DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

422

THE ANALYSIS OF 

SILICATE AND CARBONATE ROCKS

A REVISION OF BULLETIN

BY

W. F. HILLEBRAND

CONTENTS.

Page.

Introduction.............................................................. 13

Object and scope of the present treatise................................ 13

Acknowledgments.................................................... 15

Silicate rock analysis.............:........................................ 16

Part I. Introduction.................................................. 16

1. Importance of complete and thorough analyses .................. 16

2. The constituents occurring in silicate rocks ...................... 22

3. The distribution and occurrence of certain minor constituents..... 23

4. Summation of analytical results and limits of allowable error ..... 27

5. Statement of analyses.......................................... 29

6. Time needed for making an analysis............................ 30

7. Useful appliances and apparatus.......................'......... ' 30

A. Crucible tongs............................................ 30

B. Kadiators for volatilizing liquids and solids.................. 31

C. Perforated disk for crucibles................................ 32

D. Weighing scoop or trough................................... 33

E. Colorimeters.............................................. 33

a. First Survey form ..................................... 33

b. Second Survey form (Steiger's)......................... 35

c. Schreiner's form.....................................'.. 37

8. Preliminary qualitative analysis................................ 38

9. Quality of reagents............................................. 39

Part II. Methods applicable to silicate rocks........................... 41

1. Introductory remarks...'....................................... 41

2. Specific gravity (porosity).......... '. ............................ 43

General remarks............................................. 43

A. By suspension in water.................................... 43

a. Ordinary method for specific gravity.................... 43

b. Method for specific gravity and porosity combined.....'.. 45

c. Penfield's method for mineral fragments................. 46

B. Pycnometer method....................................... 47

a. Ordinary method.................................... .. 47

b. Kefined method ,. s..................................... 48

C. Heavy solutions not suitable for rocks ...................... 50

3. Preparation of sample for analysis .............................. 50

A. Quantity of rock to be crushed............................. 50

B. Crushing..................................'............... 50

a. Survey methods...................................... 50

b. Washington's method................................. 52

C. Grinding ................................................. 52

. . D. Abrasion of mortar and pestle.............................. 56

E. Weight of sample ......................................... 56

3
4 CONTENTS.

Silicate rock analysis Continued.

Part II. Methods applicable to silicate rocks Continued. Page.

4. Water. General considerations....... ......................... 57

A. The r61e of hydrogen in minerals.......................... 57

B. Water taken up or lost on grinding........................ 64

C. Importance of employing air-dry powder for analysis........ 65

D. Argument in favor of including hygroscopic water in the

summation.............................................. 66

5. Water. Methods of determination.............................. 67

A. Indirect methods. ......................................... 67

a. General considerations................................. 67

b. Methods involving the use of dehydrating agents"..'...... 67

c. Methods involving application of heat................... 69

a. Fractional determinations.......................... 69

P. "Loss on ignition" method for total water.......... 71

B. Direct methods without absorption tubes Penfield's methods. 72,

a. For minerals easily deprived of their water.............. 72

b. For minerals not easily deprived of their cwater.......... 73

C. Direct methods with absorption tubes................... 1.. 73

a. General considerations................................. 73

b. Penfield's procedure................................1.. 74

c. Steiger's application of the toluene oven................ 75

d. Chatard's oven for temperatures up to 300° and over..... 76

e. Gooch's apparatus..................................... 78

f. Merits of the above forms of apparatus.................. 82

g. Jannasch'smethods...........'......................... 82

6. Silica, separation from alumina, etc............................. 83

A. Alternative methods of decomposing the rock............... 83

a. General considerations.................................. ' 83

b. Decomposition of refractory silicates by hydrochloric acid

under pressure...................................... 85

c. The boric-oxide method of Jannasch and Heidenreich... 86

a. Preparation of the boric oxide...................... 86

ft. Treatment of easily decomposable silicates........... 86

y. Treatment of refractory silicates.................... 86

S. Further treatment after fusion...................... 87

s. Possible objections to the boric-oxide method-....... 87

d. The sodium-carbonate method.......................... 87

a. Advantages of sodium carbonate over sodium potassium carbonate.................................. 87

/?. Purity of the sodium carbonate.................... 88

y. The fusion with normal sodium carbonate.......... 88

8. Fusion with sodium bicarbonate.................... 90

£. Treatment after fusion.............................. 90

B. Subsequent treatment..................................... 91

a. Separation of silica.................................... 91

a. Reasons for adoption of accepted procedure......... 91

/3. Procedure in absence of notable amounts of fluorine. 92

y. Procedure with rocks" and minerals containing fluorine. 94

b. Ignition of silica...................................... 94

c. Correction for impurities in the silica................... 95

d. Accuracy of the silica determination .................... 96

e. Composition of the residue obtained from the silica '...... 96

f. Platinum in filtrates.............................'....... 97

7. Metal precipitable by hydrogen sulphide....................... 98
CONTENTS. 5

Silicate rock analysis Continued.

Part II. Methods applicable to silicate rocks Continued. Page.

8. Aluminum total iron......................................... 98

A. Indirect method for aluminum (titanium).................. 98

a. Preliminary remarks................................... 98

b. Precipitation of aluminum, iron, etc., without precipitating manganese.................................. 99

a. Precipitation by ammonia......................... 99

j3. The basic-acetate precipitation..................... 100

c. Precipitation of 'iron, aluminum, etc., together with

manganese...................................... 102

a. By ammonia and ammonium persulphate.......... 102

ft. By ammonia and ammonium sulphide.............. 103

d. Kecovery of iron and aluminum from the filtrates....... 103

a. After an ammonia precipitation.................... 103

ft. After a basic-acetate precipitation.................. 103

y. After precipitation by ammonia and ammonium

persulphate..................................... 104

e. Ignition of the precipitate of iron, aluminum,' etc., oxides.. 104

f. Recovery of silica and possible barium in the alumina precipitate. ........................................ 105

a. Silica............................................. 105

P. Barium........................................... 107

B. Determination of iron in the precipitate of alumina, etc...... 107

a. Without regard to the presence of vanadium.... t ....... 107

a. Eeduction of the iron............................. 107

ft. Titration of the iron............................... 108

y. Further treatment of the solution after titration..... 109

b. Having regard to the presence of vanadium............. 109

c. Determination of the true value for ferric iron........... 110

C. Methods aiming at the more or less direct determination of

aluminum .......................................... Ill

a. After first removing iron as sulphide.................... Ill

b. By extraction with a fixed caustic alkali................ Ill

c. Methods of Dittrich.................................... 112

d. Direct precipitation of aluminum by phenylhydrazine... 112

9. Manganese, nickel, cobalt, copper, and zinc..................... 113

A. Difficulties in the way of a correct gravimetric determination

of manganese........................................... 113

B. Precipitation of the group and separation of its constituents.. 114 

a. The ammonium-sulphide method....................... 114

a. Its advantages and disadvantages.................. 114

ft. Precipitation by ammonium sulphide and separation of

manganese and zinc from nickel, cobalt, and copper. 11.5 

b. Manganese and /inc................................... 115

c. Nickel, cobalt, copper.................................. 116

C. Colorimetric determination of manganese................... 116

a. Preliminary treatment................................. 116

b. Colorimetric determination of manganese by ammonium

persulphate......................................... 117

10. Calcium and strontium (barium)............................... 118

A. Separation from magnesium................................ 118

a. Precipitation and ignition of calcium and strontium oxalates together....................................... 118

b. Notes on double precipitation, washing, and ignition of the

oxalates............................................ 119
6 CONTENTS.

Silicate rock analysis Continued.

Part II. Methods applicable to silicate rocks Continued.

10. Calcium and strontium (barium) Continued. Page.

B. Separation of strontium (barium) from calcium .............. 119

a. By ether-alcohol....................................... 119

b. By amyl alcohol....................................... 120

C. Behavior of barium........................................ 120

D. Separation of barium from strontium ........................ 120

E. Other'methods of determining the weight of calcium ........ 121

General statement........................................ 121

a. Volumetric method..................................... 122

b. By weighing as the carbonate .......................... 122

c. By weighing as the sulphate............................ 122

d. By weighing as the fluoride ..---....--...---...-.-----. 123

11. Magnesium ._......................-..........--..-..-....... 123

A. Precipitation.............................................. 123

a. Conditions necessary for the production of a normal precipitate........-...........-.....--.-..-----.---..... 123

b. Precipitation............................--_......-..-. 124

a. First precipitation................................. 124

ft. Second precipitation................................ 125

B. Methods of collecting and igniting the precipitate ........... 125

a. Ordinary procedures.....................---...--..---. 125

b. Modification of Ulbricht............................... 126

C. Contamination by and removal of barium, calcium, and manganese........................................ ..---..-.-. 126

a. Barium............................................... 126

b. Calcium .............................................. 127

a. Preferred method ..............----......--.....-. 127

ft. Alternative method ............................... 127

c. Manganese.......-.-........--....-.--..--- r -.-------- 127

D. Liability to error in the average magnesium determination... 128

12. Titanium ..................................................... 128

A. Colorimetric determination with hydrogen peroxide...-...-. 128 

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

affect it.............................................. 128

b. Preparation of the standard ............................ 130

c. The test solution....................................... 130

d. The color comparison..............--....---...---...-. 132

e. Correction for the color of ferric sulphate................ 133

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

test solution..................................... 133

ft. By addition of iron to the standard................. 133

y. By the use of phosphoric acid...................... 134

f. Correction for the effect of alkali sulphate............... 134

B. Gravimetric methods...................................... 134

a. Gooch's method....................................... 134

a. Description of the method ..........'............... 134

ft. Gooch's method not directly applicable to rocks containing zirconium ............................... 136

b. Methods of Dittrich and Freund........................ 136

C. Superiority of the colorimetric and Gooch methods over the

older ones .............................................. 138

13. Barium (zirconium, rare earths, total sulphur, chromium) ...... 138

A. The general method....................................... 138

B. The method without regard to zirconium and sulphur....... 140
CONTENTS. 7

Silicate rock analysis Continued.

Part II. Methods applicable to silicate rocks Continued. Page.

14. Zirconium .1................................................. 140

A. Author's method.......................................... 141

B. Other methods............................................ 142

15. Bare-earth metals other than zirconium........................ 143

A. Usual method ............................................ 143

B. Alternative method ....................................... 143

16. Phosphorus ..............................i................... 144

A. Procedure when material is ample.......................... 144

a. Washington's method of preliminary treatment.......... 144

b. Alternative method of preliminary treatment............ 144

c. Subsequent treatment.................................. 145

B. Procedure when material is scanty......................... 145

17. Chromium .:..............................,.. ............... 146

A. Gravimetric method ...................................... 146

B. Colorimetric method...................................... 147

a. Preparation and strength of standard solution.... .i . 147

/?. Preparation of test solution........................ 147

y. Comparison of colors....... ...................... .147

C. A few comparative data................................... 148

18. Vanadium (chromium) and molybdenum ...................... 148

A. Distribution of vanadium and molybdenum................. 148

B. Condition of vanadium in rocks ........................... 149

C. Author's method.......................................... 150

a. Description of the method.............................. 150

b. Confirmatory qualitative tests.... 1..................... 151

c. Application of the method in presence of relatively much

chromium ........................................... 152

D. Colorimetric method for vanadium................:........ 154

19. Ferrous iron.............................. ......... ........... 154

A. Oxidation of ferrous iron in minerals by grinding preparation of sample...............................:............ 154

B. Comparison of sealed-tube and hydrofluoric acid methods 

comparative worthlessness of the former in rock analysis.... 157

C. The modified Mitscherlich method......................... 159

a. Strength of acid................................... 159

ft. Filling, sealing, and heating of the tube............. 160

y. Reason for introducing gas and sealing as above

directed ...........................:............ 160

D. The hydrofluoric acid method.....................'......... 161

a. Principle of the method................................ 161

b. Defects of the method.................................. 162

a. Oxidizability of divalent manganese by permanganate

in presence of hydrofluoric acid.....:............ 162

ft. Extreme oxidizability of divalent iron by free oxygen

in presence of hydrofluoric acid or a fluoride...... 163

c. Influence of sulphides, vanadium, and carbonaceous matter 

on the determination of ferrous iron by the hydrofluoric acidmethod.................,.:............ 165

or. Sulphides ........................................ 165

ft. Vanadium........................................ 166

y. Carbonaceous matter.............................. 166
8 CONTENTS.

Silicate rock analysis Continued.

Part II. Methods applicable to silicate rocks Continued.

19. Ferrous iron Continued.

D. The hydrofluoric acid method Continued. Page,

d. The method in its various modifications................ 167

a. According to Pratt(modified)...................... 167

/?. According to Cooke................................ 168

y. According to Treadwell.......... .................. 170

E. Uncertainties of the ferrous-iron determination............. 171

20. Alkalies ..................................................... 171

A. The J. Lawrence Smith method............................ 171

a. Its advantages......................................... 171

b. Reagents and apparatus................................ 171

c. Treatment of the mineral powder....................... 172

d. Separation of calcium and sulphuric acid................ 173

e. Precipitation of potassium............................. 173

f. Sodium and lithium.................. ................. 174

a. Gooch's method for separating lithium ............. 175

B. Preliminary treatment by other methods................... 176

a. The mercuric oxide method............................ 176

b. The ammonium carbonate method...................... 176

c. The amyl alcohol method.............................. 177

C. Direct separation of potassium by sodium cobaltinitrite...... 177

a. Preparation of the reagent............................. 177

b. Application of the method .............................. 178

a. Determination as chlorplatinate.................... 178

/?. Determination as perchlorate........................ 178

21. Carbon dioxide, carbon....................................... 179

A. Qualitative test for carbon dioxide......................... 179

B. Quantitative tests for carbon dioxide........................ 179

a. Direct method......................................... 179

b. Indirect method...................................... 181

C. Carbon................................................... 182

22. Chlorine..................-........................-^........' 182

A. Condition in rocks........................................ 182

B. Determination of water-soluble chlorine.................... 183

C. Determination of acid-soluble chlorine...................... 183

a. By nitric acid......................................... 183

b. By nitric and hydrofluoric acids........................ 184

D. Determination of chlorine by alkali fusion.................. 184

23. Fluorine (silica in presence of fluorine)........................ 184

A. Imperfection of the qualitative test for fluorine.............. 184

B. Direct quantitative determination of fluorine................ 184

a. The method of Berzelius............................... 184

b. Testing of the calcium fluoride.......................... 186

c. Accuracy of the method............................... 187

d. Determination of silica................................. 188

C. Indirect quantitative determination of fluorine.............. 188

a. Steiger's method...................................... 188

b. Merwin's modification of Steiger's method.............. 191

a. Introductory remarks ............................. 191

ft. Merwin's method................................. 192
CONTENTS. 9

Silicate rock analysis Continued.

Part II. Methods applicable to silicate rocks Continued. Page.

24. Sulphur...................................................... 193

A. The determination of sulphur as barium sulphate........... 193

a. The errors involved.................................... 193

b. Avoidance or correction of errors....................... 195

B. Determination of the condition of sulphur in rocks.......... 197

C. Quantitative determination................................ 198

a. Total'sulphur......................................... 198

b. Fractional determinations ............................. 198

25. Boron ....................................................... 199

26. Certain constituents in minute traces.......................... 201

27. The gases and vapors expelled by heat...........I.--..-...... 201

28. Special operations ............................................ 203

A. Detection of nepheline in presence of oli vine................ 203

B. Determination of soluble silica............................. 203

Carbonate rock analysis.................................................. 205

Part I. Introduction.................................................. 205

29. Qualitative comparison of carbonate and silicate rocks.......... 205

30. Mineral composition of carbonate rocks........................ 207

31. Behavior toward different reagents as a means of distinguishing

different carbonates......................................... 209

a. Differing solubility in tartaric and citric acids and in acid

potassium sulphate .................................. 210

b. The Meigen reaction for distinguishing calcite from

aragonite............................................ 210

c. Distinguishing between calcite and dolomite ............ 211

Part II. Eefined methods of analysis................................... 212

32. Silica, its separation from alumina, etc.........................'. 212

A. Methods of decomposing the rock .......................... 212

a. When the inorganic residue is to be separately analyzed.. 212

b. When the inorganic residue is not to be separately analyzed. 213

a. By solution in acid after strong ignition............. 213

ft. By solution in acid after heating with sodium carbonate .......................................... 214

B. Separation of silica........................................ 214

33. Aluminum, total iron, titanium (silica, manganese); precipitation

in company with phosphorus, etc............................ 215

A. Precipitation of aluminum, iron, etc........................ 216

a. Collective precipitation of aluminum, iron, manganese,

titanium, and phosphorus by ammonium sulphide..... 216

b. Precipitation of aluminum, iron, titanium, and phosphorus by ammonia.................................. 216

c. Precipitation of aluminum, iron, titanium, and phosphorus by the basic-acetate method................... 217

B. Treatment of the filtrates from alumina, etc................ 217

C. Solution and separation of the oxides obtained in A and B.... 218

a. Silica (barium)..--.---------------.................... 218

b. Iron.................................................. 218

c. Titanium............___.......__................. 219

d. Aluminum...-----------.------____...__-.__........_. 219
10 CONTENTS.

Carbonate rock analysis Continued.

Part II. Refined methods of analysis Continued. . . Page.

34. Manganese ........-..._..............._.__,..__..,__.__.._... 219

A. In the filtrates from 33.B..............'.................... 219

B. Separate determination of manganese....................... 220

35. Copper, nickel, cobalt, lead, zinc, rare earths, chromium, vanadium, molybdenum....................................1... 220

36. Calcium, strontium, barium, magnesium (manganese)........... 221

37. Phosphorus .................................................. 222

38. Ferrous iron ................... i.............................. 222

A. In the absence of carbonaceous matter!..................... 222

a. Ferrous iron soluble in sulphuric acid................... '222

b. Ferrous iron in the insoluble residue.................... 223

. c. Total ferrous iron...................................... 223

B. In presence of carbonaceous matter..........::............ 223

39. Alkalies ..................................................... 224

40. Carbon dioxide, carbon (water)................................ 224

A. Determination of carbon dioxide............................ 224

B. Determination of carbon of carbonaceous matter....... 1.... 224

C. Simultaneous determination of water and of total carbon in

both forms .............................. ^............... 225

41. Chlorine ..................................................... 225

42. Fluorine ..................................................... 226

43. Sulphur...................................................... 226

A. Tests as to its condition; determination of sulphate sulphur.. 226

B. Determination of total sulphur............................. 226

a. Methods of converting sulphides to sulphates............ 226

a. By ignition without flux........................... 226

/?. By ignition with sodium carbonate................. 227

b. Treatment after ignition................................ 227

44. Water ....................................................... 227

A. Hygroscopic water ........................................ -227

B. Combined water....................................:...... 228

Part III. Condensed analysis.......................................... 228

45. Decomposition and solution ................................... 228

46. Silica........................................................ 229

47. Aluminum, iron, etc '.........:................................. 229

48. Calcium...................................................... 230

49. Magnesium .................................................. 230

50. Alkalies...................................................... 231

51. Carbon dioxide............................................... 231

52. Sulphur...................................................... 231

53. Water .....:.......'.......................................... 231

54. Ignition loss.............. 1................................... 231

Index.......-........*.-................................................. 233
ILLUSTRATIONS.

Page.

FIG. 1. Platinum-tipped crucible tongs.................................... 30

2. Radiator for rapid and safe evaporation ............................ 31

3. Device for excluding flame gases from crucibles during ignition...... 32

4. Weighing trough of platinum...................................... 33

. 5. First Survey form of colorimeter .................................. 34

6. Second Survey form of colorimeter (Steiger's)...................... 35

7. Schreiner's colorimeter ........................................... 37

8. Moore's device to remove air from mineral powders....... j......... 49

9. Ellis's steel mortar ................................................ 51

10. McKenna ore grinder............................................. 55

11. Penfield's tubes for water determination ........................... 72

12. Penfield's oven for water determination ........................... 73

13. Penfield's tube for water determination............................ 75

14. Steiger's drying apparatus. -...........'............................. 76

15. Chatard's drying oven for water'determination..................... 77

16. Modified form of Gooch tubulated platinum crucible for water determination ...................................................... 78

17. Arrangement of Gooch apparatus during drying.................... 80

18. Arrangement of Gooch apparatus during fusion..................... 81

19.° Glass tube for determination of water (Jannasch) ................'.. 82

., 20. Glass tube for determination of water in special cases (Jannasch).... 83

21. Cooke's apparatus for ferrous-iron determination ................... 169

22. Tread well's apparatus for ferrous-iron determination................ 170

23. The J. Lawrence Smith crucible for alkali determinations........... 172

24. Apparatus for carbon dioxide determinations....................... 180

25. Kreider's apparatus for indirect determination of volatile substances.. 181

26. Steiger's curve for fluorine ........................................ 189

27. Merwin's diagrams for fluorine.................................... 191

11

THE ANALYSIS OF SILICATE AND 

CARBONATE ROCKS.

By W. F; HlLLEBRAND.

INTRODUCTION. 

OBJECT AND SCOPE OF THE PRESENT TREATISE.

The following paragraphs are reprinted from Bulletin 305, of which 

the present volume is a revision.

The literature relating to analysis of silicates is extensive but scattered, and in no 

single paper up to the time of the publication of Bulletin No. 148 of this Survey 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, have been of 

late years recognized as occurring persistently in small amounts. It was not the 

intention to make the chapter on rock analysis in that bulletin 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 same 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 it by chemists led to the republication of a portion 

of Bulletin No. 148 in more extended form as Bulletin No. 176. Since the publication 

of the latter bulletin in 1900 two other treatises on rock analysis have appeared: 

Manual of the Chemical Analysis of Rocks, by Dr. H. S. Washington (1904), and 

Anleitung zur Gesteinsanalyse, by Dr. Max Dittrich (1905). The former is based 

largely on Bulletin No. 176; the latter, while adopting some of the methods advocated 

in that bulletin, adheres more to methods which are in greater favor in Germany 

than in this country. They both differ from Bulletin No. 176 in devoting less space 

to a discussion of principles and to the determination of the less common constituents 

of rocks. Doctor Washington's book enters into considerable detail in describing 

manipulations, since it was written for chemists, petrologists, mining engineers, and 

others who have not made a particular study of quantitative analysis. These books 

have not, therefore, rendered the Survey publication superfluous. On the contrary, 

since some methods have undergone improvement or been superseded by better ones, 

the time seems ripe for its republication in revised form.

Experience has shown that for the use of the student the outlines of some methods 

and procedures were too briefly sketched in the earlier publications. Where it seemed 

called for, therefore, these have received considerable elaboration.

13
14 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

For the reasons that the chief carbonate rocks form BO important an element in the 

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

moment to the geologist as well as to the cement maker, who now makes enormous 

use of them, a special section devoted to their analysis has been added. The methods 

applied to their analysis differ in but unimportant respects from those used with the 

more siliceous rocks, since they are to a great extent themselves siliceous, contain 

essentially the same constituents, and therefore the same principles apply to both. 

Naturally they demand and receive briefer treatment.

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 that 

kind should never be intrusted to the novice, but only to the chemist who has a 

knowledge of the composition and properties of the peculiar mineral constituents of 

those bodies and a judgment fit to cope with the oftentimes difficult problems presented 

by them.

The methods described in the following pages are not restricted altogether to those 

actually in use in the Survey laboratory. A number of alternative ones are given 

which are known or believed to be good, in order that those who may wish to use this 

treatise as a practical guide shall have some choice of selection in case the expensive 

apparatus or complicated arrangements sometimes preferred are not available. Where 

silicate and limestone analyses are very frequently made, however, it is a saving of 

time and money in the end to set up permanent arrangements for convenience in 

determining water, carbon, dioxide, ferrous iron, in making reductions in hydrogen, etc.

It was my intention to prepare a chapter on the mechanical separation in a small way 

of minerals by the various processes more or less in vogue> as panning, upward flow 

of water, heavy solutions, and magnetism, but lack of time, and in fact insufficient 

experience with some of the methods and solutions, have prevented its development. 

To those seeking information on some of these methods reference is made to the works 

of Rosenbusch-Wulfing, Mikroscopische Physiographic der Mineralien und Gesteine, 

volume 1 (1904); Rosenbusch-Iddings, Microscopical Physiography of Rock-making 

Minerals, fourth edition (1903); and Ferdinand Zirkel, Lehrbuch der Petrographie, 

second edition, volume 1.

As the edition of Bulletin 305 approached exhaustion the question 

arose whether it should be reissued or revised. In view of certain 

discoveries that had been made since the appearance of that bulletin 

in 1907, which necessitated not only a rather radical change in the

manner of preparing samples for analysis, but also modifications in 

some analytical procedures, the decision was made to revise it. This 

seemed all the more desirable, because a German translation of Bulletin 305, with considerable new matter added by myself, had been 

prepared, and has since been published.

The following are the more important changes and additions in the 

present volume as compared with Bulletin 305. The preparation of 

the sample has been much modified in the endeavor to meet the need 

for one that shall not have taken up water from the air or have 

suffered oxidation with respect to ferrous iron or sulphides during 

grinding. The effect of fine grinding on the composition of the 

sample has necessitated changes in carrying out certain determinations, notably that for ferrous iron. The chapters on water have 

been rearranged, and that devoted to general considerations is now 

introduced by a section on the r6le of hydrogen in minerals. The
OBJECT AND SCOPE OF PBESENT TBEATISE. 15

chapter on the determination of titanium, has been in part rewritten, 

in consequence of the discovery of the bleaching effect of alkali salts 

on the color produced by hydrogen peroxide. This discovery called 

also for an important addition to the chapter on fluorine. That on 

sulphur has been supplemented by a section on the errors involved in 

the determination of sulphur as barium sulphate and their avoidance 

or correction. Many other minor additions and alterations have 

been made.

The author's transfer in 1908 from the Geological Survey to the 

Bureau of Standards has made it impossible for him to keep as 

closely in touch with the literature of methods pertaining to or applicable to mineral analysis as he would have liked. This must serve 

both as excuse and apology if, as is probable, some new methods or 

modifications of methods that deserve recognition find no mention in 

. the present volume.

ACKNOWLEDGMENTS.

To Drs. F. W. Clarke, E. T. Alien, E. C. Sullivan, R. C. Wells, A. 

L. Day, and F. K. Cameron, and Messrs. George Steiger and W. T. 

Schaller, my thanks are freely rendered for friendly criticism, advice, 

suggestions, and occasional direct assistance.
SILICATE ROCK ANALYSIS.

PAKT 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 u 

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 outgrowth71 

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

the more or less complex mixtures of them the rocks to aid whos 

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

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 ever 

expanding 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 on inorganic lines fifty perhaps were engaged in erecting the present enormous structure of carbon chemistry. The instruction afforded 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

16
IMPOKTANCE OF COMPLETE AND THOKOUGH ANALYSES. 17

of heav}^ solutions, whereby, on the one hand, the qualitative mineral 

composition of a rock could be preliminarily ascertained with considerable certainty, and on the other 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 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; 

;ome 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 

cagps it appeared that the failure to report the presence of one or more 

elements had obscured relations and differences which more thorough 

^urination showed to exist (see p. 19). Consequently there arose a

*^ing of distrust of much of the older work in the minds of those 

:.emists and petrographe'rs who were best fitted to judge of its probable qualities. This, and the incompleteness of nearly all the earlier 

work (and much 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.0

And yet these demands on his part are, with few exceptions, by no 

means so exacting as they should be. Frequently the analysis is 

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 may be little superior to his 

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

analysis is expected to be solved by a tyro, and his results are complacently accepted and published broadcast without question. Even to 

those thoroughly familiar with the subject rock analysis is a complex 

and often trying problem. Although long practice may have enabled

a Dr. Henry S. Washington, in Professional Papers Nos. 14 (Chemical analyses of igneous rocks published from 1884 to 1900, 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 Survey, has done a most important work in 

sifting the great mass of data accumulated in the thousands of analyses published since 18R9. After 

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

f,ny of these values may be incorrect, but in most cases they undoubtedly give a fairly true measure

 he weight to be attached to a particular analysis.

20091 Bull. 422 10 2
18 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

one to do certain parts of it almost mechanically, perplexing questions still'arise which require trained judgment to properly meet and 

answer, and there is yet room for important work in some of the supposedly simplest quantitative determinations. If 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 fifteen 

to twenty-five 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 in 

number, 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 lines 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 

woful inability to obtain agreeing 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 

silicate analysis has resulted from the investigations set on foot and 

the recommendations made by these committees, and further improvement may be expected, but the situation is yet anything but satisfactory. 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 is so 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 pf 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.0

o For a further presentation of this subject from the view point of an experienced petrographer, see 

Washington, H. S., Manual of the Chemical Analysis of Bocks, 1904, pp. 8-17.
IMPOETANCE OF COMPLETE AND THOEOUGH ANALYSES. 19

The importance of the points indicated in the foregoing paragraphis shown by the difference between the analyses given below. The 

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 rod; mass at different dales.

SiOj..........................

TiOs.. .......................

AlsOa.. ......................

FczOs

FcO..........................

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

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

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

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

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

K2O............:.............

Na»O........................

Earlier 

analysis.

54.42

13.37

6.61

63.52

4.33

6.37

10.73

1.60

Later 

analysis.**

53.70

1.92

11.16

.04

3.10

1.21

.04

 } AR

19

.62

6.44

11.16

1.67

Li 20. .......................

H 20 below 110°.............

COs.. .......................

P206 . .......................

SOs-..- .....................

F...... ..................... ci. ..........................

Earlier 

analysis.

Trace.

C2.76

1.82

99.58

Later 

analysis.o

Trace.

.80

2.61

1.75

.06

.44

.03

.19

100. 21

» 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 ZrOs, incorrect becaus'e of the error in AlsOa resulting 

from having counted thoZrOsas AljOs, and from the fact that titanium is not fully precipitable in presence of zirconium by Gooch's method (the one employed). Thi8 latter error involves both the TiOiand 

the A1 2O8. (See ft, p. 136.)

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.

<: In the published analysis it docs 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, P2O5 , and S03 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 mineralogical 

nature of the rock.

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

TiOa. .........................

AlsOa.........................

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

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

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

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

K»0.. .........................

Earlier 

analysis.

17.20

3.73

.10

6.57

3.64

Later 

analysis.

44.65

.95

 13.87

6.06

2.94

.17

9.57

<J.37

.76

5.15

NaaO ........................

LiaO .........................

COs..........................

PaO5 ... ......................

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

SOs..........................

^

Earlier 

analysis.

4.45

.77

3.30

99.11

Later 

analysis.

5.67

Trace.

.95

2.10

.11

1.50

.61

99.92

Not entirely free from CaO.
20 ANALYSIS OF SILICATE AND CAKBONATE BOOKS.

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

titanic 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 tnen 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 far 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 

last instance 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 to-day 

are not.

Again, vanadium is an element which few chemists have 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
IMPORTANCE OF COMPLETE AND THOEOUGH ANALYSES. '21

comprise, as the pentoxide, up to 0.1 per cent of many French and 

Australian" 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 /?, p. 166), a matter of considerable importance, since the 

petrographer lays great stress1 on accuracy in their determinations. 

' The same investigation has also thrown 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 of late years 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 riot have been suspected (see B, p. 157).

While strongly upholding the necessity for more thorough work, 

necessarily somewhat at the expense of quantity, it is far from rny intention to demand that an amount of time altogether disproportionate to 

the immediate objects to be sought should be expended on every analysis. But it is maintained 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 , 

A12O3 , 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.

Finally, whenever possible, a thorough microscopical examination of 

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

o J..C.H. Mingaye has lately confirmed its wide distribution in Australian rocks, coals, etc. (Records 

Geol. Survey New South Wales, vol. 7, pt. 3,1903, p. 213.)
22 ANALYSTS OF SILICATE AND CARBONATE ROCKS.

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. ° 

If the point be 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 have been to a considerable degree evolved during a personal experience of over twentyfive years in this line of work, and that frequently the exigencies were 

such as to compel restriction in the examination. Where the latter 

has been the case, subsequent developments have in some cases shown 

it to be bad policy in every respect. It is better, for both the geologist and the chemist, to turn out a limited 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 concentrations 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. 6 

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 in a limited amount of the sample say from one-half 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 sediiSee also Washington, H. S., Chemical Analysis of Rocks, 1904, 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.

& F. Sandberger's researches have shown to what extent this is true of a large number of those elements 

contributing to the filling of metalliferous veins, and L. Dieulafatt by his elaborate qualitative researches showed how universal was the distribution of copper, zinc, barium, strontium, etc., in the 

primordial rocks.
CONSTITUENTS IN SILICATE ROCKS. 23

mentary 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:

Si02 , Ti02 , ZrO2 , A12O3 , Fe2 03 , Cr2 03 , V,03 , FeO, MnO, NiO, CoO, 

MgO, CaO, SrO, BaO, ZnO, CuO, K2O, Na2 0, Li2 0, H2 0, P2 05 , S, a 

S0a , C,& C02 , PI, 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, glucmum," 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 

overlooked 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 Doctor Washington's book (Manual 

of the Chemical Analysis of Rocks, pp. 18-21), already more than 

once referred to.

Doctor Washington says:

"The increased number of analyses of igneous rocks, especially 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 rare 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 be safely 

neglected.''

Titanium. Not long ago held to be rare, this element is now recognized to be one of the most universally distributed 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, 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

a Usually as pyrite, occasionally as lazurite, not infrequently as pyrrhotite. 

6 As graphite or coaly matter.

cFor probably the best method of separating even very small amounts of glucinum from iron and 

aluminum see Parsons, C. L., Jour. Am. Chem. Soc.,vol. 28,1906,p. 1589; Chem. News, vol.95,1907,p. 188.
24 ANALYSIS OF SILICATE AND CARBONATE ROCKS.'

seemingly present even in the most siliceous rocks, it is most abundant 

in the so-called basic ones. Its chief mineral occurrences are as 

rutile, octahedrite or anatase, ilmenite, titanite, and perofskite, but 

it is also a component in smaller amounts of many pyroxenes, hornblendes, biotites, and garnets. 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 up 

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

most apt to occur in granites, rhyolites, syenites, and in nephelite 

syenites, phonolites, tinguaites, and tephrites, and is most abundant 

in those which are high in soda, such as the last four. It is rarely 

met with in the more basic rocks, especially those 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 the 

rare minerals eudialyte, lavenite, and rosenbuschite."

Chromium. "Chromium is almost wholly confined to the basic 

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 olivines. It may occur up to one-half of 

1 per cent of O2CV

Vanadium. The distribution of this element has been in part covered by the remarks on pages 20-21. To leave out of account the wellcharacterized mineral vanadates, its most stable and normal form in 

the silicates seems to be that of trivalency, corresponding to the oxide 

V2O3 , in which form it replaces alumina and possibly ferric oxide to a 

very limited extent a few hundredths of one per cent in pyroxenes, 

hornblendes, and biotites. It hence predominates in the less siliceous 

igneous rocks. As the mineral roscoelite, essentially a vanadioalumino-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. a 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.

oHillebrand, W. F., and Ransome, F. L., Am. Jour. Sci.,4th sen, vol. 10,1900, p. 120; Bull. U. S. GeoL 

Survey No. 262, 1905, p. 9.
MINOR CONSTITUENTS. 25

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 0 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 sometimes appear, particularly on surfaces of limestones and sandstones, 

in a more or less peroxidized condition. Its amount will rarely exceed 

0.3 per cent. I fully agree with Doctor 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 

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

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

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 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 these elements, the former almost always in excess of the latter. 

