Property of the United States Government.

Bulletin No. 305 Series B, Chemistry and Physics, 49

DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

CHARLES D. WALCOTT, DIRECTOR

THE ANALYSIS OF 

SILICATE AND CARBONATE ROCKS

BY

W. F. HILLEBRAND

WASHINGTON

GOVERNMENT PRINTING OFFICE

1907

CONTENTS.

Introduction........................................................... 11 

Object and scope of the present treatise............................... 11

Acknowledgments........ ^............................. - r ............ 13

Silicate rock analysis.................................................... 14

Part I. Introduction................................................... 14

1. Importance of complete and thorough analyses ................... 14

2. The constituents occurring in silicate rocks...................... 20

3. The distribution and occurrence of certain minor constituents..... 21

4. Summation of analytical results and limits of allowable error...... 25

5. Statement of analyses......................................... 27

6. Time needed for making an analysis............................. 28

7. Useful appliances and apparatus............................... 28

A. Crucible tongs............................................ 28

B. Radiators for volatilizing liquids and solids.................. 29

C. Perforated disk for crucibles............................... 30

D. Weighing scoop or trough................................... 31

E. Colorimeters.............................................. 31

a. Survey form........................................... 31

b. Schreiner's form ........................................ 33

8. Preliminary qualitative analysis. ... J........................... 34

9. Quality of reagents....................'..........-.............. 34

Part II. Methods applicable to silicate rocks......'..................... 37

1. Introductory remarks .......................................... 37

2. Specific gravity (porosity)...................................... 38

General remarks.............................................. 38

A. By suspension in water................................... 39

a. Ordinary method for specific gravity.................... 39

b. Method for specific gravity and porosity combined........ 40

c. Penfield's method for specific gravity of minerals......... A42

B. Pycnometer method...................................... 42

a. Ordinary method... .\................................. 42

b. Refined method...................................... 43

C. Heavy solutions not suitable for rocks....................... 45

3. Preparation of sample for analysis............................ 45

A. Quantity of rock to be crushed ............................ 45

B. Crushing.................................................. 45

a. Survey methods...........'............................. 46

b. Washington's method ................................. 47

C. Grinding.................................................. 47

D. Weight of ground sample................................... 50

4. Water hygroscopic, zeolitic, crystal............................ 50

A. General considerations..................................... 50

a. Importance of employing air-dry powder for analysis...... 50

b. Temperature of drying................................. 50

c. Indirect methods ...................................... 51

d. Direct method......................................... 53

3
4. CONTENTS.

Silicate rock analysis Continued. Page. 

Part II. Methods applicable to silicate rocks Continued.

4. Water hygroscopic, zeolitic, crystal Continued. 

A. General considerations Continued.

e. Argument in favor of, including hygroscopic water in summation ........'.....................................- 53

f. Separate entry of hygroscopic and combined water....... 54

- g. Is all true hygr^copic water expelled at 100° ?........... 54

B: Apparatus for the direct determination of water at different

temperatures............................................ 56

General precautions...............'....................... 56

a. Steiger's application of the toluene bath................. 56

b. Chatard's oven for temperatures up to 300° and over...... 57

5. Water total or combined....................................... 59

A. Arguments against "loss on ignition" method............... 59

B. Direct weighing of the water without the use of absorption

tubes Penfield's methods........'....................... .59

a. For minerals easily deprived of their water............... 59

b. For minerals not easily deprived of their water............ 60

C. Direct weighing .of the water in absorption tubes ............. 61

a. Penfield's procedure................................... 61

b. Gooch's apparatus.................... f ................ 62

c. Merits of the above forms of apparatus.................... 66

d. Jannasch's methods.................................... 66

6. Silica, separation from alumina, etc............................ 68

A. Alternative methods of decomposing the rock................ 68

a. General considerations................................ 68

b. Decomposition of refractory silicates by hydrochloric acid

under pressure....................................... 69

c. The boric-oxide method of Jannaschand TIeidenreich..... 70

a. Preparation of the boric oxide...................... 70

ft. Treatment of easily decomposable silicates ......... , 70

y. Treatment of refractory silicates.................... 70

8. Further treatment after fusion ...................... 71

e. Possible objections to the boric-oxide method ....... 71

d. The sodium-carbonate method .......................... 71

a. Advantages of sodium carbonate over sodium potassium carbonate......................'............ 71

ft. Purity of the sodium carbonate..................... 72

y. The fusion with normal sodium carbonate ........... 72

S. Fusion with sodium bicarbonate .................... 74

£. Treatment after fusion............................. 74

B. Subsequent treatment.................................... 75

a. Separation of silica.................................... 75

a. Reasons for adoption of accepted procedure.......... 75

/3. Procedure in absence of notable amounts of fluorine.. 76

y. Procedure With rocks and minerals containing fluorine. 78

b. Ignition of silica....................................... 78

c. Correction for impurities in the silica.................... 79

d. Accuracy of the silica determination................... 79

e. Composition of the residue obtained from the silica....... 80

f. Platinum in filtrates.................................. 80

7. Metals precipitable by hydrogen sulphide ....................... 81
CONTENTS. 5

Silicate rock analysis Continued. Page. 

