from iron_________ 129, 

131,132 (footnote), 166, 175 

Dittrich, M., and Leonhard, A., cited- 198 

Doring, Th., cited______ 208 (footnote) 

Dolomite, definition of ________ 247 

tests for __ __ 251-252 

Don, J. R., cited____________ 242 

Drying before analysis, usclessness

of____________ 71 

Drying for hygroscopic tests, process

of _____________ 73-70 

Dunnington, F. P., cited _ 156 

Duschak, L. H., and Hulett, G. A.,

cited______231 (footnote)

E.

Eakins, L. G., pycnometer method of

for specific gravity 54 

Eddy, E. A., and Gooch, F. A., cited- 214
278 INDEX.

Page.

Edgar, G., cited __________ 123 

Eitel, W., and Dittrich, M., method 

of, for water determination ___ _____ 84 

Electrification of glass tubes, influence of, on weight__ 80 

Ellis, C.. W. H., mortar of, description and figure of__ 58> 

Erdniann, H., cited-_____ __ 242 

Error in analysis, allowable limits

of__________.__ 30-31 

in calculation of feldspars_ 22 

Errors due to, abrasion of crushing 

and grinding implements-_____ 58-59, 63-64 

failure to determine sulphur 23 

grinding of sample_ ____ 6O-61, 

69-71,189-192

variation of blast temperature______ 103(footnote>

F.

Faber, P., cited _______ 156,161 

Feldspars, error in calculation of__ 22 

Ferguson, J. D., cited_________ 175 

Ferguson, J. B., cited_________ 125 

Ferric chloride, volatilization of__ 108

(footnote) 

Ferric iron, calculation of _____ 123

See also Iron.

Ferrous iron, determination of___ 189-

207, 264-265

determination of, hydrofluoricacid method of___ 196-20T 

sealed-tube method of__ 193-196 

oxidation of, by grinding. 60,189-192 

by free oxygen in presence 

of hydrofluoric acid or 

a fluoride_______ 199-200 

preparation of sample for determination of_____ 192 

uncertainties of determination *

of __ ____ 207 

See also Iron. 

Fieldner, A. C., Selvig, W. A., and

Taylor, G. B., cited__ 219, 

266 (footnote) 

Filter paper, macerated, use of, for

precipitations 108,114-115 

Fischer, T., cited __ ____ 189 

Fluid inclusions, volatilization of__ 242 

Fluorine, determination of_ 222-229, 268 

influence of, in aluminum determination 9Q( footnote), 

106(footnote)

in silica determination__ 90, 94 

(footnote)

occurrence of, in rocks- _ 29 

qualitative tests for 222 

Folin, O., cited 231 (footnote) 

Foote, H. W., and Penfield, S. L.,

cited ___________ 235 

Forchhammer, J. G., cited ____ 241 

Ford, W. E., cited__________ 235 

Foullon, H. von, cited ___ 241 

Franz, B., and Streit, G., cited 175

Page. 

Fresenius,, H., and Brinton, P. H.

McP., cited-..- 211 (footnote) i 

Fresenius, R., cited 142(footnote):, 151 . 

Freund, S., and Dittrich, M., methods 

of, in separation of 

titanium and zirconium 

from iron______ 129,131, '

132 (footnote), 166,175

Friedel, G., cited_ _ 75 

Friedheim, C., and Briihl, E., cited 135 

Friedneim, C., and Pinagel, A., cited. 99 

Funk, W., basic acetate method of 111

(footnote) 

G.

Galena, occurrence of, iu carbonate

rocks __________ 249 

Gallo, G., cited____________ 168 

Gases, evolution of, on heating

rocks _________' 242-243 

Gautier, A., cited___________ 242 

Gibbs, W., cited____________ 149 

Gilbert, J. P., cited_______ 98,250 

Glassware, action of reagents on 43 

quality and composition of___ 42 

rules for use of___________ 43 

Glass sands, determination of iron in 125 

Glucinum, occurrence of, in rocks__ 25, 29 ', 

Gold occurrence of, in rocks 29 

substitute for platinum _ 44 

Gooch, F. A., apparatus of, for water ' 

determination, descrip- , 

tion and figures of 85-88 

cited _____ 132,133,234(footnote) 

method of, in determination of

lithium. ___ 212-213 

in determination of titanium _______ 162-163 

Gooch, F. A., and Austin, M., cited- 136 

(footnote) ,148,149

Gooch, F. A., and Blake, G. R., cited. 216

(footnote)

_Gooch, F. A., and Eddy, E. A., cited 214 

~Gooch, F. A., and Boynton, C. N.,

cited_____ 145 (footnote) 

Gooch, F. A., and Jones, L. C., cited. 234

(footnote) 

Gooch, F. A., and Kobayashi, M.,

cited ______ 226 

Gooch, F. A., Reckert, "B. C., arid

Kuzirian, S. B., cited 105 

Grassi, L>, and Bellucci, L, cited 164> 

Grinder, mechanical. __ 61-63 

Grinding, effect of, on composition of

sample-60-61, 69-71,189-192 

methods of. 60-64 

Gurevich, L. J., and Wichers, E.,

cited __ 44 (footnote)

H.