According to Washington, there is considerable evidence, in part 

unpublished, that barium is apt to be most abundant in rocks which 

are high in potassium. It occurs "in orthoclase (as the hyalophane 

molecule) and possibly also in labradorite and anorthite (as celsian) 

as well as in a few biotites and muscovites." It 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 percenta As to the Peruvian occurrence see Hewett, Foster, Eng. Min. Jour., vol. 82, 1900, p. 385; Bravo, Jose J., 

Bol. Soc. Ing. (Lima), vol. 8,1900, p. 171; Hillebrand, W. F., Am. Jour. Sci.,4th ser., vol.24,1907,p. 141; 

and Jour. Am. Chem. Soc., vol. 29, 1907, p. 1019.'
26 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

age 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, it is almost never met with 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 especially affects 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 in 

almost every case 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 which 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 S03 instead of S. It may now and then occur in both 

states, but much more often only in the sulphide condition.

Chlorine. "Chlorine is present most abundantly in rocks which

are high in soda, and especially when so low in silica that iiepheliteis 

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 [also noselite W. F. H.], 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 fluicl inclusions in 

minerals sometimes contain sodium chloride, which would be largely 

extracted from the powder by water.

Fluorine. "Fluorine seems to have no special preference as to 

magma, though, on the whole, it is found more frequently in acid than 

in basic rocks. It is also apparently most apt to be met with as fluorite in rocks containing nephelite, as foyaites and tinguaites. It is 

an essential constituent of fluorite and most apatite, and as an integral
, MINOR CONSTITUENTS. 27

part of the last mineral is almost universally present. It also occurs 

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 c, p. 187).

Other minor constituents. "Glucinum, as a component of beryl, is 

most frequent in granites, pegmatites, and quartzose gneisses. Tin 

is confined to the acid rocks, granite, quartz porphyry, and rhyolite, 

and its presence is due [often W. F. H.] to pneumatolytic processes. 

It occurs as cassiterite, and in traces in ilmenite, micas, and feldspars. 

The rare-earth metals occur in allanite, xenotime, monazite, and 

other minerals of even greater rarity, and seem to be especially frequent in acid rocks and possibly those with much soda. 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.I Platinum is,found 

almost exclusively in peridotites, but is occasionally met with in connection with gabbros. Boron, 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/' some of the British 

Guiana rocks 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 are eventually 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.

uRept. Sci. and Agr. Dept. British Guiana, 1906.
28 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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.

Doctor 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. Doctor Washington has proposed the following,61 with which the independent experimental values of Doctor Dittrich6 are in substantial agreement: For 

Si02 and others which amount to 30 per cent and over, from 0.2 to 0.3 

per cent; for A12 03 and others which amount to from 10 to 30 per cent, 

0.1 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 caii 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.

"Manual of. the Chemical Analysis of Rocks, 1604, p. 24. 

fcNeues Jahrb. f. Min. u. Geol., vol. 2, 1903, p. 69.
INTRODUCTION. 29

5. STATEMENT C>F ANALYSES.

Until recently it has been the practice in this 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 19.

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.

Of late, petrographers .have begun to 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." a

. In accordance with this demand it is now our practice to follow 

pretty closely the arrangement proposed by Pirssoii and later strongly 

advocated by Washington, 6 namely:

Si02; A1203 , Fe203 , FeO, MgO, CaO, Na20, K20, H20 (above 105- 

110°), H20 (below 105-110°), C02 , Ti02 , Zr02 , P205 , S03 , Cl, Fl, 

S (FeS2), Cr203 , V203 , NiO, CoO, CuO, MnO, SrO, BaO, Li20, 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 greatly facilitating the comparison of different 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 : C02 is placed next after H20, since these two are generally a 

measure of the alteration the rock may have undergone. Ti02 and 

Zr02 naturally follow C02 on chemical grounds, and S03 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.

a Washington, H. S., The statement of rock analyses: Am. Jour. Sci., 4th ser., vol. 10, 1900, p. 61. 

6 Loc. cit.
30 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 days, after the completion of the 

first analysis, barring accidents and delays, one of 

a series of rocks of generally 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.

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 this 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 since they are adapted 

to the determination of a variety of substances 

their description finds most appropriate place here. FIG. 1. Platinum-tipped 

crucible tongs. The 

parts A,B, also of heavy 

platinum, are hollow, 

to serve as sockets for 

the cheaper metal of 

the handles.

A. CRUCIBLE TONGS.

Fig. 1 represents a form of platinum-tipped 

crucible tongs devised by Dr. 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
USEFUL APPLIANCES AND APPARATUS. Ol

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.

Fig. 2 represents a very useful adjunct to the worktable and especially to the draft cupboard, whereby the liquid contents of crucibles 

can be speedily evaporated at almost any desired temperature and the

FIG. 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 underlying crucible.

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 here for over twenty years and is identical in 

principle with the " Nickel-becher " of Jannasch. Nickel undoubtedly 

has a certain advantage in not rusting as does iron, but the form 

depicted in fig. 2 can easily be made 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 uniformly heated by hot air, and large quantities of
32 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

liquid, even sulphuric acid, can be thus volatilized 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 is usually possible to replace it 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 fig. 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 the 

edge of the former, but 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 

sometimes be substituted for the 

radiator.

FIG. 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 twothirds 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 combination 

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 their enveloping the mouth of the 

crucible. In the Jack of platinum a perforated 

asbestos board alone will yield fair service with 

a blast, fbut not as a rule with an ordinary 

burner.

C. PERFORATED DISK 

CIBLES.

FOR CRUFig. 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
USEFUL APPLIANCES AND APPARATUS. 33

alkali carbonate. The original idea of J. Lowe a 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 some extent. 

By neither of these is it easy to secure a very high temperature in the 

crucible. Therefore a disk of platinum is 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 conveniently used 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 OK TROUGH.

Fig. 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 of 

ready introduction of its contents into narrow-mouthed receptacles when desired.

E. COLORIMETERS.

a. FIRST SURVEY FORM.

FIG. 4. Weighing trough of plati-

._, ~ '/ ! i num, to be balanced by counterThe Survey form of colorimeter shown poisc of ieaci. Length of trough

in fig. 5 consists of two glass reservoirs ,and about 7 * cm- ; width beforc benda darkened box. The glasses, G, may be

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. 6 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 light 

shall penetrate around their sides or between them. Immediately 

back of the glasses is a partition, P, with openings of appropriate size

a Zeitschr. anal. Chemie, vol. 20,1881, p. 224.

6 The allowable error in distance between the corresponding pairs of'sides of the two glasses should 

not in any case 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. It is, however, 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, as the solution at once becomes turbid.

20091 Bull. 422 10 3
34 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

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 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 be 

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 preferable likewise, so far as my experience goes, 

to expensive instruments like the colorimeter of Soleil-Duboscq, etc.

FIG. 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 ground-glass 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,

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 matched solutions.
USEFUL APPLIANCES AND APPARATUS.

b. SECOND SURVEY FORM. (STEIGER'.S.)

35

The colorimeter shown in fig. 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 Mr. Steiger excellent service. Its construction and use are thus described by himself."

Instruments using the principle upon 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

(.0 (b)

FIG. 0. Steiger's colorimeter (second Survey form).

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 coler, but also 

of the color itself, making it impossible to find a point at which two solutions of different concentratisms 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), AAis a piece of finelyground 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 perpendicularly 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 CC can be moved 

back and forth, and the hole E, which admits light reflected by the mirror B of fig.6 (a).

. o Jour. Am. Chem. Soc., vol. 30,1908, p. 215.
36 ANALYSIS OF SILICATE AND CABBONATE BOCKS.

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 of 45°. 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). 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 h and then be 

reflected to t. From t to w it will go through the colorimetric solution, and this distance is therefore the length to be measured. A point, H, is marked on the mirror 

near the outer edge, so that it may be seen in the same line of 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 £'P being 

the same at tw, the distance desired can 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 (H7 ), 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 hosues, 

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 colorimetric 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 ;s 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.
USEFUL APPLIANCES AND APPAEATUS. 37

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. SCHREINER'S FORM.

Dr. Oswald Schreiner, of the United States Department of Agriculture, has devised a colorimeter (fig. 7), a which has done good senrice in colorimetric work on phosphates, etc. Its description, personally communicated by Doctor 

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 immersion 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 

I), 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.

Fig. 7. Schreiner's colorimeter.

oJour. Am. Chem. Soc., vol. 27, 1905, p. 1192.
38 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

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 concave. 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. 3 , the other for 100 cm.3.

The smaller tubes are likewise 25 cm. long, with outside diameter not greater than 20 

mm. and not less than 18mm., 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 colorimetric 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

 p 

the colorimetric solution of unknown strength c, then c = 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 has occurred, 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 the recent publications of A. A. Noyes, W. C. Bray, and E. B. Spear a a vast fund

. a. Jour. Am. Chem. Soc., vol. 28,1907, p. 137; vol. 30, 1908, p. 481; vol. '31,1909, p. 611; Chem. Nev.-s, 

vol. 95, 1907, pp. 89, etc.; vol. 98,1908, pp. 6, etc.
QUALITY 61? fiEAGENTS; SO

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 the work is less restricted than its title 

might be-thought to imply, for such elements as glucinum, uranium, 

vanadium, titanium, zirconium," and thorium are included.

. 9. QUALITY OF REAGENTS.

Unquestionably the greatest hindrance to good work.in otherwise 

well-equipped laboratories is the difficulty in securing satisfactory 

reagents. This fact early became apparent to the Survey chemists, 

and it is mainly to their strenuous complaints and initiative that 

the present movement in favor of better quality is due. Much of 

the glassware on the market is of a very inferior grade and utterly 

unsuited for analytical work.

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." 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.a 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 these 

in most cases 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 (C. b, p. 184). 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.

<* Die Priifung der chemischen Reagentien, 3d ed., Berlin, Julius Springer, 189G. English translation 

by .T. A. Williamson, D. Van Nostrand Co., 1902.
40 ANALYSIS OP SILICATE AND CARBONATE BOCKS.

Ammonia ought always 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. . . 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, arid 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 latter rise copiously. On cooling, the 

masss 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 has 

first to 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 should, however, 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 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,® 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 

gently ignite the precipitate. Treat it with dilute acetic acid, drop 

by drop, till the calcium carbonate is dissolved, filter, wash, gently 

ignite the residue, and test it with strong sulphuric acid in the usual 

way for fluorine. The perhydrol of E. Merck, now on the market, 

is a very pure and strong peroxide.

Sodium carbonate, one of the most important reagents in silicate 

analysis, sometimes can be had which does not carry more than 2£ mg.

oZeitschr. anal. Chemie, vol. 42,1903, p. 518.
SILICATE BOOKS. 41

of total impurity (see/?, p. 88) in 20 grams (0.01.2 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 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. Not long ago 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 maole 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.

Platinum ware may be mentioned here, too, although not a reagent. 

Recently iron in large amount has been found in shipments fresh 

from the factory. It may be readily detected by digesting hydrochloric acid in the ware, and sometimes shows on the surface, after 

ignition, as a red coating.

Owing to the solvent action on glass of many solutions of solid 

reagents, these solutions should be made up at frequent intervals in 

limited 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.

PART 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 conveniently determined in the same portion of rock powder. Thus, in the main portion 

are usually determined SiO2 , Ti02 , MnO, NiO, CaO, SrO, M'gO, total 

iron, and the combined weight of all the following: A12 03 , Ti02 , P2O5 , 

Zr02 , all iron as Fe2O3 , and nearly if not quite all vanadium, as V2OS , 

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, 

Zr02 , BaO, rare earths, and total sulphur are very conveniently deter-
42 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

mined. For V2 03 and Cr2 03 still another and usually much larger 

portion is to be used. Determinations of C02 , C, H2O, Fl, Cl are all 

best made in separate portions of substance, though various combinations are possible, as CO2 and H2 0, C and H2O, or H2 0, Fl, .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 A, page 138, 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 23 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 larger the 

precipitate of alumina, etc., is apt to be unwieldy. Its weight 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 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 a larger weight than 2 grams is usually 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,* 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 to be there, on the other. These cautions are 

especially urgent in the case of those having 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.

a Quantitative Classification of Igneous Rocks, 1903, University of Chicago Press, 286 pp.
SILICATE ROCKS. . . 43' 

2. SPECIFIC GRAVITY. (POROSITY.) 

c 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 carried out, 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 to1 be 

achieved only with the most painstaking precautions (see B. b, 

p. 48). Without this care the error in the second decimal may, and 

often does, amount to several points. 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 comparative 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 FOR SPECIFIC. GRAVITY.

This determination', when required, 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 is, of course, a much less effective 

means of removing air than the air pump, and 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 weight is at 

once taken. 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 carefully transferred 

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 

weighted. 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 certainly expel all absorbed water, and
44 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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;0 but the difference will only 

in exceptional cases affect the second decimal by more than a single 

unit. 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 3.00 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, since it is likely to 

consist largely ofc the most easily abraded minerals and consequently 

not to have the average composition of the mass. By following the 

instructions given above, loss of material is absolutely avoided, a 

decided saving in time is effected, and considerable weights can be 

easily employed with consequent lower probable error in the results. 

To vesicular rocks, however, notably certain lavas, the above proaln view of the uncertainty as to what constitutes hygroscopic water (see pp. 58-59), 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 afterwards 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 unhesitatingly be used and incinerated with the powder, owing to the small amount of which

last the error due to loss of even all its water during ignition is quite negligible.

Since the first publication of the foregoing in Bulletin No. 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 to constant weight. It was observed that some lost weight from 

the start, while others gained. For instance:

14.3803 9.5342 17.0846

.3730 .5178 .1089

.3666 .5121 .1159

.3483 .5024 .1413

.3481 .5016 .1388

. 3450 .5016 .1379

.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 be sometimes of value as a test for the presence of zeolitic minerals in advance of or as 

confirmation of the microscopic diagnosis.
SPECIFIC GRAVITY. 45

ceclure is, of course, inapplicable, since it is probable that many of the 

interior pores would be inaccessible to penetrating water.

b. METHOD FOR SPECIFIC GRAVITY AND POROSITY COMBINED.

E. R. Buck-ley a has called deserved attention to the faultiness of 

the methods generally employed for the determinations of these 

constants as applied to building stones, and has brought together in 

the work cited 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. 

These are dried for at least twenty-four 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 stopcock, ends near the bottom of the bottle and 

leads 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 seventy-two hours, 

experiment having shown that little or no absorption takes place after 

this lapse of time. Water is slowly let in from time to time, till the 

cubes are wholly immersed. In this way it is thought that thorough 

saturation can be -attained. The saturated samples are transferred to 

an open dish filled with water and taken to the balance, where tlieir 

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. 6 They are dried at 110° for twentyfour hours and again weighed. The second dry weight was found 

by Doctor Buckley to vary rarely from the first 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

a Building and ornamental stones of Wisconsin: Bull. Wisconsin Geol. Nat. Hist. Survey No. 4, 1898, 

pp. 03, 70.

6 The above procedure differs from that of Doctor 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 effective 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) Doctor Buckley states 

that he has reduced the time of immersion to twenty-four hours and the vacuum to one-fourth of an atmosphere, without finding appreciable differences in the results obtained.
46 ANALYSIS OF SILICATE AND CABBONATE EOCKS.

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

(B A) sp. gr. + A~~ r 

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 

obtained is always much higher than that ordinarily taken as the 

measure of porosity. This last would better be called, according 

to Doctor Buckley, "ratio of absorption/' being found by dividing the 

weight of water absorbed by the dry weight of the stone an,d multiplying by 100. Doctor 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

A B-C'

in which A is the dry weight, B the saturated weight, and C the 

weight in water.

T. W. Thorner a and H. Seger and E. Cranier b 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.

c. PENFIELD'S METHOD FOR MINERAL FRAGMENTS.

Penfield c 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 

wife 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. :

a Chem. Zeitung, vol. 29,1905, p. 744. c Am. Jour. Sci., 3d ser., vol. 50,1895, p. 448. 

6 Idem, p. 884.
SPECIFIC GKAVITY. . 47

This 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. '

B. PYCNOMETER METHOD/

a. ORDINARY METHOD.

If the pycnometer has to be used, as is generally the case when the 

density of any one of the mineral ingredients of a rock is desired after 

separation by one of the approved methods, it being then in a more or 

less finely divided state, a good procedure is that adopted in this laboratory by L. G. Eakins a number of years ago, provided there is no 

evaporation whatsoever around the stopper, a condition seldom, if 

ever, fulfilled, unless a thin film of vaseline is used, the weight of

which need not exceed a half milligram. The pycnometer used is 0116 

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 similar shape to 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 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 pycnometer in use, and these 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 in this c*ase is now 

determined in much the same way as in A. a, page 43, after the unstoppered pycnometer containing it and nearly filled with water has stood
48 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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 a portion from 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 that in the flask; or, 

after weighing, the contents of the flask may be emptied into a tared 

dish and the water slowly evaporated of! 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 ° 

Drs. A. L. Day and E. T. Alien found the ordinary methods of specific-gravity determination of powders by the pycnometer to be 

affected with grave errors. In the following is given their procedure, 

slightly modified since publication, for obviating them to such a 

degree that 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 slightly vaselined before 

the final weighing. If the excess 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, 

and Day and Alien now have them made with 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 per half hour.

To obviate another serious source of error, incomplete removal of 

air from the powder and undue loss of powder during filling and stoppering, the device of G. E. Moore b is made use of, slightly modified, 

as shown in fig. 8. The flask containing the powder is attached to a 

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 latter into water

a Pub. Carnegie Institution of Washington, No. 31; and in less detail in Am. Jour. Sci., 4th ser., vol. 19, 

1905, p. 93; Zeitschr. phys. Cnemie, vol. 54, 19H5, p. 1. 

& Am. Jour. Sci., 3d ser., vol. 3,1872, p. 41; Jour, prakt. Chemie, vol. 2,1870, p. 329.
SPECIFIC GRAVITY. 49

warmed to 40° to 50 °, in order to produce boiling witnin 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.

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

Pycnometer 

with-charge/^

FIG. 8. Moore's device to remove air from mineral powders.

may have to remain in the thermostat several hours .to allow complete settling before wiping the neck, vaselining, and stoppering. 

When filled and stoppered, it is advisable to return it 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 quickly wiped 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 the accuracy 

attainable in this way is subject to a correction for buoyancy.

(See p.- 64 for remarks by Doctors Day and Alien on another source 

of error in the determination of the specific gravity of powders.) 

20091 Bull. 422 10 4
50 ANALYSIS OF SILICATE AND CARBONATE BOCKS. 

C. HEAVY SOLUTIONS NOT SUITABLE FOE. ROCKS.

Because of their roughness, porosity, and complex mineral composition the density of rock fragments can not be accurately determined 

by that of heavy solutions in which they may remain suspended.

' 3. PREPARATION OF SAMPLE FOR ANALYSIS. 

A. QUANTITY OF ROCK TO BE CRUSHED.

In the great majority of cases a few chips from a hand specimen 

will well represent the average of the mass, but with rocks in which 

a porphyritic structure is strongly developed the case is different. 

Here 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, since 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 4£ 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 hammer. 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
PKEPARATION OF SAMPLE. 51

fig. 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. 52), as to furnish by the aid of a fine sieve, preferably of 

the best silk bolting cloth, a powder that is at once 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 shiftings 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 limited extent, the powder will, by contrast, 

be perceptibly dark after grinding in the mortar. The hardest steel 

is very susceptible to abrasion by minerals less hard than quartz.0 

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

a 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, apparently, for the most part not in splinters but as 

thin films on the mineral grains. Its presence can be readily shown 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 lor native iron in rocks, provided the use of steel for crushing could altogether be avoided.

FIG. 9. Ellis's mortar for crushing coarse materials. 

All parts of best chilled and surface-hardened tool 

steel. A, Block, 12J by 12i by 0 cm., with depression 

in center 0.0 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.
52 ' ANALYSIS OF SILICATE AND CARBONATE EOCKS.

will not occasion further loss of flying particles, since the portions 

lost will, in case of all but glassy or very fine-grained material, not 

have the same composition as those retained.

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 twenty minutes by boiling dilute1 

hydrofluoric acid (see C, below, and 19, p. 157). 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 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 intd a cylindrical glass box 

about 3.5 cm. deep and 7.5 cm. 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 all has passed 

the sieve. It will, of course, not do to reject any portion, for thereby 

the composition of the mass will be affected. The sample is now fine 

enough to be reduced by grinding in a large agate mortar.

Doctor 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 introduction of cloth fiber is negligible. 

This last will hardly be true of the method practiced in parts of 

Europe (the German "beuteln"), which, at least as it was carried out 

in Bunsen's laboratory, differs in essential points from the gentle 

sifting of Doctor Washington.

C. GRINDING.

Ordinarily an extremely fine state of division is unnecessary, 

except in the case of those portions in which alkalies and ferrous iron
PREPARATION OF SAMPLE. 53

are to be determined, or where soluble constituents are to be removed 

by acids, etc., and in such cases the final grinding can be done at the 

balance table on a small portion 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 recently shown,0 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 b 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 myself (see 

19, p. 154). The necessity for an entire reversal of the hitherto 

prevalent practice of preparing a very fine powder for the ferrousiron 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 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 in another respect differ 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. 56), 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

a The determination of ferrous iron in rock analysis: Sveriges Gcol. Undersokning, Arsbok 1,1907, No. 3. 

6 The influence of fine grinding on the water and ferrous iron content of'minerals and rocks: Jour. Arn. 

Chem. Soc., vol. 30,1908, p. 1120; Chem. News, vol. 98,1908, pp. 205, 215.
54 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

it of oxygen.0 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 under 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 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 Company (Limited), Pittsburg, Pa., is shown in fig. 10, with the addition 

of simple attachments intended to keep metal dust and oil out of the 

mortar. These additions have been found to be quite essential for 

our work. As made for the technical industries the machine is 

largely of brass, nickel plated, but the latest made for the Survey 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 our work, on account of the da'nger of copper, 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 proo Jour. Am. Chem. Soc., vol. 30, 1908, p. 1120; Chem. News, vol. 98,1908, pp. 205, 215.
PREPARATION. OF SAMPLE. 55

tection, 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

FIG. 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 shpuld 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 ball and socket 

supporting side arm reduces the hardest ore very rapidly." Iron Age.

revolution is too high. In our actual practice, 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.
56 ANALYSIS OF SILICATE AND CAEBONATE ROCKS. 

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 the above than with hand grinding, notwithstanding 

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.

Dr. 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 0.1455 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, bu-t, on the other hand, the material was all quartz, 

a mineral much harder than most of those constituting the average 

rock.

W. Hempel 0 has experimentally tested 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. Rock analysis has in this respect an

a Zeitschr. angew. Chemie, 1901, p. 843.
DETERMINATION OF WATER. 57

advantage over mineral analysis, since material is almost always 

available iri 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, often 

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.

Although the condition of the hydrogen that is a constituent of all 

rocks is of less concern to the petrographer than that in minerals is 

to the mineralogist, yet the subject is of sufficient importance to the 

former and to the analyzer of rocks to warrant some discussion with

regard to both rocks and minerals.

It is unnecessary to enter upon an historical discussion of the 

views that have prevailed as to the conditions of and the rdle that 

hydrogen plays in minerals and of the causes that have led to changes 

in those views.0 It will suffice to present the existing situation as it 

appears to the writer.

Broadly, we have to consider (1) hydrogen that is essential to the 

chemical or physical structure that is, constitutional in either the 

chemical or the physical sense and (2) that which is physically held 

otherwise and is unessential.

. The subdivisions of the first of these greater divisions are (a) hydrogen that is constitutional in the sense of possessing basic or acidic 

character, (I) the hydrogen of water of crystallization, (c) the hydrogen of solid solutions, which is commonly referred to the physical 

division.

For convenience in discussion we may adopt, as sanctioned by 

common usage, the term "water" instead of hydrogen, since in all its 

forms the hydrogen is expelled as water by heat.

i The following authors in particular have contributed to our present understanding of the r61e of water 

In minerals:

Van Bemmelen, J. M., Zeitschr. anorg. Chemie, vol. 13,1897, p. 233; and subsequent volumes down to 

the present time.

Tammann, G., Zeitschr. phys. Chemie, vol. 10,1892, p. 255; vol. 27,1898, p. 323; Zeitschr. anorg. Chemie, 

vol. 15, 1897, p. 319.

Le Chatelier, H., Zeitschr. phys. Chemie, vol.1,1887, p. 396; Compt. Rend., vol. 104,1887, pp. 1443,1517; 

Bull. Soc. franc, min., vol. 10,1887, p. 204.

Zambonini, F., Mem. Accad. Sci. fls. e mat. di Napoli, vol. 14, ser. 2, No. 1,127 pp.

Tschermak, G., Zeitschr. phys. Chemie, vol. 53,1905, p. 349; Zeitschr. anorg. Chemie, vol. 03,1909, p. 109.

Lowenstein, E., Zeitschr. anorg. Chemie, vol. G3,1909, p. 69.

The list does not include all worthy of mention. Others had anticipated to some extent the major conclusions of Van Bemmelen and Tammann, without receiving the recognition that is now seen to be their 

due, as is fully set forth in the paper of Zambonini.
58 ANALYSIS OP SILICATE AND CARBONATE ROCKS.

The minerals of groups a and I are generally in a state of stable 

equilibrium with their surroundings over a considerable range of 

temperature and water-vapor pressure. Expulsion of their water 

is accomplished in theory either all at a certain temperature or vapor 

pressure or by steps. In those of group c this is not true, but their 

water is progressively removable by increase of temperature or reduction of the water-vapor pressure of the surrounding medium. 

It is in respect to this third group that the above broader division 

shows deviation from the common, but the inclusion of this group in 

division 1 seems fully justified by the fact that in all three groups a 

change in at least some of the physical properties of the mineral 

necessarily accompanies loss of moisture. In other words, on the 

presence of the water in minerals of these groups depend certain 

of the physical properties. Without it the minerals as we know 

them could not exist. This dependence is noted, as a rule, most 

conveniently and quantitatively, by following the changes in certain 

optical properties that accompany variations in the water content, 

though at times other changes are more prominent. The hydrogen 

of subdivision a, probably also of 5, forms part of the chemical 

molecule, while that in c is supposed not to.

. The subdivisions of the second of the larger divisions, aside from 

actual inclusions of liquid water, are less easy to define, as is apparent from the terms that are in more or less common use hygroscopic, 

adsorbed, absorbed, occluded, imbibed, in addition to dissolved and 

solid solution already mentioned as transferred to the first division. 

Much uncertainty and confusion prevail, not only in the use of these 

terms but also in the meanings attached to them by different writers. 

Their number should certainly be reduced, for some are synonymous. 

Such differences as there may 'be between those physical conditions 

that seem to merit distinct recognition are probably rather of degree

than of kind, conditioned by a more or less open structure of the solid 

particles. There is no certainty that a loose molecular or submicroscopic structure differs fundamentally in its attractive power for 

water from one in which the pores are visible, or in which, finally, 

only plane surfaces are concerned.

Certainly there does not seem to be any good ground for specific 

discrimination between hygroscopic water and that which is held 

to be adsorbed. Both are assumed to be results of surface attraction. Further, fine grinding of anhydrous minerals results in the 

assumption not only of loosely held (hygroscopic) water, removable 

at and below 100°, but also of water that may require a temperature 

of several hundred degrees for its complete expulsion. If the curve 

representing the progressive loss of such water at or slightly above 

the boiling point were found to end there, a difference of condition 

would have to be admitted. An actual interruption in the escape of
DETERMINATION OF WATER. 59

water at this point seldom and perhaps never occurs. A break there 

may be, but not a total cessation of the upward trend of the curve 

representing loss of water. Such a break might be due merely to the 

fact that water happens to undergo a physical change at that point, 

and its sharpness will vary with different substances. Experiments 

made for the express purpose of testing this hypothesis are lacking, 

but are needed.

That, however, a distinction between this kind of water and that 

regarded as absorbed or imbibed may be justified is shown by the 

observation that the amount of the former depends on the fineness 

of division of the mineral particles, while there are many .minerals, 

of which the zeolites afford excellent examples, besides some igneous 

glasses, which contain in the uncrushefl state amounts of water that 

are very large, in well-defined minerals sometimes exceeding 20 per 

cent of their weight. . This water, like that adsorbed, is progressively 

removable as the temperature is increased, and it too, in many cases, 

can be reabsorbed wholly or in large part, just as happens with the 

adsorbed water. But no change in the properties of the minerals 

accompanies this loss in either case, a fact which serves to differentiate 

them from those with water in solid solution. It is desirable that 

experiments should be instituted to ascertain what effect fine grinding would have on the water content of such minerals. So far as 

known to the writer, few determinations of the water in uncrushed 

minerals of this kind have been made for comparison with that in the 

same material ground. The meager data furnished by F. von Kobell a 

afford little light on this point. 6

Whatever may be the ultimate decision as to distinguishing between so-called adsorbed (hygroscopic) water and absorbed water, 

there is no question as to the difference in meaning of the words 

themselves, and they should not be used synonymously, as is frequently done. Adsorption implies surface condensation as contrasted with the idea of penetration conveyed by absorption, even 

though, as already hinted, there may be no fundamental difference 

in the causes that produce the states. It were better to avoid the 

use of the term absorbed in the above limited sense and to adopt 

instead imbibed. Absorbed might well be employed in a generic 

sense to cover the states of imbibition and adsorption.

o Jour, prakt. Chemie, vol. 107,1869, p. 150; Chem. News, vol. 20, 1869, p. 119.

& Since the above was written a paper by St. J. Thugutt has appeared (Centralbl. f. Min., Geol. u. Pal., 

1909, p. 677) on "Sources of error in the determination of water in zeolites," which supplies in part the 

missing information. Thugutt shows, by a series of tests, that most zeolites and one or two other 

hydrous minerals examined take up water during grinding, but that the mineral apophyllite shows the 

opposite behavior. He further contends that the laws of Proust and Dalton maintain their full validity 

with respect to the zeolites, provided the material analyzed is strictly homogeneous and not too finely 

ground. As a corollary to the above he, too, advocates the double determination of water in mineral 

samples when fine grinding is necessary for the general analysis, and states that percentages should be 

reported on the basis of the water content of coarse material.
60 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

As already said, the hydrogen in all conditions, essential as well as 

unessential, is expelled from inorganic minerals in the form of water 

by elevation of temperature. The temperature need not be high 

for water of crystallization and that physically held, but may be and 

in general is high for that which is basic or acidic. Two or more of 

these conditions can exist simultaneously in a mineral, and the tern-, 

peratures at which they are in equilibrium with their surroundings may 

overlap. As full criteria are lacking for the recognition of these 

conditions, the establishment of a probable formula is very often 

most difficult and not seldom impossible.

For convenience it may be well to follow established usage and 

call hygroscopic water tha.t which is plainly not water of crystallization or of closer chemical union or of solid solution and is removable 

at or slightly above the boiling point of water or over strong dehydrants, always provided it is shown that the loss does not continue, 

even at a slower rate, above the given temperature. If such additional loss is shown to an appreciable amount, only careful study 

of the further behavior on heating and on subsequent exposure to a 

moist atmosphere will throw light on the nature of the water evolved. 

Water which is removable at the boiling point of water should also 

be removable by dehydrants like concentrated sulphuric acid or 

phosphorus pentoxide, provided time enough is allowed; the time 

will, be shorter if a vacuum instead of atmospheric pressure is employed for the test. If a mineral undergoing progressive loss of water, 

by the aid either of a dehydrant or of heat below or above the boiling 

point of water, shows no change in its optical properties, it may be 

concluded that its hydrogen is not chemically held. The converse, 

that an optical change (is proof of the presence of hydrogen in chemical combination is not, however, necessarily true, for it is not impossible that optical changes may occur from loss of imbibed water, 

the water of absorption of Zambonini. For minerals showing such 

apparent anomalies, like the zeolites, a micellar or alveolar or mesh 

structure is predicated by some writers. The high temperature is 

supposed to act on the walls of the mesh in a manner to weaken and 

finally overcome entirely their absorptive power. A contraction 

in volume accompanies the change, hence such minerals, when 

heated above a certain temperature, are able to reabsorb only a part 

or none of their original water content. The voids dimmish in number and afterward refill with increasing slowness according to the 

degree of heat and its duration. Such physical change in structure 

is believed by Zambonini and others to be perhaps sufficient to account 

for observed changes in optical behavior.

Zambonini noticed, in experiments on the rehydration of partly 

dehydrated heulandite and other zeolites, sharp variations in the 

rate of absorption, not depending solely on the quantity of water
DETERMINATION OF WATER. 61

evolved. Writing of heulandite,a he regards this observation as "in 

complete disagreement with the hypothesis that the zeolites are solid 

solutions, since in this case there ought to have been continuous 

modifications in the rate of absorption, much less sharp than those 

observed with heulandite. * * * What has been observed with 

this mineral finds perfect analogy in many properties of the hydrogels." He admits that there are close resemblances between the 

water of solid solutions and that of absorption [imbibition] compounds, and that the zeolites, "so far as concerns many of their 

physical properties, may be regarded either as solid solutions or as 

compounds of absorption." Whether or not Zambonini is right in 

his contention must be held an open question till further data on this 

obscure subject are procured and it has received adequate discussion. 

The water of solid solutions, as has been said, is in full equilibrium 

with its surroundings for a given temperature and hygrometric state

of the atmosphere. Therefore, no matter how fine a mineral containing it may be ground, the mineral should contain just as much, no 

more and no less, after grinding as before. This should, in theory, 

afford a means of distinguishing between such water and water that 

is simply absorbed or imbibed, if a distinction is really permissible, 

for it would seem as if imbibed water should be affected by the degree 

of division of the material containing it. The determination of this 

is, however, complicated by the fact that taking up of water usually 

accompanies fine grinding, so that if there were loss of water of imbibition on grinding this loss might be compensated more or less 

by adsorption or surface condensation. Viewed from this point, a 

reasonable doubt might arise whether imbibed water is really in a 

different condition from that called adsorbed.

In regard to water of solid solution it may not be amiss to refer to 

an experiment of Carl Barus,6 which has been cited more than once 

in support of the existence of solids containing water in solution 

and as explaining the high content in water of many igneous glasses, 

like the pitchstones and some obsidians, formed at great terrestrial 

depths. Barus heated to a high temperature in a closed bomb water 

and a powdered glass. After cooling under pressure, the glass was 

found to have taken up a very large volume of water (about equal to 

its own volume), and there remained a solid mass, still a glass, which 

seemed to be homogeneous and permanent. Time showed, however, 

that the water did escape, the glass becoming opaque and finally 

crumbling. It is also a fact, never published, that Barus was unable 

to cause all glasses to take up water in a similar way, and that it was 

only with the common soft glasses that the experiment succeeded as 

above outlined. This illustration serves to emphasize the concluo Op. cit, p. 109.

6 Am. Jour. Scl., 4th ser., vol. 9,1900, p. 164.
62 ANALYSIS OP SILICATE AND CARBONATE BOOKS.

sion that the igneous glasses above mentioned may be simply supercooled liquids of extreme viscosity and not comparable with the 

solutions represented by many crystallized bodies.

As to the chemically combined hydrogen, this should be evolved 

for each degree of hydration or each manner of linking in the molecule 

at a definite temperature with a constant vapor tension so long as 

any of the material in the state undergoing change is still present. 

This is in the main so for the true hydrates, but to a much less degree 

for those minerals which hold their hydrogen with a firmer bond. 

The latter usually require a much higher temperature for dehydration than the hydrates, and to account for the frequently observed 

continuous instead of discontinuous escape of their water, there has 

been suggested a contraction or sintering, whereby greater resistance 

to escape is offered, and also a possible difference of temperature between the interior of the mass of particles and those nearer the 

external source of heat (Zambonini).