Part II. Methods applicable to silicate rocks Continued.

8. Aluminum total iron........................................... 81

A. Indirect method for aluminum (titanium)................... 81

a. Preliminary remarks.................................. 81

b. Precipitation of aluminum, iron, etc., without precipitating manganese................................. 82

a. Precipitation by ammonia........................ 82

ft. The basic-acetate precipitation..................... 83

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

manganese..................................... 85

a. By ammonia and ammonium persulphate ........... 85

P. By ammonia and ammonium sulphide.............. 86

d. Recovery of iron and aluminum from the filtrates........ 86

a. After an ammonia precipitation.................... 86

ft. After a basic acetate precipitation.................. 86

v. After precipitation by ammonia and ammonium 

persulphate ..................................... 87

e. Ignition of the precipitate of iron, aluminum, etc., oxides.. 87 

f. Recovery of silica and possible barium in the alumina precipitate ............................:........... 88

a. Silica ........................................... 88

ft. Barium.......................................... 89

B. Determination of iron in the precipitate of alumina, etc...... 90

a. Without regard to the presence of vanadium............ 90

a. Reduction of the iron................................ 90

ft. Titration of the iron................'............... 91

. ;'. Further treatment of the solution after titration....... 92

b. Having regard to the presence of vanadium...;......... 92

c. Determination of the true value for ferric iron............. 93

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

aluminum......................................... 93

a. After first removing iron as sulphide .................... 93

b. By extraction with a fixed caustic alkali................ 94

c. Combination method after Dittrich..................... 95

d. Direct precipitation of aluminum by phenylhydrazine.... 95

9. Manganese, nickel, cobalt, copper, zinc......................... 96

A. Difficulties in the way of a correct gravimetric determination

of manganese...'........................................ 96

B. Precipitation of the group and separation of its constituents.. 97 

a. The ammonium-sulphide method ...................... 97

a. Its advantages and disadvantages................... 97

ft. Precipitation by ammonium sulphide and separation of

manganese and zinc from nickel, cobalt, and copper. 97 

b. Manganese and zinc.................................... 98 .

c. Nickel, cobalt, copper......... ^...................... 98

'C. Colorimetric determination of manganese .A ................ 99

a. Preliminary treatment ..............\................. 99

b. Colorimetric determination of manganese by ammon,Lum_.,' 

persulphate ...............................././...... 99

10. Calcium and strontium (barium)............................... 101

A. Separation from magnesium............................... 101

a. Precipitation and ignition of calcium and strontium oxa-

-, lates together....................................... 101

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

oxalates............................................ 101
6 . CONTENTS.

Silicate rock analysis Continued. Page. 

Part II. Methods applicacle to silicate rocks Continued.

10. Calcium and strontium (barium) Continued.

B. Separation of strontium (barium) from calcium. ............ 102

a. By ether-alcohol...................................... 102

b. By amyl alcohol....................................... 102

C. Behavior of barium....................................... 102

D. Separation of barium from strontium........................ 103

E. Other methods of determining the weight of calcium......... 104

General statement........................................ 104

a. Volumetric method .................................... 105

1). By weighing as the carbonate........................... 105

c. By weighing as the sulphate........................... 105

d. By weighing as the fluoride............................ 105

11. Magnesium.................................................. 105

A. Precipitation ............................................ 105

a. Conditions necessary for the production of a normal precipitate . . ........................................... 105

b. Precipitation......................................... 107

<*. First precipitation................................. 107

ft. Second precipitation.............................. 107

B. Methods of collecting and igniting the precipitate............ 108

a. Ordinary procedures................................... 108

b. Modification of Ullbricht.............................. 108

C. Contamination by and removal of barium, calcium, and manganese .................................................. 109

a. Barium.............................................. 109

b. Calcium.............................................. 109

c. Manganese........................................... 110

D. Liability to error in the average magnesium determination.... 109

12. 'Titanium..................................................... 110

A. Colorimetric determination Avith hydrogen peroxide.......... 110

a. Description of the method (Weller's)................... 110

b. Correction for the color of ferric sulphate ................. 112

c. Alternative mode of preparing the test solution........... 113

B. Gravimetric methods..................................... 113

a. Gooch's method....................................... 113

a. Description of the method ........................ 113

ft. Gooch's method not directly applicable to rocks containing zirconium .............................. 115