Haff, R. C., and Schwartz, E. B.,

cited __ _______ 215 

Hall, R. W., cited______ 102(footnote) 

Hamberg, A., cited ... 6f»(footnote) 

Harper, D. N., and Penfleld, S. L.,

cited __ 108
INDEX. 279

Page.

Harrington, B. J., cited____ 252 

Harrison, J. B., cited _ 27,29 

Hauynite, evidence as to presence of 230 

occurrence of, In rocks 28 

Hawley, P. G., cited 99 

Hayes, A. A., cited 22 

Haydcn, E. M., and Thornton, W. M.,

cited _________ 164,165 

Heidenreich, 0., and Jannasch, P., 

boric oxide method of, 

for decomposing silicates __________ 92-93 

Helium, occurrence of, in rocks_ 25 

I-Iempel, W., cited--_ _ 64 

Hess, W. H., and Campbell, E. D.,

cited __________ 128

Hewett, F., cited______ 27(footnote)

Hibbert, E., cited___________ 168

Hibbert, E., and Knecht, E., cited 123

168 (footnote)

Hildebrand, J. H., cited_______ 126 

Hinden, F., cited__________ 252,263 

Hinrichsen, F. W., cited- 94(footnote), 167 

Elintz, E., and Weber, H., cited__ 231

(footnote)

Holladay, J. A., cited 142(footnote), 169 

Holthof, C., cited____________ 95, 96 

Horn, D. W., cited______ 183(footnote) 

Horsch, M., cited______ 211 (footnote) 

Hostetter, J. C., cited 140(footnote), 144 

Hqstetter, J. C., and Cain, J. E.,

cited __________ 179 

Hostetter, J. C., and Roberts, H. S., 

electrometric method 

of, for iron 16,126(footnote) 

Hiittner, K., cited___________ 242 

Hulett, G. A., and Berger, C. W.,

cited _____ 102(footnote) 

Hulett, G. A., and Duschak, L. H.,

cited______ 231 (footnote) 

Hundeshagen, F., method of for inagnesite _________ 263 

Huybrechts, M., cited____ 231 (footnote) 

Hydrofluoric acid reagent, quality

of__ _______ 45 

Hydrofluoric acid method for determination of ferrous 

iron__________ 196-207 

Hydrogen, behavior of, on drying

minerals 0________ 67 

behavior of, on grinding minerals_________ 67, 69-71 

discriminating between conditions of, in minerals 64-69 

evolution of, on heating rocks_ 242 

minerals _ ,_ 68 

rOle of, in minerals________ 64-69 

system of classification of, in

minerals ___ __ 65-66 

Hydrogen peroxide reagent, quality

of___________,__ 46 

Hydrogen sulphide, as impurity in

carbon dioxide-120(footnote) 

evolution of, on heating rocks 242 

occurrence of, in carbonate

rocks 250

I. Pag*.

Hygroscopic water, determination of_ 73-76

See also Water.

Iddings, J. P., cited___________ 49 

Ignition, loss by carbonate rocks on_ 274 

loss on, inaccuracy of water determination by_____ 76-77 

temperature of, variations

in _ __ 103(footnote) 

Iron, correction of titanium determination for 160-101 

determination of_____ 115, 119-126, 

189-207, 257-258, 264-265, 

272-273.

effect of carbonaceous matter on___ 203, 207, 264, 265 

effect of sulphides on__ 193-194, 

201-202, 207, 233 

effect of vanadium on 121-122, 

202-203

electrometric method for_ 16, 

126(footnote)

gravimetric __ 124-125 

volumetric 119-124, 196-207 

in ceramic clays _ _ 126 

in glass sands_______ 125 

Ignition of precipitate of oxide

of ^ 114 

occurrence of, in carbonate

rocks _ 248-249 

precipitation of, with aluminum,

etc__________ 106-113. 

257-258, 272-273 

oxidizability of divalent, by free 

oxygen in presence of 

hydrofluoric acid or a 

fluoride _______ 225-226 

recovery of, from filtrate 113-114 

reduction of___________ 119,121 

separation of, as sulphide__ 124-125 

from aluminum, etc___ 132-133 

in titanium determination 162-163 

solution of oxide of, by alkali

fusion_________ 122-123 

titration of _______ 120,121,123, 

203-204, 260, 264-265 

See also Ferric iron ; Ferrous iron. 

Iron nitride, occurrence of, in lava_ 243 

Iron oxides, error in determination

of____________ 23,123, 

189-192,197-203, 207

J.