In explanation of the fact that the last traces of water are often 

removable from undoubted hydrates at a far higher temperature 

than is required for the major part, I would offer the suggestion that 

the water of crystallization may have been displaced as such at the 

proper temperature and that any water still remaining above that 

temperature is some of the original water of crystallization now 

held physically by surface attraction.

The interpretation of the analytical results obtained for hydrogen 

is thus, to repeat briefly, often a most difficult problem, one requiring much knowledge of mineralogy and of the relationships between different minerals and groups of minerals. In many cases 

it is quite impossible, with our present knowledge, to discriminate 

practically between the hydrogen of water of crystallization and that 

of closer chemical union, and even between these and some of that

physically held, especially when more than one of these conditions 

exist together. Ordinarily the two former show more or less simple 

stoichiometrical relations to the other constituents, but the hydrogen 

of chemical constitution regarded as basic or acidic offers frequent 

exceptions. This may be and often is due, no doubt, to its forming 

one of two or more members which are simultaneously present in 

isomorphous relationship t9 each other, of which hydroxyl and 

fluorine show striking examples in a number of minerals.

For the methods that have been applied in the study of water in 

minerals and the hydrogels reference must be made in part to the 

above-cited papers of Zambonini, Van Bemmelen, Tammann, and 

Lowenstein, and also of A. Hamberg,a since they apply more to the 

examination of minerals than of rocks. To . these may be added

a Geol. Fo'reningars Forhandlingar i Stockholm, vol. 12,1880, p. 591.
DETERMINATION OF WATER. 63

papers by W. W. Coblentz,0 who has applied an entirely novel 

method to discriminate between molecular water and that in the form 

of hydroxyl. As these papers have escaped the attention of mineralogists, it may be well to quote from the author's summary, although 

his deductions may not prove to be warranted:

The transmission and reflection spectra of at least 120 compounds have been examined, many of them to 15/z., by means of a mirror spectrometer, a rock-salt 

prism, and a Nichols radiometer. The interpretation of the results is based on the 

assumption that if the union of the oxygen and the hydrogen in the molecule is similar 

to that in water, then the absorption spectra of minerals containing these two elements 

thus united should show the absorption bands of water superposed upon the absorption spectrum of the other constituents. On the other hand, minerals containing 

oxygen and hydrogen as water of constitution should not show the water bands, except hydroxyl groups, which should show a band at 3/u.

The results show that of about 30 minerals containing "water of crystallization" 

there are no important exceptions to the rule that they should show the bands of water. 

On the other hand, the one important exception to the rule that minerals containing

"water of constitution" should not show water bands is cane sugar. Minerals containing hydroxyl groups generally have a marked band at 3/x. Sulphates have a strong 

band at 4.55/1 and a less constantly recurring band at 9.Lu, due to the S04 ion. On the 

other hand, silicates do not .have such definite bands, which would seem to indicate 

that the structure of the silicate radical is different in each mineral containing that 

element.

The following tentative scheme of classification summarizes the 

foregoing very brief discussion. In this discussion I have refrained 

from any direct comparison of the condition of the water held by 

amorphous bodies with that in crystallized minerals. Our knowledge 

of colloids and gels is too meager to make comparison profitable. 

Where, or whether at all, such bodies fit in the classification is therefore left open.

Provisional classification of the condition of hydrogen in minerals. 

A. Essential or structural hydrogen:

 fDiscontinuously removable for 

a. Basic and acidic. ft iyen form of union_that

b. In water of crys- ^ ftt ft fixed t rature or 

talhzation. vap0r pressure.

c. In solid solution (dissolved).

Loss of any of these necessarily involves a change 

in physical properties of 

the mineral, for example, 

optical properties.

B. Unessential hydrogen:

a. Liquid inclusions of water, 

b. Absorbed as water:

Progressively removable 

with increase of temperaa. Adsorbed, including as "hygroscopic" that 

removable at the boiling point of water.

ture or reduction of vapor 

pressure without necessa- Imbibed, as water is held by a sponge....... rily involving changea in

optical properties.

o Carnegie Institution of Washington, Pub. No, 05,190G; Bull, Bureau of Stauaards, vol. 2, No. 3, 1906, 

p. 457.
64 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

B. WATER TAKEN UP OR LOST ON GRINDING.

Before considering methods of determination 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. 53.) The following table contains typical data on this subject. For fuller details see the paper already cited.0

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.

\Altered basaltic green- 

/ stone.

ViJnglazed Berlin porce- 

/ lain.

Condition.

Ground 120 min. ......................................

<60 meshes to 1 cm ...................................

<60 meshes to 1 cm ...................................

/Coarse. ................................................

\ Ground 600 min. ......................................

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.6 

The inference is obvious that water of crystallization should be determined on unground material, if possible.

The following excerpt from the work of Doctors Day and Alien 0 on 

the feldspars, already cited, has direct relation to 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.

o Jour. Am. Chem. Soc., vol. 30,1908, p. 1120; Chem. News, vol. 98,1908, pp. 205, 215.

6 Idem.

c Pub. Carnegie Institution of Washington, No. 31, pp. 56-57; Am. Jour. 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. 44 of the present volume.
DETERMINATION OF WATER. 65

Determination of moisture in 1 gram of powdered mineral upon exposure to the air. 

[<= finer than. >=coarser than.]

Mineral.

Ab (natural crystal) . .....................................................

Do. ...................................................................

Do. ...................................................................

Fineness (meshes to 

the linear inch).

. <150..............

<100>120.........

<100>120.........

<100>120.........

<150..............

<120>150.........

<150....... .......

Still finer.........

Everything<100..

>150..............

Moisture.

Gram. 

0.0061

.0000

.0010

.0007

.0010

.0006

.0069

.0011

.0031

.0059

.0065

.0022

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 Bunseno 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 ifi 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 adsorbed 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 

tube moisture-ladened air enters and is inclosed with the remainder 

of the dry powder. Therefore, it may very well happen that a 

powder at first dry will, after several openings of the tube, especially 

at considerable intervals, be nearly as moist as when first inclosed. 

Dittrich has expressed views similar to the above.

20091 Bull. 422 10-

Wiecl. Ann., vol. 24, 1885, p. 327. 

 5
66 ANALYSIS OF SILICATE AND CAKBONATE KOCKS.

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 estimated, 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 powders of this 

grade the moisture will fall very often below 0.1 per cent, whereas 

in those that have been ground for one to two hours it may easily 

exceed 1 per cent.

D. 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 its separate determination and entry in the analysis entirely 

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°, a question that 

has been covered to some extent in section A.

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. Since 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 to false conclusions and possibly serious confusion. (See 

also second paragraph of footnote, p. 44, and examples cited on p. 69.)

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
DETERMINATION OF WATER. 67

lithologist an indication of the mineral character of one or more of 

the rock constituents, thus perhaps confirming the microscopical 

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 it is therefore 

improper to incorporate it in the analysis; but this variation is 

ordinarily not at all great if the powder is coarse.

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 chapter 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. In any event duplicate determinations should 

be made until the analyst has acquired the experience that will 

permit him sometimes to make exceptions.

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 con-
68 ANALYSIS OF SILICATE AND -CARBONATE ROCKS.

centration if detailed study of the behavior of a mineral during dehydration is in progress. I have shown a 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.

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 twenty-four 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 sulphurio acid.

Time 

exposed.

Hours. 

 18 

26 

23 

24 

23 

24 

25

Loss.

Oram. 

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 one hundred and thirty-eighth hour, when a loss of but 0.1 milligram was shown during twenty-four hours; but nevertheless a 

nearly steady loss of 0.3 mg. per day took place for six days more, 

and might have been longer observed but for the interruption of the 

experiment. 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. Given 

sufficient time, the use of a dehydrant entirely without water-vapor 

tension should be as effective as a temperature corresponding to the 

boiling point of water, provided the surrounding medium is itself 

entirely dry. , '

a Am. Chem. Jour., vol. 14,1892, pp. 6-7.
DETERMINATION OF WATER. 69

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 p'hosphorus 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.

ex. Fractional determinations. As to the temperature to be adopted 

for drying in order to determine so-called hygroscopic moisture, the 

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, 

since no greater loss is experienced at the higher than at the lower 

temperature, given a sufficient time for the latter. It is the present 

practice in this 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, after several hours heating at the latter temperature, placed in 

a desiccator over sulphuric.acid and weighed as soon as cold, 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 experiment was 

much shorter and the..intervals between weighings were but a few 

hours each.

An important research of G. Friedel a well shows what errors are 

possible in the determination of this easily removable water, since he 

found that certain zeolites which had been largely dehydrated but not

o Bull. Soc. min., vol. 19,1896, pp. 14,94; Compt. Rend., vol. 122,1896, p. 1006.
70 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 partially 

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 Priedel 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 largely left to the judgment of the operator, who will often be guided by the mineral 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 contents in 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 the substance can not, therefore, 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 phosphoric 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 temperatures no bath is required, but for 

artificial temperatures the tube should pass through a suitable 

thermostat.

a LOG. cit.
DETERMINATION OF WATER. 71

/?. "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 rarely be used with safety. 

Only when the rock is free from fluorine, chlorine, sulphur, carbon, 

carbon dioxide, and fixed oxidizable or reducible (Mn02 ) constituents can the loss be accepted as the true index of the amount of water 

present, and it is rare 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 

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 has published a paper 6 on recent methods of rock 

analysis, in which he 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.

a 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.

6 Australasian Assoc. Adv. Sci., Adelaide meeting, 1907.
*72 ANALYSIS OF SILICATE AND CARBONATE ROCKg.

B. DIRECT METHODS WITHOUT ABSORPTION TUBES PENFIELp's

METHODS.

a. FOR MINERALS EASILY DEPRIVED OF THEIR WATER.

If no other volatile constituents than water are present, the beautifully simple method first used by Prof. G. J. Brush and extended 

by Prof. Si L. Penfield a leaves nothing to be desired for accuracy. 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 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

C

FIG. 11. Penfield's tubes for water determination in minerals, a, b, c, Different forms of tubes; d, thistle 

tube for introducing the powder; e, capillary-tipped stopper.

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 fig. 11.

Before using, even if apparently dry, "these tubes must be thoroughly dried inside, which is best accomplished by heating and 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.

o Am. Jour. Sci., 3d ser., vol. 48,1894, p. 31; Zeitschr. anorg. Chemie, vol. 7,1894, p. 22.
DETERMINATION OF WATER. 73

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. It may, however, be used with the addition of a retainer for fluorine, sulphur, etc., 

in the shape of calcium, lead, or bismuth oxides. It gives, of course, 

the total water.

b. FOR MINERALS NOT EASILY DEPRIVED OF THEIR WATER.

When minerals are present that do not give up their water wholly, 

even over the blast, as talc, topaz, chondrodite, staurolite, etc., Penfield's simple combination of fire-brick and charcoal oven, depicted 

in fig. 12, must be used, either with or without a retainer 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

FIG. 12. Penfleld's fire-brick and charcoal oven for use in determining water.

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.

In whichever way the apparatus may be used, the water found is 

the total water, from which that found separately at 105° may be 

deducted if desired. . -

C. DIRECT METHODS WITH ABSORPTION TUBES.

b

a. GENERAL CONSIDERATIONS.

In general it is preferable to collect and weigh the water in suitable 

absorption tubes after its expulsion from the mineral or rock. The 

method is especially suited for the determination of total water or 

of that escaping above 105° when the apparatus of Gooch (e, p. 78.) is 

employed. It is less so for those fractional determinations where 

the escape of water is very slow at the different temperatures, for 

the absorption tube may in such cases 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 

long blank test.
74 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

A precaution too often overlooked is to see that the drying agent 

used for the air current 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 as well, especially with calcium chloride. Therefore, the contents of drying and absorption 

apparatus should be changed often, and when 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 

exposure of rubber. With long rubber connections the error may be a 

very sensible plus one. Again, between refillings of the absorption 

tube the direction of the air current through it should always be the 

same. 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 makesitself apparent by marked 

irregularities in the swing of the needle. While more pronounced in 

cold weather, the phenomenon is not peculiar to winter.0

The absorption tubes should not in general weigh over 30 grams 

each, filled with calcium chloride. Those preferred by me are shown 

in fig. 15 (p. 77), 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.

b. PENFIELD'S PROCEDURE.

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 77, the determination of the hygroscopic as well 

as any other fraction of the water, is the following glass-tube arrangement (fig. 13) of Penfield,6 whereby the brick and charcoal oven 

already referred to (fig. 12) comes again into play, but without the 

half brick shown in that figure.

<J With regard to electrification, consult also Bornemann, Ernst,. Chem. Zeitung, 1908, pp. 125, 220. 

6 Am. Jour. Sci., 3d sen, vol. 48, 1894, p. 37; Zeitschr. anorg. Chemie, vol. 6,1894, p. 22.
'DETERMINATION OF WATER. 75

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 

1 cm. in diameter, which have been previously bent around glass tubes of such a size 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 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

FIG. 13. 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, b, 

Cross section of platinum boat.

apparatus must be carefully screened by asbestos board. By .constructing a cover 

for the boat no material need be lost by spattering, 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.

c. STEIGER'S APPLICATION OF THE TOLUENE OVEN.

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. 14). 

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
76 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

shutting off the air current, and the weighed powder quickly introduced by means of the clean metal trough in which it has . been 

weighed (fig. 4, p. 33). The stopper is as quickly replaced and the

dehydration begins at 

once and is often nearly 

finished by the time the 

thermometer indicates the 

maximum temperature.

By employing a U tube , with glass stoppers, like 

A, fig. 15, it would be 

quite possible to ascertain the loss in weight 

of the powder as well as 

the gain of the absorption 

tube, or to do away with 

the latter 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 ori the top 

of the bath would suffice

FIG. 14.-Steiger's form of drying apparatus. A, Toluene oven; to ^Vent Condensation 

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.

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.

d. CHATARD'S OVEN FOR TEMPERATURES UP TO 300° AND OVER.

A form of drying oven devised by Dr. T. M. Chatard ° is in use in 

this laboratory for determining water at different temperatures up to 

350°, and gives entire satisfaction. It is an asbestos-covered copper 

box, B, shown in different aspects and parts in fig. 15. The box is 

so constructed that the tube with its contents can be removed withof moisture before reach-

 ,, nh^orntion lng tne aDSOrptlOn

o Am. Chem. Jour., vol. 13,1891, p. 110; Bull. U. S. Geol. Survey No. 78,1891, p. 84.
DETERMINATION OF WATER. 77

out detaching from either the drying or collecting tubes, which is a 

great advantage if it is desired to apply afterwards the direct heat 

of a lamp in order 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.

FIG. 15. Chatard's form of drying oven for water determinations. B, Copper box, 18 cm. long, 10J 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, 0, 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'in fig. 15, permits a less complicated construction of box and stand than that here shown, 

since round holes in opposite ends of the box admit the ignition tube, and the roller base is then superfluous.

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 

one, 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, O, after the tube is in place, but before 

closing the front.
78 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

For other forms of tubes adapted to similar determinations, see 

pages 75 and 82-83.

6. GOOCH S APPARATUS.

Of more elaborate apparatus, designed to be used with fluxes, the 

tubulated platinum crucible invented by Doctor Gooch 0 is capable 

of affording most excellent service, and it is the one by which far 

the larger number of water determinations in this laboratory have 

been and are made.

FIG. 16. Modified form of Gooch tubulated platinum crucible for the determination of water, one-half 

natural size. Weight about 75 grams.

Fig. 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. The form 

of apparatus depicted in fig. 16 differs from that given in Bulletin 176 

by a considerable shortening in length of the inlet and especially the 

outlet tube, whereby the cost is reduced and attachment can be 

made to a glass-stoppered U tube, which is the most satisfactory 

form for absorption tubes. With tubes of the lengths shown in the

o Am, Chemr Jour., vol. 2,1880, p. 247; Chem. News, vol. 42,1880, p. 320,
DETERMINATION" OF WATER. 79

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 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," 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, B/, 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 b 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 up by the lower ring, R" (figs. 17 and 

18), until the platinum crucible is sufficiently immersed, 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 (see below, p. 81), 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.

o This has been heated for a length of time to near its fusing 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 fifteen minutes. Potassium carbonate and potassium-sodium carbonate are too hygroscopic by far to 

be available.

b Private advice from E. 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.
80 ANALYSIS OF SILICATE AND CAEBONATE KOCKS.

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 temperature. The defect can be 

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

FIG. 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, O; F, asbestos-board shield.

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 

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
DETERMINATION OF WATER. 81

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.

In this apparatus only the water expelled above 100° to 110° 

should as a rule be determined, and to effect drying of the mixed 

mineral powder and sodium carbonate, after luting the tubulated cap 

on the cylindrical crucible with sodium tungstate, the tube is sunk 

through a round hole in the cover into a small cylindrical air bath

Fio. 18. Arrangement, during fusion, of Gooch apparatus for determining water. R'", Blast-fed ring 

burner; P, protective asbestos shield resting on ring R"; F, asbestos-board 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.

(fig. 17), which can be heated from beneath by the same ring burner 

which is subsequently to fuse the flux. A slow current of air is then 

forced through and the drying satisfactorily accomplished.

The reason why it is unsafe to attempt estimation of "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 in part retained 

by the dried sodium carbonate. 

20091 Bull. 422 10 6
8'2 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

.f. MERITS OF THE ABOVE FORMS OF APPARATUS.

The apparatus described in 1) and e 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.

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 tube, is fully made up 

in time by its durability. . '

g. JANNASCH'S METHODS.

Jannasch, that zealous deviser of methods for mineral analysis, has 

published in the Zeitschrif t f iir anorganische' Chemie and the Berichte 

der Deutschen chemischen Gesellschaft several papers dealing with 

the problem of water determination in minerals, and in his textbook a these are collected in more or less modified form.

b

FIG. 19. Glass tube for determination of water (Jannasch). 6, Mixture of mineral powder with^ borax; 

c, c, plugs of glass wool; a, layer of lead'chromate or lead oxide. Total length of the tube, 33 cm.; inside 

diameter, 12-14 mm.

For the majority of silicates he finds dehydrated borax powder a 

most efficacious flux, usually at a very moderate temperature. The 

fusion is accomplished either in a platinum boat within a glass tube 

or in a tube of the form and dimensions shown in fig. 19.

For rocks or minerals containing not much fluorin'e a retaining 

layer of granular lead chromate, or of previously fused and powdered 

lead oxide, is used as shown at a. Plugs of glass wool are used, at 

c, c. Whether or not the boat is employed, the borax is first introduced and, together with the retainer, is thoroughly dried out in an 

asbestos oven by a hot-air current. Then", after cooling, the mineral 

powder is added and thoroughly mixed with the borax. Heat is 

applied by a flat flame to the mixture, which soon melts and forms 

a clear fusion, when the "action is complete. The 'blast may be used 

in extreme cases. The layer of retainer must be kept warm by an 

auxiliary flame, and the absorption tube must be removed before 

the flame under the fused mass is extinguished, for the glass breaks 

as soon as this is done. Carbon dioxide can simultaneously be 

determined by attaching a soda-lime tube to the calcium-chloride

o Praktischer Leitfaden der Gewichtsanalyse, Leipzig, von Veit & Co..(1897); 2d ed., 1907.
SILICA. 83

tube. For one-half to 1 gram of silicate Jannasch uses 1£ to 2 grams 

of dehydrated borax.

Regarding the borax method, its invem>f?br insists on the following 

points as essential to success, especially when the blast can not be 

applied: Most thorough mixing of flux and mineral powder and a 

most impalpable fineness of the latter. This last condition is a 

most serious objection to the method, in view of the effect, of fine 

grinding on the water content of minerals. (See pp. 53 and 64.)

The borax itself is prepared by heating pure crystallized borax in a 

platinum dish till- a small portion has melted. That remaining 

unfused is powdered and again heated in the dish to dull redness for 

fifteen minutes, with constant stirring. The powder is placed in a 

tube with tightly fitting glass stopper and kept over sulphuric acid. 

It must not be kept long without reheating, because of being hygroscopic.

Another form of tube used by Professor Jannasch for special purposes and recommended by Doctor Dittrich is shown in figure 20. Minerals, such as topaz,, which is not fully decomposed by the borax

Fto. HO: Glass tube for determination of water in special cases (Jannasch). Length from a to e, 20 cm.; 

inside diameter somewhat over 1 cm.; volume of bulb b, 25 cm.3 ; c d,. retaining layer of lead oxide 

between plugs of glass wool; /, calcium-chloride absorption tube; g, protective tube.

method and which contains a large amount of fluorine, are fused at & 

with, about six times their weight of lead oxide. A layer of lead 

oxide' (equal parts of oxide and peroxide Dittrich) between c and d 

serves to retain any fluorine escaping from the fusion. Doctor Dittrich uses this form generally for substances which can not be heated 

in- the simplest form of Penfield tubes >and for those which give off 

their water on simple ignition, without admixture of lead oxide, 

though, of course, with the retainer for sulphur, fluorine, etc.

If carbon dioxide is to be simultaneously determined, any carbonate in the lead oxide must be first destroyed by heat. As in the 

preceding description the layer of retainer must be kept continually 

hot by an auxiliary flame.

6. SILICA, SEPARATION FROM ALUMINA, ETC.

A. ALTERNATIVE METHODS OF DECOMPOSING THE ROCK.

a. GENERAL CONSIDERATIONS.

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
84 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

in principle, was long ago abandoned by me after fair trial, owing 

to the disturbance sometimes occasioned by incomplete expulsion of 

fluorine a 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 has always been employed. 

In the case of rocks rich in fluorine strict accuracy would require the 

separation of silica to be made as in the Berzelius method for fluorine 

estimation (see p. 184, also footnote, p. 86), but in practice it is not 

often necessary to resort to this tedious procedure, since the amount 

of fluorine is usually small and it can by no possibility cause a loss 

of much more than three-fourths its own weight of silica by volatilization as silicon fluoride when the sodium-carbonate fusion is evaporated directly with hydrochloric acid. Probably the loss is less, since ' 

some fluorine perhaps escapes as hydrofluoric acid. However this 

may be, the error is of comparatively slight importance, since it 

always attaches to the constituent 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. Professor 

Jannasch and his pupils have been especially active in this line of 

work, as is evidenced by their numerous published papers. 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 usually determined in the silica portion. Where the material

is limited, as it so often 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 is usually ample, it is rarely 

worth considering. A still further point in their favor 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 min-. 

eral to an impalpable powder, with the result of introducing serious 

analytical complications. (See ante, p. 53.) And the flux itself 

may need considerable hand pulverization. Once introduced, they

o 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.
SILICA. 85

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, since 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, since certain minerals do not 

fully succumb 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, it is very improbable that the 

anticipations of Professor Jannasch, to the effect that the boric-oxide 

method will soon supersede the alkali-carbonate fusion method in rock 

as well as in mineral analysis,-will be speedily 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 weir as to complex mixtures of them.

b. DECOMPOSITION OK REFRACTORY SILICATES BY HYDROCHLORIC ACID UNDER

PRESSURE. .

Jannasch a 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 

Maimesmann 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 

decomposition less complete tb.an if the material were spread evenly 

throughout the length of the tube.. Further, the acid strongly 

attacks the platinum 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 are 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.

a Her. Deutsch. chem. Gesell., vol. 24,1891, p. 273; Zeitschr. afoorg. Chernie, vol. 0, 1894, p. 72.
86 ANALYSIS OF SILICATE AND CARBONATE KOCKS. '

C. THE BORIC-OXIDE METHOD OP JANNASCH AND HEIDENREICH.0

a. Preparation of the boric oxide. This 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 

suddenly cooled to cause the anhydride to crack into pieces of a size 

convenient for powdering, which are to be kept in a tight .glass and 

powdered as needed, since the anhydrous oxide is hygroscopic.

/?. Treatment of easily decomposable .silicates. To this flux Jannasch 

and Heidenreich find 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 the most 

resistant, the authors recommending the expenditure of one-half to 

one hour's time for the grinding of one-half to 1 gram of powder. A 

low burner heat is applied for five to ten minutes till water is expelled; 

the heat is then gradually increased 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.eclge 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 twenty to thirty minutes, but dep.ends much 

on the character of the .mineral.

f. 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, .Jannasch ,and Weber & use a 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 

are added and the oxygen blast is applied till, in ten or fifteen minutes, the fusion is as transparent as glass. 0

oZeitsc.hr. anorg. Chemie, vol. 12,1896, .p. 208. This method of decomposing rooks 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" (Rhil. Trans., 1805, 

p. 231; Ann. d. chim., vol. 60, 1806, p. ,294; Gilbert's Annal., 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.

& Ber. Deutsch. chem. Gesell., vol. 32,1899, p. 1670.

cAn 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 fluorids without loss of silica. If this should prove to be generally true, an easy way 

is at last afforded for determining silica in such cases, where even its detection, when present in small 

amount, has heretofore been difficult.
SILICA. 87

§. Further treatment after fusion. From this point the further 

treatment is the same in both cases and, as modified by Jannasch 

and Weber, 0 is as follows:

The hot crucible is cooled in cold water and the contents are turned 

into a very larga porcelain or platinum dish, tp which, after covering 

with a glass, a saturated solution of hydrochloric-acid gas in methyl 

alcohol is added. 6 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 ten to 

fifteen 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 is 

claimed by Jannasch for this method, but with all its undoubted merit 

there .are two points which may militate against it. 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. The second objection attaches to th,e 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 slowly but wholly 

volatilized over the ordinary blast, hence there is great reason to 

fear sufficient loss at this much higher -temperature to give rise to 

serious error at times.

d. THE SODIUM-CARBONATE 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

a Ber. Deutsch. chem. Gesell., vol. 32,1899, p. 1070.

i>Made by passing dry hydrochloric-acid gas into cooled methyl alcohol for from one to two hours.
88 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

carbonate and potassium bicarbonate. As Dittrich says,a 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.

/?. 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 milligram 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 milligram in 10 grams. The invariable contaminating 

substances aside from sand and straw, which have sometimes been 

found are silica, alumina, irqn, 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. An article of the above degree of purity is satisfactory in 

almost all imaginable cases, since 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. 

This error is undoubtedly 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 

for fusions of the kind now contemplated. In fact, C. Holthof b 

most strongly recommends using the bicarbonate itself as a flux 

instead of the normal carbonate. (See d, .p. 90.)

if. The fusion with normal sodium carbonate. Ordinarily from 4 to 6 

parts ,of the flux should be used to 1 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 in isolated instances to be needed. 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

a Anleitung zur Gesteinsanalyse, 1905, p. 5. 

b Zeitschr. anal. Chemie, vol. 23,1884, p. 499.
SILICA. 89

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 cautiously lifted 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'decomposition 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 do, 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 

arid bottom, nor should the flame be allowed to 'envelope the whole 

crucible. These precautions apply in all ignitions of reducible substances, and yet they are rarely observed. 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 darkening 

due to oxidation of reduced iron which had alloyed with the platinum. 

This may in exceptional cases 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 best done 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 sometimes happens 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
90 ANALYSIS OP SILICATE AND CARBONATE ROCKS.

side by side or successively, under apparently similar conditions, 

may in one case show little or no manganese, in the otfrer considerable. 

This observation has been frequently made, 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 expecte4 that the 

green color can show until all other oxidizible 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.

d. Fusion with sodium bicarbonate. C. Holtho.f, who recommends a 

this flux strongly, uses 12 to 15 parts of it to 1 .of the -sample. One 

quarter of this is placed on the bottom of the crucible, a second quarter is thoroughly mixed with the rock'-powder in a small warmed 

dish, and the mixture 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 is heated over a low flame till the bottom is dull red, then, during fifteen minutes the flame is increased till 

the lower quarter of the crucible is dull red, in which state it is maintained for fifteen minutes. Then fusion is brought about by the full 

flame and maintained for a time. He 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. 30), 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 platinuni 

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 gradually added in excess. The depth of the evanescent pink color 

usually produced on addition of the acid allows of judging approxiaZeitschr. anal. Chemie, vol. 23,1884, p. 499.
SILICA. 91

mately 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 

pla.tinum.

B. SUBSEQUENT TREATMENT.

From this point the treatment will ordinarily be the same whether 

the boric-oxide or the sodium-carbonate method of decomposition 

has been employed.

a. SEPARATION OP SILICA.

a. 'Reasons for adoption of accepted procedure. The once 

practice .of employing a single evaporation with hydrochloric acid for 

the dehydration -of silica has been thoroughly discredited by the work 

of a number of writers. R. Bunsen a 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, 6 and still later, C. Meineke, c 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, d 

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 balance of the 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,

« Ann. Chem. Pharm., vol. Gl, 1847, p. 205. 

ft Zeitschr. anal. Chemie, vol. 9, 1870, p. 321. 

c Repert. anal. Chemie, vol. 7, 1887, pp. 215, 757. 

d Chem. News, vol. 09, 1894, p. 171.
92 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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, 0 drying temperatures above that of the 

steam bath offer 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 

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. c 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. 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.

C. Friedheim and A. Pinagel d 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.

(3. Procedure in absence of notable amounts of fluorine. Based on 

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.

a Tech. Quart., vol. 3,1890, p. 61; Abstract in Zeitschr. anal. Chemie, vol. 29,1890, p. 688.

6 Chem. News, vol. CO, 1889, p. 14.

c 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.

d Zeitschr. anorg. Chemie, vol. 45,1905, p. 411.
SILICA. 93

The evaporating dish should be of platinum and as large as possible 

to permit considerable surface distribution of the dry mass. Those 

used in the Survey have a capacity of about 1 liter. 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 in the late 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 

Mall generally vary from 1 to 3 per cent of the amount present, and 

is but little less after twenty hours drying than after one-tenth of that 

time." Upon the seemingly dry mass is poured -enough strong 

hyrdochloric acid to thoroughly drench it, b then an equal bulk of 

water, and the dish is placed covered on the bath for ten to thirty 

minutes and the contents occasionally stirred. It is quite permissible 

and sometimes advisable to defer adding the water till the strong 

acid has been in contact with the salts for ten or fifteen minutes. 

More water is then added and filtration proceeded with, first by decanta.tion, leaving nearly all the silica in the bottom of the dish. It 

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 

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/ 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 with advantage be used 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 in the majority 

of cases have no bad effect, except to increase the amount of insoluble

a See Jour. Am. Chem. Soc., vol. 24,1902, p. 366; Chem. News, vol. 80,1902, p. 80.

b 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 sv 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.

c 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 the very material error that often results from neglect 

to recover this silica.)
94 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

matter other than sjlica. If the data of experiments 6 to 9 in the 

paper already cited* 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. 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 are by no means 

pure silica.

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, 6 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. Since this contamination is very large (see e, p. 96) with highly titaniferous and ferruginous rocks and minerals, the operator should use discretion in his 

choice of a high drying temperature.

f. 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/ and will be considered in 

detail under the head of "Fluorine" (p. 184).

b. 1GNITIOS OF SILICA.

The application of a strong blast d for twenty to thirty minutes 

with crucible covered is absolutely necessary to expel all moisture 

from the silica, and the latter is then not hygroscopic. The first of

a Jour. Am. Chem. Soc., vol. 24,1902; p. 30fi; Chem. News, vol. 80,1902, pp. 79, 89.

b Jour. Soc. Chem. Ind., vol. 21,1902, p. 1217.

c See a, p. 83, and footnote, p. 86.

d 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. 20,1904, 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
SILICA. . 95

these statements, long extant in the literature, has been disputed by 

G. Lunge and C. Millberg a on the basis of experiments made on silica 

obtained by the decomposition of silicon tetrafluoride by water. ' It 

has been shown, 6 however, that, while the objection holds good for 

silica thus prepared, it does not for silica obtained by the decomposition of ail alkali silicate by means of an acid. F. P. Treadwell has 

confirmed the observation as to the difference in behavior of the two 

forms of silica, but regards the blast as unnecessary if a Teclu instead 

of a Bunsen burner is used. My experience is not in agreement with 

this. c

Although the above time limit usually suffices with a powerful blast, 

and may be materially shortened 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 . d

C. CORRECTION FOR IMPURITIES IN 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 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 the author's experience it never has 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

attainable in the furnace at the Survey, medium-sized crucibles lost approximately 1 milligram 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 platinu"m \vy ire 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 recently in platinum 

ware in large amount (see p. 41).

a Zeitschr. angew. Chemie, 1897, p. 425.

6 Hillebrand, W. P., Jour. Am. Chem. Soc., vol. 24,1902, pp. 372-373; Chem. News, vol. 80,1902, p. 91.

c It was thought that the observation reported by E. Jorclis and E. 1-1. Kanter (Zeitschr. anorg. Chemies 

vol. 35,1903, p.1C), to the effect that artificially prepared silica when digested with hydrochloric acid take, 

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 wcighable amount was also absent. Evidently, as stated by Jordis and Kanter, the chlorine compound 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.

d For the proof see Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 24,1902, p. 373; Chem. News, vol. 80, 

1902, ]>. 91. The duty of every analyst to test the efficiency of his blast or muffle can not be too strongly 

emphasized. The discordance of many statements and results on a variety of subjects is to be 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°.
96 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

crucible should be 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 drops of sulphuric acid 

diluted one-half suffice, but with less siliceous rocks the amount ought 

to be increased, not only in order to surely afford acid enough for 

the conversion of all the contaminating bases to sulphates, but also 

to prevent loss of titanium by volatilization as fluoride, since 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 but slowly dissolved 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.

tl. 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 inevitably are to be found 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 this residue varies with different 

rocks less than its quantity. It 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. It is usually 

much greater, and 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 onethird 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
SILICA. 97

of rocks,a 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 S03 over BaO will any of the latter be present 

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 more conveniently recovered later, together with the silica 

accompanying the precipitate of alumina, etc. (f. /?, p. 107).

Quite as rarely is calcium ever a component of the residue ifc the 

decomposition of the rock powder was complete at the outset. I have 

frequently found that the residue, after re-solution, is quantitatively 

precipitable by ammonia in presence of an ammonium salt. W. R. 

Bloor, b 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. 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 is 

mentioned by Gmelin-Kraut,c and can be readily demonstrated by 

evaporation of ferric chloride in platinum.

The removal of this platinum before precipitating alumina and iron 

is not necessary (but see third footnote, p. 107), and to do so involves 

the reoxidatipn 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. Nevertheless, if time is not a prime 

object, its removal by hydrogen sulphide is to be recommended. In

o See second footnote, p. 107.

6 Jour. Am. Chem. Soc., vol. 29,1907,p. 1003.

e Anorg. Chemie, Gthrev. ed.,vol. 3,1875, p. 359.

20091 Bull. 422 10 7
98 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

the following descriptions, however, it is assumed that the platinum 

has not been gotten rid of at this stage.

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. ALUMINUM TOTAL IRON.

A. INDIRECT METHOD FOR ALUMINUM (TITANIUM), 

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 fully recognized that there are objections to parts 

of the procedure that is usually followed in this laboratory, but the 

same may be said of any other known procedure, including that preferred by Dittrich. It is believed that the Survey method, which 

in its main features is closely modeled after old and well-known 

methods, will in competent hands give better results on the whole 

than any other.