b. Baskerville's method .................................. 115

c. Method of Dittrich and Pohl........................... 115

C. Superiority of the colorimetric and Gooch methods over the

older ones.............................................. 116

13. Barium (zirconium, rare earths, total sulphur, chromium) ....... 116

A. The general method ...................................... 116

B. The method without regard to zirconium and sulphur ........ 118

14. Zirconium................................................... 118

A. Author's method ......................................... 118

B. Other methods............................................ 119

15. Rare-earth metals other than zirconium........................ 120

A. Usual method .......................................'...,.. 121

B. Alternative method ....................................... 121
CONTENTS. 7

Silicate rock analysis Continued. Page. 

Part II. Methods applicable to silicate rocks Continued.

16. Phosphorus..................................................... 121

A. Procedure when material is ample........................... 121

a. Washington's method of preliminary treatment........... 121

b. Alternative method of preliminary treatment.............. 122

c. Subsequent treatment................................... 122

B. Procedure when material is scanty.......................... 122

17. Chromium.................:..........................-........ 123

A. Gravimetric method........................................ 124

B. Colorimetric method........................................ 124

a. Preparation and strength of standard solution.......: 124

ft. Preparation of test solution........................... 124

y. Comparison of colors ................................ 124

C. A few comparative data.................................... 125

18. Vanadium (chromium) and molybdenum ........................ 126

A. Distribution of vanadium and molybdenum ................. 126

B. Condition of vanadium in rocks............................. 126

C. AuthorVmethod........................................... 127

a. Description of the method............................... 127

b. Confirmatory qualitative tests........................... 129

c. Application of the method in presence of relatively much

chromium............................................ 129

D. Colorimetric method for vanadium........................... 131

19. Ferrous iron.................................................... 131

A. Comparison of sealed-tube and hydrofluoric-acid methods 

Comparative worthlessness of the former in rock analysis. .. 131

B. The modified Mitscherlich method........................... 133

a. Strength of acid.................................... 133

ft. Filling, sealing, and heating of the tube............. 134

y. Reason for introducing gas and sealing as above

directed......................................... 134

C. The hydrofluoric-acid method .............................. 135

a. Principle of the method ............................'..... - 135

b. Defects of the method...................:.............. 135

a. Oxidizability of divalent, manganese, by permanganate in presence of hydrofluoric acid .............. 136

ft. Extreme oxidizability of divalent iron by free oxygen

in presence of hydrofluoric acid or a fluoride....... 137

c. Influence of sulphides, vanadium, and carbonaceous matter 

on the determination of ferrous iron by the" hydrofluoric-acid method.............................. 138

a. Sulphides.......................................... 138

ft. Vanadium............ N............................. 140

y . Carbonaceous matter................................ 140

d. The method in its various modifications.................. 140

a. According to Cooke ......... ^...................... 140

ft. According to Pratt (modified)....................... 142

Y. According to Treadwell............................. 143

D". Uncertainties of the ferrous-iron determination ............... 144

20. Alkalies...................................................... 144

A. Trie J. Lawrence Smith method........"..................... 144

a. Its advantages ........................................... 144

b. Reagents and apparatus................................. 144
O CONTENTS.

Silicate rock analysis Continued. pagc. 

Part II. Methods applicable to silicate rocks Continued.

20. Alkalies Continued.

A. The J. Lawrence Smith method Continued.

c. Treatment of the mineral powder........................ 145

d. Separation of calcium and sulphuric acid ................ 146

e. Precipitation of potassium............................... 147

f. Sodium, and lithium..................................... 147

a. Gooch's method for separating lithium................ 148

B. Separation of alkalies by other methods ..................... 148

a. The mercuric-oxide method ............................. 149

b. The ammonium-carbonate method........................ 149

c. The amyl-alcohol method................................ 149

21. Carbon dioxide, carbon........................................ 150

A. Qualitative test for carbon dioxide.......................... 150

, B. Quantitative tests for carbon dioxide......................... 150

a. Direct method ......................................... 150

b. Indirect method ........................................ 152

C. Carbon..................................................... 153

22. Chlorine....................................................... 153

A. Condition in rocks........................................... 153

B. Determination of water-soluble chlorine...................... 154

C. Determination of acid-soluble chlorine....................... 154

a. By nitric acid........................................... 154

b. By nitric and hydrofluoric acids......................... 155

D. Determination of chlorine by alkali fusion................... 155

23. Fluorine (silica in presence of fluorine)........................... 175

A. Imperfection of the qualitative test for fluorine.............. 155 -

B. Quantitative determination of fluorine........................ 155

a. The method............I................................ 155

b. Testing of the calcium fluoride........................... 157

c. Accuracy of the method................................. 158

C. Determination of silica...................................... 159

24.' Sulphur...................................................... 159

A. Determination of its condition.............................. 159

B. Quantitative determination................................. 160

a. Total sulphur........................................... 160

b. Fractional determinations................................ 160

25. Boron........................................................ 161

26. Certain constituents in minute traces........................... 162

27. The gases and vapors expelled by heat............................ 163

28. Special operations.............................................. 164

A. Detection of nepheline in presence of olivine................ 164

B. Determination of soluble silica............................... 165

Carbonate rock analysis...................................................... 167