Jakob W., method of, in determina- .

tion of chromium___ 181 

Jannasch, P., cited ___ 34, 80, 

91,112(footuote) 

silicate decomposition methods

of ____________ 91-93 

Jannasch, P., and Cloedt, E. v., cited- 135 

Jannasch, P., and Heidenreich, 0.,

boric oxide fusion,

method of 92-94 

Jannasch, P., and Weber, H.,

cited__ 92-93, 93 (footnote) 

Jannettaz, E., cited___ 251 

Jarvinen, K. K., cited 149,151
280 INDEX.

Johnson, A., cited______. 

Johnston, J., and Adams,

cited___ 55 

Johnston, J., and Alien,

cited______ 

Johuston, J., Merwin, H.

Williamson,

cited -_______

Jones, L. C., and Gooch,

cited______ 

Jordis, E., and Kanter,

cited________

Jordis, E., and Ludewig, W.

K.

Page. 

._ 66 (footnote)

L. H., 

(footnote), 231

E. T.,

______ 231 

E., and 

E. D., 

_____ 251

F. A., 

234 (footnote).

E. H.,

103 (footnote) 

, cited 100 

(footnote)

Kaiser, H., and Weiss, L., cited 127,156 

Kallauner, O., and Preller, L, cited 142,

143, 263 

Kanter, E. H., and Jordis, E., cited 103

(footnote).

Karaoglanow, Z., cited__ 231 (footnote) 

Karaoglanow, Z.,_and Dimitrow, P.,

cited__-149,151 (footnote)

Knecht, E., cited________-__ 168

Knecht, E., and I-Iibbert, E., cited 123,

168 (footnote)

Knop, .A., cited________ 119 (footnote) 

Knowles, H. B., acknowledgments to_ 17 

Knowles, H. B., and Lundell, G. E.

F., cited____ 108, 164, 165 

Kobayashi, M., and Baxter, G. P.,

cited _____ 216 (footnote) 

Kobayashi, M., and Gooch, F. A.,

cited __ 226 

Koch, A. A., and Treadwell, F. P.,

cited__________ 224, 225 

Koninck, L. L. de, cited________ 193 

Koningh, L. de, cited__ 182 (footnote) 

Koppe, P., and Miiller, E., cited-__ 139 

(footnote), 197 (footnote) 

Kortright, F. L., cited__ 100 (footnote) 

Krauch, C., cited____________ 45 

Kruys, M. J., van't, cited_ 231 (footnote) 

Kuzirian, S. B., cited_________ 105 

method of, for water determination __________ 88-89 

Kuzirian, S. B., Gooch, F. A., and

Reckert, F. C., cited 105

L.

Lang, W. R., and Manning, R. J.,

cited _____ 234 (footnote) 

Langmuir, I., cited_____ 65 (footnote) 

Larsen, E. S., and Wherry, 'E. T.,

cited______ 69 (footnote) 

Lazurite, evidence of presence of,

in rocks_________ 230

occurrence of, in rocks_____ 28

Lea, Carey, cited __ 60 (footnote)

Lead, determination of _ 261

occurrence of, in rocks_____ 29, 249

Le Chatelier, H., cited___ 65 (footnote)

Le Chatelier, H., and Bogitch, F.,

cited _______ 49 (footnote) 

Le Clere; A., cited_____ 101 (footnote)

Page.

Lemberg, J., cited___________ 252 

Lenher, V., and Truog, E., cited_ 97,

101,103,105 

Lenher, V., and Wells, J.. S. C.,

cited___________ 240 

Leonhard, A., and Dittrich, M.,

cited___________ 198

Limestones, causes of color in___ 250

minor constituents of_- ____ 248-249

Limestones, dolomitic, definition of- 247

magnesian, definition of_ __ 247

Lindemann, 0., cited________ 185

Lindo, D., cited ___________ 98

Lithium, determination of____ 211-214

occurrence of, in rocks__"___ 28

Lowe, J., clay disks of_ ___ 35

Lowenstein, E., cited____ 65 (footnote)

Low, W. H., cited___ 234 (footnote), 240

Luck, E., cited_______ 151 (footnote)

Ludewig, W., and Jordis, E., cited 100

(footnote).