The common practice in this laboratory is to find alumina by difference, after deducting from the precipitate produced by ammonia or 

sodium acetate the sum of all other oxides this precipitate may contain. Of these, only ferric oxide, titanic oxide, and the«trace of silica 

are determined in this portion (see also third footnote, p. 107), those of 

phosphorus, vanadium, chromium, zirconium, and sometimes manganese being looked for in other portions of the rock powder. This 

throws on the alumina all errors involved in their separate determinations ; but these errors may balance, and in any case the probable error 

can hardly be as high as that involved in the direct weighing of the 

alumina itself, considering the difficulty of effecting a satisfactory
ALUMINUM TOTAL IRON. 99

separation of it from all the other admixtures, an operation which 

would, moreover, immoderately extend the time required for each 

analysis.

b. PRECIPITATION OF ALUMINUM, IKON, ETC., WITHOUT PRECIPITATING MANGANESE.

a. Precipitation by ammonia'. Two precipitations by ammonia at 

boiling heat are usually quite sufficient to separate iron, aluminum,® 

phosphorus, vanadium, chromium, titanium, and zirconium, if all 

these are present, from nickel, manganese, the alkaline-earth metals, 

and magnesium, provided ammoniacal salts are present in sufficient 

quantity. This last point is of special importance 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 better obtained 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 £he 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.

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 Jena or Nonsol type. The ammonia should be 

as free from carbonate as possible, as well as from any nonvolatile 

matter, and it need not be added in any great excess. The complete 

boiling off of this excess is unnecessary, as pointed out by Genth and 

Penfield, since it is apparently the washing with pure water and not 

the free ammonia which carries small amounts of alumina into the filtrate. S. L. Penfield and D. N. Harper & recommend washing with a 

dilute solution of ammonium nitrate (20 cm.3 nitric acid, neutralized 

by 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 being no chloride to remove, both of which are excellent suggestions.0

« It is well to bear in mind that in presence of fluorine, aluminum is very incompletely precipitated by 

ammonia. Consult also Veitch, F. P., Jour. Am. Chem. Soc., vol. 22,1900, p. 246; and Hinrichsen, F. W., 

Ber. Deutsch. chem. Gesell., vol. 40,1907, p. 1497, and Zeitschr. anorg. Chemie, vol. 58,1908, p. 83.-

6 Am. Jour. Sci., 3d ser., vol. 32,1886, p. 112.

c A single objection, and this 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 1;o drive off the mixed ammoniacal salts in platinum. With much iron present the final precipitation from a nitric-acid solution is a decided advantage, but is less so in the case of alumina free or nearly 

free from iron. Contrary to numerous statements and general belief, there is no danger of loss of aluminum 

chloride by volatilization when the precipitate is ignited before complete removal of ammonium chloride.
100 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

For a reason mentioned under e (p. 104) the final precipitation 

may with advantage be made in the presence of "macerated filter 

paper, as recommended by Dittrich.®

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. 6

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 Mn2 03 state and remains so 

when redissolved, being then in a fit condition for reprecipitation.

/?. The basic-acetate precipitation. Although for this 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 afterwards 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 

that none of the methods of making the basic-ace,tate 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.

The cold and not excessively acid solution, not exceeding 100 cm. 3 

in bulk and contained in a beaker of Jena or Nonsol glass, is first 

neutralized with great care by adding a freshly prepared solution of

a Anleitung zur Gesteinsanalyse, 1905, pp. 10,11,14; Ber. Deutsch. chem. Gesell., vol. 37,1904, p. 1840.

& The fact must not be overlooked that certain of the rare earths may pass completely into the nitrate 

if the basic-acetate method is followed. If, then, later, on rendering the combined nitrates ammoniacal, 

an unexpectedly large precipitate appears, this should be carefully examined 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.
ALUMINUM TOTAL IRON". 101

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 

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 conveniently brought upon it 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 a, washed, 

sucked dry, and treated as in e (p. 104), after recovery as in d (p. 103) 

of the portions of aluminum and iron that may have passed into 

the filtrates."

 "Mittasch's method for the basic-acetate separation of manganese from iron. A study of the conditions 

necessary for successful separations of large or small quantities of manganese 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 

nol; 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 (NH<) 

CslTsOa.CaHiOs, is used, or 10 cm. 3 if the normal salt is used. This last is made by neutralizing acetic acid 

with ammonia. The solution is then diluted with water to about 400cm.» and brought nearly to the boiling 

point. Any precipitate that may have appeared being disregarded, 20 cm.3 of the acid acetate (one-half 

molar) or 5 cm.3 of acetic acid and 10 cm. 3 of the normal acetate (molar) is added, and the boiling temperature 

is maintained for a minute longer. Precipitation is complete even at C0°, but filtration 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 film is removed from theglass with hydrochloricacid 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.

The Brunck-Funk separation of iron as basic acetate from manganese, zinc, nickel, and cobalt. The following method of O. Brunck (Chem. Zeitung, vol. 28,1904, p. 614), slightly modified and extended by W. Punk
102 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

C. PRECIPITATION OP IRON, ALUMINUM, ETC., TOGETHER WITH MANGANESE.

of. By ammonia and ammonium persulphate. 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. 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 f. /?, page 107.

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 in this laboratory to warrant its unqualified recommendation.

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 manganese when made ammoniacal (see b. 

a, p. 99). Heat is applied, and about 1 gram of ammonium persulphate a free from all interfering impurities is added. When the liquid 

begins to boil, ammonia is added carefully till in decided excess, as 

shown by the odor, and boiling is kept up for several minutes. The 

precipitate is allowed to settle and is quickly filtered and washed with 

hot water three or four times and sucked dry by the pump. It has

(Zeitschr. anal. Chemie, vol. 45,1906, p. 181) is claimed to afford a complete separation by one treatment. 

Its applicability to aluminous materials has, however, 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 is as follows:

To the chloride solution in a large dish is added potassium chloride (about 0.35 gram to 0.1 gram of iron) 

the solution is evaporated to apparent dryness on the steam bath, but without expelling all of the free 

acid. The residue is brokenup superficially and the drying on the bath continued for five to ten 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 NaCQHsOz.SHzO 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, 

decanted, collected on the filter, and washed with hot water.

a This reagent as sold must be purified. Jannasch (Prakt. Leitfaden d. Gewichtsanalyse, 2d ed., 1904, 

p. 179) accomplishes this as follows: To a saturated warm solution (not over 95°) ammonia is added till its 

odor persists. [More will have to be added at intervals, since 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, since 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 externally. 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 thoroughly removed. [ A commercial article purified thus by me was found to contain 

no interfering impurities, though not free from alkali. W. F. H.]
ALUMINUM TOTAL IRON. 103

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 reprecipitated 

precisely as the first time. It may then be washed three or four times 

with hot water containing a few drops of ammonia, then ignited in the 

paper, and weighed as A1203 , Fe203 , Mn3 04 , Ti02 , and P205 . 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. 7-, page 104, and should be added to the 

main precipitate above. It is not best to attempt to determine the 

chromium colorimetrically in the filtrate.

/?. By ammonia and ammonium sulphide. Although this old 

method of precipitation can be employed in special cases, it is not 

well adapted generally to silicate rocks, and will, therefore, not be 

described in this connection.

d. RECOVERY OP IRON AND ALUMINUM FROM THE FILTRATES.

a. After an ammonia precipitation. The filtrates are. evaporated, 

always in platinum if possible and allowable, to a small volume. 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 (and usually iron hydroxide) that will invariably 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 hot water, burned, and added to the main 

one.

/?. 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 

amraoniacal 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 precipitate on the filter. 

Both dishes and the filter are finally rinsed with hot water. The
104 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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.

f. After precipitation by ammonia and ammonium persulphate. 

The filtrates are evaporated as in a. The second 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 usually be shown 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 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 10 (p. 118).

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 (p. 102).

6. IGNITION OF THE PRECIPITATE OF IRON, ALUMINUM, ETC., OXIDES.

The combined precipitates of alumina, etc., obtained in either a, b, 

c, or d, are ignited without preliminary drying in the crucible containing the residue from the silica (6. B. c, p. 95), 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, after ignition, 

lumpy, and any magnetic oxide that may have been formed can not 

be wholly reoxidized by heating or by treatment with nitric acid (see 

5. A. c. /?, p. 71). They are also slow to yield to subsequent treatment. 

A precipitate formed in presence of thoroughly macerated paper, 

as recommended by Dittrich, on the other hand, yields on ignition a 

powder, and the fine state of division makes reoxidation of any
ALUMINUM TOTAL IEON". 105

reduced iron easy, besides wonderfully shortening the time required 

for subsequent re-solution.

Alumina in the quantities ordinarily found can not be fully dehydrated by the full heat of the Bunsen burner. It must be blasted 

for five or ten minutes. If iron is present in large amount this last 

operation must be conducted so as to insure access of air to the crucible (p. 89).

For ignitions of this kind, which involve no very prolonged heating, an electric furnace is admirably 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 empty weight of the crucible, which may have changed since 

igniting the silica in it, is found after treatment of its contents as in 

the next section.

f. RECOVERY OF SILICA AND POSSIBLE BARIUM IN THE ALUMINA'PRECIPITATE.

a. Silica. The weighed precipitate is transferred as far as possible 

to another crucible of 25 to 30 grams weight. The small adhering 

residue, chiefly that originally derived from the 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. 0 The hot liquid is poured 

onto the main mass of precipitate in the other crucible, more pyrosulphate 6 is added (up to 7 grams in all c ) and the fusion is renewed

a It will l>e remembered (see page 94, footnote d) that long blast 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. With crucibles of American manufacture the average loss up to this point due to blasting 

both silica and alumina in one and the same crucible may reach 0.8 mg. (mean of six tests by R. C. Wells, 

ranging from 0.6 to 1 .fi mg.).

* A chief objection 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 the frothing has ceased. To effect this change it is only necessary to melt a large 

amount of the salt in a platinum dish and keep it in fusion till spattering ceases and white fumes begin to 

como off freuly. 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.

Of late, 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
106 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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* 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 cthan 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 

washed with hot water, burned, and weighed in a platinum crucible. 

Being rarely 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 

B, page 107, after filtering from barium if present (see ft p. 107).

The amount of silica thus recovered varies from 2 to 4 milligrams 

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 alumina precipitate to be recovered. 6 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. It is, however, but a small

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, since 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.

c 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. 134).

o Should a small portion of the precipitate have escaped solution no particular harm is done. The further 

treatment is not thereby changed.

b For proof see Jour. Am. Chem. Soc., vol. 24,1902, pp. 368-370; Chem. Nftws, vol. 86,1902, pp. 79,89.
ALUMINUM TOTAL IRON. 107

portion of what the alumina held, the greater part having formed 

alkali silicate during the fusion and remaining in solution afterwards, 

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 milligrams for a single 

precipitation and a total of 1 centigram of silica in the experiments 

detailed else where a ) 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.

/?. Barium. Should by any chance the alumina precipitate have 

held barium sulphate, something which has not happened in my 

experience with rocks, unless ammonium persulphate was used as in 

c. oc } page 102, 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 in the form of sulphate, b and can be separated by flotation from 

the heavier platinum.

B. DETERMINATION OF IRON IN THE PRECIPITATE OF ALUMINA, ETC. 

a. WITHOUT REGARD TO THE PRESENCE OP VANADIUM.

a. Reduction of the iron. Into the cool filtrate obtained in f. 

a, ft, pages 105-107, 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 1?

» Jour. Am. Chem. Soc., vol. 24,1902, p. 369; Chem. News, vol. 86,1902,p. 90.

i> Some years ago, in a series of analyses of rocks from the Leucite 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 Ti0 2 and 

PaOs, with perhaps a little ZrOa. By repeated fusion with acid potassium sulphate and leaching with cold 

 water it could be gradually brought into solution. It was these rocks which furnished the most striking 

Instance of the peculiar milky sulphate residues mentioned on p. 9C as derived from the ignited silica.

Knop (Zeitschr. Kryst, yol. 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. x

<=It may be mentioned, that 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 silica precipitate was ignited 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 isnot due to retention of platinum by the main AhOa, 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 rjlatinum formed during evaporation and drying of the silica. It may also be in
108 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 filtered0 

warm into a half-liter flask, hydrogen sulphide is again introduced 

for a few minutes, with production of slight milkines£ 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, 6 the end point being 

found by occasional testing of the escaping gas with lead-acetate 

paper. c When this point is reached, the flame is removed and tlje 

flask allowed to cool without interrupting the gas current. The 

cooling is hastened by placing the flask in a basin of cold water.

/?. Titration of the iron. 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

part or wholly due to contamination from reduction of platinum during evaporation of the filtrate from 

the basic-acetate separation. It will be remembered that from this filtrate a small amount of iron 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. 98.)

a. Filtration is not necessary if only precipitated sulphur and no sulphides are in suspension, since this 

is without reducing action on cold permanganate solution, as H. L. Wells and W. L. Mitchell and others 

before them have pointed out. The above 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.

6 The gas generated from every .new lot of marble must be carefully tested for hydrogen sulphide. Even 

pure white marble is freq uently not free from soluble sulphides probably pyrrhotite, sphalerite, or galena 

and the amount may be enough to appreciably affect 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 asolution of copper 

sulphate.

c 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 ten to twenty 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 ncid 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.
ALUMINUM TOTAL IRON. 109

the solution, which is kept in rotatory agitation by an appropriate 

movement of one hand. The bulk of the solution will be from 100 

to 200 cm. 3 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.

The results are strictly accurate, with the limitations set forth in 

the paragraph below, when care is taken with the reduction by hydrogen sulphide. The method is superior to that involving the use of 

zinc, since 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 03 . a

j-. Further treatment of the solution after titration. The titrated

solution is returned to a dish, which may be of porcelain, and evaporated to a bulk of much less than 100 cm. 3 if the rock is supposed to 

contain less than 1 per cent-of titanium. For each additional 1 per 

cent of titanium the final bulk may be larger by 100 cm. 3 The solution is transferred to a graduated flask with a capacity of 50, 100, or 

200 cm. 3 or more, as the case may be, enough hydrogen peroxide 

free from fluorides is added to fully peroxidize the titanium, the 

flask is filled to the mark and well shaken, and the titanium is determined colorimetrically (see p. 128).

b. HAVING REGARD TO THE PRESENCE OP VANADIUM.

If vanadium is present the value found for iron will be in error by 

the amount of permanganate required to oxidize V204 to V2 05 . b The 

amount of the correction will differ according as titration of the iron is 

made after reduction by hydrogen sulphide or nascent hydrogen. If 

the former is used, as should always be the case, because of the ever 

present titanium, the vanadium is reduced by it to V2O4 , which in its 

action on permanganate is equivalent to two molecules of FeO, while 

the reduction goes further with hydrogen. After the first transitory 

pink blush throughout the liquid, the more slowly acting vanadium

o The statement in the foregoing paragraph regarding the superiority of the reduction by hydrogen sulphide is subject to correction if the method recently proposed by F. A. Gooch and H. D. Newton (Am. 

Jour. ScS., 4th ser., vol. 23,1907, p. 365; Chem. News, vol. 96,1907, p. 148; Zeitschr. anorg. Chemie, vol. 54, 

1907, p. 1213) reveals no defects after thorough trial. Those authors find that after reduction by zinc, titanium is completely oxidized to the quadrivalent state by either cupri'c oxide or bismuth oxide and that 

these oxides do not oxidize ferrous iron. They therefore reduce with zinc the solution of titanium and Iron; 

to the fliisk containing the cooled solution free-from metallic zinc they add a little of one of the oxides (preferably that of bismuth), shake, gently, filter quickly, and titrate with potassium permanganate. The 

results they furnish are very satisfactory.

6 This statement holds true also for, the method of Gooch and Newton, referred to in the foregoing footnote, for the oxides of copper and bismuth do not, according to my tests, convert VjO4 to VaOe. According 

to a private communication from Newton bismuth trioxide converts vanadium that has been reduced 

to VjOa by zinc, only to VaOs if the solution is strongly acid (10 per cent HjSO< by volume) and cool, but 

toward VjO« If warm or less acid.
110 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

may require the addition of a drop of two more of permanganate 

before a comparatively permanent coloration appears.

When the amount of vanadium 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 precipit ability - with alumina and iron by ammonia 

and ammonium acetate, though Carnot a 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 b 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 but appreciable fraction 

of a per cent of iron, as I have repeatedly found 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.

C. DETERMINATION OF THE TRUE VALUE FOR FERRIC IRON.

The total iron in the rock having in one way or another been found, 

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. 165-166.) . ^c

a Compt. Rend., vol. 104,1887, p. 1803; Zeitschr. anal. Chemie., vol. 32, -1893, p. 223. 

6 Jour. Soc. -Chem. Industry, vol. 7,1888, p. 73.
ALUMINUM TOTAL IRON.

C. METHODS AIMING AT THE MORE OR LESS DIRECT DETERMINATION OF

ALUMINUM.

a. AFTER FIRST REMOVING IRON AS SULPHIDE.

Should it be desirable for any reason to effect an actual separation 

of aluminum, this may best be done, up to a certain point, after the 

pyrosulphate fusion (f, p. 105),by removal of the iron a by ammonium 

sulphide in ammonium-tartrate solution, evaporation of the filtrate, 

ignition of the residue, with sodium carbonate and nitrate, and extracttion with water, whereby 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 the chromium 

and vanadium is outlined under "Phosphorus" (B, p. 145). This is 

as far as the separation can well be carried, and the A12 03 must still be 

found by subtracting the P2O5 from the combined weights of the 

A12 03 and P2 05 . The possibility of loss of some P2 05 by volatilization b during the bisulphate fusion must be borne in mind here, for 

if it takes place the final weight of A1203 + P2 05 will not contain all 

the P2Or> .

Some writers have recommended dissolving the ignited alumina, 

iron oxide, etc., in hydrochloric acid, but when the precipitate has 

been heated over the blast, as it should be, this is very ineffective.

b. BY EXTRACTION WITH A FIXED CAUSTIC ALKALI.

A favorite practice in some countries of Europe has been to fuse the 

ignited precipitate containing A12 03 , Fe2 03 , Ti02 , P2 05 , etc. or that 

of the A12 03 , Ti02 , P2 05 , 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, c who 

showed that pure titanic oxide is markedly soluble under both conditions of treatment. Experiments made by myself 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 Ti02 , 

or about 7 per cent, determined colorimetrically. When freshly precipitated and boiled with the alkali, the solubility was less. When

a This being first reduced to the ferrous condition by hydrogen sulphide in acid solution in order to obviate 

the possibility of precipitating some titanium, which otherwise is likely to happen. (Cathrein, Zeitschr. 

Kryst., vol. C, 1882, p. 240, and vol. 7,1883, p. 250.

t> H. B,ose speaks of such loss when volatilizing sulphuric acid in presence of phosphoric acid (Handb. 

f. quant. Anal., Finkener ed., vol. 2,1871, p. 575, and elsewhere), and the fact of such loss to a very marked 

extent has been confirmed in this laboratory.

c Proc.. Am. Acad. Arts Sci., vol. 12,1885, p. 430; Bull. U. S. Geol. Survey No. 27,1880, pp. 16, 17.
112 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 not been 

removed.

C. METHODS OP DITTRICH.

Evidently with a view to eliminating some sources of error inherent 

in the methods outlined in a and b above, Dittrich evolved a procedure 0 which is a combination of both and includes methods of separating and determining titanium and zirconium. In outline it is as 

follows, the starting point being the precipitate produced by ammonia 

and hydrogen peroxide, and containing several or all of the oxides: 

Fe2 03 , A12 03 , Cr2 03; Ti02 , Zr02 , Mn3 04 , P2 05 , and Si02 .

After weighing, this precipitate is fused in a silver crucible with 

sodium hydroxide, whereby A12 03 and P2 05 are brought into solution. 

If manganese has been in part dissolved as manganate, it is rendered 

insoluble by digesting the aqueous solution of the melt with hydrogen 

peroxide.

The filtrate is evaporated with hydrochloric acid to separate Si02 , 

and the A12O3 and P205 are precipitated by ammonia and weighed 

together. Then the P2O5 in the mixture is determined, if present, 

thus giving the A12O3 by difference. Chromium is not considered by 

Dittrich in this scheme, but its determination colorimetrically would 

present no difficulty (17, p. 147).

The treatment of the oxides insoluble in sodium, hydroxide is described under b, page 136, according to the more recent directions of 

Dittrich and S; Freund. 6

d. DIRECT PRECIPITATION OF ALUMINUM BY PHENYLHYDRAZINE.

A recent and promising method for the "direct determination of 

alumina in presence of iron, manganese, calcium, and magnesium" 

is that of Hess and Campbell, 0 but, as with the methods just considered, it involves finally weighing aluminum, phosphorus, and 

titanium 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.

a Dittrich, M., Anleitung zur Gesteinsanalyse, 1905, pp. 9-31.

6 Zeitschr. anorg. Chemie, vol. 56,1905, p. 337.

cjour. Am. Chem. Soc., vol. 21,1899, p. 776; Chem. News, vol. 81,1900, p. 158.
MANGANESE, NICKEL, COBALT, COPPER, AND ZINC. 113

Phenylhydrazine "precipitates aluminum from its solutions quantitatively as the hydroxide without a trace of the precipitate being 

redissolved in excess of the precipitant."

Dr. E. T. Alien has investigated the method in this laboratory0 

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 jnilli- 

. gram 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 Doctor 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 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 o:f phenylhydrazine, & 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. 3 of this are used in 100 cm.3 of hot water.

9. 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

o Jour. Am. Chem. Soc., vol. 25,1903, p. 421.

b 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.

20091 Bull. 422 10 8
114 ANALYSIS OF SILICATE AND CAEBONATE BOOKS.

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.a

If the directions already given have been carefully followed, however, there will be little chance of error due to foreign contamination, 

either by alumina or magnesia, a sufficiency of ammonium salts 

being a guaranty against the latter. Regard 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 second 

footnote, p. 100), for they will appear at this stage. .

B. PRECIPITATION OF THE GROUP AND SEPARATION OF ITS

CONSTITUENTS.

a. THE AMMONIUM-SULPHIDE 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 in rock analysis probably of more consequence than the

a 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 has been determined by George Steiger in .the 

Survey laboratory recently, while 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.

Tests showing distribution of manganese in gravimetric separations.

No.

957.................

973..................

974.................

975.................

1126................

1128................

1130................

1131................

Partial composition of rock.

A12 03, 

Fe2O8.

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 

, A12 08 , 

Fe2O3 (by 

difference).

0.085 

.036 

.301 

.088 

.030 

.019 

.016 

.032

CaO.

0.011 

.023 

.087 

.016 

.030 

.055 

None. 

.101

Mg2P2O7 .

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.
MANGANESE^ NICKEL; COBALT, COPPEK, AND-ZINC. 115

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 neecl 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 readily corrected for by the colorimetric 

method described on page 116.

The. precipitation of manganese in alkaline solution by hydrogen 

peroxide, as proposed by P. Jannasch and E. v. Cloedt, a a method 

which appeared to be simple and accurate, besides affording a separation from zinc, has been shown by C. Friedheim and E. Bruhl 6 to be 

valueless.

/?. Precipitation ly 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. A. d. a and ft, p. 103), 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 twelve hours, and preferably twenty-four, or even longer. The precipitate, collected and 

washed 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 10, p. 118.)

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 reprecipitated 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 Mn3 04 and calculated to MnO, or,

a, Zeitschr. anorg. Cherale, vol. 10,1895, p. 405. 

6 Zeitschr. anal. Chemie, vol. 38,1899, p. 681.
116 ANALYSIS OF SILICATE AND Ci BBONATK KOCKS.

if present in some quantity, it may preferably be weighed' as the 

sulphate,0 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, COPPER.

The paper containing nickel, cobalt, and copper is incinerated in 

porcelain, dissolved in a few drops of aqua regia, and 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 of nickel after filtering is simply burned and weighed as 

oxide its weight being always very small, hardly ever over 0.3 or 

0.4 milligram and 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 if the evaporations have been conducted, 

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 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. 98.) 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. 113), 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

a Volhard, J., Ann. Chem., vol. 198,1879, p. 329. Gooch, F. A., and Austin, Martha, Am. Jour. Sci., 4th 

ser., vol. 5,1898, p. 209; Zeltschr. anorg. Chemie, vol. 17,1898, p. 264.
MANGANESE; NICKEL, COBALT, COPPEK, AND ZINC. 117

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 cru- 

.cible (placed in the radiator shown in fig. 2, p. 31) 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 sma,ll 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.«

This method 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 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 conveniently made 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.

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. There is now added about 1 

gram of solid ammonium persulphate and the flask is placed on the 

steam bath or hot plate. Very soon the pink color of permanganic 

acid begins to appear and rapidly increases 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

a Walters, H. E., Chem. News, vol. 84,1901, p. 239; Proc. Eng. Soc. West. Pa., vol. 17,1901, p. 257.
118 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

great the solution must be poured into a larger flask. The flask is 

.filled with water to the mark and the contents 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 qf 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.3 is drawn off 

into one of the comparator cylinders shown in fig. 5 (p. 34), 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 34. If the form of colorimeter depicted in figs. 6-7 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 (due to deficiency of silver salt), 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.

10. CALCIUM AND STRONTIUM (BARIUM).

A. SEPARATION FROM MAGNESIUM, 

a. PRECIPITATION AND IGNITION OF CALCIUM AND STRONTIUM OXALATES TOGETHER.

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 (9. B. a. (3, pp. 114-115). Itsseparatiqn at this or any other stage is quite unnecessary; nor is the removal 

of ammonium chloride usually demanded, since there is no undue 

amount present in most cases, the first precipitation of-alumina, etc., 

having been by ammonium or sodium acetate.® 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 redissolved in 

hydrochloric acid, boiled with ammonia to throw out traces of alumina 

sometimes present, filtered and reprecipitated as before, but in a small 

bulk of solution. It is weighed as oxide, transferred to a small flask of 

20 cm.3 capacity, dissolved in nitric acid, evaporated to dryness at 150°

a 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.
CALCIUM AND STRONTIUM. 119.

to 160°, and the separation of strontium from calcium effected by 

ether-alcohol 0 as described below.

The weight of strontia found deducted from that of the two oxides 

gives that of the lime. For treatment of the filtrates see " Magnesium" (11, p. 123).

b. NOTES ON DOUBLE PRECIPITATION, WASHING, AND IGNITION OF THE OXALATES.

It may be said with regard to the separation of calcium from magnesium that two precipitations by ammonium oxalate are essential to 

the attainment of correct results, not only for the complete removal of 

magnesium but of sodium as well, the retention of compounds of the 

latter element by calcium oxalate being now generally known. This 

subject has been thoroughly studied by T. W. Kichards, C. T. McCaffrey, and H. Bisbee.6 They also call attention to the danger of 

too long washing with hot water because of the very appreciable

solubility of calcium oxalate. This is a point that needs greater

attention than it ordinarily receives from analysts.

The ignition is started with the precipitate moist. After charring 

and burning off the paper the crucible is to be covered 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 

ordinarily ample-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, since I was able by it to reduce 3 grams 

of calcium carbonate in fifty minutes 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.

B. SEPARATION OF STRONTIUM (BARIUM) FROM CALCIUM, 

a. BY ETHER-ALCOHOL.

The thoroughly dried nitrates obtained in A. a are treated with as 

little (rarely over 2 cm.3 ) 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 

are 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

« See R. Fresenius, Zeitschr. anal. Cheinie, vol. 32, 1893, pp. 189, 312, for the latest improvements in 

this method, in their application to considerable quantities. 

6 Proc. Am. Acad. Arts Sci., vol. 36,1901, p. 375; Zeitschr. anorg. Chemie, vol. 28, 1901, p.-71.
120 ANALYSIS OP SILICATE AND CARBONATE ROCKS.

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. BY AMYL ALCOHOL.

Because of the slight solubility of strontium nitrate in amyl alc.ohol 

the method of Browning 0 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

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. b If present with them, 

however, 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. (See "Barium," 

13, p. 138.

D. SEPARATION OF BARIUM FROM STRONTIUM.

Profiting by the experience of R, Fresenius and others, A. Skrabal

and L. Neustadl c 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 grams, neutralized by ammonia, to the liter. 

Ammonium acetate, b, 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

o Am. Jour. Sci., 3d ser., vol. 43,1892, pp. 50, 314.

frHillebrand, W. F., Jour. Am. Chem. Soc., vol. 16,1894, p. 83; Chem. News, vol. 69,1894, p. 147.

c Zeitschr. anal. Chemie, vol. 44,1906, p. 742.
CALCIUM AND STRONTIUM. 121

while swirled about 5 cm.3 of the bichromate solution is added. 

After settling and cooling the^clear liquid is decanted through a filter 

and the precipitate washed by decantation with ammonium acetate 

(solution 1)} 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 b}^ 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 THE WEIGHT OF CALCIUM.

GENERAL STATEMENT.

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 any one of them will apparently afford good results if no account 

is to be taken of that element. The methods have, however, not been 

tested in this laboratory, though the several gravimetric methods have 

been compared by 0. Brunck,0 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. Our 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

a Zeitschr. anal. Chemie, vol. 45,1906, p. 77.
122 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

the employment of a vertical instead of an inclined flame. The complete conversion of the oxide to sulphate by treatment with either 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 readily be demonstrated 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.

a. VOLUMETRIC 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 best against pure Iceland 

spar dissolved in hydrochloric acid and precipitated as the oxalate.

b. BY WEIGHING AS THE CARBONATE.

 The oxalate is gently 

o »/ ignited o

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 gently ignited to just 

visible dull redness and weighed. The treatment with ammonium 

carbonate, etc., is repeated till constant weight is reached.

C. BY WEIGHING AS THE SULPHATE.

The strongly ignited oxalate is cautiously slacked 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. 31). The dry sulphate is then moderately ignited (to dull redness 

for a short time) and weighed, the treatment with acid, etc., being 

repeated to constant weight.
MAGNESIUM. 123

d. BY WEIGHING AS THE FLUORIDE.

The strongly ignited oxide is slacked 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 carbonate or sulpha'te method, and in the hands of the inexperienced leads to better 

results, though he regards the sulphate method as the best in experienced hands.

11. MAGNESIUM. 

A. PRECIPITATION.

a. CONDITIONS NECESSARY FOR 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,a confirmed in part and supplemented by F. A. Gooch 

and Martha Austin/ 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. 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 differs from the normal in containing relatively more ammonium and less magnesium for instance, 

an admixture of such a molecule as Mg(NH4 ) 4 (P04 ) 2 the result being 

that when ignited in the ordinary way too much magnesium is found 

because of formation of some metaphosphate. To obviate this error, 

Neubauer considers it absolutely necessary to blast the precipitate for

oZeitschr. angew. Chemie,, 1890, p. 435.

6 Am. Jour. Sci., 4th ser., vol. 7,1899, p. 187; Chem. News, vol. 79,1899, pp. 233, 244, and 255; Zeltschr. 

anorg. Chemie, vol. 20,1899, p. 121.
124 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

half an hour and then to repeat the blasting for a second half hour to 

see if constant weight has been reached. The phosphate is then 

entirely pyrophosphate, which is quite unaffected by further blasting. 

(See, however, B, a, p. 125.) ' The intense heat has caused a decomposition of the metaphosphate with volatilization of P2 O5 , as follows: 

2Mg(P03 ) 2=Mg2P2 07 + 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,0 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 b reports to the contrary. 

This chemist obtained a normal precipitate by either of two methods 

of his own, of which he regards the following as more convenient and 

reliable, because ammonium salts exert no influence on the result. 

It is likewise applicable to the precipitation of phosphoric acid by 

magnesia mixture.

The hot magnesium solution, containing at least 2 to 3 grams of 

ammonium .salts (to prevent precipitation of magnesium hydroxide) 

and 20 to 30 cm.3 of 10 per cent ammonia solution for 0.4 gram 

Mg2P207 , is heated to boiling and the precipitant is added slowly. 

Then more ammonia is added and the solution allowed to cool. A 

coarsely crystalline precipitate forms which, it is claimed, consists 

entirely of dimagnesium-ammonium phosphate. This procedure of 

Jarvinen was employed where but a single precipitation of the magnesium was intended, and it does not seem to be adapted for a second 

precipitation. As this is always called for in rock analysis, it does not

appear best to adopt his procedure for our purposes.

E. Raff a c has also studied the conditions under which a precipitate 

of normal composition is afforded, but his directions will seldom be 

of use in mineral analysis. They are therefore not repeated here.

b. PRECIPITATION.

of. First precipitation. This is made without special precautions 

in the filtrate from the first calcium-oxalate separation (p. 118) by 

sodium-ammonium-hydrogen phosphate (microcosmic salt)d in indefinite decided excess and without the great excess of ammonia usually 

prescribed. It is not necessary to first remove ammoniacal salts

a Am. Jour. Sci., 3d ser., vol. 5,1873, p. 114. 

& Zeitschr. anal. Chemie, vol. 44,1905, p. 335. 

c Gazz. chim. ital., vol. 38, pt. 2,1908, p. 556.

<J The objection that has been made by one writer to the use of this salt instead of disodium-hydrogen 

phosphate is, so far as our experience teaches, entirely groundless.
MAGNESIUM. 125

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 quantity of magnesium 

present.

/?. 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 solution thus obtained is united with that of the residue from evaporation and. ignition of the second filtrate from the Calcium oxalate (10. A. a, p. 118), and is diluted if necessary. A fewdrops of sodium-ammonium-phosphate solution are now added, and 

ammonia, drop by drop, in slight excess, with constant stirring till 

the crystalline precipitate has well formed. Once formed a few cubic 

centimeters more of ammonia are to be added.

31. METHODS OF COLLECTING AND IGNITING THE PRECIPITATE.

a. ORDINARY PROCEDURES.

Were it not for the necessity of examining the precipitate for impurities after ignition (C, p. 126), it were best collected in a Gooch crucible, 

provided the asbestos felt is well constructed and not of the serpentine variety so largely on the market. It is therefore well to use an 

ordinary crucible of platinum. Neubauer ignites slowly in platinum 

after drying, without removing from the paper, and applies the blast 

only when the carbon has been wholly burned off. a The danger of 

attack of the platinum by thus igniting the precipitate in contact with 

the paper is extremely slight, though it has happened once or twice in 

our 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 precipitate, wrapped in its moist paper, is best dried in the 

crucible itself, the paper then slowly charred without allowing it to 

ignite, the carbon burned off over a gradually increasing flame, and 

finally a weak blast applied for a long time and repeated to constant 

weight to insure volatilization of any excess of P205 over and above 

that required for the pyrophosphate formula. (See A. a, p. 123.)

a Zeitschr. anal. Chemie, vol. 33,1894, p. 362.
126 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 crucible 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.

b. MODIFICATION OF ULBRICHT.

At one time the procedure first recommended by R,.°Ulbricht, later 

by K. Broockmann, and also by L. L. de Koninck, was used'. It consists in dissolving the ammonium-magnesium phosphate off the filter 

with nitric acid, collecting the filtrate in a weighed crucible, evaporating the contents to dryness, a and subsequently igniting, the product 

being presumably pyrophosphate. But it was soon observed that 

the ignited salt, especially when large in amount, does not always dissolve completely in hydrochloric acid, but that sometimes a white 

residue is left in light lumps which appear to be quite insoluble in 

acids. This residue contains no silica, but only the constituents of a 

magnesian phosphate, and it may be a peculiar metaphosphate.

Whether its appearance is due to an abnormal composition of the 

original magnesian precipitate or to conceivable change during evaporation in the crucible with nitric acid remains to be determined. Until 

this is done the employment of this method of igniting is not to be 

recommended.

C. CONTAMINATION BY AND EEMOVAL OF BAEIUM, 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.

a A pink color of varying intensity almost invariably becomes apparent as the mass approaches dryness, 

giving a most delicate test for the traces of manganese which always escape precipitation by ammonium 

sulphide or bromine.
MAGNESIUM. 127

b. CALCIUM.