Part I. Introduction.................................................... 167

29. Qualitative comparison of carbonate and silicate rocks ........... 167

30. Mineral composition of carbonate-rocks........................... 169

31. Behavior toward different reagents as a means of distinguishing

different carbonates......................................... 171

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

potassium sulphate................................... 172

b. The Meigen reaction for distinguishing calcite from

aragonite............................................ 172

c. Distinguishing between calcite and dolomite.............. 173
CONTENTS. 9

Carbonate rock analysis Continued. Page.

Part II. Refined methods of analysis................................... 174

32. Silica, its separation from alumina, etc........................... 174

A. Methods of decomposing the rock............................. 174

a. When the inorganic.residue is to be separately analyzed... 174

b. When the inorganic residue is not to be separately analyzed 175

a. By solution in acid after strong ignition.............. 175

ft. By solution in-acid after heating with sodium carbonate .......................................... 176

B. Separation of silica...-._.................................... 1.76

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

in company with phosphorus, etc.............................. 177

A. Precipitation of aluminum, iron, etc ........................ 178

a. Collective precipitation of aluminum, iron, manganese,

titanium, and phosphorus by ammonium sulphide...... 178

b. Precipitation of aluminum, iron, titanium, and phosphorus by ammonia ............. ^....................... 179

c. Precipitation of aluminum, iron, titanium, and phosphorus by the basic-acetate method.................... 179

B. Treatment of the filtrates from alumina, etc.................. 179

C. Solution and separation of the oxides obtained in A and B.... 180

a. Silica (barium). . ...................................... 180

b. Iron................................................... 181

c. Titanium.............................................. 181

d. Aluminum............................................ 181

34. Manganese............................................. '. ...... 181

A. In the nitrates from 33 B .................................. 181

B. Separate determination of manganese. ...................... 182>

35. Copper, nickel, cobalt, zinc; rare earths, chromium, vanadium,

molybdenum............................................... 182

36. Calcium, strontium, barium, magnesium (manganese)............ 183

37. Phosphorus.................................................. 184

38. Ferrous iron.................................................. 184

A. In absence of carbonaceous matter.........................' 184

a. Ferrous iron soluble in sulphuric acid ................... 184

b. Ferrous iron in the insoluble residue...................... 185

c. Total ferrous iron. . .................................... 185

B. In presence of carbonaceous matter........................ 186

Alkalies...................................................... 186

Carbon dioxide, carbon (water)................................ 186

A. Determination of carbon dioxide............................. 186

B. Determination of carbon of carbonaceous matter. ............ 186

C. Simultaneous determination of water and of total carbon in

both forms............................................. 187

41. Chlorine..................................................... 188

42. Fluorine...................................................... 188

43. Sulphur ...................................................... -188

A. Tests as to its condition; determination of sulphate sulphur .. 1.88

B. Determination of total sulphur............................. 189

a. Methods of converting sulphides to sulphates ............ 189

cr. By ignition without flux........................... 189

/? . By ignition with sodium carbonate .................. 189

b. Treatment after ignition................................ 189
10 CONTENTS.

Carbonate rock analysis Continued. Page. 

Part II. Refined methods of analysis Continued.

44. Water........................................................ 190

A. Hygroscopic water......................................... 190

B. Combined water........... ; ............................... 190

Part III. Condensed analysis......................................... 190

45. Decomposition and solution ................................... 191

46. Silica.......................................................... 191

47. Aluminum, iron, eic ...............................\. .\...... 192

48. Calcium.................... .-*- .-............................. 192

49. Magnesium.................................................. 193

50. Alkalies..................."................................... 193

51. Carbon dioxide.............................................. 193

52. Sulphur...................................................... 193 .

53. Water......................................................... 193

54. Ignition loss................................................. 193

Index.................................................................... 195

ILLUSTRATIONS.