Ludwig, E., cited-___________ .98 

Luedeking, C.,' and Wheeler, H. A.,

cited___________ 243 

Lundell, G. E. F., acknowledgments

to_____________ 17 

cited 90 (footnote), 101 (footnote), 

108, 143,152, 173, 180 

Lundell, G. E. F., and Knowles, H B.,

cited ______ 108, 164, 165 

Lunge, G., cited __ 35,231 (footnote), 245 

Lunge, G., and Millberg, C., cited- 102, 244 

Lunge, G., and Stierlin, R., cited 231

(footnote)

M. '

McBride, R. S., cited___ 120 (footnote) 

McBride, R. S., and Scherrer, J. A.,

cited__ 119 (footnote)-, 180 

(footnote), 187 

McCaffrey, C. T., Bisbee, H., and

Richards, T. W., cited- 140, 

141

McKenna Brothers Brass Co., ore 

grinder of, description 

and figure of______ 61-63 

Macerated filter paper, use of, for

precipitation- 108, 114-115 

Makinen, E., cited"____.______ 210 

Magnesite, analysis "of ________ 263 

Magnesium, determination of_ 148-152,

263, 273

error in determination of__ 153-154 

occurrence of, in carbonate

rocks _____'.- 247, 249 

precipitation of ________ 148-150 

essentials of ^_____ 148,149 

separation of, in alkali determination _____;___ 213, 214 

from calcium _______ 140 144 

Magnesium-ammonium p h o s phate,

ignition of ______ 150-151 

Maillard, L., cited___________ 189 

Mallett, J. W., cited_____ 60 (footnote),

74 (footnote) 

Manasse, 0., cited_____ 186 (footnote)
INDEX. 281

Page.

Manganese, determination of__ 134-140, 

153,260-261,263

occurrence of in rocks____ 27, 248 

oxidizability of divalent, in presence of hydrofluoric 

acid__________. 197 

precipitation of- 111-113, 135-136, 257 

removal of, from magnesium

pyrophosphate _____ 153 

separation of, from cobalt, copper, zinc, and nickel_ 136 

Mannich, J., and Priess, I-L, cited__ 240 

Manning, R. J., and Lang, W. R.,

cited______ 234 (footnote) 

Mar, F. W., cited____________ 172 

Marble, contamination of, by sulphides____ 120 (footnote) 

Marrs, L. E., and Metzger, F. J., 

method of, for manganese___________ 139 

Marshall, H., cited_____ 137 (footnote) 

Mauzelius, R., cited___ 60,70 (footnote), 

189 (footnote)

Meade, R. K., cited___ 255 (footnote) 

Meineke, C., cited___________ 98 

Mellor, J. W., cited__ 1G, 43, 126,162, 209 

Merrill, P. W., cited__________ 42 

Merwin, H. E., acknowledgments to_ 17, 64

(footnote)

cited_____ 112 (footnote), 156,157, 

161, 227 (footnote)

method of, for fluorine ___ 227-229 

Merwin, H. E., Johnston, J., and

Williamson, E. D., cited 251 

Merwin, H. E., and Posnjak, E.,

cited ___ 66 (footnote) 

Merwin, H. E., Wright, F. E., and 

Hillebrand, W. F., 

cited ____ 68 (footnote) 

Meteorites, analysis of________ 16 

Methane, evolution of, on heating

rocks ___ __ 242 

Metzger, F. J., and Marrs, L. E., 

method of, for manganese _ 139 

Microscopic examination, value of 24 

Microcosrnic salt reagent, quality of- 46 

Millberg, C., and Lunge, G., cited- 102, 244 

Mingaye, J. C. H., cited___ 23(footnote) 

Minor, .T. C., and Penfield, S. L., cited 224 

Mitchell, W. L., and Wells., H. Li,

cited _____ 119 (footnote) 

Mitscherlich, A., cited- 115(footnote), 192 

method of ferrous-iron determination of______ 193-195 

Mittasch, A., basic acetate method of 111

(footnote)

Moissan, H., cited_______ 234(footnote) 

Molybdenum, determination of 184,

186, 261

distribution of, in rocks.___ 184 

occurrence of, in rocks_ 23, 29, 184, 250 

Moore, G. E., device of, to remove 

air from mineral powders, description and 

. .. figure of ___ 55-56

Page.

Morgan, G. T., cited________ 217,267 

Morley, E. W., cited__ 86 (footnote) 208

(footnote)

Morozewicz, J., cited__,__ 211 (footnote) 

Mortar, for crushing__________ 58 

Motherwell, H. A. B., cited_____ 99 

Moureu, C., cited_______ 242(footnote) 

Miiller, E., and Koppe, P., cited__ 139 

(footnote), 197 (footnote) 

Murmann, E., cited__,._______ 143 

method of, for separating calcium and magnesium. 143 

Murphy, R. K., and Neumann, B.,

cited __ 130(footnote), 168

'. NNephcline, detection of, in presence

of olivine______ 243-244 

Neubauer, H., cited______ 148, 149, 151 

Neumann, B., and Murphy, R. K.,

cited __ 130(footnote), 168 

Neustadl, L., and Skrabal, A., cited- 145 

Newton, H. D., cited_____ 121, 122, 167' 

Nickel, determination of____ _ 136 

occurrence of, in rocks_____ ' 27 

precipitation of __________ 135 

separation of, from manganese

and zinc-______ 135-136 

Nicolardot, P., and Reglade, A.,

cited __________ 173 

Nitrogen, occurrence of, in rocks 242 

Noselite, evidence as to presence of,

in rocks_________ 230

occurrence of, in rocks 28

Noyes, A. A., and others, cited _ 41

Noyes, W. A., cited _ _ 160

O.