Calcium, however, is probably never absent, and has to be estimated 

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 the true figure for magnesia. The alcoholic filtrate is to be 

evaporated, ignited to destroy organic matter, and tested for manganese, as under c below.

/?. 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 an'alysis, 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 now and then happens that a little 

fiocculent matter fails to dissolve. This is to be removed, ignited, 

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, 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 twelve hours, if necessary. Almost 

invariably a small precipitate shows itself, which, if fine grained and 

nona.dherent to the glass, may be regarded as pure calcium oxalate; 

otherwise it contains or may largely consist of magnesium oxalate. 

It is in that case 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 treat-
128 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

ment 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 proportion 

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 solusolution. 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 

remove all traces of chlorine, and united with the small solution above 

mentioned. The manganese is now determined colorimetrically, as in 

9. C. b, page 117, 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 114.

D. LIABILITY TO ERROR IN THE AVERAGE MAGNESIUM DETERMINATION.

Experience has shown that the majority of analysts are pretty sure 

to make a very serious plus error in determining moderate amounts 

of magnesia, such as are found in limestones and Portland cements. 

The 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.

12. TITANIUM. 

A. COLORIMETRIC DETERMINATION WITH HYDROGEN PEROXIDE.

a. PRINCIPLE OF THE METHOD (WELLER's) a AND THE CONDITIONS THAT AFFECT IT.

The method consists in comparing the color of a known bulk of solution to be tested with that of a standard solution of titanium 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 bleacha Ber. Deutsch. chem. Gesell., vol. 15,1882, p. 2593.
TITANIUM. 129

ing the yellow color/ hence care should be exercised as to the character of the peroxide, of which the commercial brands often contain 

fluorine. (For method of testing see page 40.) For the same reason 

the peroxide should be free from appreciable traces of phosphoric 

acid. (See e. 7-, p. 134.) The " perhydrol" of Merck is a most excellent 

preparation, though some commercial brands are satisfactory.

Dunnington 6 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 c 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. He 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. 133.)

In 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/ hut in a very recent paper H. E. Merwin-f maintains that alkali sulphates bleach markedly unless .much sulphuric 

acid is present. He gives the following data:

Sulphate

(grams).

3

6

Acid

(cm.3).

0.5

2.0

8.0

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 (y, p. 109) in amounts up to or exceeding 6 grams, he concludes, perhaps without sufficient reason, that all 

titanium determinations hitherto made by colorimetry are too low.

oHillebrand, 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. 

6 Jour. Am. Chem. Soc., vol. 13,1891, p. 210. 

c Chem. Zeitung, 1907, p. 263. 

d Zeltschr. anal. Chemie, vol. 46,1907, p. 277. 

« Jour. Am. Chem. Soc., vol. 30,1907, p. 219. 

/ Am. Jour. Sci., 4th sen, vol. 28,1909,.p. 119.

20091 Bull. 422 10 9
130 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Merwin's statements as to the bleaching effect of alkali sulphates 

(p. 191) and the counteracting effect of a sufficiency of sulphuric 

acid have been confirmed.

Merwin has 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.

b. PREPARATION OF THE STANDARD.

Potassium titanium fluoride, K,TiF6 , best serves 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 the standard sulphate solution 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. Two 50 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 weights found the 

strength of the standard is calculated and the result affixed to the 

bottle containing it. The stopper of the bottle should be coated 

with vaseline and the needed quantities of solution should be withdrawn by a pipette, never poured. In1 a solution so prepared there 

is not enough alkali sulphate to" weaken the color when peroxidized.

The stock solution so prepared is made to hold as nearly as may be 

1 centigram of Ti02 in 10 cm.3 Of this 5 cm.3 (or 10 if the larger 

amount is needed) are mixed with a sufficiency of hydrogen peroxide (2 cm.3 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 0.1 mg. of Ti02 .

C. THE TEST SOLUTION.

(1) Titanium can be determined, as a rule, most conveniently in 

the solution which has served for the titration of total iron (7-, p. 109). 

The direct use of this solution involves, however, for accurate work, 

corrections for its iron and alkali sulphate contents, as given later,
TITANIUM. 131

The effect of the latter can be overcome by an ammonia precipitation, 

moderate washing of the precipitate, and its solution in 5 per cent 

sulphuric acid.

(2) The error accompanying 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,6 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 low, "as already stated (p. 128), 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) Both the iron and alkali effects are excluded if the determination is made on the precipitate of Ti02 and Zr02 obtained as in B. b 

(p. 136). Here, however, errors have to be considered that are 

incident to prior fusion with sodium, hydroxide in a silver crucible 

and to possible incomplete precipitation of the titanium by one or 

another of the methods outlined on page 137.

(4) At times the -residue from an alkali carbonate fusion of the 

rock powder, which has been obtained as in 13. A (p. 138), and from 

which zirconium has been separated (14. A, p. 141) can be used conveniently. The prior removal of zirconium is called for because for 

the titanium determination there must be far more sulphuric acid 

present than is JDermissible for the .zirconium separation. However, the conditions here are such as to involve corrections for the 

iron of the rock, and for phosphoric acid and alkali sulphate also, 

if the latter had been added in considerable amounts for the precipitation of zirconium. In the majority of cases the amounts of sodium 

phosphate needed for two precipitations of the zirconium should 

produce no sensible error in the value found for the titanium. The 

precaution should never be omitted, when determining the titanium

«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.

t> 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 thoroughly fused with sodium carbonate, leached with water, fused with potassium pyrosulphate,dissolvedindilutesulphuric acid, filtered, and the filtrate added to the main one. The 

will now be chiefly barium sulphate, for the further treatment of which see 13. A, pagte 135-
132 ANALYSIS OF SILICATE AND CABBONATE ROCKS.

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 decide which of the 

above courses 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. It is much to be desired, however, that 

the exact conditions for securing the best results in presence of disturbing agents should be further studied, in order that more positive 

directions may be formulated than is now possible.

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,

d. THE COLOR COMPARISON.

The sulphate solution containing the titanium, having been evaporated, if necessary, to less than 100 cm. 3 , is to be fully oxidized 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. One of the rectangular 

glasses (fig. 5, p. 34) being filled with the solution to be tested, 10 cm. 3 

of the diluted standard are run into the other from a burette, and 

water 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 Schreiner (figs. 6-7, pp. 35,37), or the 

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 sharply estimated 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. TiO2 per cubic centimeter.
TITANIUM. 133 

6. CORRECTION FOR THE COLOR OF FERRIC 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 allowing for the coloring power of the iron in the test solution. 

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 Fe203 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 Fe3 03 . The following methods are 

probably more exact with high iron percentages, though not so expeditious : v

/?. By addition of iron to the standard. W. A. Noyes 0 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. 35-37), though practicable with Nessler tubes. In using the 

Survey colorimeter (fig. 5, p. 34), 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. 6 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. 

The amount to be used per cubic centimeter of diluent is calculated 

as follows: Let A be the number of cubic centimeters of the test solution, a of the standard used, 1) of the water needed to dilute the 

standard in the preliminary test, p the weight of iron in terms of 

Fe2O3 in A, and x the weight of iron in terms of Fe2O3 to be contained 

in each cubic centimeter of water used for diluting the standard in

the final tests. Then x = TT- p. It will of course be understood

« Jour. Anal and Appl. Chem., vol. 5,1891, p. 39.

b Ferric-ammonium alum is most convenient for the purpose, but its use Introduces an error due to the 

bleaching effect of the ammonium sulphate it contains. The amount of this Is, however, so small as to give 

rise to an error that is probably negligible.
134 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

that a new test solution requires the preparation of a new iron solution with which to dilute the standard.

f. By the use of phosphoric .add. 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, a in-the paper already cited on page 129, and J. H. 

Walton, jr., b 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. CORRECTION FOR THE EFFECT OP 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 7-; or Merwin's c corrections 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 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."

B. 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, among the few that have been thoroughly

a Chem. Zeitung, 1907, p. 263.

6 Jour. Am. Chem. Soc., vol. 29,1907, p. 481.

e Am. Jour. Sci., 4th ser., vol. 28,1909, p. 119.
TITANIUM. 135

tested that of Doctor Gooch0 is unequaled. With one or two minor 

modifications introduced by Dr. T. M. Chatard, 6 it is as follows:.

Any solution of the rock freed from silica can be used, and the first 

step is to remove the iron. This is best done, after adding tartaric 

acid and reducing the iron by means of hydrogen sulphide to the ferrous condition, by rendering the solution ammoniacal and introducing 

more hydrogen sulphide. If the iron is -not thus reduced before precipitation,, titanium will be in part thrown down also. 0 The amount 

of tartaric acid is to be gaged according to the combined weights of 

the oxides to be held by it in solution, and three times this weight is 

ample. After removing the iron s'ulphide by filtration ^little washing 

suffices; because of the relatively small amount of titanium commonly 

present the tartaric acid is destroyed as follows:

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 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 earlier removed, 

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, and leached 

with water t6 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

a Proc. Am. Acad. Arts Sci., n. s., vol. 12, p. 435; Bull. U. S. Geol. Survey No. 27, 1880, p. 10; Chem. 

News,' vol. 52, 1885, pp. 55, 68.

b 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.

c Cathrein, A. Zeitschr. 1. Kryst., vol. 6,1882, p. 243; vol. 7,1883, p. 250.
136 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 7 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.

/?. Gooch's method not directly applicable to rocks containing zirconium. Prior to the adoption of the colorimetric method, Doctor 

Gooch's was invariably used in this laboratory. Occasional inability 

to secure clean and complete precipitation by it was experienced, 

especially with a certain series of rocks rather poor in titanium. Long' 

research 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 Zr02 , 

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 (14. A,

p. 141), no difficulty was experienced in precipitating all the titanium 

with the usual ease.

b. METHODS OP DITTRICH AND FREUND.

In recent papers M. Dittrich and S. Freund a have proposed the 

several methods below, involving no new principles, by which they 

separate completely, so they claim titanium and zirconium from 

iron as well as manganese. These methods, except, perhaps, the 

third, presuppose, in rock analysis, the prior separation of aluminum 

and phosphorus by fusion with sodium hydroxide in a silver crucible 

(c, p. 112). Attention has been directed (8. C. b, p. Ill) to the error 

resulting from attempting to separate aluminum from titanium by 

either fused or dissolved sodium hydroxide in absence of appreciable

a. Zeitschr. anorg. Chemie, vol. 56, 1907, pp. 337, 348.
TITANIUM. 137

amounts of iron and to the fact that when iron is present in some 

amount this error does not seem to arise.

If such a fusion has been made the insoluble residue may be dissolved in sulphuric or hydrochloric acid, according to the method 

that is to be followed, or a bisulphate fusion of the ignited oxides 

may be employed if alumina is absent. Care must be taken to remove 

all silver derived from the silver crucible by the alkali fusion.

(1) Titanium and zirconium are precipitated free from iron, provided this is kept wholly in the ferrous state by boiling with sodium 

acetate under carefully prescribed conditions.

(2) Under proper conditions titanium and zirconium are also precipitated free from iron by sodium thiosulphate.

(3) Titanium and zirconium are separated from all but a trace of 

iron by boiling with sulphurous acid in a stream of carbon dioxide 

after prior reduction of the iron in hydrochloric acid solution and 

careful neutralization of the acid by ammonia. This is merely a 

modification of the method of Baskerville a to maintain (as in 4 

below) complete reduction of the iron. BaskervihVs method, as 

applied at one time by me to the analysis of titaniferous iron ores, 

yielded after one precipitation about 0.0025 gram of Fe203 in a weight 

of 0.08 to 0.10 gram Ti02 .

(4) The authors regard the following method as relatively the 

simplest: 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 separately 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 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 (f, p. 105); and titanium and zirconium are 

determined, the one colorimetrically, the other by difference. In 

view of the very small amounts of zirconium in rocks, and also of the

a Jour. Am. Chein. Soc., vol. 16,1894, p. 427.
138 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

author's analytical data, it is far preferable to find it directly (14. A, 

p. 141) instead of by difference. 0

In the nitrate from the oxides Dittrich and Freund precipitate iron 

and manganese by ammonia and hydrogen peroxide, and then, presumably as in earlier directions of Dittrich, determine the manganese 

in this precipitate (after getting the whole into solution) by digesting 

the sulphate solution with hydrogen peroxide, filtering, and repeating the precipitation.

C. SUPERIORITY OF THE COLORIMETRIC AND GOOCH METHODS OVER

THE OLDER ONES.

In view of the good results obtainable by the colorimeter method in. 

most cases, and by the Gooch method in the absence of zirconium, it is 

inexplicable that the old method of precipitation by many hours' 

boiling in a nearly neutral sulphate solution in presence of sulphurous 

acid should still find adherents in any part of the world.

13. BARIUM (ZIRCONIUM, RARE EARTHS, TOTAL SULPHUR, CHROMIUM).

These five constituents can with great economy of time and labor 

be determined 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 (18. C, 

p. 150). It has been said above (10. C, p. 120) 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 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 sulphurfree sodium carbonate and an amount of niter insufficient to injure 

the crucible (one-half 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. 32) 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

a The new 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.
BARIUM. 139

melt in water, to which a drop or two of methyl or eth/y 1 alcohcl has 

been added for the purpose of reducing manganate, the solution is 

filtered 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.

The filtrate contains, after reduction of the manganate by alcohol, 

silica, alumina, and all the other acid constituents except titanium, 

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," 24. C, 

p. 198, and "Chromium/' 17.B, p. 147.

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 amount if barium 

only is sought). 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 Erlenrneyer 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 14. A, p. 141, and 15. A, p. 143.)

The ignited residue last obtained is 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
140 ANALYSIS OP SILICATE AND CARBONATE ROCKS.

chlorides and to apply to the mixture the ammonium-chromate 

method of separation (10. D, p. 120).

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.

The procedure outlined in the foregoing paragraphs for the estimation of calcium, strontium, and barium in silicate rocks is the one 

which long experience has shown to be best adapted for securing the 

most satisfactory results with a minimum expenditure of time.0 

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 6 method 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 zirconium and sulphur are not to be looked for, the simplest 

procedure is to decompose the powder by sulphuric and hydrofluoric 

acids (see c. 2, p. 131, under "Titanium"), and to complete the purification of the barium sulphate thus obtained in the manner described 

in the fourth paragraph of A above.

14. ZIRCONIUM.

This element is rarely 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. It may in most exceptional cases 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.

a For details consult Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 16,1894, p. 83; Chem. News, vol. 69, 

1894, p. 147. 

b Am. Jour. Sci., 3d ser., vol. 43,1892, p. 521.
ZIRCONIUM. 141

A. AUTHOR'S METHOD.

For its detection and estimation in such cases, or whenever a search 

for it seems called for, the following procedure, based on a method 

used by G. H. Bailey,a 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 preliminary treatment of the rock powder has been fully given 

under "Barium" (13. A, p. 138), where the separation from barium 

has been described and also the concentration of the zirconia in a 

small amount of very dilute sulphuric solution. This should probably 

not contain much above 1 per cent of sulphuric acid, though the actually permissible limit has not been established. To the solution, 

which should be in a small flask, is now added hydrogen peroxide to 

oxidize the titanium, and then a few drops of a soluble orthophosphate 

solution. The flask is set aside in the. cold for twenty-four to fortyeight hours. If the color 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, 

which at this stage is not always pure.6 (For the treatment of the nitrate see "Rare-earthmetals," 15. A,p. 143.) No matter how small or 

insignificant, it is collected on a filter, ignited, fused with sodium carbonate, leached with water, the filter again ignited, fused with very 

little potassium or sodium pyrosulphate, brought into solution in hot 

water with a few drops of dilute sulphuric acid, poured into a flask or 

beaker of about 20 cm.3 capacity, a few drops of hydrogen peroxide 

and of sodium phosphate are added, and the flask set aside. Titanium 

is now almost never present, and the zirconium soon appears as a 

colorless flocculent precipitate, which can be collected and weighed as 

phosphate. For the small amounts usually met with it is safe to 

assume that it contains 50 per cent of .Zr02 (51.8 by theory). If the 

amount is rather large, it may be safer to 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 amicrochemical 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 milligram of dioxide and with proper 

care for as small an amount as 0.3 milligram (Dr. H. N. Stokes). No 

element other than thorium is ever likely to contaminate the zirconium thus precipitated.

"Jour. Chem. Soc., vol. 49,1886, pp. 149, 481.

 !> I f the rock contains much iron the precipitate may contain or consist largely of a ferric phosphate. Titanium may also be precipitated to some extent as a phosphate. The degree of such precipitation will be 

greater as the acidity of the solution is less.
.142 ANALYSIS OF SILICATE AND CAEBONATE BOOKS.

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, Zr205 , or Zr03 .° 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 phos,- 

phoric acid would certainly be a great improvement on the method 

described above.

Were it not for the necessity of precipitating the zirconium in a 

weakly instead of strongly acid solution, its separation could be made 

in the same portion in which the titanium is colorimetrically determined.

B. OTHER METHODS.

G. Streit and B. Franz b claim 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 from time to time recommended, but without any 

data showing its value. The single separation made by Streit and 

Franz was far from perfect.

J. T. Davis c separated zirconium sharply from aluminum, but not 

from iron, by precipitation as an oxyiodate in a boiling neutralized 

solution of chlorides, but the method is hardly applicable for rock 

analysis.

C. Baskerville rf has proposed a method for the separation of zirconium from iron and aluminum similar to his method for the separation of titanium from those elements (12. B.b. 3, p. 137). 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 (b. 3, p. 137), 

and have also devised a method for the direct separation of zirconium from titanium by precipitation with ammonium salicylate/

a Chem. News, vol. 60,1889, p. 6. 

b Jour. f. prakt. Chemie, vol. 108,1869, p. 65. 

. c Am. Chem. Jour., vol. 11,1889, p. 27.

d Jour. Am. Chem. Soc., vol. 16,1894, p. 475; Chem. News, vol. 70,1894, p. 57. 

eZeitschr. anorg. Chemie, vol. 56,1907, p. 344.
EAEE-EAETH METALS. 143 

15.' RARE-EARTH METALS OTHER THAN ZIRCONIUM.

For the cases in which it may be necessary, to look for rare earths 

other than zirconia, the following procedures will prove satisfactory 

and not at all difficult: 0

A. USUAL METHOD.

The filtrate from the zirconium phosphate (14. A, p. 141) or, if zirconium is not to be determined, the earlier solution (13. A, p. 138) 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) 

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 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 

Irydrochlpric 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.

The amounts are too small to permit separation into further groups, 

but the presence of cerium can be readily shown if a strong yellow 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 zircooM. Dittrich (Ber. Deutsch. chem. Gesell., vol. 41, 1908, p. 4373) calls attention to the fact that ferric, 

aluminum, and chromic, as well as urariic, 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 the above 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,
144 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

nium 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 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.

16. PHOSPHORUS.

It is sometimes possible to extract all phosphorus from a«rock by 

simple digestion with nitric acid, but quite as often, if not oftener, 

this fails; 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 secure accurate results.

A. 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.0

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, 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.

a The method as originally described in Washington's Manual of the Chemical Analysis of Rocks has 

been modified by Doctor Washington and myself independently to the extent of doing away with the 

filtration of the precipitate of silicofluorides and fluorides before proceeding with the evaporation.
PHOSPHORUS. 145

C, SUBSEQUENT TREATMENT.

Add to the solution obtained in a or b ammonium nitrate and 

molybdate solution as ordinarily prescribed.

The turbidity often observed on' dissolving the precipitated and 

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 re-fused with 

sodium carbonate, extracted with water, and the filtrate otherwise 

treated as above, in order to secure the phosphorus in it.

According to F. A. Gooch and M. Austin,0 in order to secure a 

magnesium-ammonium phosphate of normal composition, the procedure at this point should be as follows: To the phosphate solution, 

containing not more than 5 to 10 per cent of ammonium chloride and 

a slight excess of magnesia mixture, a little ammonia is added, and 

the precipitate is washed in due time with weak ammonia water. In

general, however, as these conditions can seldom be fulfilled, they 

recommend to decant the supernatant liquid through the filter which 

is later to receive the precipitate, to dissolve this in as little hydrochloric acid as possible, to reprecipitate by dilute ammonia without 

further addition of magnesia mixture, and to wash finally with weakly 

ammoniacal water. Excess of ammonia, of ammonium salts, and of 

precipitant are all objectionable. In rock analysis the second precipitation will seldom be necessary. (For ignition, etc., of the precipitate, see this subject under "Magnesium," 11. B. a, p. 125.)

B. PROCEDURE WHEN MATERIAL IS SCANTY.

The following procedure admits of determining in the same portion, 

besides phosphorus, barium, iron, vanadium, chromium, and titanium, 

the last two either colorimetrically or gravimetrically, and is in large 

part extracted from a paper by Dr. T. M. Chatard. b

Silica is removed by hydrofluoric and sulphuric acids, excess of fluorine expelled, 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 A1203 , P2O5 , Cr2 03 , Fe2 03 , and Ti02 are dissolved in 

hot hydrochloric acid and filtered into a large platinum crucible, the 

filter burned and added, the solution evaporated to pastiness, a little

a Am. Jour. Sci., 4th ser., vol. 7,1899, p. 187; Zeitschr. anorg. Chemie, vol. 20,1899, p. 121; Chcm. News, 

vol. 79,1899, pp. 233, 244, 255.

6 Am. Chem. Jour., vol. 13,1891, p. 106; Bull. U. S. Geol. Survey No. 78,1891, p. 87; Cbem. News, vol. 

63,1891, p. 267.

20091 Bull. 422 10 10
146 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 washed with very dilute 

sodium-carbonate solution. In the residue iron and titanium can be 

determined by the methods already described/ In the filtrate chromium can be determined colorimetrically if present in sufficient 

amount to give a pronounced color. (See 17. B, p. 147.) 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 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 nitrate from the aluminum and phosphorus, containing chromium and vanadium, can be 

treated as detailed in the following sections. .

17. CHROMIUM.

If vanadium is absent, or nearly so, as is apt to be the case 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 of vanadium, and it is best generally to assume its 

presence, the colorimetric method should always be adopted.

A. GRAVIMETRIC 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 a by dissolving in nitric acid, evaporating nearly to dryness, and 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, acid sodium carbonate 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.

a Bull. Soc. chimique, n. s., vol. 42,1884, p. 291; Chem. News, vol. 50,1885, p. 18. 
CHROMIUM. 147

The separation of aluminum from chromium by hydrogen peroxide in ammoniacal solution, as recommended by P. Jannasch and 

E. v. Cloedt,a has been shown by C. Friedheim and E. BriihP to be 

valueless.

B. COLORIMETRIC METHOD. .

For this very accurate and by. far the quickest method 0 for determining chromium in rocks and ores 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, 

under "Phosphorus," B, p. 145) 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 corresponds to 0.1 or 0.2 mg. of chromic oxide (Cr2O3 ), 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 figure given.

/?. 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 exactly measured. 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" (18. C, p. 150); 

otherwise it may be difficult or impossible, because of the large 

amount of alkali carbonate present, to obtain a filtrate of sufficiently 

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 temperature 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, is not. to be ascribed to chromium.

f. Comparison of colors. The final solution is transferred to a 

graduated flask of such size that its color shall be weaker than that 

of the standard chromium solution. Definite amounts of the latter

nZeitschr. anorg. Chemie, vol. 10, 1895, p. 402.

b Zeitschr. anal. Cheinie, vol. 38, 1899, p. 681.

c 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. T'yds. voor 

Phiirm., Chem. en Tox., 1889) for the estimation of chromium in foodstuffs. '
148 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

are then diluted with water from a burette until of the same strength 

as the test solution, exactly as described on page 34. 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.0

C. A FEW 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.

Percentage determinations of chromium (CV203).

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.

18. VANADIUM (CHROMIUM) AND MOLYBDENUM. 

A. DISTRIBUTION OF VANADIUM AND MOLYBDENUM.

The wide distribution of vanadium throughout the earth's crust 

has in recent years been clearly established (see pp. 20-21), not only 

in ores and in coals, but in clays, limestones, sandstones, and igneous rocks. 5 I have shown 0 that vanadium occurs in appreciable 

amounts in the more basic igneous and metamorphic rocks up to

a D. W. Horn has studied the "Variable sensitiveness in the colorimetry of chromium." See Am. Chern. 

Jour., vol. 35, 1906, p. 253; vol. 36, 1906, p. 196.

6 Hillebrand, W. F., Distribution and quantitative occurrence of vanadium arid 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.

cLoc. cit.
VANADIUM AND MOLYBDENUM. 149

0.08 per cent or more of V2 03 , but that it seems to be absent or 

nearly so from the highly siliceous ones. Some of their ferric aluminous silicate constituents carry still higher percentages up to 0.13 

per cent V2 03 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 

le:ss 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 8. B. b, p. 

109; 19. D. c. ft p. 166).

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 V2 03 and not as V2 05 .

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 (V2 05 ), but my work on certain remarkable 

vanadiferous sandstones a of western Colorado, in which it unquestionably occurs as trivalent vanadium (V2 03 ), has led to a decided 

unsettling of this view. It is proper to recall that C. Czudnowicz, 6 

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 

such ores to be in a lower condition of oxidation (V2 03 ). 0. Lindemann's c contrary conclusion with regard to certain iron ores, because 

the vanadium was extracted as V2 05 by sodium-carbonate fusion 

without niter, is not valid, since this would probably be the case even 

if it existed in the ore as V2 03 .

« Hillebrancl, W. F., and Ransome, F. L., Am. Jour. Sci., 4th sen, vol. 10,1900, p. 120; Bull. U. S. Gcol. 

Survey No. 2f,2, 1905, p. 9. 

'' Pogg. Ann., vol. 120,1863, p. 20. 

c Dissertation, Jena, 1878, through Zeitschr. anal. Chcinie, vol. IS, 1879, p. 99.
150 ANALYSIS 0.1? SILICATE AND CABBONATE ROCKS.

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 

(17. B, p. 147), the latter volumetrically, in the same solution.*1

Five grams of the rock are 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. 6 The aqueous extract is next nearly neutralized by nitric acid, the amount to be used having been conveniently ascertained by a blank test with exactly 20.grams of sodium 

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 1-arge. 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 estimated 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 

resulting from the decomposition of the mercurous nitrate. Precipitating in a slightly alkaline instead of a neutral solution renders 

the addition of precipitated mercuric oxide unnecessary for correcting 

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

a 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. 

t> Am. Ghem. Jour., vol. 8,1886, p. 437.
VANADIUM AND MOLYBDENUM. 151

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 (17. B, p. 147). 

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. a If the color of the precipitate indicates 

absence of arsenic the filter with its contents is carefully ignited 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 a beautiful blue color is proof of the presence of 

molybdenum.

The filtrate, in bulk from 25 cm.3 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 ing. of 

V2 05 per cubic centimeter, as calculated from the iron strength of the 

permanganate, one molecule of V2 05 being indicated for each one of 

Fe2 03 . 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, b 

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

b. CONFIRMATORY 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

a From a sulphuric solution the separation of platinum and molybdenum by hydrogen sulphide is 

much more rapid and satisfactory than from a hydrochloric solution.

b The direct use of a solution of sulphur dioxide or of an alkali sulphite is inadmissible unless these have 

been freshly prepared, since 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 traces of sulphur dioxide is said to be more effectively accomplished 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. Phann., vol. 240,1887, p. 23; Zeitsehr. anal. Chemie 

vol. 32,1893, p. 225).
152 ANALYSIS OF SILICATE AND CARBONATE ROCKS."

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 OP THE METHOD IN PRESENCE OP RELATIVELY MUCH CHROMIUM.

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 excess of permanganate, but in a 

hot and especially a boiling solution the oxidation of the chromium 

itself takes place so rapidly that a very large excess of the reagent

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. Ridsdalea 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

a Jour. Chem. Soc., vol. 7,1888, p. 73.
VANADIUM AND MOLYBDENUM.

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

0

7

Chromic 

oxide.

Milligrams

1

1

1.5

2

3

3

3.5

Vanadium 

peutoxide.

Milligrams

9.37

.94

5.25

5. 02

4.08

5. 02

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

11

1-2

13

14

15

Chromic 

oxide.

Milligrams

3.5

0

0

0

10

10

10

25

87.5

Vanadium 

pentoxide.

Milligrams

18.74

5.0

4.08

5. 02

5.02

23. 52

40. 85

23.52

23. 52

Vanadium 

pentoxide 

found.

Milligrams

18. 97

0.1

' 4.78

5.58

5.58

23.81

23.71

40.98

47.20

23. 05

23.75

23.71

Error.

Milligram

+0.23

+ .50

+ .10

- .04

- .04

+ .29

+ .19

+ .13

7+ .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.

10

17

18

19

20

21

Chromic 

oxide.

Milligrams.

20

20

20

30

30

02

Vanadium 

pentoxide.

Milligrams.

, 0.94

1.87

18. 74

1.87

1.87

'40.85

Vanadium pentoxide

found.

Uncorrected.

Milligrams.

1.59

2.09

2.39

2.59

19.4

19.3

19.3

2.99

2.79

2.79

2.09

2. 09

2.09

2.89

2.89

2.79

48. 00

Corrected

Milligrams.

0.99

2.09

1..79

1.99

18.73

18.03

18.03

2.14

1.94

1.94

1.84

1.84

1.79

2.09

2.09

1.99

47. 00

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.3

50 tolOOcrn.3

50 to 100 cm.3

About 1.00 cm.3

200cin.3

200 cm3 .

In 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 a 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

a Inaugural Dissertation, Rostock, 1894.
154 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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. COLORIMETKIC METHOD FOR VANADIUM.

In the paper already cited a the possibility of a colorimetric method 

for vanadium, based on its behavior toward hydrogen peroxide, was 

suggested. L. Maillard6 has since developed such a method, though 

it has not been tested in the Survey laboratory.

19. FERROUS IRON.

A. OXIDATION OF FERROUS IRON IN MINERALS BY GRINDING PREPARATION OF SAMPLE.

< As already pointed out under 3. C (p. 52), the effect of grinding 

in air is to lower the FeO and increase the Fe2O3 in a mineral powder 

that contains FeO. c 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, but 

not enough so to permit the substitution in general practice of one 

of these media for air. Grinding in a wholly inert atmosphere, such 

as nitrogen (not carbon dioxide, which I find seems to form carbonates) 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

o 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.

b Bull. Soc. chim., vol. 23, 1900, p. 559.

cCf. Mauzelius, R., Sveriges Geol. Undersokning, 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.
FERROUS IRON". 155

in promoting oxidation, but probably local heating as the grains are 

fractured and rubbed under the pestle. The effect seems to be 

iniluenced 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,0 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 

sis'.e of grain of bulk

sample.

Basalt, 0.08mm...........

Diabasic norite or gabbro..

Altered basaltic greenstone, 0.18 mm.

Quartz diorite, 0.11 mrn. ..

Altered basaltic rock. 0.18 

mm.

Conditions of grinding.

No.

la 

Ib

1C

Id 

2a 

2b 

2c 

2d 

2o 

3a 

3b

3c 

3d

3e 

4a 

4b 

5a

5b 

Oa 

6b 

7a 

7b 

7c 

7d 

8a 

81) 

8c 

Sd

Grams.

Unground.

4 

4

4 

Unground. 

4 

4 

4 

4 

Unground. 

4

4 4-

4' 

Unground. 

4 

Ungrouud.

4 

Unground. 

4 

Unground. 

4 

4 

4 

Unground. 

4 

4 

' (?)

Time 

(minutes).

30 

80

120

 120 

120 

140 

120

20

00 

30

120

CO

120

120

120 

SO 

120

120 

SO 

(?)

Medium.

Abs. ale. 

Air.

Air.

Abs. ale.

ecu.

H2 0. 

Air.

Abs. ale.

ecu.

Air. 

Air.

Air.

Air.

Air.

Abs. ale. 

Air. 

Air.

Abs. ale. 

Air. 

Air.

FeO (percent).

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. 04 

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

The experiments carried out by me show several things: (1) Although comparatively brief grinding (fifteen to thirty minutes) in 

air and long grinding under alcohol does 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

a Jour. Am. Chern. Soc., vol. 30, 1908, p. 1120; Chem. News, vol. 98, 1908, pp. 205, 215.
156 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

to be a little more effective in preventing oxidation than water. It 

has the further advantage that it can be more quickly removed 

afterwards. (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. (6). 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 oxidizable 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 

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
FERROUS IKON. 157

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. 50) serves as the starting point. If trial shows 

that gentle boiling of it for twenty 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. ft, f) will be less applied 

than the one (D. d. or) 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 (5. B, p. 64).

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
158 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

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 hav.e 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. Wiilfing a 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 Koninck6 a 

good many years ago, but remained unknown to the chemical world 

by reason of its obscure medium of publication until rediscovered by 

Dr. H. N. Stokes in this laboratory, during an investigation on the 

action of ferric salts on pyrite and other sulphides. 0 That oxidation 

of the sulphide and reduction of the ferric salt hereby takes place was 

recognized by J. H. L. Vogt/ 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 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. «, p. 165) 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.

oBer. Deutsch. chem. Gesell., vol. 32,1899, p. 2217, footnote.

&Arm. Soc. g<5ol. Belgique, vol. 10, 1882-83, p. 101; Zeitschr. anorg. Chemie, vol. 26, 1901, p. 123. .

c Bull. U. S. Geol. Survey No. 186,1901; Am. Jour. Sci., 4th ser., vol. 12,1901, p. 414.

d Zeitschr. prakt. .Geol., 1899, pp. 250-251.
FERROUS IRON. 159

because of the greater surface of pjrite 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 six 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. 0

Of course carbonaceous matter will, under the conditions of the 

Mitscherlich method, likewise reduce sulphuric acid and cause the 

determination of ferrous iron to be faulty.

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 some-

<» 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 Hillebrand, W. F., 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.
160 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

times 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.

/?. 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 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 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 a 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,6 fully shows. The material used was the oxide of

, C., Zeitschr. angew. Chemie, 1893, p. 274; Zeitschr. anal. Chemie, vol. 33, 1894, p. 582. 

6 Bull. U. S. Geol. Survey No. 78, 1891, p. 50; Chem. News, vol. 64, 1891, p. 232. ,
FERROUS IRON. 161

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 oil. 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 HYDROFLUORIC ACID METHOD.

a. PRINCIPLE OF THE METHOD.

This 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 almost exclusively used in the 

Survey laboratories. The form of apparatus employed until recently 

is the original one devised by J. P. Coolie" (fig. 21, p. 169). This 

does not permit driving off the superfluous hydrofluoric acid, as 

does that of Tread well (fig. 22, p. 170) to some extent, which latter 

ought therefore, for a reason developed below, to afford slightly 

lower and more accurate results, other conditions being equal. But 

the method as ordinarily carried out is subject to two defects of opposite sign but unequal value, the second and greater of which has 

remained unsuspected until recently. b

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. 3 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 naturally 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.

a Am. Jour. Sci., 2d ser., vol. 44,1867, p. 347.

6 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= 

Fe3 F8+FeO+3H2 0+H202 . The experiments described on the following pages do not indicate such 

action, at least in presence of sulphuric acid.

20091 Bull. 422 10 11
162 ANALYSIS OF SILICATE AND CARBONATE HOCKS.

b. DEFECTS OF THE METHOD.

 a. Oxidizability of divalent manganese by permanganate in 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 explains the fact that in presence of hydrofluoric acid 

divalent manganese is readily oxidized by permanganate, whereby 

a sharp end reaction is rendered unattainable in 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 rapidly 

disappears, the more rapidly the greater the amount of hydrofluoric 

acid or of manganous salt present. The oxidizer 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. The 

decolorization due to this cause is hence 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.