Fig. 1. Platinum-tipped crucible tongs.................................... 28

2. Radiator for rapid and safe evaporation............................. 29

, 3. Device for excluding flame gases from crucibles during ignition...... 30

4. Weighing trough of platinum..................................... 31

5. Survey form of colorimeter .......................t ............... 32

6. Schreiner's colorimeter........................................... 33

7. Moore's device to remove air from mineral powders................. 44

8. Ellis's steel mortar............................................... 46

9. McKenna ore grinder ............................................. 48

10. Steiger's drying apparatus......................................... 57

11. Chatard's drying oven for water determination....................... 58

12. Penfield's tubes for. water determination............................ 60

13. Penfield's oven for water determination........................... 61

14. Penfield tube for water determination.............................. 61

15: Modified form, of Gooch tubulated platinum crucible for water determination ....................................................... 63

16. Arrangement of Gooch apparatus during drying..................... 64

17. Arrangement of Gooch apparatus during fusion...................... 65

18. Glass tube for determination of water (Jannasch).................. 66

19. Glass tube for determination of water in special cases (Jannasch)..... 67

20. Cooke's apparatus for determination of ferrous iron.................. 141

21. Treadwell's apparatus for ferrous-iron determination................. 143

22. J. Lawrence Smith's crucible for alkali determinations. ............. 145

23. Apparatus for carbon-dioxide determinations...................... 151

24. Kreider's apparatus for indirect determination of volatile substances.. ' 152
THE ANALYSIS OF SILICATE AND 

CARBONATE ROCKS.

By W. F. HlLLEBRAND.

INTRODUCTION.

OBJECT AND SCOPE OF THE PRESENT TREATISE.

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

11
12 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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.

For the reasons that the chief carbonate rocks form so 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-
ACKNOWLEDGMENTS. - 13

Iddings, Microscopical Physiography of Rock-making Minerals, 

fourth edition (1903); and Ferdinand Zirkel, Lehrbuch der Petrographie, second edition, volume 1.

ACKNOWLEDGMENTS.

To my colleagues, Drs. F. W. Clarke, E. T. Alien, and E. C. Sullivan, and Messrs. George Steiger and W. T. Schaller, my thanks are 

freely rendered for friendly criticism, suggestions, and occasional 

direct assistance.
SILICATE ROCK ANALYSIS.

PART I. INTRODUCTION.

1. IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES.

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

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

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

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

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

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

thankful. Considering the limited facilities at their disposal in the 

way of laboratory equipment and quality of reagents, the general 

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

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

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

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

many decades annually turned out hundreds of analyses of all grades 

of quality and completeness. With the growth and extraordinary 

development of the so-called organic chemistry inorganic chemistry 

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

a part-of the curriculum of study, became but a prelude to the 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.

Witruthe introduction of improved methods of examination by the 

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

14
IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES. J

. of heavy solutions, whereby, on the one hand, the qualitative mineral 

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

some had to be discarded altogether; others were still utilizable after 

modification. In the light thus shed it became possible to explain 

many hitherto incomprehensible variations in the composition of some 

rock species or types, as shown in earlier analyses, and in not a few 

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

elements had obscured relations and differences which more thorough 

examination showed to exist (see p. 17). Consequently there arose a 

feeling of distrust of much of the older work in the minds of thosechemists and petrographers 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.a

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

o Dr. Henry S. Washington, in Professional Papers Nos. 14 (ChemicaJ 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 1869. After 

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

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

of the weight to be attached to a particular analysis.
16 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 the last five 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 onh* 

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

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

instances of totally inaccurate conclusions to be dra\vn 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.a

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

Washington, IT. S., Manual of the Chemical Analysis of Rocks, 1904, pp. 8-17.
IMPORTANCE OF COMPLETE AND THOROUGH ANALYSES. 17

The importance of the points indicated in the foregoing paragraph 

is 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 rock mass at different dates.

Si02 ..........................

TiOt. ........................

A1 2 03 ... .....................

CriQa.. ......................

Fe&a. .......................

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

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

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

Q-/"i

MgO. ....:...................

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

Na20. .......................

Earlier 

analysis.

54.42

13.37

6.61

b 3.52

4.38

6.37

10.73

1.60

Later 

analysis."

53.70

1.92

11.16

.04

3.10

1.21

.04

3.46

1Q

.62

6. 44

11.16

1.67

LisO........ ................

H 2O below 110°.............

H2O above 110°.... ..........

C02 .. .......................

PA- .......................

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

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

01. ..........................

Earlier 

analysis.

Trace.'

C2.76

1.82

99. 58

Later 

analysis."

 Trace.

.80

2.61

1.75

.06

.44

.03

100. 40

.19

100.21

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

that this 'later analys.s' 1 is itself probably incomplete and incorrect in part incomplete because of 

the probable presence of 0.2 per cent or more of ZrOj, incorrect because of the error in A1 2 03 resulting 

from having counted thcZr02 as AI 2Os, and from the fart that titanium is not fully precipitable in presence of zircon.um by Gooch's method (the one employed). This latter error involves both theTiO'.and 

the A1 2 03. (See/3, p. 115.)