Organic matter, removal of_____ 254 

Oxidation, incompleteness of, on ignition of ferrous compounds _______ _ 76-77

P.

Palau, substitute for platinum___ 44 

Panichi, U., cited_____'._ 65 (footnote) 

Parsons, C. L., cited__._ _ 25(footnote) 

Penfield, S. L., cited____ 53, 86 (footnote) 

method of, for water determination ________ 77-79, 83 

apparatus for, showing

figures _______ 78, 79, 83 

Penfield, S. L., and Foote, H. W.,

cited __________ 235 

Penfield, S. L., and Harper, D. N.,

cited ___________ 108 

Penfield, S. L., and Minor, J. C.,

cited ___________ 224 

Penfield, S. L., and Sperry, E. S.,

cited _____ 234 (footnote) 

Perhydrol reagent, quality of 46 

Permanganate solution, standardization of __ 120 (footnote) 

Peters,.C. A., cited_______ 140(footnote) 

Peters, R., cited 199
282 INDEX.

f> Page. 

Pettijohn, E., and Sidener, C. F.,

cited _____ 108 (footnote) 

Pfaff, F. W., cited__________ 247; 

Phenylhydrazine reagent, contamination of___ 129(footnote) 

Phosphoric acid, decolorant for ferric solutions______ 161 

effect of, on color of titanium

peroxide _____._ 156,159 

Phosphorus, determination of __ 177-180,

263-264, 273

loss of, by volatilization 116 

occurrence of, in rocks _ 28, 250 

precipitation of, with aluminum,

etc__ 106-113, 180, 257-258 

recovery of, after separation of

iron as sulphide__ 126-128 

separation of, from iron, titanium, and zirconium. 126-128 

Phosphorus salt reagent, quality of_ 46 

Piedmontite, rare earths in_ 109 (footnote) 

Pinagel, A., and Friedheini, C., cited- 99 

Pirsson, L. V., cited_____ 31, 243 

and others, cited 49 

Pisani, F., cited ______ 167, 226

Platino, substitute for platinum 44

Platinum, occurrence of in rocks_ 25, 29

precipitation of__ 105, 119 (footnote)

reduction of, from solution__ 211

(footnote)

solubility of, in ferric chloride

solution__________ 105

Platinum crucibles, attack of, by

caustic lime_______ _ __ 147

sodium carbonate fusion___ 96

loss in weight of-_ - 102 (footnote)

Platinum substitutes_____ __ 44

Platinum ware, calcium in 44

iron in_ _ ______ 43

quality of ' ________ 43

Pope, F. J., cited__ 108,109 (footnote), 

162 (footnote)

Porcelain ware, action of reagents on_ 43

quality of 42

rules for use of 43

Porosity, determination of ____ 49, 51-53

Posujak, E., and Merwin, H. E.,

cited______ 66 (footnote) 

Potassium, determination of_____ 207-

211,214-216,

as chlorplatinate____ 210-211, 216 

as perchlorate __________ 216 

separation of, by sodium cobaltinitrite ________ 214-215 

Potassium bisulphate reagent, conversion of to pyrosulphate _ ______ ' 46 

advantages and disadvantages

of ______ 116 (footnote) 

quality of __ 46 

relative solubility of carbonates

in ____________ 251 

Potassium pyrosulphate reagent, advantages in use of __ 116 

(footnote)

Page. 

Powell, N. S., and Richards, J. W.,

cited .___ 251 

Pratt, J. H., method of, in ferrousiron determination__ 200, 

203-204

Precht, H., cited_______ 211 (footnote) 

Preller, I., and Kallauuer, O., cited- 142,

143, 263

Priess, H., and Mannich, C., cited_ 240 

Pycnometer method of specific gravity determination _ 54-57 

Pyrite, effect of, on ferrous-iron determination ______ 201 

insolubility of, in nonoxidixing

acids-____ 241 (footnote) 

occurrence of, in rocks_____ 28, 249 

Pyrrhotite, evidence as to presence

of, in rocks_____ 230, 233 

occurrence of, in rocks_____ 28

Radiators for evaporating solutions, 

description and figure 

of ____________ 33-35 

Radium, occurrence of, in rocks 29 

Ransome, F. L., cited _ 27 (footnote), 

184 (footnote)