E. Deussen,0 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, as shown by the 

fact that the addition of a drop or two of this 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 man 

ganous sulphate, and by the above-mentioned very evident partial 

reoxidation of the reduced manganese. This last, the oxidation of 

divalent manganese by permanganate in presence of hydrofluoric acid, 

can be effected with the greatest ease in entire absence of ferric iron.

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 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

a Zeitschr. anorg. Chemie, vol. 44,1905, p. 425. See also Monatsh. f. Ghemie, vol. 28,1907, p. 163.
FEBBOUS IBOF. 163

toward high results, .but in most cases the results were identical with 

those obtained in 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 titer. The 

personal factor enters here, G. Steiger having found slightly greater 

differences, but it is possible that they resulted from the titrating in 

more concentrated solutions, for with greater dilution 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 TreadwelPs apparatus accomplishes this, but, as 

the experiments show, its complete expulsion is unnecessary."

/?. Extreme oxidizability of divalent iron l)y free oxygen in 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 aci<J was present. An observation made by R. Peters, b 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 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 just 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.

o 11. B. Gage (Jour. Am. Chem. Soc., vol. 31,1909, p. 381) claims to overcome the harmful effect of free 

hydrofluoric acid by adding a solution of calcium phosphate immediately before titrating, thus forming 

calcium fluoride. His procedure in other respects follows closely that hereinafter described, and.was 

used by him in analyzing magnetite.

b Zeitschr. phys. Chemle, vol. 26,1898, p. 193,
164 ANALYSIS OF SILICATE AND CAKBONATE 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 or -the Tread well apparatus involves long contact 

of the mineral with the acids, and as the experiments last mertioned 

were favorable in their results, it seemed as if the simple method of 

J. H. Pratta 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. 3]

Time of 

boiling.

Minutes.

10

10

10

10

10

10

10

10

Permanganate 

used.

cm. 3

4.9

4.8

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 

boiling.

Minutes.

10

10

15

15

15

20

20

Permanganate 

used.

cm. 3

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 has been 

tested during the last two years in comparison with that of Cooke 

with favorable results, a few of which are shown in the table 

under A, page 155. It is the method now 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 or the Treadwell method. However, since the exigencies 

of the FeO determination are now known to demand a powder as

a Am. Jour. Sci., 3d ser., vol. 48,1894, p. 149.
FERROUS IRON. 165

coarse as possible, a longer treatment has to be given than was called 

for by the fine powders used by Pratt.

C. INFLUENCE OF SULPHIDES, VANADIUM, AND CARBONACEOUS MATTER ON THE DETERMINATION OF FERROUS IRON BY THE HYDROFLUORIC 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 readily recognized 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, since 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 24. C. b, p. 198, under "Sulphur").

In order to obtain quantitative data regarding the effect of pyrite 

on the ferrous-iron estimation by the hydrofluoric acid method the 

following tests were made: Part of a fine crystal of pyrite was rather 

finely powdered and boiled with dilute sulphuric acid, which extracted considerable ferrous iron, derived presumably from admixed 

or intergrown pyrrhotite, since 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 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.

Since, however, Dr. H. N. Stokes has found a that the oxidizing 

effect of ferric salts on pyrite and other sulphides is vastly greater than

a Bull. U. S. Geol. Survey No. 186,1901; Am. Jour. Sci., 4th ser., vol. 12,1901, p. 414.
166 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

seems to have been suspected (see p. 158), 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 10.02, 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. 

/?. Vanadium. If vanadium, when present, exists in the trivalent 

condition, it necessarily affects with an error varying with its amount 

the result of titration for ferrous iron. If the amount of vanadium is 

known, a correction can be applied as follows: One molecule of V2O3 

(150.8) in oxidizing to V205 requires as much oxygen as four molecules 

of FeO (288) when oxidized to Fe2O3 . The proportion, 150.8 : 288 : : 

V2O3 present : x, 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 at once evident from the following 

perhaps extreme example:

Found 2.50 per cent apparent FeO in a rock containing .13 per cent V203 .

Deduct .25 per cent FeO equivalent in its action on KMn04 to .13 V2 03 .

Leaving 2.25 per cent FeO corrected.

Found 5.00 per cent apparent total iron as Fe203 in the same rock.

Deduct .14 per cent Fe203 corresponding to .13 per cent V203 .

Leaving 4.86 per cent corrected total iron as Fe203 .

Deduct 2.50 per cent Fe203 equivalent to 2.25 per cent FeO.

Leaving 2.36 per cent Fe203 in the rock.

Failure to correct for the vanadium in both cases would have made 

the figures for FeO and Fe203 , respectively, 2.50 and 2.22 instead of 

2.25 and 2.36 as shown above.

f. Carbonaceous matter. As said before (c, p. 165), matter of 

organic origin other than graphitic carbon renders the results of the 

ferrous-iron determination altogether unreliable.
FEREOUS IRON. 167

d. THE METHOD IN ITS VARIOUS MODIFICATIONS.

a. According to Pratt (modified). One-half to 1 gram of the 

coarsest powder a 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 effervescence, 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 CH1.3 ) 

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 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 necessary or allowable. Then the crucible, still covered, is transferred with the tongs shown in fig. 1 (p. 30) to the titration dish,, containing, cold freshly boiled water (usually about 300 cm.8 ), 

and additional sulphuric acid, which is already under the burette, the 

contents of the crucible are quickly poured in with the rinsings, and 

the permanganate is run in as rapidly as possible with constant but 

gentle stirring till the first pink blush appears throughout the whole 

liquid for at least a couple of seconds. With little iron the color will 

last some time, but with increasing amounts, as also with increasing' 

amounts of hydrofluoric acid, it fades out with ever greater rapidity. 

In making a duplicate it is well to run in a little less than the full 

amount of permanganate before introducing the iron solution.

The method should first be tested 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

<» The fineness of grinding will depend on the nature of the rock. Most granitic rocks require but 

moderately fine grinding, those high in ferruginous and refractory minerals generally, as tourmaline, need 

to be very fine.
168 ANALYSIS OP SILICATE AND CARBONATE ROCKS.

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 a 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 undecomppsed portion are certainly different from those in the part dissolved. 

 ; /?. According to Cooke. b The apparatus, as shown in fig. 21, 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 &, p. 108.)

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 

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 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.

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

a Am. Jour. Sci., 3d set., vol. 48,1894, p. 150. 

6 Am. Jour. Sci., 2d ser., vol. 44,1867, p. 347.
FERROUS IRON. 169

can longer be felt or when experience tells that decomposition must 

be complete, the gas current is again turned on, the lamp extinguished, 

and the water flow increased to the capacity of the outlet tube from 

the bath. In fifteen minutes the crucible and contents should be 

cool. The rod is then removed and placed in the titration vessel 

containing freshly boiled water (usually about 300 cm.3 ) and addiFIG. 21. Cooke's apparatus for ferrous-iron determination.

tional sulphuric acid, which is already under the burette, the contents 

of the crucible quickly follow with the rinsings, and the titration is 

made as in a. Until the operator has become experienced a duplicate determination should always 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.
170 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

Instead of allowing the crucible to cool in a current of carbon 

dioxide, it may be at once transferred 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.

f. According to TreadweTL.^ The specially ground powder in a dish 

or capacious crucible is placed, after stirring up with 5 or 10 cm.3 of 

dilute sulphuric acid, on a support of glass or platinum a in the lead 

box C, which in turn is supported in a paraffin bath B, fig. 22. After 

covering the box with its leaden cover there is introduced through 

A a rapid current of carbon dioxide ° until the air is displaced.

CO,

FIG. 22. Treadwell's apparatus for ferrous-iron determination. B, Paraffin bath; C, lead box with 

closely fitting cover of same material; a, platinum dish resting on glass support.

The cover is then quickly raised. Concentrated hydrofluoric acid 

(5 to 7 cm.3 ) is added to the dish and the cover is replaced without 

interrupting the current. The contents of the dish are stirred with a 

platinum rod through the opening directly over the dish. The bath 

has meanwhile been brought to about 100°, a temperature which is 

maintained with occasional stirring for from one-half to one hour or 

more, according to the resisting quality of the powder. Then the 

temperature is raised to about 120° for an hour to expel most of the 

hydrofluoric acid. The flame is then extinguished and the solution 

allowed to cool as quickly as may be, still in the gas current. When 

cool, the contents of the dish are titrated, as in a.

Although the chief object of this method is to remove the excess of 

hydrofluoric acid and thus avoid one source of error in titration, it 

may be said, so far as my own limited experience with it goes, .that 

the expulsion is by no means perfect at 120° and that the long 

duration of the experiment renders it likely that lower results will be

o See footnote b, p. 108.
ALKALIES. . 171

obtained than with the variations of the hydrofluoric-acid method 

described in a and /?, by reason of greater oxidation of ferrous iron. 

The need of a fine powder is a serious objection, as with the Cooke 

method.

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 absence of decomposable sulphides and 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.

20. ALKALIES.

A. THE ,J. LAWRENCE SMITH METHOD, 

a. ITS ADVANTAGES.

% The various methods of getting at the alkalies in insoluble 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,a 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.

b. REAGENTS 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 best obtained from pure calcite by 

solution and reprecipitation. 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

a Am. Jour. Sci., 2d ser., vol. 50, 1871, p. 209; Am. Chemist, vol. 1, 1871; Annalen Chem. und Pharm., 

vol. 159,1871, p. 82.
172 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

in the blank test comes from the carbonate. Much hot water is used 

for the analysis and a hot-water bottle, even of Jena 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.0 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 this laboratory (fig. 23) for 

one-half 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 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 chloride, and the 

two thoroughly ground together. 

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. 

23) or through a hole in a piece of stout asbestos board clamped in a 

vertical position, and heated for about tenminutes by alowflame placed 

at considerable distance beneath. As soon as the odor of ammonia is ho

FIG. 23. The J. Lawrence Smith crucible for 

alkali determinations. For dimensions see 

text.

o 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. E. W. Morley (private communication) uses with good effect as a lid 

a closely fitting small platinum dish filled with cold water.
ALKALIES. 173

longer perceptible the nearly full flame of two Bunsen burners is substituted, and continued for forty to fifty minutes. The sintered cake ° 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.

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. 32). 

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 untarect 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, again evaporated, ignited, 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 in part found 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 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 OP POTASSIUM.

To the solution of the chlorides in a small porcelain 6 dish an excess 

of chlorplatinic acid solution is added. The dilution should be such 

that when heated on the water bath any precipitate that may form

« 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. Mr. Steiger finds that the slacking of the cake is aided by using but 

1 or 2 cm.a of water at first.

6 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 Bonn, F., Zeitschr. anal. Chemie, vol. 38,1899, p. 349.)'
174 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

wholly redissolves. Evaporation is then carried on till the residue 

solidifies on cooling. It is then, drenched with alcohol ° 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 afterwards 

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 r,esultant 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 K2O, 

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 text-books, a factor 

based on the analysis of commercial potassium salts. If thought 

desirable the potassium salts 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 readily be, done by evaporation of the alcoholic 

filtrate from the potassium chloroplatinate, reduction of the platinum by hydrogen or otherwise as mentioned in the footnote, 6 filtration, 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.

a 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. 790). According to Morozewicz, absolute alcohol partly decomposes Na2PtCl6 with formation of NaCl, 

which goes to increase the weight of the KjPtCIe. 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 KjPtCls in 80 per cent alcohol can be used, namely, 1 :~26400.

6 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 

(Sonstadt, E., Jour. Chem. Soc., vol. 67,1895, p. 984, thus reduces potassium chlorplatinate in order to 

weigh its platinum).
ALKALIES. 175

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. 173) the few tenths of a milligram of calcium chloride that escaped precipitation should now be separated from the 

sodium and the proper correction made.

a. Gooch's method afor separating lithium. This method is described 

as follows:

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, previously 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 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 

vis 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.

fiProc. Am. Acad. Arts 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.
176 ANALYSIS OP SILICATE AND CARBONATE BOCKS.

B. PRELIMINARY TREATMENT BY OTHER METHODS.

When, as may happen in rare instances, it is necessary t,o estimate 

alkalies in the main portion after elimination of silica, alumina, lime, 

etc., in one of the usual ways, the question of a suitable method for 

separating magnesium becomes important.

a. THE MERCURIC OXIDE METHOD.

The old barium hydroxide method is not to be recommended. 

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.

Lately the once favored method of precipitating the magnesium 

by neutral ammonium carbonate in concentrated solution has been 

again recommended.a 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 was used. 

After a time a crystalline precipitate falls a double carbonate of 

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 redissolve and reprecipitate, to make sure of getting all alkali in the filtrate, especially 

potassium.

F. A. Gooch and E. A. Eddy b find that, when carried out as 

directed above by Wulfing, 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 of 180 cm.3 ammonia [density 0.92?], 800 cm.3 water 

and 900 cm. absolute alcohol. The solution containing the chlorides

o Wulfing, E. A., Ber. Deutsch. chem. Gesell., vol. 32,1899, p. 2214. The neutral carbonate is prepared 

by dissolving 230 grams of ammonium carbonate in ISO cm.3 of ammonia of 0.92 specific gravity and 

enough water to make 1 liter. This is sometimes called Schaffgotsch's solution.

6 Am. Jour. Sci., 4th ser., vol. 25,1908, p. 444; Chem. News, vol. 97,1908, p. 280.
ALKALIES. 177

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 saturated ammoniacal 

ammonium carbonate solution containing 50 per cent of alcohol, and 

the mixture is allowed to stand twenty minutes, with stirring for 

five minutes. If the amount of alkali salts originally present is 

small, the precipitate may be collected on asbestos in a perforated 

crucible, washed with the precipitant, dried, ignited, and weighed as 

magnesium oxide. When the amount of alkali salt originally present 

ie la^ge, 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. The second precipitate, collected upon 

the filter originally used, leaves, upon ignition, practically pure magnesium oxide.

C. THE AMYL ALCOHOL METHOD.

Under certain circumstances, notably absence of lithium, the 

method of Gooch developed by Riggs a 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 (f. a, p. 175) in 

the description of Gooch's method.

0. DIRECT SEPARATION OF POTASSIUM BY SODIUM COBALTINITRITE.

It may sometimes happen that of the alkalies present the percentage 

of potassium alone is desired. In this case use may be made of 

the method of W. Autenrieth, b which has 'afforded its author results 

that are in good agreement with those afforded by the J. Lawrence 

Smith method.

a. PREPARATION OP 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 NaN02 ) 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.

a Am. Jour. Sci., 3d ser., vol. 44,1892, p. 103. 

b Centralbl. Min., 1908, p. 513.

20091 Bull. 422 10 12
178 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

b. APPLICATION OP THE METHOD.

The mineral powder (1 to 3 grams) is decomposed with hydrofluoric and sulphuric acids, the excess of the latter 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 Jena glass (or in a 

platinum dish), is added 10 cm.3 of a saturated solution of potassiumfree sodium acetate a and the mixture is boiled for from ten to fifteen 

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 are added and, after stirring, the 

liquid is let stand for twenty-four hours, cold. The yellow precipitate 

is filtered, washed with cold water containing a little of the reagent, 

and dried at 100°. Since it is not free from sodium, it is useless to 

weigh it in this condition.

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. 173.

/?. 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 hydro-* 

chloric 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. The residue of perchlorates is then extracted with 10 cm.3 of 96 per cent alcohol, containing 0.2 per cent 

of perchloric acid, and allowed to stand for some minutes. The 

insoluble, white, sandy potassium salt is collected in a Gooch crucible 

having a thick felt and washed, first- with a few cubic centimeters of 

the alcoholic solution, then with a mixture (usually 20 cm.3 suffice) 

of equal parts alcohol and ether, till a few drops of the filtrate show 

on evaporation no residue. The precipitate is dried at 120° to 130° 

to constant weight.

» Five grams dissolved in water should give no yellow precipitate with the cobalt reagent after twentyfour hours.
CARBON DIOXIDE, CARBON. 179

21. 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 very well be overlooked. Moreover, the powder should 

first be agitated with a little hot water, to remove all entangled air 

which might otherwise be mistaken for carbon dioxide. In order not 

to overlook traces the test is best 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 TESTS FOR CARBON DIOXIDE.

a. DIRECT METHOD.

For the quantitative determination of carbon dioxide an apparatus 

permanently set up is used, of which several forms have been described 

by different writers." The one depicted in fig. 24 is a compact 

arrangement at present 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 C02-free air with which 

to sweep out the apparatus before and after the experiment, and for 

a slow current during its continuance. The results are very accurate 

and the determination can be quickly carried out.

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 C02-free air is forced through the whole system, except the weighed 

absorption tubes, until the original air has. been displaced, the observation bulbs E being attached directly to the drying system B. The

a For a simple and convenient form, see Tread well's Quantitative analysis, American edition, p. 298.
180 ANALYSIS OF SILICATE AND CAKBONATE BOOKS.

stopcock in the separatory funnel is then closed, the latter half filled 

with hydrochloric acid (1:1), the rubber stopper of the funnel replaced, 

the absorption tubes inserted between B and E, and the acid allowed 

to flow into the 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

FIG. 24. 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 in 

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 as it takes up the water set free from the soda lime in C during its conversion to carbonate. E, 0 bservation bulbs containing sulphuric acid to show the rate of gas flow.

through the condenser started. The flame is kept low, so as to secure 

steady but quiet ebullition, and the gas current is not interrupted, 

although reduced to a slow rate. With much carbon dioxide the 

rate of absorption is very readily noted by holding the hand to the 

soda-lime tubes, which become hot or warm where absorption is
CABBON DIOXIDE, CABBON. 181

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.

For the simultaneous determination of carbonates and the carbon 

of carbonaceous matter see C, page 182.

It has already been shown, under "Water" (5. C. f, p. 

82) how in case of need, as paucity of material, the 

determination of carbon dioxide can be combined with 

that of water by fusion with lead chromate. Soda-lime 

absorption tubes then follow the calcium chloride tube 

in carrying out the determinations there referred to.

b. INDIRECT METHOD.

The older forms of apparatus for the indirect determination of carbon dioxide are too well known to 

need description. Some are fragile or cumbersome 

and great care is requisite to the attainment of good 

results. The form recently devised by J. L. Kreider a 

(fig. 25) has the merit of simplicity, cheapness, and 

ease of. manipulation. It is adapted for determining 

not only carbon dioxide, but also other volatile substances produced by a variety of reactions, as hydrogen resulting from the action of an acid on certain 

metals, nitrogen from urea, ammonium oxalate or 

ammonium chloride by the action of sodium hypobromite, etc. Kreider's test results are excellent, though 

with carbonates generally low to the extent of about 

0.06 to 0.1 per cent.

FIG. 25. Kreider's 

apparatus for indirect determination of volatile 

substances.

The apparatus * * * is light and easily made from three test tubes. * * * 

The test tube A is changed in no way from its original form; B is perforated in the bottom with a hole about 1 cm. in diameter and fits tightly within A; and C, so selected 

that it fits loosely within B, is draAvn out to a small capillary tube.

"When the apparatus is to be used, the capillary of C is pushed through the hole of B, 

packed loosely with cotton; B is filled to the depth of from 6 to 8 cm. (about two-thirds 

of its contents) with granular calcium chloride, and B and C are adjusted as shown.

To the test tube, C, is fitted a one-hole stopper, through which passes a short glass 

tube which is closed by a rubber cap and plug. Upon removing the plug and applying suction to the short tube the reagent employed to liberate the volatile product to be 

determined is drawn up through this capillary until C is sufficiently filled. Upon 

replacing the plug the reagent remains within C, held by atmospheric pressure.

The tubes A and B may be so selected that very little of the product evolved can 

escape between them, but in case they fit very loosely a ring of paraffin melted into the 

mouth of A, about B, by means of a hot iron or wire, seals the joint securely. A. very 

convenient way to attach the paraffin is to melt it between A and another tube, which

a Am. Jour. Sci., 4th ser., vol. 19,1905, p. 188; Zeitschr. anorg. Chemie, vol. 44,1905, p. 154.
182 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

fits A as does B and may be removed by a turning motion, leaving the ring into which 

B will fit, and which then requires very little heating to make a tight joint. If care be 

used in taking apart A and B at the close of an experiment, such a ring of paraffin 

remains in place and may be used many times without replacement, being remelted 

by a touch of the hot wire before every new experiment.

In making the determination the substance under examination is weighed and 

placed in the bottom of A. The reagent to be employed, 10 to 15 cm: 3 , is drawn into 

C and held there in the manner described. The test tube A is slipped over B and this 

joint is sealed with paraffin, as has been shown. . The apparatus is wiped, placed on 

the balance, and weighed.

Upon removing the cap from the small tube in C the reagent runs from C into A. 

The volatile product is formed, is forced upward through the drying column of calcium 

chloride, and escapes through the annular space between B and C. When the action 

ceases a current of dry air is forced through C to drive all the volatile products from 

the apparatus, the cap is then replaced, and the whole placed on the balance to be 

weighed. The loss in weight represents the volatile product.

C. CARBON.

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. 179), and by a second determination, as just referred 

to, the total carbon in both forms can be found as C02 , whence that 

of the graphite is derived by difference. Or, according to G. T. 

Morgan," 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 .

22. 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 separately extracted 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.

o Jour. Chem. Soc., vol. 85,1904, p. 1001.
CHLORINE. 183 

B. DETERMINATION OF WATER-SOLUBLE CHLORINE.

A suitable amount, which may be several grams, of the powder is 

extracted with water. The filtrate is very often 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

gently heated, 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 it.

C. DETERMINATION OP 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 readily 

decompose apatite 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.
184 ANALYSIS OF SILICATE AND CARBONATE ROCKS, 

b. BY NITRIC AND HYDROFLUORIC ACIDS.

In many cases in order to obtain all the chlorine it is sufficient to 

attack the powder (which usually must be much finer 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 for the last reason, 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 acidification 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 and C, 

according to its amount and freedom from contamination.

23. FLUORINE (SILICA IN PRESENCE OF FLUORINE). 

A. IMPERFECTION OF THE QUALITATIVE TEST FOR FLUORINE.

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 piece of curved platinum 

foil inserted into one end of a glass tube, or in a bulb tube, is not to be 

relied on in all cases. While as little as 0.1 per cent of fluorine can 

sometimes be thus detected with ease, much larger amounts in another 

class of rocks may fail to show. (See C for indirect method.)

B. DIRECT QUANTITATIVE DETERMINATION OF FLUORINE.

a. THE METHOD OF BERZELIUS.

For the reason that the fluorine minerals occurring in rocks are 

mostly attacked but partly, if at all, by strong hot sulphuric acid, 

none of the methods depending on the volatilization of silicon fluoride 

can be used. There is further reason that even with decomposable 

fluorides it is impossible to obtain quantitative results in presence of 

amorphous silica or silicates. a Only with quartz powder is volatilia See Daniel, K., Zeitschr. anorg. Chemie, vol. 38,1904, pp. 257-306.
FLUORINE. 185

zation 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 c 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.

Two grams of the rock powder are 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 the fluoride, just as with the alkaline-earth 

phosphates. But this will probably 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 ammonium carbonate are added, the liquid is digested at a gentle-heat (40°) 

 for some time, and on cooling more carbonate is introduced.0 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£ 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, b 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,

<* The use of ammonium nitrate or chloride, instead of carbonate, for throwing out the silica arid alumina 

is not to be recommended because of loss of fluorine on subsequent evaporation (H. Rose).

f> Made by precipitating pure zinc chloride solution with potassium hydroxide, filtering, washing, and 

dissolving the precipitate in ammonia. 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 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. 17C. 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 thia 

reagent are 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 ammonuim carbonate.
186 ANALYSIS OF SILICATE AKD CAEBONATE EOCKS.

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 for complete precipitation of 

the phosphate and chromate. After slight heating and filtering, the 

excess of silver is removed by sodium chloride and 1 cm.3 of 2 N sodiumcarbonate 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 mixture of calcium carbonate and fluoride, the former serving to aid 

nitration 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 thus 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 gently ignited.

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 a 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 milligram, 

F. P. Treadwell and A. A. Koch 6 take the next to the last weight as 

correct.

b. TESTING OF THE CALCIUM FLUORIDE.

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 former should be 

dissolved in hot nitric acid and tested for phosphorus by ammonium

a Am. Jour. Sci., 3d ser., vol. 47,1894, p. 389. 

bZeltschr. anal. Chemie, vol. 43,1904, p. 469.
FLUORINE. 187

niolybdate 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 that 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 : 2 F : : Diff. between impure CaS04 and CaF2 : x.

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,

C. 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 a 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 can be still 

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 entirely 

escape observation.

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 6 has 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

"Zeitschr. anal. Chemie, vol. 43,1904, p. 409. 

6 Idem, vol. 44, 1905, p. 343.
188 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 do not confirm, 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 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.

d. DETERMINATION OP SILICA.

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 separated by the processes detailed 

in 6, page 83. These may be greatly simplified, if bases are not likewise to be determined, by evaporating the first filtrate from the silica 

with much sulphuric acid as in the last part of f. <*, page 105.

C. INDIRECT QUANTITATIVE DETERMINATION OF FLUORINE.

a. STEIGEIi'S METHOD.

George Steiger has recently devised in the laboratory of the Geological Survey an indirect method a for the determination of fluorine 

that seems full of promise.

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.

a Jour. Am. Chem. Soc., vol. 30,1908, p. 219.
FLUOKINE. 189

In rock mixtures containing only a few tenths of a per cent of fluorine, 2 grams of 

the finely ground rock powder are fused with four or five times its weight of a mixture 

of sodium and potassium carbonates. It may be necessary in the case of a subsilicic 

rock to add silica, 50 per cent of which should be present.

From the aqueous leach of the fusion all of the alumina, and most of the silica, are 

separated by adding ammonium carbonate, heating on the water bath for fifteen or

.0035

.0020

.0015

LJ

z

IE 

O

D 

-I 

^.0010

.0005

95 -90 85 80 75 

APPARENT PERCENTAGE OF TiOE

FIG. 26. Steiger's curve for fluorine.

70 65

twenty minutes, allowing to cool an hour or more and filtering. The filtrate is evaporated to small bulk (25 or 30 cm. 3 ) and filtered a second time to insure a perfectly 

clear solution, a condition absolutely necessary for a satisfactory comparison of the 

color. After this treatment the solution should be entirely free from alumina and 

contain 110 more than 25 mg. of silica. This amount of silica is not sufficient to interfere 

with the reaction.
190 ANALYSIS OF SILICATE AND CAKBONATE BOOKS.

The solution is now put into a 100 cm.3 measuring flask, sulphuric acid added 

to almost neutral reaction with care not to add an excess, and well shaken to free 

from the excess of carbon dioxide, and then fully acidified. Care should be taken 

not to have an excess of acid present before shaking, for the reason that -the escaping 

gas will carry off some fluorine; even under the above conditions a slight loss occurs. 

If a considerable amount of fluorine is present, an aliquot part of the solution should 

be used containing not more than 2 or 3 mg. 20 cm.3 of standard titanium sulphate 

solution ° (1 cm. 3 of which contains 0.0001 gram Ti02 ) are now added, together with 

2 or 3 cm.3 of hydrogen peroxide, and the flask filled to the mark with water. The 

solution is now ready to be compared with the standard. The latter is prepared by 

using 20 cm. 3 of the standard titanium solution, 2 or 3 cm.3 of H202 and bringing the 

volume up to 100 cm. 3 with water.

These two solutions containing the same amount of titanium per cubic centimeter 

should be of the same depth of color, but the one having the fluorine present will be 

found to be of a lighter shade, owing to the bleaching effect which that element has 

on a solution of titanium oxidized by H2 02 . The extent of this bleaching is not 

directly proportional to the amount of fluorine present, but by reference to the curve 

below, the quantity corresponding to a given bleaching can be found.

The two solutions are now compared in a colorimeter and their ratio recorded. Suppose a ratio, for example, of 100 to 85 that is, the fluorine present has caused a bleaching of the solution equivalent to 15 per cent of the titanium present; then by finding 

the point on the abscissa marked 85, with the help of the curve the amount of fluorine 

(0.00055) can be directly read off on the ordinate.

It is necessary to employ a colorimeter whose error is not more than 2 or 3 per cent.

This method is not suited for large percentages of fluorine.

Mr. Steiger studied the effect on the determination of some of 

the more important elements that may occur in the test solution. 

Sodium salts in large amount make the observed reading for the 

titanium somewhat high, but not enough to affect the results seriously (but see p. 129). 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.

Various mixtures were made roughly representing commonly cccurring rock mixtures, containing accurately known amounts of fluorine. Results of the fluorine 

determinations in these mixtures follow:

Si02 .

0.60

"

a

bO.70

".

"

n

"

"

a

A1203 .

0.20

"

a '

0.15

"

"

"

"

a

"

FeaO3.

0.05

"

a

0.05

!<

a

n

it

it

tt

MgCOa. CaC03 .

0. 03 0. 05

" "

0. 10

0. 05 . 05

" "

n it

a tt

tt n

n it

a it ~

NaIINH4P04

0.01

a

it

n

"

tt

"

it

it

. Ti02 .

.....

0.008

.01

.005

"

"

a

"

"

"

F calculated.

0. 0114

.0052

.00284

. 0005.

. 00526

. 00526

. 00253

. 01228

. 00516

. 00536

F found.

0.0102 Gram.

/ . 00525

.0027

.0003

.0056

.0040

.0020

.0089

. 00486

. 00530

o For its preparation, see footnote *>, p. 130.

6 In this detennination the fusion of the mixture was made as usual, and the fluorine added to the leach 

water before the treatment with ammonium carbonate,
FLT70EINB. 191 

b. MERWIN'S MODIFICATION ,OF STEIGER'S METHOD.

a. Introductory remarks. Mention has been made (p. 129) of a paper 

by H. E. Merwin, a in which it was shown that alkali sulphates and

130 140 160 180 200%

\

\

*>

\

\

\

40% 100%

Gram

0.0010

.0020

.0030

.0040

.0010

.0030 -

.0050

FIG. 27. Merwin's diagrams showing theeflect of fluorine with different concentrations of acid, and the 

effect of temperature. A. Coloration in peroxidized titanium solutions in presence of fluorine and free 

sulphuric acid. The fluorine in grams is read on the ordinate. The percentage ratios of depths of color in 

the standard solution to depths of color in the test solutions are read on the abscissa. For given amounts 

of fluorine and acid the ratio is found above the intersection of the lines representing the fluorine and 

acid. The curves are plotted for a temperature of 22° C. The line M migrates to D as the solution is 

heated to 32° C. B. The percentage of bleaching by fluorine may be found from these curves in the 

same way that the coloration ratios were found from the curves of A. C. Showing the rise in percentage 

of coloration due to heating. Curve E for a solution containing 1 cm. 3 of sulphuric acid and 0.0014 gram 

of fluorine; F for 3.5 cm.8 of acid and 0.0037 gram of fluorine; G for 3.5 cm. 8 of acid and 0.0019 gram of 

fluorine; H for a solution standard at 22° C.

also the concentration of acid as well as the temperature affect the 

color of titanium solutions peroxidized by hydrogen peroxide. The

. Jour. Sci-.^th ser., vol. 23,1909, p. 119.
192 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

salts cause bleaching, while addition of acid counteracts this effect 

to a considerable degree and increase of acid deepens the color. The 

effect of the alkali salts is opposed to that reported by Steiger (p. 190), 

but Merwin's statements have been confirmed by tests made at 

my instigation by Dr. William Blum at the Bureau of Standards. 

Steiger's observations as to the effect of other compounds 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 can not be matched. This was so, for instance, with 3 mg. 

fluorine and 2 per cent sulphuric acid, but with 10 per cent acid 

a fairly satisfactory comparison was possible with as much as 5 mg. 

fluorine.

Merwin found in his study of the estimation of fluorine "that when 

the Nessler tube method was used the percentage ratios obtained by 

dividing the depth of each solution bleached by fluorine by the depth 

of its matched standard could be plotted in lines so nearly straight 

that from the lines simple formulas could be derived for use in 

analysis. The same ratios are obtained by dividing the final volume 

of the standard by the volume of the test in cases in which a colorimeter is used which requires the standard to be diluted."

The full lines of fig. 27, A, were thus plotted. Suppose this ratio r in a particular 

case is 142, and that there is 0.5 cm.3 of acid in the test solution, then the corresponding

amount of fluorine is 0.0006 gram.. The formula expressing this relation is yn QQQ 

grams of fluorine. With 3.5 cm.3 of acid in the test solution the formula is 92 QOQ~

grams of fluorine. By the conditions of the first formula amounts of fluorine between 

0.00005 and 0.001 gram can be estimated accurately within 0.00005 gram, by the last 

formula amounts between 0.001 and 0.004 gram can be estimated within 0.00015 gram. 

By doubling the amounts of titanium and acid in the test solution and making it up 

to 100 cm. 3 , 0.01 gram of fluorine can be estimated. 

The above formulas can not be used in rock analysis because of the disturbing

effects of the alkali sulphates necessarily present in the test solution. In order to 

make it possible to know accurately the composition of the solution in which fluorine 

is to be determined in rock analysis, the following method has been worked out:

/?. Merwin's method:

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. 3 in volume 3 or 4 cm. 3 of hydrogen peroxide, and then 

cautiously 10 cm. 3 of standard titanium solution a (containing 0.01 gram Ti02). Including the acid in the titanium solution, about 4 cm. 3 of strong sulphuric acid are

a The hydrogen peroxide prevents the precipitation of the titanium by the alkali carbonate.
SULPHUR. 193

required 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. In the vast 

majority of cases this amount is less than 0.0025 gram (0.125 per cent of the sample). 

For such amounts there is added to the neutralized solution 3 cm. 3 of concentrated 

sulphuric acid, and the solution is made up to 100 cm. 3 . After being cooled to 22° C. 

the solution is compared with a 100 cm. 3 solution containing 0.01 gram of Ti02 , 4 cm. 3 

of H202, and 2 or 3 cm. 3 of concentrated sulphuric acid. The ratio, r, of depths (or 

volumes) of the solutions is obtained as described in the preceding section. This 

ratio is, however, much larger than the fluorine would give, owing to the alkali sulphates. The ratio that the alkali sulphates alone would give, if free from interfering 

substances, is about 125. Different samples never give quite the same ratio. Those 

that give a ratio much higher than 125 probably contain fluorine. The safest way is to 

make determinations of this ratio on two 8-gram portions of the carbonates used in 

the fluorine estimation,« and to use this ratio in making the correction. Having

T inn obtained this ratio call it m the formula for computing the fluorine is oq 000=

grams of fluorine. Accuracy to 0.0002 gram may be expected. * * * If the

fluorine expected amounts to 0.0025 to 0.0120 gram, the test solution is made acid with 

12 cm. 3 of concentrated sulphuric acid, and compared as before described. The

formula is ,. = grams of fluorine; m is to be determined and should not much 

exceed 108. Accuracy to 0.0005 gram may be expected.

It is very evident that the amounts of alkali salts and of acid must 

be taken into account and that the analyst should always take his 

readings at about the same temperature. For anyone who has 

frequent occasion to determine fluorine in this indirect way, it is 

desirable that he should prepare diagrams indicating the corrections 

to be made under his own conditions of operation.

24. SULPHUR.

A. THE DETERMINATION OF SULPHUR AS BARIUM SULPHATE, 

a. THE ERRORS INVOLVED.