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

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

given for the two oxides in the first analysis were accidentally transposed.

c Jn the published analvsis it does not appear whether this is total water or. as seems probable, only 

that remaining above 100°.

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

Ti02 , BaO, SrO, 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.

T\0t....... ...... ..........&.

AhOs. ................ -..-.-..

FeO

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

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

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

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

KsO.. .........................

Earlier 

analysis.

44.31

17.20

4.64

3

70

.10

10.40

G ET

3.64

Later 

analysis.

44.65

.95

13.87

6.06

2.94

.17

9.57

o.37

.76

4.49

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

Li2 0. ........................

H2O below 110°..............

H2O above 110°.. ............

CO2 ... .......................

PsO5 .... .....................

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

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

Earlier 

analysis.

.77

3.30

. 99. 11

Later 

analysis.

5.67

.95

2.10

.11

1.50

.61

99.92

Not entirely free from CaO.

Bull. 305 07-
18 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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

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

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

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

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

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

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

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

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

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

region, so far as examined, show 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 socks 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 THOROUGH ANALYSES. 19

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. 140), a matter of considerable importance, since the 

petrographer lays great stress 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 not have been suspected (see A, p. 131).

While strongly upholding the necessity for more thorough work, 

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

the immediate objects to be sought should be expended on every anatysis. 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 SiO,, 

A12 03 , 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 

anatyses.

Finally, whenever possible, a thorough microscopical examination of 

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

n J. C. II. Miugaye has lately confirmed its wide distribution in Australian rocks, coals, etc. (Records 

Ceol. Survey New South Wales, vol. 7, pt. 3, 1903, p. 213.)
20 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. a 

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 sedioSee 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, vok 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. 78,1893, p. 216: and Bull. U. S. Geol. Survey No. 167,1900, p. 49.

b 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. Dieuiafait by his elaborate qualitative researches showed how universal was the distribution of copper, /Jnc, barium, strontium, etc., in the 

primordial rocks.
CONSTITUENTS IN SILICATE ROCKS. 21

inentary 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:

Sj.O2 , Ti02 , ZrO2 , A12OS , FeA, Cr2O3 , V2O3 , FeO, MnO, NiO, CoO, 

MgO, Ca(), SrO, BaO, ZnO, CuO, K2 0, Na,0, Li2 0, H2 0, P2 05 , S,° 

S03 ,C,6 C02 , Fl, Cl, N.

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

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

boron, glucinum, 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. -
22 ANALYSIS OF SILICATE AND CAKBONATE 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."

CJiromium. "-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 Cr2 (X"

Vanadium. The distribution of this element has been in part covered by the remarks on pages 18-19. 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 

V^Oa, 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 siliceousigneous 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.

a Hillebrand, W. F., and Ransome, F. L., Am. Jour. Sci.,4th scr., voJ'. 10,1900, p. 120; Bull. U.S. Geol. 

Survey No. 262, 1905, p. 9.
MINOR CONSTITUENTS. 23

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 aiid 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 percento As to the Peruvian occurrence see Hewett, Foster, Eng. Min. Jour., vol. 82, 1906, p. 385, and 

Bravo, Jose J., Bol. Soc. Ing. (Lima), vol. 8,1906, p. 171,
24 ANALYSIS OF-SILICATE AND CARBONATE ROCKS.

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 niore 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 nephelite is 

present, though it is also found sometimes in nephelite-free rocks, and 

in a few cases in quartz-bearing ones. It is an essential component 

of sodalite [ also noselite W. F. II.], and is also present in scapolite 

and in a 'few apatites." Its amount when present rarely exceeds 

0.2 or 0.3 per cent. When seeking for the chlorine of these minerals 

it is always well to extract the powder first with cold water (see preceding paragraph). It is to be remembered that fluid inclusions in 

minerals sometimes contain sodium chloride, which would be largely 

extracted from the powder by water.

Fluorine. "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. 25

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. 158).

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. PL] 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.] 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/4 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.

"Kept. Sci. and Agr. Dept. British Guiana, 1906.
26 ANALYSIS OF SILICATE AND CARBONATE BOCKS'.

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 anatysis 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/' with which the independent experimental values of Doctor Dittrich* 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 percent. These percentages are in terms of the 

whole rock and not of the particular constituent.

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

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

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

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

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

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

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

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

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

and his methods.

Manual of the Chemical Analysis of Rocks, It04, p. 24. 