Rare earths, caution against overlooking of__ 109 (footnote), 

135

determination of 170- 

172, 176-177, 261

occurrence of, in rocks_ ___ 25, 26 

precipitation of, with aluminum,

etc ____ 106-109,111-113 

Rawson, F. G., method of, for separation of barium and 

strontium from calcium_____________ :__________ 145

Reagents, quality of 45-47 

Reckert, F. C., Gooch, F. A., and

Kuzirian, S. B., cited 105 

Reglade, A., and Nicolardot, P., cited- 173 

Rhotanium, substitute for platinum. 44 

Richards, J. W., and Powell, N. S.,

cited __________ 251 

Richards, T. W., McCaffrey, C. T.,

and Bisbee, H., cited 140,141 

Ridsdale, C. H., cited_______ 122,188 

Ries, H., cited____________ 247 

Riggs, R. B., method of, for separation of magnesium from 

alkalies _ _ 214 

Roberts, H. S., and Hostetter, J. C., 

electrometric methods 

of, for iron. 16, 126(footnote) 

Robertson, J. D., cited__ _____ 241 

Rose, H., cited__ 116, 223(footnote), 242 

Rosenbladt, Th., cited 234(footnote) 

Ross, W. II., and Wagner, C. R.,

cited __________ 226 

Rossi, J., cited '130

Sale, P. D., and Burgess, G. K., cited 44

(footnote)
INDEX. 283

Page.

Sample, contamination of, by agate 03-64 

by steel_____ 58, 59(footnote), 60 

fineness of ____________*._ 59, 60 

preparation of_______ 57-63,192 

weight of__ _ ____ 64 

S&nchezr J. A., basic acetate method

of- ______ 110(footnote) 

Sandberger, F., cited___ 24(footnote), 241 

Sargent, G. W., cited__ 234(footnote), 235 

Scandium, occurrence of, in rocks__ 26 

Schaefer, C., and Schubert, M., cited 60

(footnote) 

Schaffgotsch's solution, character

of _______ 213(footnote) 

use of-'_____ 213-214, 233(footnote) 

Schaller, W. T., cited___ 209(footnote) 

Scherrer, J. A., and McBride, R. S.,

cited. 119 (footnote), 183 

(footnote), 187 

Schirmeister, H., and Bornemann, K.,,

cited __________ 133 

Schreiner, O., colorimeter of, description and figure of 39-41 

Schroeder, K., cited____ 164 (footnote) 

Schubert, M., and Schaefer,. C., cited- 66

(footnote) 

Schwartz, E. H., and Haffir R. C.,

cited _________ 215

Scoop. (Stee Weighing, scoop. 

Seemanr F., cited____ 223(footnote), 225 

Seger,, H., and Cramer, E., cited 53 

Selch, E., cited_____ 90(footnote), 118' 

Selvig, W. A.^ Fieldner, A. C., and

Taylor, G. B., cited- 219,. 266 

(footnote)

Separations, miscellaneous -r aluminum, iron, titanium, 

zirconium, chromium, 

rare earths, phosphorus, vanadium___ 126-134 

Shinier, P. W., cited_____ 255(footnote) 

Shimer, P. W., and E. B., cited 167,169 

Sidener, C. F., and Petttjohn, E.,

cited ___ 108(footnote)

Sieves, metal, unavailability of- 58

Silica, adherence of, to dish__ _ 100

contamination of precipitated 104

determination of__ 89-104, 116-118,

226, 253-256, 259, 271

accuracy of ______ 104,118

ignition of __________ 102-103 

impurities in, correction for-_ 103 

recovery of, from alumina precipitate _______ 116-118 

removal of, in fluorine determination ________ 222-223 

in sulphur determination 232 

residue from, composition- of_ 104-105 

separation of, from alumina, etc.

97-102,253-256, 271-272

fluxes used ln__-_ _ 90

solubility of__ 98, 99,. 101 (footnote)

Silica, soluble, determination of 244-245

Silicate rocks, analysis of-_____ 18-245

analysis of, methods of_ 48-245

constituents in__ _______ 24-30

Page.

Silicate rocks, decomposition of, by 

hydrofluoric and sulphuric acids _ ____ 89,158 

inethods of decomposition of_ 89-97 

Siliceous limestones, character of_ 249 

Silver, occurrence of in rocks___ 29 

Silvestri, 0., cited___________ 243 

Sive, B. E., cited_______ 112(footnote) 

SJollema, B., cited__________ 255 

Skinner, W. W., and Collins, W. D.,

cited_____ 212(footnote) 

Skrabal, A., and: Neustadl, L., cited 145 

Smith, G. McP., cited____ 231 (footnote) 

Smith, J. Lawrence, cited 117(footnote) 

method of, for alkali determination _________ 207-209

apparatus for, figure showing __________ 209 

Sniither,. F.. W., and Walker, P.. H.,

cited _____ 42 (footnote) 

Smoot, A. M., cited_____ 231 (footnote) 

Sodium, determination of __ 211-212 

Sodium bicarbonate, fusion with- 96 

Sodium bisulphate, advantage and

disadvantage of_ 117 

(footnote)

reagent _ _ 46: 