Owing to the small amounts of sulphur in rocks, special precautions in making the precipitation or special purification of the barium 

sulphate obtained as in C are hardly ever needful, especially as the 

precipitation is usually made in absence of iron. But when large 

amounts of sulphur are in question the case is very different. The 

causes of varying results by different chemists have given rise to 

many investigations and the end is not yet. Perhaps the most of 

these have had to do with the determination of sulphur in the commercially important pyrite, and it is now understood that only after 

solution of that mineral in aqua regia and removal of the iron by 

ammonia in a prescribed manner is it permissible to proceed to the

a The 8 grams of carbonates dissolved in about 75 cm.a of water are treated precisely like the filtered 

fluorine solution.

20091 Bull. 422 10 13
194 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

precipitation of the sulphur, and further that only when this is done 

under certain well-defined conditions is the result approximately 

correct, and then through compensation of considerable plus and 

minus errors.a

In rock and most mineral analyses the prior precipitation of interfering elements by ammonia will hardly ever be permissible, because 

there are almost invariably present others than iron, which, as, for 

instance, alumina, would tend to carry down the sulphate ion to a 

greater extent than does iron. Hence the conditions of the Lunge 

method will not be considered here, but chiefly those produced by 

leaching an alkali carbonate fusion or by direct solution in hydrochloric acid where this is permissible.

For the errors now known to arise under these conditions the 

following causes have been ascribed or tentatively suggested: Carrying down of barium chloride, of normal and acid sulphates of the 

alkalies, of complex salts like BaCl.HS04 (BaCl) 2S04 , (M'S04 ) 2Ba, 

(HS04 ) 2Ba. Of the above, BaCl.HS04 by itself would be presumably 

without influence on the final result after ignition of the precipitate. 

(BaCl2 ) and (BaCl) 2S04 , singly or together, would occasion excessive 

weights. All others of the above-mentioned compounds would have 

an opposite effect, either because of the loss of sulphuric acid from 

acid salts (and of ammonium sulphate in special cases), or because of 

the low atomic weights of the alkali metals as compared with that of 

barium. The composition and concentration of the solution and the 

manner of precipitation will determine which of these undesirable 

products will contaminate the barium sulphate. For a given solution it is sometimes possible to regulate the conditions so as to reduce 

one or the other of the above to a minimum.

The presence of chlorine in barium sulphate precipitates was

formerly ascribed solely to occlusion of barium chloride, but it

seems to be now well established that this explanation can be only 

in part true; otherwise it would be difficult to account for the escape 

of hydrochloric acid on ignition. G. A. Hulett and L. H. Duschak 

have suggested 6 as an explanation for this escape the existence of 

HSO/ and Bad' ions in the solution and consequent formation of 

insoluble BaCl.HS04 , which strong heat would decompose into BaS04 

and HC1. But not all the chlorine can be thus removed, and the

« The latest important contributions to this subject are those of E. Hintz and H. Weber (Zeitschr. anal. 

Cheniie, vol. 45,1906, p. 31); G. Lunge and R. Stierlin (Zeitschr. angew. Chemie, vol. 18,1905, p. 1921; 

Kept. Internat. Committee Appl. Chem. at Rome, 1900, p. 399); O. Folin (Jour. Biol. Chem.. vol. 1,1906, 

p. 131); and E. T. Alien and J. Johnston (as yet unpublished}. The results of the most careful and 

elaborate investigation of the two last-named authors have been communicated to me as it progressed and 

lam indebted to them for some of the statements made in section A. The manuscript of Alien and Johnston was offered to me for perusal only as the correcting of the proof of this volume was ended, hence I 

am unable to cite their work as much as I would like. It embodies a great mass'of important quantitative data.

b Zeitschr. anorg. Chemie, vol. 40,1904, p. 196.
STJLPHUB. 195

weight of the barium sulphate is still sometimes excessive. According to Hulett and Duschak this might be accounted for by the following ionic reactions:

1. 2BaCl + S04 = (BaCi)2S04 .

2. 2HS04 + Ba=(HS04 ) 2Ba.

By interaction of the resulting hypothetical salts when ignited 

together, either hydrochloric acid or sulphuric acid, or both, might 

be set free, according to the relative amounts of the respective salts. 

Notwithstanding the fact that Hulett and Duschak failed to find 

support for these reactions by proving the escape of sulphuric acid 

from their precipitates, Otto Folin has succeeded,0 as have also 

E. T. Alien and J. Johnston in the geophysical laboratory of the 

Carnegie Institution at Washington (private communication). The 

results may then, according to the conditions of precipitation, be too 

high or too low. In. further explanation of too high results Folin 

suggests that, in presence of soluble sulphates of univalent metals, 

MSO/ ions may take part in the reactions, yielding (MS04 ) 2Ba, 

which, as well as (BaCl) 2S04 , should .be stable on moderate ignition. 

That alkalies in the form of stable sulphates (assumed normal) do 

form part of'the precipitate of barium sulphate that is formed in 

alkali chloride solutions, Hintz and Weber 6 have pointed out, and this 

Alien and Johnston have conclusively and quantitatively proved by 

direct determination. The extent of such contamination has been 

so great as to give the last-named authors losses of 0.5 per cent or 

more of the total sulphur in artificial mineral sulphides of ideal composition. This discovery did not, however, account for all the deficit 

regularly observed by them. The balance was found to be due to loss 

of sulphuric acid on ignition of the precipitate. Lunge and Stierlin, 

in the paper already cited, also made correction for normal alkali 

sulphates, but, so far as can be judged, without direct determination. 

Other sources of error are due to solvent action of hydrochloric 

acid and of alkali salts in the solution. 0 For these it is not difficult, 

ordinarily, to correct by appropriate treatment of the filtrates. 

Still others, mentioned by I. Pattinson and J. T. Dunri, d may arise 

from the presence of sulphides in some barium chloride and from red 

rubber stoppers. Finally, there is the possibility of reduction to 

barium sulphide if the precipitate is ignited in contact with paper.

b. AVOIDANCE OR CORRECTION OF ERRORS.

It is thus apparent that the accurate determination of the sulphate 

ion is one subject to many varying errors and that the .methods of 

procedure and correcting for impurities must be varied to suit the

"Jour. Biol. Chem., vol. 1,1906, p. 131.

b Loc. cit.

c Alien and Johnston seem to have shown that alkali salts are practically without effect In this respect.

d Jour. Soc. Chcm. Ind., vol. 29,1905, p. 10; Chem. Zeitung, vol. 29,1905, p. 29.
196 ANALYSIS OF SILICATE AND CAKBONATE -KOCKS.

conditions. General directions to meet all conditions can not be 

given. Hintz and Weber a obtain with pyrite, after separation of the 

iron, correct weights by adding the precipitant all at once in order to 

offset the effect of normal or acid alkali sulphates by increase of 

occluded barium chloride. Allowable and satisfactory as this may be 

for commercial analysis, when results of the highest accuracy are 

sought the errors must be each and every one measured. The results 

are then more concordant than by the method of Hintz and Weber 

(Alien and Johnston).

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 reagents 

involves the presence of certain amounts of salts, one or another of 

which may be fatal to the attainment of acceptable results.

In general, there should be present the least amount of free hydrochloric acid that will prevent hydrolysis of salts in the hot solution, 

since the acid has marked solvent effect on barium sulphate. 6 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, in fine 

drops, preferably from a capillary tube, into the nearly boiling test 

solution. The precipitate will then be well crystallized and will contain a minimum and sometimes entirely negligible amount of chlorine, 

whereas with rapid precipitation its amount may be several milligrams per gram of precipitate.

The chlorine in the ignited precipitate may be. determined and 

deducted (if known to be present as such) from the gross weight. 

Hulett and Duschak c dissolve the ignited and weighed sulphate

in concentrated sulphuric acid at 100° while a current of air carries 

the freed hydrochloric acid over into a dilute solution of silver 

nitrate.

If contaminating alkali is to be determined, a paper filter should be 

used for the collection of the precipitate. In the latter case the paper 

should be charred very slowly and without any active combustion, 

otherwise there may be marked reduction of the sulphate to sulphide (E. T. Alien). After ignition the precipitate is to be dissolved 

in the least amount of hot concentrated sulphuric acid, the resulting 

solution is to be poured into cold water, heated for some time, filtered, the filtrate evaporated in platinum, the excess of acid expelled,

a Loc. cit.

6 With alkali sulphates Alien and Johnston get the best results when .the solution contains only 0.1 cm.3, 

of concentracted HC1 in volume of 350 cm. 3 . 

eZeitschr. anorg. Chcmie, vol. 40.1904, p. 106.
SULPHUR. 197

and the residue of alkali sulphate weighed and tested as to purity. 

Its amount is to be increased-by 10 per cent for that still retained by 

the barium sulphate (Alien and Johnston).

Loss of sulphuric acid by decomposition of an acid salt or volatilization of ammonium sulphate can be measured, so far as known at 

present, only by conducting the ignition so as to permit the collection 

of the escaping gases. Since these gases may contain sulphur dioxide and oxygen, as well as sulphur trioxide, they should be passed 

through a solution of bromine or hydrogen peroxide. For this 

determination a perforated filter of deep and narro^v form should be 

used, which can be inserted into the decomposition apparatus and 

weighed after the ignition is over.

The application of all three of these corrections can seldom be 

possible, for as a rule each of them calls for a separate portion of a 

very large precipitate, or else there must be available three different

large precipitates with exactly the same amounts of contamination, 

a condition difficult if not impossible to secure. The determination of fixed chlorine and volatile sulphuric acid might, however, be 

made with one and the same portion, the volatile sulphur being first 

determined and afterwards the chlorine. It is to be borne in mind, 

however, that, as shown by Hulett and Duschak, the so-called fixed 

chlorine itself begins to escape above 700°, the residue then showing 

alkalinity.

Errors due to the solvent action of hydrochloric acid or of ammonium or fixed salts in the solution can usually be corrected by 

evaporating the filtrates from the barium sulphate, destroying or 

expelling ammonium salts if present, treating the residue with water 

slightly acidified with hydrochloric acid, and collecting and purifying 

the barium, sulphate that may be left undissolved.

B. DETERMINATION OF THE CONDITION OF SULPHUR IN ROCKS.

Before proceeding to the determination of sulphur, its condition, if 

present, should be ascertained.

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 sulphide may be arsenopyrite, 

which, however, is of very rare occurrence in igneous rocks, if, indeed, 

it is ever found there.
198 ANALYSIS OF SILICATE AND CARBONATE HOCKS.

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.

C. QUANTITATIVE DETERMINATION, 

a. TOTAL SULPHUR.

Although the sulphur of sulphides may sometimes be wholly 

extracted with aqua regia or some other powerful oxidizer, in the 

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 fig. 3 (p. 32), in order to 

exclude access of sulphur from the flame gases. This determination 

may very conveniently be combined with those of barium, titanium, 

zirconium, and rare earths (p. 138). 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." It is well that this is so, for evaporation on a bath heated 

by gas to remove silica would in many cases involve 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.

If the amount of precipitate is large enough to permit and the 

circumstances demand, other corrections should be applied before 

ignition, as mentioned under A. b, page 195.

b. FRACTIONAL DETERMINATIONS.

If traces of water-soluble sulphates are present, they can ber removed 

when desired by boiling water.

a The results of C. W. Stoddart (Jour. 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 possibly be that Stoddart acidified his solutions hot or used too strong an acid and had some silica 

precipitated.
BOKON; 199

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.a In the residue the sulphur of the insoluble 

siulphides can be estimated, or from the total sulphur found in another 

portion its amount can be calculated. 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 

«et free as such from pyrrhotite would escape estimation and introduce further uncertainty. In general, it would be safe enough to 

assume the composition Fe7S8 for pyrrhotite. However carefully all. 

i:hese 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 c. a, p. 165).

25. BORON.

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 6 are given the most important

o With pyrrhotite a small fraction of its sulphur one-eighth if the formula Fe?S8 is adopted is liberated 

as free sulphur and not as hydrogen sulphide.

&Th. Rosenbladt (Zeitschr. anal. Chemie, vol. 20, 1887, p. 21) used magnesia for binding the boron, 

while F. A. Gooch (Proc. Am. Acad. Arts Sci., 1886, p. 167; Bull. U. S. Geol. Survey No. 42, 1887, p. 04; 

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
200 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 beten shown by several workers, most 

recently by Chapin. Before Chapin it was considered necessary to 

extract with water the alkaline fusion of a mineral and to treat 

the extract for the boron. A cause for 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 a, by G. W. Sargent 6 , and by W. E. Ford c 

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. It 

is, however, a method which depends on the titration of the boron 

in the distillate, and is hence less satisfactory than one which permits 

weighing the boron and then making sure of its presence by a qualitative test.

E. T. Wherry d has 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.

H. Moissan (Compt. Rend., vol. 116,1893, p. 1087; Bull. Soc. chim., vol. 12,1894, p. 955), who modiaes 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).

The latest 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 (BOZ)2, and by Wilson H. Low (Jour. Am. Chem. Soc., vol. 28,1906, p. 807), who modiaes 

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 modiacations to borosilicates, but prefers mannite to glycerin.

a Am. Jour. Sci., 4th ser., vol. 7,1899, p. 97.

6 Jour. Am. Chem. Soc., vol. 21,1899, p. 858.

c Am. Jour. Sci., 4th ser., vol. 14,1903, p. 195.

d Jour. Am. Chem. Soc., vol. 30,1908, p. 1687.
GASES AND VAPORS. 201

26. 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 .then be 

looked to with the utmost care. Special directions to meet such cases 

can not now be given, 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 0 "Ueber den Gang und die Ausfuhrung der 

chemischen Untersuchung," following Sandberger's own paper 6

in the general report "Untersuchungen der Nebengesteine der Pribramer Gange." I have published a few data as to gold, silver, lead, 

zinc, etc., c in S. F. Emmons's report on "The geology and mining 

industry of Leadville;" J. S. Curtis/ in his report on "The silverlead deposits of Eureka, Nev.," has given his method of assaying 

rocks for traces of gold and silver; in volume 7 of the Reports of the 

Missouri Geological Survey, page 740, are to be found the methods 

used by James D. Robertson for the determination of lead, zinc, and 

copper in silicate and carbonate rocks of Missouri. The earlier work 

of J. G. Forchhammer e and L. Dieulafait/ the latter of whom examined many hundreds of Archean rocks, was of a qualitative nature.

27. 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

a Jahrb. der Bergakad. Leoben u. Pribram, 1887, p. 363.

6 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 a, p. 165.)

cMon. U. S. Geol. Survey, vol. 12,1886, Appendix B, pp. 592-596.

d Idem, vol. 7,1884, pp. 120-138.

t Pogg. Ann., vol. 95,1855, p. 60.

/Annales chim. phys., vols. 15,17,18, 21,1878-1880.
202 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

may have been held dissolved in the rock, particularly in.those not 

wholly crystallized. But from the experiments of some recent investigators, especially Morris W. Travers,a A. Gautier, 6 and K. Huttner, c 

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. d

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 was long since thus 

recognized. H. Rose e says that pitchstone gives off ammoniacal 

water on heating; A. Delesse-^ found ammonia in rocks, and A. Gautierlater made quantitative tests; H. Erdmann^ found that ammonia was 

obtained by acting on various minerals of ancient igneous rocks with a 

caustic alkali; C. Luedeking and H. A. Wheeler 71 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 character- 

 istic 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, in part 

at least, evolved as such, imparting a strong alkaline reaction to the

a Proc. Roy. Soc., vol. 64,1899, p. 130.

6Compt. Rend.,vol. 131,1900,p. C47; vol. 132, 1901, pp. 58 and 189; vol. 136, 1903, p. 16; Annales chim. 

phys.,7thser., vol. 22,1901,p. 97; Annales des Mines, 10thser., vol. 9,1906,p. 316.

c Zeitschr. anorg. Chemie, vol. 43,1905, p. 8.

d 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. ' 

« Quantitative Analyse, Finkener ed., p. 673.

/ Annales des mines, vol. 18, I860, p. 151.

g Ber. Deutsch. chem. Gesell., vol. 29,1896, p. 1710.

A Am. Jour. Sci.,3dser.,vol. 42,1891,p. 495.
SPECIAL OPERATIONS. 203

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, 0. Silvestri a having observed a nitride of iron on a lava from 

Etna.

28. SPECIAL OPERATIONS.

. The problem often presents itself of ascertaining the composition of 

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 th'e 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, Prof. L. V. Pirsson 6 

has indicated a means of detecting nepheline in presence of olivine, as 

in nepheline basalts, based on the very ready solubility of nepheline, 

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 Professor Pirsson was led to 

believe from his original tests. If, therefore, on evaporation of the 

filtrate, much iron is indicated, the gelatinization may well be due to 

olivine alone or in part, and then the quantitative relation of silica to 

iron plus magnesium should be ascertained. It must also be borne in 

mind 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 discrimio Gazz. chim. ItaL, vol. 5,1876, p. 301. &Am. Jour. Sci., 4th sen, vol. 2,1890, p. 142.
204 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

Hate 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 a have conclusively shown 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 

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 6 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 solution within 1 per cent, whereas the solubility of quartz 

powder was only 1.2 per cent after two days.

a Zeitschr. angew. Chemie, 1897, pp. 393, 425.

o 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. Zeit., Rep., 1903, p. 21.
CARBONATE ROCK ANALYSIS.

PART I. INTRODUCTION.

29. QUALITATIVE COMPARISON OF CARBONATE AND SILICATE ROCKS.

The analysis of an ideally pure carbonate of any one metal is of 

great simplicity. Occasionally the carbonates met with in nature 

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, cerussite, etc. 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 point beyond which the rocks cease to be 

classified as limestones or dolomites, but rather as calcareous shales, 

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 transformations 

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 rocks. These constituents are furthermore necessarily those 

common to silicate rocks of the earth's crust, hence the carbonate 

rocks differ qualitatively in no essential respect from their silicate 

associates except as to the more common occurrence of carbonaceous

205
206 ANALYSIS OF SILICATE AND CAKBONATE BOCKS.

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 their 

delimitation, and from the necessity of the case any rule must be 

purely arbitrary, since there is absolutely no break in the series between limestones and dolomites. The last name strictly applies only 

to the equiatomic double salt of calcium and magnesium, CaMg (C03) 2 , 

and by some it is held that this should be its only application. On the 

other hand, the opposite extreme has been approached in contending 

that all limestones with as much as 1 or 2 per cent of magnesium 

carbonate should be classed as dolomites. According to H. Hies a 

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. PfafP calls limestones with 11 to 46 per cent of 

MgC03 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 1 

rocks with any great attention to detail. The majority of analyses 

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

 o Bull. New York State Mus. No. 44,1901, p. 644. 

t> Neues Jahrb. Min. Geol. Pal., Beil. Band 23,1907, p. 529,
MINERAL COMPOSITION OF CARBONATE ROCKS. 207

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 Fe203 , water 

and carbonaceous matter have been entirely overlooked or neglected, 

as also titanium, phosphorus, and the rarer constituents, and sulphur 

has been almost uniformly reported as S03 . 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.

30. 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 Fe2 03 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, however, 

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
208 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

times from carbonaceous matter. It is hence 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 the 

excepted cases it is sometimes 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 

its presence if often 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 at times or again 

give rise by oxidation to equally or even more valuable ores of a 

different sort. The strongly metamorphosed siliceous limestones are, 

however, 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, zircon, etc. These latter 

may be often 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 the case of 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 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.
BEHAVIOR TOWARD REAGENTS. 209

The condition of phosphorus when it occurs in only minute amounts 

is not determinable with certainty. It may sometimes doubtless be 

found in traces in the form of heavy phosphates like monazite and 

xenotime in the insoluble residues, and at others 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.. Recent 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 frequently alluded to 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 Prof. 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 those undertaking their analysis. Ignorance of the mineral composition in respect to the minor 

components has been a prolific source of error on the part of those 

analyzing these rocks.

31. 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. 

20091 Bull. 422 10 14
210 ANALYSIS OP SILICATE AND CARBONATE BOCKS.

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,a and many of his results were long afterwards confirmed by J. W. Richards and N. S. Powell. b Solid organic 

acids like citric and tartaric were found to be well adapted for distinguishing between many carbonate minerals by the difference in 

the degree of action on them. Potassium acid sulphate had earlier 

been used to some extent by E. Jannett.az, c 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.

For the present purpose it"is more important to present in brief the 

methods proposed for distinguishing between calcite and aragonite 

and between relatively pure limestones and those high in magnesium.

b. THE MEIGEN REACTION FOR DISTINGUISHING CALCITE FROM ARAGONITE.

According to W. Meigen, d calcite powder when boiled with a dilute 

solution of cobalt nitrate remains white or, in presence of organic 

matter, becomes yellowish, while aragonite turns lilac red from formation of a basic cobalt carbonate. G. Panebianco e obtained different results. Calcite after a minute's boiling with the cobalt nitrate 

reagent became sky blue and after four minutes lavender blue. 

Aragonite became at once lilac and later violet, the difference in the 

colors being supposedly due to different basic carbonates. Panebianco also observed that the reaction was useless for proving absence 

of calcite when mixed with aragonite, for the color characteristic of 

the latter still appeared when 19 parts of calcite were mixed with but 

1 of aragonite. Freshly precipitated gelatinous calcium carbonate, 

as well as that from warm solutions, gives the ara'gonite reaction, but 

that formed at 0° affords the calcite reaction.

A. Hutchinson-f seems to have shown that the disagreement 

between the results of these investigators is to be attributed to the 

presence of iron in the cobalt nitrate used by Meigen.

According to Meigen, barium and strontium carbonates, but not 

that of magnesium, behave like aragonite, and calcium phosphate 

produces a blue powder.

« Ann. New York Acad. Sci., vol. 1,1877-1880, pp. 1,153; vol. 2, p. 1; Proc. Am. Assoc. Adv. Sci., vol. 

31, 1883, p. 271;'Chera. News, vols. 36, 37, 38, 43, 47, 1877-1883; Kept. Brit. Assoc. Adv. Sci., 1880, p. 506; 

Min. Mag., vol. 4,1880-81, p. 181; Ber. Deutsch. chem. Gesell., vol. 13,1880, p. 726.

b Jour. Am. Chem. Soc., vol. 22,1900, p. 117.

cCompt. Rend., vol. 77,1873, p. 838; vol. 78,1874, p. 852.

dCentralbl. Min., 1901, p. 577.

e Rivista min. crist. ital., vol. 28, 1902, p. 5.

/Min. Mag., vol. 13,1903, p. xxviii.
BEHAVIOR TOWARD REAGENTS. 211 

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 

calcite, and not of calcite with 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.

J. Lemberg a 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 twenty-five minutes with replacement of 

the escaping water. The deep-violet solution is then filtered.

Coarsely powdered Iceland spar and Carrara marble became violet 

after five to ten 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, since after twenty 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 6 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.

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.

aZeitschr. Deutsch. geol. Gesell., vol. 40,1888, p. 357. 

6 Verb. Naturforsch. Gesell. Basel, vol. 15,1905, p. 1.
212 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

PART II. REFINED METHODS OF ANALYSIS.

32. 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 filtered 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 (d, p. 87 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 fig. 2 (p. 31). 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 (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 33. A. a, page 216.

If the original residue is small, and accurate knowledge of its composition is desired, several grams of the rock may be dissolved and the
KEFINED METHODS OF ANALYSIS. 213

whole filtrate best treated for dissolved iron, aluminum, and manganese as in 33. A. a, page 216, but only an aliquot part of the subsequent filtrate should then be used for the determination of calcium 

and magnesium.

In case the filtrate from the residue is perceptibly colored by dissolved organic matter, a condition that may occasionally arise, 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 under b, below, for the bulk analysis.

b. WHEN THE INORGANIC RESIDUE IS NOT TO BE SEPARATELY ANALYZED.

This will be the usual case. 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. This is the best method 

to employ in all cases where the ratio of insoluble to soluble compounds is not less than is found in an argillaceous limestone that is 

directly suited for burning to Portland cement that is to say, when 

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 ten to fifteen 

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.

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.
214 . ANALYSIS OF SILICATE AND CARBONATE ROCKS.

The strong heating is usually stopped after ten or fifteen 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.0 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 

undissolved 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.

B. 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 power 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, 6 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 magnesiah limestones and for cement 

rocks containing as little as 50 per cent of lime. c

B. SEPARATION OF SILICA.

In this connection the remarks under 3, page 92, 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 B, 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

a Thechanges that take place during the ignition compriseloss 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-trioxide from the calcium sulphate and later the alkalies, 

tvhichcan be wholly volatilized in an hour or fess by a powerful blast. With an inclined blast the alkalies 

condense in part on the under side of thelid as a soluble and powerfully alkaline deposit, sometimes weighing 

several milligrams, but in the time above set no loss of alkali appears to occur.

fcShimer, P. W., in Meade, R. K., The Chemist's Pocket Manual, p. 162.

c Personal communication from R. K. Meade.
ALUMINUM, TOTAL IRON, TITANIUM. 215

treatment, but for a highly magnesian limestone the temperature 

should not exceed 120°, according to J. P. Gilbert,0 because of 

recombination of silica and magnesia, with subsequent re-solution 

of the silica when acid is added.

Bertram Blount claims b 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 ten 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 dry ness, 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 ten 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 c (p. 95). 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.

33. ALUMINUM, TOTAL IRON, TITANIUM (SILICA, MANGANESE); PRECIPITATION IN COMPANY WITH PHOSPHORUS,

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 are all methods of separation that may

o Technology Quart., vol. 3, 1890, p. 61; abstract in Zeitschr. aual. Chemio, vol. 29, 1890, p. C88. 

6 Jour. Soc. Chem. Incl., vol. 21, 1902, p. 1217. 

c See also 8, p. 98.
216 ANALYSTS OF SILICATE AND CARBONATE ROCKS.

be capable of affording good results noticed. There are some that 

seem promising but that have not yet been studied sufficiently in this 

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 been as yet ascertained.

A. PRECIPITATION OF ALUMINUM, IRON, ETC.

a. COLLECTIVE PRECIPITATION OP ALUMINUM, IRON, MANGANESE, TITANIUM, AND PHOSPHORUS BY AMMONIUM SULPHIDE.

If these elements collectively represent 2 or 3 per cent or less of the 

rock, the filtrate from the silica (32. B, p. 214), 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 twelve 

to twenty-four hours. Its contents are then collected on a filter of 

small size (7 cm.) and washed with water containing a little ammonium 

sulphide and nitrate. 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 36, p. 221.)

The paper and its contents, having been washed with ammonium 

nitrate, 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 five minutes, represents ALO3 , 

Fe203 , Mn304 , Ti02 , and P2 05 . (For the separation of these, see C, 

p. 218.)

This method is inapplicable for phosphatic limestones containing 

insufficient aluminum to more than combine with the phosphorus, for 

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. PRECIPITATION OP ALUMINUM, IRON, TITANIUM, AND PHOSPHORUS 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 of strong 

nitric acid, till all trace of bromine or chlorine is gone. Then hydro-
ALUMINUM, TOTAL IRON, TITANIUM.

chloric acid is added, if not already present, in amount sufficient to 

prevent precipitation of magnesium when rendered ammoniacal. 

Ammonia is added to the boiling solution (in platinum if possible), 

100 to 200 cm. 3 in volume, in slight excess, and the boiling is continued for two or three minutes. The precipitate is allowed to settle 

in the covered vessel, collected quickly on a filter, washed with hot 

water two or three times, and sucked dry. It is then redissolved in 

hct 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 just as 

described once, twice, or even three times, 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 nitrate. 

('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 Fe2 03 , A12 03 , Ti02 , and P205 . (For separation of 

the ignited oxides, see C, p. 218.)

C. PRECIPITATION OF ALUMINUM, IRON, TITANIUM, AND PHOSPHORUS BY THE BASICACETATE METHOD.

This 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 basic-acetate 

process, and hence of their more ready separation by ammonia from 

appreciable quantities of manganese. (For its application, see A. b. 

/?. p. 100, giving due regard to the smaller amounts of iron, etc., 

involved in the case of limestones.)

B. TREATMENT OF THE FILTRATES FROM 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 bulk 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 ammo-
218 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

niacal filtrate. The alumina and perhaps trace of iron oxide thus 

obtained are added to that already found (A. b or c, pp. 216-217). 

(For treatment of the filtrate, see 34, p. 219.)

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, 

pages 216-217, 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 a 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 ten or fifteen 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.

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 

due 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 8. B.-a, page 107. The amount of vanadium present is, so far as 

known, always so small as to make it unnecessary to follow the procedure under 8. B. b, page 109.

a For its preparation see p. 40.
MANGANESE. . '219

C. TITANIUM.

After titration of the iron the solution is treated exactly as prescribed under 8. B. a. 7-, 'page 109, and the titanium is determined 

colorimetrically (p. 128).

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 (p. 222), 

and further the manganoso-nianganic oxide, if this had intentionally 

been precipitated along with the iron and aluminum as in A. a, page 

216. (For the discussion of the relative merits of this indirect and 

the direct methods for arriving at the aluminum, see 8. A. a, p. 98, 

andC, p. 111.)

34. MANGANESE.

A. IN THE FILTRATES FROM 33. B (p. 217).

The filtrates containing the calcium, magnesium, and manganese 

are caught in a flask of about 150 cm.3 capacity, 2 cm.3 of ammonia 

are added, and hydrogen-sulphide gas is introduced to saturation, 

then additional ammonia is added to equal that just prescribed. The 

flask is set aside, stoppered for twelve to twenty-four hours, the precipitate (perhaps colored dark by a little platinum, iron, or other 

heavy-metal sulphide*) is collected on a 7-cm. filter and washed with 

a dilute solution of ammonium chloride carrying a little ammonium 

sulphide. 6 (For treatment of'the filtrate, see 35, p. 220.)

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 tile manganese sulphide. Thefiltrate is treated exactly as under 9. B. b,page 115, 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 9. A,p. 113),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 (9. C. b, p. 117).

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

« 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 

thon appear at this stage. Hence, prior ignition of the limestone is imperative in such cases.

'' This is best prepared by considerably overneutralizing a little hydrochloric acid in a small beakor, 

an3 then adding hydrogen sulphide water or introducing hydrogen sulphide gas for a few moments, aud 

further diluting if need be.
220 ANALYSIS OF'SILICATE AND CAKBONATE BOCKS.

hundredths of a per cent are present, its separation at this stage may 

be altogether omitted.

B. SEPARATE DETERMINATION OF MANGANESE.

Small amounts are always best determined 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 9. C. b, page 117. 

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 9. C. b, page 117.

35. COPPER, NICKEL, COBALT, LEAD, ZINC, RARE EARTHS, CHROMIUM, 

VANADIUM, MOLYBDENUM.

It is useless, as a rule, to look for any one of these constituents in 

the amount of sample taken for the general analysis. From 50 to 

500 grams of material will be required. This is dissolved in hydrochloric acid and the residue separated by filtration. If it is desired to 

examine this residue it is best done by analyzing it separately, after 

fusion with sodium carbonate and leaching with water. Vanadium 

and molybdenum will then be found in the filtrate, the other metals 

in the residue. The former can be determined according to 18, page 

148; the latter by the usual methods.

For the hydrochloric acid solution, which will contain the above

elements mainly or wholly, the treatment given under 33, A. a, page

216, 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 aci'd, 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 to be freed 

from oxalic acid by evaporation and gentle ignition and the residue 

redissolved and tested for nickel, cobalt, zinc, chromium, vanadium, 

find molybdenum by approved methods. It must not be forgotten
CALCIUM, STRONTIUM, BAEIUM, MAGNESIUM. 221

that the filtrate from the original precipitation by ammonium sulphide may hold vanadium, 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 18. C, page 150.

36. CALCIUM, STRONTIUM, BARIUM, MAGNESIUM (MANGANESE).

The filtrate obtained in 33. A. a, page 216, or 34. A, page 219, is 

treated for the most part as in silicate analysis (pp. 118-128).

With dolomitic limestones and dolomites it will be usually impossible to obtain a correction by the method given in C. b, /?, page 127, 

: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 hot 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.

For the utmost refinement in the determination of the magnesium 

it is probably best to evaporate the filtrates from the calcium oxalate 

to dryness, expel the ammonium salts by ignition, add hydrochloric 

acid and reevaporate, take up again with as little acid as possible, and 

filter through the smallest filter. The filter is preserved for later use. 

To the filtrate, which should be very small in volume, a few drops of 

sulphuric acid are added, and if after some hours a precipitate of 

barium sulphate has appeared it is collected and burned in platinum 

with the previous filter and its contents. The ignited matter is 

treated as in the preceding paragraph.

To the filtrate is added enough hydrochloric acid to prevent precipitation of magnesium when rendered ammoniacal. 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 redissolved and reprecipitated. In the filtrate the magnesium is precipitated, together 

with any manganese that may be present, in the manner elsewhere 

detailed (p. 124).
222 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

37. PHOSPHORUS.

The rock is dissolved in dilute nitric acid, 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 treated by one of the 

approved methods.

38. 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 ABSENCE OF CAEBONACEOUS MATTER.

a. FERROUS IRON SOLUBLE IN SULPHURIC ACID.

The powder, one 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
FERROUS IRON. ' 223

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 potassiumbichromate 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 subsequent 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 19. D. d, page 167.

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 19. D. d, page 167, 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 

ma.de as there directed.

B. IN 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 quickly filtered 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.

/Is in A. a, page 222, hydrochloric acid and titration by dichromate 

may be used in-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 the insoluble
224 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

matter is usually not worth attempting, because of the admixed 

organic matter.

39. ALKALIES.

The alkalies in carbonate rocks are, of course, constituents of the 

siliceous components. Since these are usually subordinate, it is advisable 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 (p. 171). 

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.

40. CARBON DIOXIDE, CARBON (WATER). 

A. DETERMINATION OF CARBON DIOXIDE.

This determination is made precisely as under 21. B, page 179. 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.

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 now and then 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 filled
CHLOKINE. 225

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 WATER AND OF TOTAL CARBON

IN BOTH FORMS.

In presence of sulphides or soluble organic matter the following

method will sometimes answer for the simultaneous determination 

of the first two or even all three of the above-enumerated constituents.

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. 78), 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 

rock as well as that derived from the hydrogen of the organic matter.

A separate determination of the carbon dioxide (see A, p. 224) 

gives the data for calculating the carbon of the organic matter.

According to G. T. Morgan a the two conditions of carbon can be 

successively determined 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.

41. CHLORINE.

Several grams of the rock are 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 22. A, B, and C, pp. 182-184.)

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 hot

oJour. Chcm. Soc., vol. 85, 1904, p. 1001.

20091 Bull. 422 10 15
226 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

water and the filtrate acidified with cold dilute nitric acid, or it may 

be decomposed directly with the acid and the solution filtered. The 

further treatment is as above given.

42. 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 solution of 

sodium carbonate till in some slight excess, boil, and treat the precipitate of calcium carbonate and possible fluoride as on page 186. 

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 

23. B. a, page 184.

43. 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.

B. DETERMINATION OF TOTAL SULPHUR, 

a. METHODS OP CONVERTING SULPHIDES TO SULPHATES.

<T. By ignition without flux. In a rock that is not heavily charged 

with sulphides the following method of my own has afforded excellent 

results, even in the presence of 1 per cent of organic matter, though 

its range of application has not been ascertained:
WATER. 227

The platinum crucible containing 1 or 2 grams of the rock powder 

is placed in the perforated disk (fig. 3, p. 32) 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 32. A. b. a, 

p. 213.)

/?. By ignition with sodium carbonate. One to 2 grams of powder 

are 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 at times 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 /?, 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 

neArer 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.

44. WATER. 

A. HYGROSCOPIC WATER.

B'rom one to several grams of the air-dry powder are heated in a 

current of air dried by calcium chloride in a glass tube at 100 to 105° 

and the escaping water collected in a calcium chloride tube, or the air 

may be dried by sulphuric acid and the water collected in sulphuric
228 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

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. COMBINED WATER.