Jahrb. f. Min. u. Geol., vol. 2, 1903, p. 09.
INTRODUCTION. . 27

5. STATEMENT OF 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 SiO2 as the chief constituent and grouping 

together all chemically related oxides, as shown, for instance, on 

page 17.

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 emplo}Ting the arrangement so 

valuable in stating water anatyses.

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 Pirsson and later strongly 

advocated by Washington, 5 namely:

Si02 , A12 03 , Fe2 03 , FeQ, MgO,.CaO, Na20, K20, H2 0 (above 105- 

110°), H2 0 (below 105-110°), C02 , Ti02 , Zr02 , P205 , S03 , Cl, Fl, 

S (FeS2 ), O2 03 , V2 03 , NiO, CoO, CuO, MnO, SrO, BaO, Li 2 0, 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 b)^ the following considerations : C02 is placed next after H2 0, since these two are generally a 

measure of the alteration the rock may have undergone. TiO2 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. 

b Loc. cit.
28 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 coni'- 

plete 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 

metal ''

A. CRUCIBLE TONGS.

Fig. 1 represents a form of platinum-tipped 

cmcible 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 APPAEATUS. 29

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 (Janr 

nasch). 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 A is by turning the cogs of B up and over those of A. Evaporation may be greatly 

hastened when desired by placing upon A 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 uniformty heated by hot air, and large quantities of
30 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 lack of platinum a perforated 

asbestos board alone will yield fair service with 

a blast, but not as a rule with an ordinary 

burner.

C. PERFORATED DISK FOR CRUCIBLES.

Fig. 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. 31

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. SURVEY FORM. '

FIG. 4, Weighing trough cf plati-

~, 0 , . , num, to be balanced by counterThe burvey form of colorimeter shown poise of ]ead . Length of trough

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

of square or rectangular section, 8 to 12 cm. high and 3 to 3J 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 w&y 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.

t> 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.
32 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 conies 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. Survey form of apparatus for colorimetric determinations, in different aspects. G, One of 

two glasses of square or rectangular section, 8 to 12 cm. high and 3 to 3J 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 APPAKATUS. 33

b. SCHREINER'S FORM.

Dr. Oswald Schreiner, of the United States Department of Agriculture, has devised a colorimeter (fig. 6) ; a working on the same 

basic principle as the far more expensive one of Soleil-Duboscq, 

which has done good service 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, 

D, below, which carries a white sheet of 

cardboard or opal glass, and after passing 

through the tubes the light is reflected by a 

mirror, E, in the upper part of the instrument to the eye of the observer at F. The dimensions of the camera are about 70 by 32 

by 16 cm. Standard glass slides may be inserted at G below one of the immersion tubes 

in place of the tube containing the standard solution, the immersion tube being retained 

so as to give similar images when viewed from above.

The measuring colorimeter tubes, B, are 25 cm. long, with inside diameter as nearly as

' practicable 27 mm.; in no case less than 25 mm. and not greater than 29 mm. The glass

should be colorless and the bottoms well ground and polished, with internal surfaces of the

bottoms plain, in no case appreciably convex or concave. The bottoms must be ground

FIG. 6. Schreincr's colorimeter.

Bull. 305 07-

a Jour. Am. Chem. Soc., vol. 27, 1905, p. 1192. 

-3
34 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 18 mm., with the thickness of the glass the same in all the tubes. 

The bottoms of these tubes must be carefully ground and polished and the inside of thebottom 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 tube's 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 E, is the reading of the standard solution of 

strength S, and r the reading of the colorimetric solution of unknown strength s, then

s = S. 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.

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
QUALITY OF REAGENTS. 35

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.® The "guaranteed" reagents 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 

need no redistillation except for special experiments.

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. 155). 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.

Ammonia ought always to be redistiiled 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, and digest 

on the steam bath to coagulate the silica, which is then filtered; or, 

the salt may be dissolved in water and evaporated with a large 

excess of sulphuric acid till fumes of the latter rise copiously. On 

cooling, the mass is dissolved and treated as above. If a satisfactory article is not to be purchased, it can be made from equivalent 

parts of potassium sulphate and sulphuric acid. Even then the normal salt has first .to be examined, for it has been found to contain

<*.Die Prufung der chemischen Reagentien, 3d ed., Berlin, Julius Springer, 1896. English translation by J. A.- Williamson, D. Van Nostrand Co., 1902,
36 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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, can be had which does not carry more than 2-| milligrams 

of total impurity (see ft, p. 72) in 20 grams (0.012 per cent). This 

should be reserved for the main portions, in which silica, alumina, 

etc., are to be determined." For other constituents, as phosphoric 

acid, fluorine, sulphur, a poorer grade is quite allowable, provided it 

is free from the element to be determined and from 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 an otherwise acceptable 

article was encountered, namely, fluorine. The explanation of its 

presence is probably that cryolite had been used as the source of 

the carbonate. Sodium phosphate in small amounts seems to be a 

common contaminant of even good grades of sodium carbonate.