Sodium carbonate, effect of, on platinum during fusion 96 

fusion with_____________ 95-96 

melt, effect of leaching of, with

water ___ 170-171 

Sodium carbonate reagent, quality

of '___________ 46-47

Sodium cobalinitrite reagent _ 215 

Sodium hydroxide- reagent, quality

of___________ 47 

Sodium phosphate reagent, quality

of__________ 46 

Sodium-potassium carbonate, comparison of sodium carbonate and __ 94 

uses and advantages of- 117(footnote) 

Sodium pyrosulphate reagent, preparation of__-_____ 46 

Solutions, heavy, unavailability of,

in specific gravity de- . 

termination of rocks 57 

Sonstadt, E., cited __ 211 (footnote) 

Spear, E. B., and others, cited _ 41 

Specific gravity, determination of 49-57 

Sperry, E. S., and Penfleld, S. L.,

cited :_ _ 234(footnote) 

Sphalerite, occurrence of in carbonate rocks- _ _ 249 

Starck, G., cited -__-_____ 226 

Steiger, G., eited _ 134(footnote), 

156,173,199,209 

(footnote), 228- 

colorimeter of, description and

figures of _ __ 37-39 

drying apparatus of, description

and figures of____ 81

method of, for fluorine___ 227

Steiukonig, L. A., cited_______ 229

Steinlen, R. L., cited ____ 208 (footnote)
284 INDEX.

Page.

Stierlin, R., and. Lunge, G., cited_ 231

(footnote)

Stoddart, C. W., cited 232(footnote)

Stokes, H. N., cited________ 174,193,

194(-footnote), 202

Stolberg, C., cited___________ 143 

method of, for separation of calcium and magnesium 143 

Streit, G., and Franz, B., cited____ 175

Strontium, determination of__ 146, 262

occurrence of, in rocks____ 22, 28

separation of, from barium__ 145-146

from calcium________ 144-145

from magnesium______ 140 141

Strontium sulphate, spectroscopic

testing of ________ 172 

Suleiman, A., and Wunder, H.,

cited _______ 99 (footnote)

Sullivan, E. C., and Taylor, W. C.,

cited -__________ 16 

Sulphides, conversion of, to sulphates 

in limestones on heating ____________ 274 

influence of, on determination

of ferrous iron___ 201, 207 

Sulphur, condition of. determination

of____________ 230 

determination of________ 170-172, 

230-233, 268-269, 274 

failure to determine, error arising from_ _____ 23 

fractional determination of__ 233 

occurrence of, in rocks__ 23, 28, 249 

removal of, in alkali determination ____________ 210

Sulphur dioxide reagent, quality

of _______ 186(footnote)

T.

Tammann, G., cited-_____ 65 (footnote) 

Tantalum, occurrence of, in rocks_ 25, 30 

Tartaric acid, relative solubility of

carbonates in ______ 251

Taylor, G. B., Fieldner, A. C., and

Selvig, W. A., cited__ 219, 

266(footnote) 

Taylor, W. C., and Sullivan, E. C.,

cited ___________ 16

Thin, R. G., and Gumming, A. C.,

cited 216 (footnote)

Thorner, T. W., cited _ ____ 53

Thorium, occurrence of, in rocks__ 25, 29

separation of, from iron_____ 129

Thornton, W. M., cited__ 127(footnote),

164, 165, 175

method of, for titanium__ 164-166 

Thornton, W. M., and Hayden, E. M.,

cited _______ 164, 165 

Thorpe, T. E., cited.__________ 22

Thugutt, St., J., cited_____ 65 (footnote) 

Tin, occurrence of, in rocks_____ 25, 29 

Titanic oxide, solubility of, in alkalies __ __ 132

Page.

Titanium, contamination of silica by- 104

determination of_____ 154-170, 260

 colorimetric _______ 155-162

gravimetric __>_____ 162-166

volumetric ________ 166-170

loss of, by volatilization- ' 158 (footnote)

occurrence of, in rocks'______ 25

precipitation of________ 106-113,

119(footnote), 257-258

recovery of, after separation of

iron as sulphide__ 126-127 

separation of, from iron- 128-130, 133 

from iron and aluminum- 130-132 

Titanium sulphate reagent, preparation of__________ 157 

Toluene bath, description and use

of _!___________ 81, 86 

Tongs, crucible, description and

 figure of ____^___ 33 

Trace, definition of ________ 32

Trautmann, W., cited ^__ 118 

Travers, M. W., cited 242, 242 (footnote) 

Treadwell, F. P., cited_______ 102, 223 

method of, for ferrous-iron determination ___ 207 

Treadwell, F. P., and Koch, A. A.,

cited _________ 224, 225 

Trickett, A. B.) cited__________ 99

Truog, E., and Lenher, V., cited_ 99,

101.103,105

Tschermak, G., cited_____ 65 (footnote) 

Tucker, F. H., and Cain, J. R.,

cited___________ 179 

Tungsten, occurrence of, in rocks_ 29 

Turner, W. A., cited__________ 232 

Tyrolite, drying of, experiment on__ 74, 75

U.