This may be ordinarily determined on the air-dry sample Ijy 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. e, p. 78) or with anhydrous borax according to 

Jannasch (5. C. g, p. 82). From the result thus found the separately 

determined hygroscopic water is to be deducted. It is to be remembered that the result will be in error by the amount of water afforded 

by the hydrogen of any organic matter there may be in the limestone.

PART III. 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 II. 

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 details of 

manipulations are referred to the corresponding sections of Part II.

45. DECOMPOSITION AND SOLUTION.

If the substance is convertible by blasting into a condition wholly 

decomposable by hydrochloric acid, one-half to 1 gram of the fine

powder is strongly ignited in a covered platinum crucible over the

blast for fifteen minutes, or longer if the blast is not very powerful.

If the material is very impure, one-half 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, arid 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 dryness 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.
CONDENSED ANALYSIS. 229 

46. SILICA.

The residue is treated with 5 to 10 cm.3 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 ten 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, but in smaller 

amount, and the second portion of usually dark-colored 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 five to fifteen 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. 31), 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, 

but it should never be omitted if this latter correction is contemplated.

47. 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.

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
230 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

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 charged, then ignited over a gradually increased 

flame, and finally over the blast for two to five minutes. The weight 

found represents the oxides of ferric iron, aluminum, titanium, phosphorus, and manganese, the last presumably Mn304 .

The iron, titanium, and silica in the ignited oxides are determined, 

after fusion with potassium or sodium pyrosulphate, exactly as 

detailed in 33. C, p. 218. The phosphorus and manganese having 

been determined in different portions (37, p. 222, and 34. B, p. 220), 

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, phophorus, and some 

of the manganese, where no attempt has been made to separately 

determine these.

48. 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 

20 cm.3 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 per-.

manganate.

49. 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 con-
CONDENSED ANALYSIS. 231

siderable excess. After several hours, twelve or fifteen if the precipitate is very slight, the solution is filtered, the precipitate redissolved in hydrochloric acid and reprecipitated by ammonia in moderate excess and a drop of the phosphate precipitant in the usual 

manner. After two hours the precipitate is filtered on paper or on 

a Gooch filter, ignited, and weighed as pyrophosphate.

50. ALKALIES.

See 39, p. 224.

51. CARBON DIOXIDE.

See 40, p. 224.

52. SULPHUR.

See 43, p. 226.

53. WATER. 

See 44, p. 227.

54. IGNITION LOSS.

This determination has little significance, though it affords a more 

or less correct indication of the proportion of carbonates in the rock. 

Since it is a determination commonly made in commercial labora-. 

tories, 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 v 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
232 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

unite with the lime. By proper regulation 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.

One-half 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. 32), and an inclined blast flame of considerable power is caused 

to play against the- bottom of the covered crucible for fifteen or 

twenty 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.......................... 51

of mortar...'............................. 50

Absorption tubes, use of, in water determination ........................ 73-83

Acids, quality of............................ 39

Acknowledgments to those aiding........... 15

Alkalies, determination of................. 171-178

determination of, apparatus for, figure

showing......................... 172

Alien, E. T.,cited...................... 50,113,190

Alien, E. T., and Day, A. L., cited....... 48-49,68

pycnometer method of.................. 48-49

Alien, E. T.,and Johnston, I., cited. 194 (footnote),

195,190,197

Aluminum, concealment of, by manganese.. 114 

direct determination of................ 111-113

indirect determination of... 98-110,215-219,229 

ignition of precipitate of oxide of....... 104-105

precipitation of..... 99-103,112-113,216-217,229

recovery of, from filtrates...... 103-104,217-218

separation of,from iron................ 111-113

Aluminum chloride, loss of.................. 99

Ammonia, occurrence of, in rocks.......... 202-203

Ammonia reagent, preparation of............ 40

Ammonium chloride reagent, quality of..... 40

preparation of.......................... 99,171

Ammonium oxalate reagent, quality of...... 40

Ammonium ])ersulphate reagent, purification of.................. 102 (footnote)

Analysis, allowable error in.................. 28

completeness and thoroughness of, importance of................... 16-22,42

crushing of rock for...................... 50-52

diversity of, for same rock............... 18-19

grinding rock for........................ 52-50

methods of.............................. 14

neglect of certain factors in, consequences

of................................ 19-21

preparation of sample for................ 50-57

quantity of rock required for.... 22,42,50,50-57

statement of............................. 29

time required for........................ 30

See also Carbonate rocks; Silicate rocks. 

Analysis, qualitative, usefulness of........... 38

Appliances and apparatus, descriptions and

figures of........................ 30-38

Aragonite,tests for.......................... 210

Atterberg, A., cited................. 174 (footnote)

Austin, M., and Gooch, F. A., cited. 110 (footnote),

123-124,145 

Autenrieth, W., cited ....................... 177

B.

Page. 

Bailey, G. H.,cited....................... 141,142

Barium, determination of. 119-121,138-140,218,221 

ignited silica free from .................. 97

precipitability of, by ammonium persulphate. ........................ 102

occurrence of, i.n rocks............... 20,25,198

recovery of, from alumina precipitate.... 107

removal of, from magnesium pyrophosphate............................ 120

separation of, from strontium.......... 119-120

Barium sulphate, speftroscopic testing of.... 140

Barus, Carl, cited............................ 61

Baskerville. C., method of, in determination

of titanium...................... 137

method of, in determination of zirconium. ........................... 142

Baubigny, H., method of, in determination

of chromium.................... 140

Bayly, P. G. W., cited...................... 71

Bemmelen, J. M. van, cited................. 57,02

Berger,C.W., and Hulett, G. A., cited. 94(footnote) 

Berzelius, J. .T., method of, or fluorine....... 185

Bibliography of rock analysis................ 13

Bisbee, H., Richards, T. W., and McCaffrey,

C. T., cited...................... 119

Blair, A. A., crucible tongs of................ 30

Blast, temperature of, test of......... 95 (footnote)

Bloor, W. R., cited.......................... 97

Blount, Bertram, cited..................... 94,215

Blum, William, cited........................ 192

Bolm, F., cited..................... 173 (footnote)

Bolton, H.C., cited......................... 210

Boric oxide, fusion of........................ 80

Boric oxide reagent, preparation of.......... 80

Boron, determination of................... 199-200

occurrence of, in rocks................... 27

Bornemann, E., cited................ 74 (footnote)

Bravo, Jos6 J., cited......................... 25

Bray, W. C., cited........................... 38

Broockmaun, K., cited...................... 126

Browning, P. E., cited...................... 120

Briihl, E., and Friedheim, C., cited....... 115,147

Brunck, 0., cited.......................... 121,123

basic-acetate method of, in separation of

iron,manganese, etc. 101-102 (footnote) 

Brush, G. J., method of, in water determination............................. 72

Buckley, E. R., method of, for determination of porosity.................. 45-46

Bunsen, R., cited............. Co, 91,174 (footnote)

233
234 INDEX.

C. Page. 

Calcite, tests for....................... 179,210-211

Calcium, determination of. 118-119,121-123,221,229 

ignition of oxalate of..................... 119

precipitability of, by ammonium persulphate. ........................ 102

removal of, from magnesium pyrophosphate.......................... 126-127

in alkali determination.............. 173

separation of strontium from........... 119-120

Calcium chloride reagent, deterioration of ... 74 

Calcium fluoride, testing of precipitate of.. 186-187 

Calcium oxalate, solubility of................ 119

Cameron, A., cited.......................... 91

Campbell, E. D., and Hess, AV. H., cited.... 112

Carbon, determination of.............. 182,224-225

effect of, on ferrous-iron determination... 165,

166,222,224 

occurrence of, in rocks............. 165.182,209

Carbonate rocks, analysis of............... 205-232

analysis of. defects of, as usually made.. 206-207 

condensed forms of................ 228-232,

detailed methods of................ 212-228

causes of color of......................... 208

ignition loss of......................'.., 231-232

importance of.........'................... 14

impurities in............................ 209

methods of decomposing........... 212-214,228

mineral composition of................. 207-209

qualitative comparison of silicate rocks

and.............................. 205

 qualitative tests of..................... 209-211

Carbonates, qualitative tests of............ 209-211

Carbon dioxide, direct determination of...... 179-

181,182,224 

direct determination of, apparatus for,

figure showing................... 180

expulsion of, by heat......:........... 200-201

indirect determination of.............. 181-182

Carbon monoxide, evolution of, on heating

rocks............................ 201

Carnot, A.,cited............................. 110

Cathrein, A., cited.... Ill (footnote), 1-35 (footnote)

Cerium, detection of......................... 143

occurrence of, in piedmontite... 100 (footnote) 

Chalcopyrite, occurrence of, in rocks......... 26

Chapin, W. II.. cited........................ 200

Chatard, T. M., cited...................135,145-146

drying oven of, description and figure of.. 76-77 

Chlorine, condition of, in rocks............... 182

determination of................... 183-184,225

occurrence of, in rocks................... 26

Chromium, colorimetric determination of.... 138-

139,147-148,150-154,220 

colorimetric determination of, comparison of gravimetric method and... 148 

effect of vanadium on................ 146

gravimetric determination of............. 146

occurrence of, in rocks................... 24,154

Citric acid, relative solubility of carbonates in. 210 

Claasen, Edo, cited.......................... 150

Clarke, F. AV., cited......................... 20

Classen, A., cited............................ 40

Cloedt, E. v., and Jannasch, P., cited...... 115,147

Cobalt, detection of.......................... 115

determination of....................... 116,220

occurrence of, in rocks................... 25

Coblentz, AV. AV., cited...................... 63

Page. 

Colorimeters, description of and figures

showing. ........................ 33-38

Colorimeteric methods, for determination of

chromium ..................... 147-148

for determination of chromium, comparison of gravimetric method 

and............................. 148

for determination of manganese ....... 116-118

of titanium ........................ 128-134

of vanadium ........................ 154

Columbium, occurrence of, in rocks .......... 27

Contamination of sample by agate ........... 56

by steel. ................................ 51

Cooke, J. P., method of, for determination

of ferrous iron ............. 161, 168-170

method of, apparatus for, figure showing. i70 

Coppadoro, A., cited ................ 108 (footnote)

Copper, determination of .................. -116, 220

occurrence of, in' rocks ................... 25

Cramer, E., cited............................ 40

Cross, AV., and others, cited. ................ 42

Crucible, disk for, description and figure of . . 22-23 

tongs for, description and figure of ....... 30

Crucibles, platinum, loss of weight of ........

 94-95 (footnote), 105 (footnote) ' 

Crushing, methods of ........................ 50-52

Crystal water. See AVater.

Curtis, J. S., cited. . ......................... 201

Czudnowitz, C., cited ....................... 149

Daniel, K., cited. .................. 184 (footnote)

Davis, J. F., cited........................... 142

Davy, Humphrey, cited ............. 86 (footnote)

Day, A. L., and Alien, E. T., cited. . ..... 48-49, 60

pycnometer method of .................. 48-49

Delesse, A., cited............................ 202

Desiccators, use of ........................ 68, 69, 70

Determinations, importance of order of ...... 41-42

Deussen, E., cited ................. 105 (footnote),

161 (footnote), 162 

Dieulafait, L., cited. .......... 20, 22 (footnote), 201

Dittrich, Max, cited ........... 13, 28, 65, 83, 88, 100,

105, 112, 138, 143 (footnote), 176 

Dittrich, Max, and Freund, S., methods of, 

in separation of titanium from 

iron ...................... 112, 136-138

methods of, in separation of zirconium

from iron........... 138 (footnote), 142

Dolomite, definition of ...................... 206

tests for ................................. 211

Drying before analysis, uselessness of ........ 65-66

Drying for hygroscopic tests, process of ...... 67-70

Dunn, J. T., and Pattinsofi, I., cited. ...... 195

Dunnington, F. P., cited.................... 129

Duschak, L. H., and Hulett, G. A., cited. . . 194,

196, 197 

E.

Eakins, L. G., cited. ... 1 .................... 47-48

Eddy, E. A., and Gooch, F. A., cited. ...... 176

Electrification of glass tubes, influence of,

on weight ....................... 74

Ellis, C. AV. H., mortar of, description and

figure of ......................... 51

Erdmann, H., cited. ........................ 202

Error in analysis, allowable limits of ........ 28
INDEX. 235

Errors due to abrasion of crushing and grindIng implements................. 51,56

grinding of sample........ 52-54,64-65,154-157

variation of blast temperature... 95 (footnote)

F. 

Faber, P., cited........................... 129,134

Feldspars, error in calculation of............ 20

Ferric iron, calculation of................... 110

See also Iron. 

Ferrous iron, determination of.... 154-171,222-224

determination of, hydrofluoric acid

method of.................... 161-171

sealed tube method of............. 157-161

oxidation of, by grinding........... 53,154-157

by free oxygen in presence of hydrofluoric acid or a fluoride......... *163

.preparation of sample for determination

of.............................. 157

See also Iron.

Filter paper, macerated, use of, for precipitations........................ 103,104

Fischer, T.,cited....... .'. ................... 153

Fluid inclusions, volatilization of........... 201

Fluorine, determination of............ 184-193,226

influence of, in aluminum determination. .................... 99 (footnote)

in silica determination.... 84,86 (footnote)

occurrence of, in rocks................ i.. 26-27

qualitative tests for..................... 184

Folin, Otto, cited.............. 194 (footnote), 195

Foote, H. W., and Penfleld, S. L., cited..... 200

Forchhammer, J. G., cited.................. 201

Ford, W. E., cited.......................... 200

Foullon, H. von, cited...................... 201

Franz, B., and Streit, G.,cited.............. 142

Fresenius, E,., cited................. 119 (footnote)

Freund, S., and Dittrich, Max., methods of, 

in separation of titanium from 

iron...................... 112,136-138

zirconium from iron........ 138 (footnote), 142

Friedel,G.,cited............................ 09,70

Friedheim, C., and Brilhl, E.,cited....... 115,147

Friedheim, C., and Pinagel, A., cited...... 92

Funk, W., basic-acetate method of, for 

separation of iron, manganese, 

etc................. 101-102 (footnote)

G. 

Gage, R. B., cited.................. 163 (footnote)

Galena, occurrence of, in carbonate rocks.... 209

Gases, evolution of, on heating rocks...... 201-203

Gautier, A., cited........................... 202

Gibbs, Wolcott, cited........................ 124

Gilbert, J. P., cited........................ 92,215

Glassware, inferiority of..................... 39

Glucinum, occurrence of, in rocks........... 27

Gold, occurrence of, in rocks................. 27

Gooch, F. A., apparatus of, for water determination, description and figures of.......................... 78-81

cited....................... Ill, 199 (footnote)

method of, in determination of lithium.. 175 

in determination of titanium...... 134-136

Gooch, F. A., and Austin,M.,cited. 116 (footnote),

123-124,145 

Gooch, F. A., and Eddy, E. A., cited........ 170

Page.

Gooch, 'F. A., and Jones, L.C., cited.. 199 (footnote) 

Gooch, F. A., and Newton, H. D., cited ..... 109

(footnote) 

Grinder, mechanical .......................... 55

Grinding, effect of, on composition of sample................... 52-54,64,154-157

methods of.............................. 52-56

H. 

Hall, R. W., cited................... 94 (footnote)

Hamberg, A., cited.......................... 62

Harper, D. N., and Penfleld, S. L., cited.... 99

Harrington, B. J., cited....................... 209

Harrison, J. B., cited........................ 25,27

Hauynite, evidence as to presence of......... 197

occurrence of, in rocks................... 26

Hayes, A. A., cited.......................... 20

Heidenreich, 0., and Jannasch, P., boricoxide method of, for decomposing silicates...................... 86

Hempel, W., cited........................... 56

Hewett, Foster, cited........................ 25

Hess, W. H., and Campbell, E. D., cited.... 112

Hinden, F., cited............................ 211

Hinrichsen, F. W., cited..................... 84,99

Hintz, E., and Weber, H., cited.... 194 (footnote),

195,190 

Holthof, C., cited............................ 88,90

Horn, D. W., cited................. 148 (footnote)

Hulett, G. A., and Bcrger, C. W., cited...... 94

(footnote) 

Hulett, G. A., and Duschek, L. H., cited.... 194,

196,197 

Hutchinson, A., cited....................... 210

Hiittner, K., cited......:.................... 202

Hydrofluoric acid reagent, quality of......... 39

.Hydrofluoric acid method of determining

ferrous iron.................... 161-171

Hydrogen, evolution of, on heating rocks.... 201

discriminating between conditions of, in

minerals......................... 58-63

r61e of i in minerals....................... 57-63

system, of class!float ion of. in minerals.... 63

Hydrogen peroxide reagent, quality of....... 40

Hydrogen sulphide, as impurity in carbon

dioxide................. 108 (footnote)

occurrence of, in carbonate rocks......... 209

Hygroscopic water, determination of........ 67-70,

73-76,227 

See also Water.

I.

Iddings, J. P., and others, cited............. 42

Ignition, loss by carbonate rocks on....... 231-232

loss on, inaccuracy of water determination by.......................... 71

temperature of, variations in..... 95 (footnote)

Iron, correction of titanium determination

for............................ 132-134

determination of..................... 107-110,

154-171,215-218,222-223,229 

effect of carbonaceous matter on..... 165,

166,222,223

effect of sulphides on.. 158-159,165-166,199 

effect of vanadium on......... 109-110,166

ignition of precipitate of oxide of...... 104-105

occurrence of, in carbonate rocks...... 207-208
236 INDEX.

Page. 

Iron, oxidizability of divalent, by free oxygen,

in presence of a fluoride......... 163

precipitation of......... 99-103,216-217,229-230

recovery of, from nitrate............... 103-104

reduction of........................... 107-108

separation of, from aluminum......... 111-113

in titanium determination......... 134-135

solution of oxide of, by alkali fusion..... Ill

titration of........ 108-110,167-170,218,222-223

See also Ferric iron; Ferrous iron. 

Iron oxides, error in determination of........ 21,

110,154-157,162-163,165-166.171

J. 

Jannasch, P., cited................. lf>2 (footnote)

nickel-becher of......................... 31

silicate decomposition methods of....... 85-86

water determinations of, apparatus for,

figure of....................... 82-83

method of........................'.-- 84

work of .......--..-......---...-.-.---- 84

Jannasch, P., and Cloedt, E. v., cited..... 115,147

Jannasch P., and Heidenreich, O., boricoxide method of................. 86

Jannasch, P., and Weber H., cited........... 86-87

Jannettaz, E., cited......................... 210

Jarvinen, K. K.,cited..................... 124,126

Jones, L. C., and Gooch, F. A., cited. 199 (footnote) 

Johnston, J., and Alien, E. T., cited. 194 (footnote),

195,196,197

Jordis, E., and Kanter, E. H., cited... 95 (footnote) 

Jordis, E., and Ludewig, W., cited... 93 (footnote)

K.

Kanter, E. H., and Jordis, E., cited... 95 (footnote) 

Kobell, F. von, cited ....................... 59

Knop, A., cited..................... 107 (footnote)

Koch, A. A., and Tread well, F. P., cited.. 186,187 

Koninck, L. L. de, cited.................. 126,158

Koningh, L. de, cited............... 147 (footnote)

Kortright, F. L., cited...................... 93

Krauch, C., cited............................ 39

Krcider, J. L., apparatus of, for determination

of volatile substances, description

and figure of.................. 181-182

L.

Lang, W. R., and Manning, R. J., cited ..... 200

(footnote) 

Lazurite, evidence of presence of, in rocks... 197

occurrence of, in rocks................... 26

Lead, determination of...................... 220

occurrence of, in rocks.................. 27,208

Le Chatelier, H., cited ...................... 57

Lemberg, J., cited........................... 211

Limestones, causes of color in................. 208

minor constituents of..................... 207

Limestones, dolornitic, definition of......... 206

Limestones, magnesian, definition of........ 206

Lindemann, 0., cited....................... 149

Lindo, D., cited............................. 92

Literature of analysis.......;................ 13

Lithium, determination of.......'.......... 174-175

occurrence of, in rocks................... 26

Low, W. H., cited.................. 200 (footnote)

L6we, J., clay disks of....................... 33

Page. 

Lowenstein, E.,cited....................... 57,62

Ludewig, W., and Jordis, E., cited.......... ' 93

Ludwig, E., cited........................... 91

Luedeking, C., and Wheeler, H. A., cited.... 202

Lunge, G., cited........................... 33,204

Lunge, G., and Millberg, C., cited.......... 95,204

Lunge, G., and Stierlin, R., cited ........... 194

 . ' (footnote), 195 

> M.

Macerated filter paper, use of, for precipitatation......................... 103,104

McBride, R. S., cited............... 108 (footnote)

McCaffrey, C. T., Bisbee, H., and Richards,

T. W., cited..................... 119

McKenna Brothers Brass Co., ore grinder

of, description and figure of...... 55-56

Magnesium, determination of.. 123-126,221,229-230 

occurrence of, in carbonate rocks......... 206

precipitate of contaminants of, removal

of............................. 120-128 '

ignition of......................... 126-127

precipitation of........................ 124-125

essentials of....................... 123-124

separation of, in alkali determination.. 176-177 

Maillard, L., cited........................... 154

Manasse, 0., cited.................. 151 (footnote)

Manganese, determination of.............. 113-118,

127-128,219-220,221,230 

occurrence of, in rocks.................. 25,207

oxidizability of divalent, in presence of

hydrofluoric acid.............. 102-163

precipitation of........ 102-103,114-115,216,217

removal of, from magnesium pyrophosphate......................... 127-128

Manning, R. J., and Lang, W. R., cited,

200 (footnote) 

Mar, F. W., cited........................... 140

Marble, contamination of, by sulphides,

108 (footnote) 

Mauzelius, R., cited.............. 53,64 (footnote),

154 (footnote) 

Meade, R. K., cited................. 214 (footnote)

Mechanical separation, literature of.......... 14

Meigen, W., cited............................. 210

Meineke, C., cited............................ 91

Merwin, H. E.,cited................... 129,130,134

method of, for fluorine................. 191-193

Meteorites, analysis of....................... 14

Microscopic examination, value of........... 17-18

Millberg, C., and Lunge, G., cited.......... 95,204

Minerals, specific gravity of fragments of..... 46-47

Mingaye, J. C. H.,cited...................... 21

Minor, J. C., and Penfield, S. L., cited....... 186

Mitchell, W. L., and Wells, H. L., cited,

108 (footnote) 

Mitscherlich method of ferrous iron deter-

 mination.................. 157,159-161

objections to............. 157,158,159 (footnote)

Mittasch, A.. basic acetate method of, for separation of manganese..... 101 (footnote)

Moissan, H., cited.............. Sr ... 200 (footnote)

Molybdenum, determination of........ 150-151,220

occurrence of.. in rocks........... 21,27,149,209

Moore, G. E., device of, to remove air from 

mineral powders, description and 

figure of......................... 48-49
INDEX. 237

Page. 

Morgan, G. T., cited....................... 182,225

Morley, E. W., cited............. 79,172 (footnote)

Morosewicz, J., cited................ 174 (footnote)

Mortar, for crushing......................... 51

Moureu, C.,cited.................... 202 (footnote)

N.

Nepheline, detection of, in presence ofolivine. 203 

Neubauer, H.,cited................. 123-124,125,126

Neustadl, L., and Skrabal, A..cited......... 120

Newton, H. D.,cited................ 109 (footnote)

Newton, H. D., and Gooch, F. A., cited,

109 (footnote) 

Nickel, determination of................... 116,220

occurrence of, in rocks................... 25

precipitation of........................ 114-115

Nickel:becher, description of................. 31

Nitrogen, occurrence of, in rocks............. 202

Noselite, evidence as to presence of........... 197

occurrence of, in rocks................... 26

Noyes, A. A., and others, cited.............. 38

Noyes, W. A., cited.......................... 133

0. 

Organic matter, removal of.................. 213

Oxidation, incompleteness of, on ignition of

ferrous compounds............... 71

P. 

Panebianco, G., cited........................ 210

Pattinson, I., and Dunn, J. T.,cited......... 195

Penfield, S. L., cited............... 46,79(footnote)

method of, for water determination...... 72,

73,74-75 

apparatus for, figures showing.... 72,73,75

Penfield,S.L.,and Foote,H. W.,cited...... 200

Penfield,S.L.,and Harper,D.N.,cited...... 99

Penfield, S. L., and Minor, J. C., cited........ 186

Penfield,S.L.,and Sperry, E. S.,cited ...... 199

(footnote) 

Peters, R., cited............................. 163

PfafT, F. W., cited........................... 206

Phenylhydrazine reagent, contamination of. 113

(footnote)

Phosphoric acid, decolorant for ferric solutions. ........................... 134

effect of, on color of titanium peroxide.... 129

Phosphorus, determination of...... 144-14C, 222,230

loss of, by vojatization........'........... Ill

occurrence of, in rocks.................. 26,209

precipitation of............. 99-103,145,216-217

Phosphorus salt reagent, quality of........ .. 40

Piedmontite, rare earths in.......... 100 (footnote)

Pinagel, A., and Friedheim, C., cited......... 92

Pirsson, L. V., cited...................... s . 29,203

Pirsson, L. V., and others, cited.............. 42

Platinum in filtrates ........................ 97

Platinum,occurrence of,in rocks............ 27

precipitation of.............. 98,107 (footnote)

reduction of,from solution....... 174 (footnote)

Platinum crucibles, loss of weight in......... 94-

95 (footnote), 105 (footnote) 

Platinum ware, iron in ........... 41,95 (footnote)

Porosity, determination of................ 43,45-46

Potassium, determination of....... 173-174,177-178

as chlorplatinate...................... ]74,178

as perchlorate........................... 178

separation of, by sodium cobaltinitrite. 177-178

Page. 

Potassium bisulphate reagent, conversion

of, to pyrosulphate.............. 40

objections to use of............. 105 (footnote)

quality of............................... 40

relative solubility of carbonates in..... 210

Potassium pyrosulphate reagent, advantages in use of.......... 105 (footnote)

Powell, N. S., and Richards, J. W., cited..... 210

Pratt, J. H., method of, in ferrous iron determination .............. 164-165,167-168

Precht, H., cited................... 174 (footnote)

Pycnometer method of specific gravity determinations ....................... 47-49

Pyrite, effect of, on ferrous iron determination ........................... 165-166

occurrence of, in rocks.................. 20,209

Pyrrhotite, evidence as to presence of, in

rocks....................... 26,197,199

R.

Radiators for evaporating solutions.......... 31-32

Rafla, E., cited.............................. 124

Ransome, F.L., cited.. 24 (footnote), 149(footnote)

Rare earths, caution against overlooking

of....................100 (footnote), 114

determination of........... 138-139,143-144,220

occurrence of, in rocks................... 23,27

Reagents, quality of......................... 39-41

testing of................................ 40-41

Richards, J. W., and Powell, N. S., cited.... 210

Richards, T. W., McCafTrey, C. T., and Bisbee, H., cited.................... 119

Ridsdale, C. H., cited..................... 110,152

Ries, H., cited.............................. 208

Riggs, R. B., method of, for separation of

magnesium from alkalies........ 177

Robertson, J. D., cited...................... 201

Rose, H., cited... Ill (footnote), 185 (footnote),202 

Rosenbladt, Th., cited.............. 199 (footnote)

S.

Sample, contamination of, by agate......... 56

contamination of, by steel....... 51 (footnote)

fineness of............................... 52,53

preparation of....................... 50-56,157

weight of................................ 56

Sandberger, F., cited............ 22 (footnote), 201

Sargent, G. W.,cited........................ 200

Schaffgotsch's solution, character of. 176 (footnote) 

use of.. '. ................ 176-177,185 (footnote)

Schaller, W. T., cited............... 173 (footnote)

Schreiner, Oswald, colorimeter of, description and figure of................ 37-38

Scoop. See Weighing, scoop for.

Seemann, F., cited.............. 185 (footnote), 187

Seger, H., cited.............................. 46

Separation, mechanical, literature of......... 14

Shinier, P. W..cited................ 214 (footnote)

Sieves, metal, unavailability of..'............ 51

Silica, adherence of, to dish.................. 93

dehydration of.......................... 91-94'

determination of........................ 83-97

] 05-107,188,206-214,218,229 

accuracy of..................... 96,106-107

impurities in, correction for.............. 95-96

precipitate of, ignition of................ 94-95

recovery of, from alumina precipitate.. 105-107
238 INDEX.

Page.

Silica, removal of, in fluorine determination. 185 

in sulphur determination............ 198

residue from, composition of............. 96-97

separation of, from alumina, etc......... 83-97,

214-215,230 

fluxes used in....................... 84-90

methods of....................... 83,91-94

Silica, soluble, determination of........... 203-204

Silicate rocks, analysis of................... 16-204

analysis of, methods of................. 41-204

constituents in.......................... 22-27

decomposition of, by hydrofluoric and

sulphuric acids.............. 83-84,131

literature of............................. 13

methods of decomposition of............. 83-90

Siliceous limestones, character of............ 208

Silver, occurrence of, in rocks................ 27

Silvestri, 0., cited........................... 203

Sjollema, B., cited........................... 204

Skrabal, A., and NeustadI, L., cited......... 120

Smith, J. Lawrence, cited.......'... 105 (footnote)

method of, for alkali determination.... 171-173

apparatus for, figure showing........ 172

Sodium, determination of................. 174-175

Sodium bisulphate, objections to.... 105 (footnote)

quality of............................... 40

Sodium carbonate fusion.................... 87-90

Sodium carbonate melt, effect of leaching of,

with water...................... 139

Sodium carbonate reagent, quality of...... 40-41,88

cobaltinitrite, reagent................... 177

Sodium hydroxide reagent, quality of....... 41

Sodium potassium carbonate, comparison of

sodium carbonate and........... S7-88

Sodium pyrosulphate reagent, preparation

of............................... 40

use of, advantages.............. 105 (footnote)

Solutions, heavy, unavailability of, in specific

gravity determinations of rocks.. 50 

Sonstadt, E., cited.................. 174 (footnote)

Spear, F. B., cited........................... 38

Specific gravity, determination of........... 43-50

Sperry, E. S., and Penfield, S. L., cited...... 199

(footnote)

Sphalerite, occurrence of, in carbonate rocks.. 209 

Steiger, George,.cited............. 114 (footnote),

129,103,173 (footnote)

calorimeter of, description and figures of. 35-37 

drying apparatus of, description and figures of.......................... 75-70

method of, for fluorine................. 188-190

Steinlen, R. L., cited............... 172 (footnote)

Stierlin,R., and Lunge, G., cited ... 194 (footnote),

195 

Stoddart, C. W., cited...;.......... 198 (footnote)

Stokes, H. N.,cited..... 141,158,159 (footnote), 165

Streit, G., and Franz, B., cited.............. 142

Strontium, determination of........... 119-120,221

occurrence of, in rocks................... 20,25

separation of, from calcium............ 119-120

from magnesium.................. 118-119

Strontium sulphate, spectroscopic testing of.. 140 

Sulphides, conversion of, to sulphates in

limestones....................... 227

influence of, on determination of ferrous

iron....................... 158,165-166

Page. 

Sulphur, condition of, determination of....... 197-

198,226 

determination of....... 138-139,198-199,226-227

errors in determination of............. 193-197

failure to determine, error arising from... 21 

occurrence of, in rocks................... 21,26

removal of, in alkali determination....... 173

Sulphur dioxide, reagent,- quality of. 151 (footnote)

T. 

Tammann, G.,cited......................... 57,62

Tantalum, occurrence of, in rocks............ 27

Tartaric acid, relative solubility of carbonates in........................... 210

removal of, in titanium.determination... 135 

Thorner, T. W., cited...'.................... 46

Thorpe, T. E., cited......................... 20

Thugutt, St. J., cited ............... 59 (footnote)

Tin, occurrence of, in rocks.................. 27

Titanic oxide, solubility of, in alkalies..... 111-112

Titanium, colorimetric determination of..... 128-

134,219

colorimetric determination of, superiority of............................ 138

gravimetric determination of.. Ill, 134-138,230 

loss of........................... 131 (footnote)

occurrence of, iu rocks................... 23-24

precipitation of.. 98,107 (footnote), 112,216-217 

Titanium sulphate reagent, preparation of.. 130 

Toluene bath, description and use of...... 75-76,79

Trace, definition of.......................... 29

Travers, M. W., cited....................... 202

Treadwell, F. P., cited..................... 95,185

method of, for ferrous iron determination ..'...................... 161,170-171

. apparatus for, figure showing........ 170

Treadwell, F. P., and Koch., A. A., cited . 186,187 

Tschermak, G., cited........................ 57

Tungsten, occurrence of, in rocks............ 27

Tyrolite, drying of, experiment on........... 68,69

U. 

Ulbricht, R., cited.......................... 126

Ullmann, C., cited.................. 1GO (footnote)

Uranium, occurrence of, in rocks. 

V.

27

Vanadium, colorimetric determination of.... 154

effect of, on iron determination. 109-110,149,166 

failure to determine, error from.......... 21

gravimetric determination of.. 150-154,220-221 

occurrence of, in rocks........... 20,24,149,209

Veitch, F. P., cited.......................... 84,99

Vogt, J. H.L., cited......................... 158

Volatile substances, determination of, apparatus for, description and figure of....'........................ 181

Volhard, J., cited................... 116 (footnote)

W. 

Walters, H. E., cited................ 117 (footnote).

Walton, J. H.,jr.,cited..................... 134

Warth, H., cited.................... 71, (footnote)

Washington, H. S., cited......... 13,17 (footnote),

18 (footnote), 22 (footnote), 23,25,28, 

29,52,108 (footnote), 114 (footnote)
INDEX. 239

Page.

Washington, H. S., method of, in determination of phosphorus.......... 144-145

Washington, H. S.; and others, cited...'...... 42

Water, direct determination of... 72-83,225,227-228 

direct determination of, apparatus for,

description and figures of........ 72-83

discriminating between conditions of, in

minerals.......................... 58-63

indirect determination of................ 67-71

methods of determination of............. 67-83

r61e of, in minerals...................... 57-63

suspension in, determination of specific

gravity by....................... 43-46

system of classification of, in minerals... 63 

Water lost by grinding........... 59 (footnote), 64

taken up by grinding... 53,59 (footnote), 64,65 

Weber, H., and Hintz, E., cited.... 194 (footnote),

195,196

Weber, H., and Jannasch, P., boric oxide, 

method of, for decomposing silicates ............................ 86,87

Weighing scoop, description and figure of.... 33

Weller, A., method of, for determination of

titanium.......:................ 128

Page. 

Wells, H. A., and Mitchell', W. L., cited.... 108

(footnote) 

Wells, R. C., cited.................. 105 (footnote)

Wheeler, H. A., and Luedeking, C., cited.... 202

Wherry, E. T., cited........................ 200

Williamson' J. A., cited..................... 39

Wulfing, E. A., cited............ 158,176 (footnote)

Z. i 

Zambonini, F., cited. ................. 57,6\), 61,62

Zeolitic minerals, dehydration of.... T. 60-61,69-70

occurrence of, in rocks........... 44 (footnote)

Zimmerman, C., method of, for separation of

magnesia........................ 176

Zinc, determination of..................... 115,220

occurrence of, in rocks.................. 27,208

precipitation of........................ 114-116

Zinc oxide solution, preparation and use of.. 185 

Zirconium, determination of.............. 111-112,

137,138-139,140-142 

difficulty with, in gravimetric titanium

determination................... 130

occurrence of, iu rocks................... 24

0