Ullmann, C., cited_____ 196 (footnote) 

Uranium, occurrence of,-in rocks__ 29

V.

Vanadium, condition of, in rocks- 184-185 

determination of, colOrimetric__ 189 

volumetric______ 185-187, 261 

distribution of, in rocks____ 184 

effect of, on iron determination ____ 121-123, 202-203 

failure to determine, error from- 22 23 

occurrence of, in rocks- 22, 26, 184, 250 

precipitation of, with aluminum,

etc___________ 106-113

qualitative tests for ______ 187

Veitch, F. P., cited_____ 90-(footnote)

Vogt, J. H. L., cited_________ 193

Volhard, J., cited_____ 134 (footnote)

W. . Wagner, L. R., and Ross, W. H.,

cited__________ 226

Wagoner, L., cited _________ 242

Walker, P. H., and Smither, F. W.,

cited______ 42 (footnote)

Waltenberg, R. G., and Burgess,

G. K., cited 44 (footnote)

Walters, H. E., cited____ 137 (footnote)
INDEX. 285

?age.

Walton, J. H., Jr., cited ' ____ 161

Wa.rth, H., cited________ 77 (footnote)

Washington, H. S., cited____«_. 16,

19 (footnote), 20 footnote), 24

(footnote), 25, 29, 30, 31, 120

'(footnote),. 134 (footnote).

method of, in crushing______ 59

in determination of phosphorus__________ 178 

Washington, H. S., and others,

cited.'_______ 49 

Water, direct determination of__ 79-80, 

267, 269-270, 274 

direct determination of, apparatus for, description 

and figures of 81-90 

discriminating between conditions of, in minerals_ 64-69 

distilled, quality of__1____ 47 

inclusion of hygroscopic, in summation_______ _ 72 

'indirect determination of____ 73-77 

. methods of determination of_ 73-89 

rOle of, in minerals_______ 64-69 

suspension in, determination of

specific gravity by 50-53 

system of classification of, in

minerals _________ 65-66

behavior of, on drying minerals- 67-68

on heating minerals_____ 68

lost by grinding _ __ 59 (footnote)

67, 69-71

taken up by grinding- 60-61, 67, 69-71 

Waters, C. E., cited___________ 42 

Weber, H., and Hintz, E., cited__ 231

(footnote)

Weber, H., and Jannasch, P., boric

oxide, method of, for

 decomposing silicates

. _____92-93* 93(footnote) 

Weighing, scoop for, description and

figure of __ - 35 

Weiss, L., and Kaiser, H., cited-.: 127,156 

Weller, A., method of, for determination of titanium 155 

Wells, H. A., and Mitchell, W. L.,

'cited____ 119 (footnote)

Wells, R. C., cited_______ 157(footnote 

Wells, J. S. C., and Lenher, V.,

cited ______ 240

Page. 

Wheeler, H. A., and Luedeking, C.,

cited ___________ 243 

Wherry, E. T., acknowledgments

to _____ 17, 64(footnote) 

cited _ _______ 234(footnote) 

Wherry, E. T., and Chapin, W. II.,

cited __________ 240 

Wherry, E. T., and Larsen, E. S.,

cited _____ 69(footnote) 

Wichers, E., cited___________ 96 

Wichers, E., and Gurevich, L. J.,

cited ______ 44(footnote) 

Wilke-DOrfurt, E., cited __ 208 (footnote) 

Williamson, J. A., cited___ 45 (-footnote) 

Williamson, E. D., Johnston, J., and

Merwin, II. E., cited 251 

Winkler, L. W., cited____ 231 (footnote) 

Wright, F., Hillebrar.d, W. F., and

Merwin, H. E., cited 68 

(footnote)

Wiilfing, E. A., cited__ 193, 213 (footnote) 

Wunder, M., and Suleiman, A., cited 99

(footnote) 

Y. 

Yttrium, occurrence of, in rocks _ 26

Z.

Zambonini, F., cited___ 65 (footnote) 

Zeolitic minerals, dehydration of .75-76 

occurrence of, in rocks_ 51 (footnote) 

Zies, E. G., and Alien, E. T., cited- 239, 240 

Zimmerman, C., method of, for separation of magnesia 213 

Zinc, determination of_______ 136,261 

occurrence of, in rocks 29, 249 

precipitation of_____ 135 

separation of, from manganese 136 

Zinc oxide solution, preparation and

use of _____ 213-214,233 

Zirconium, determination of__ 172-176 

difficulty with, in gravimetric 

determination of titanium _________ 163 

occurrence of, in rocks__-_- 26, 172 

precipitation of, with aluminum,

etc, __________ 106-113 

recovery of, after separation of

iron as sulphide - 126-128

separation of, from iron_ 128-130, 133

from iron and aluminum- 130 132

o