Sodium hydroxide made from sodium has been found with a large 

amount of lead, a fatal obstacle to successful mineral analysis, and 

also with small amounts of nickel.

anal. Chcmic, vol. 42,1903, p. 518.
METHODS APPLICABLE TO SILICATE ROCKS. 87

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, MgO, total iron, 

and the combined weight of all the following: Al2 03 ,Ti02 , P2 05 , Zr02; 

all iron as Fe2O3 , and nearty if not quite all vanadium, as V2 05 , also 

perhaps rare earths if present. In a separate portion is estimated 

FeO, and also the total iron, as well as BaO, if these last are desired 

as checks. The alkalies need a portion for themselves. In another, 

Zr02 , BaO, rare earths, and total sulphur are very conveniently determined. For V2 03 and Cr2 03 still another and usually much larger 

portion is to be used. Determinations of C02 , C, H2 0, Fl, Cl are all 

best made in separate portions of substance, tho various combinations are possible, as C02 and H2 0, C.and H2 0, 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 115, 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 21 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
88 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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, 0 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 the more serviceable the greater 

the care bestowed in obtaining them.

2. SPECIFIC GRAVITY. (POROSITY.) 

GENERAL REMARKS.

Though a knowledge of the specific gravity of rocks is seemingly 

less prized now than formerly by petrographers, it is occasionally 

needed and is ever a most important criterion in the identification of 

mineral species. As ordinarily 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 to be 

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

p.43). '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 

ismostuseful 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.

0 «Quantitative Classification of Igneous Hocks, 1003, University of Chicago Press, 280 pp.
SPECIFIC GEAVITY. 39

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 

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 view of the uncertainty as to what constitutes hygroscopic water (see e, p. 53), 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 

the error duo to loss of even all its watertluring ignition is quite negligible.

Since the first publication of the foregoing in Bulletin No. 143, 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 cturin;; 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 . 17.0840

.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 thc'prescncc 

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. Tor 

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 zeoiitization 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.
40 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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

unit. For instance, an unclried 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 of 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 procedure 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. Buckley 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,

oBuilclingand ornamental stones of Wisconsin: Bull. Wisconsin Geol. Nat. Hist. Survey No. 4, 1808, 

pp. 63, 70. * '
SPECIFIC GRAVITY. 41

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 their 

weight in water is ascertained by suspension. They are then removed 

from the water, rapidly dried on the surface with bibulous paper, and 

the weights then taken in air. a 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 of ten by not more than 0.01. "When reckoned in per cent, 

the error would be such a small fraction of 1 per cent as not to be 

worthy of attention. The specific gravity was determined by dividing the average of the two dry weights by the difference between the 

dry weight and the weight of the cube suspended in water." For 

arriving at the true porosity or actual pore space -compared with the 

volume of the sample tested, the following formula is to be used:

(B-A)sp. gr. 100 

' (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 and 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.

a 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 seen ring 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 onefourth of an atmosphere, without finding appreciable differences in the results obtained.
42 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

T. W. Thorner" and H. Seger and E. Cramer 6 -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 

wire for suspension. This is weighed full of water in another .vessel 

of water, and again after the removal of the mineral, the weight of 

which is found after drying.

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 one with 

a capillary stopper, provided with a millimeter scale etched in the 

glass, the divisions being numbered both ways from the center and 

calibrated by mercury, so that the value of each one in weight of 

water is known. The capacity of the flask filled with water to the 

zero division is then calculated for every half degree of temperature 

from 0° to 30° by making a series of careful weighings in which, the 

capacity of the stem being known, it is quite immaterial at what level 

the water stands, provided it is within the limits of the scale. The 

exact temperature is obtained by an accurate thermometer placed in 

a companion vessel of similar shape to the pycnometer and containing

aCbem. Zeit., vol. 29,1905, p. 744. c Am. Jour. Sci., 3d ser., vol. 50,1895, p. 448. 

p Idem, p. 884. .
SPECIFIC GRAVITY. 43

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 loVest 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 zerp 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 case is now 

determined in much the same way as in A. a, p. 39, after the unstoppered pycnometer containing it and nearly filled with water has stood 

with its companion vessel of water under the air pump the necessary 

length of time. The water needed to fill the flask is taken from its 

companion.

All who have used the pycnometer method for fine substances know 

the difficulty experienced in preventing 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 off in order to get the weight 

of the mineral. Usually this way is less to be recommended than the 

other.

b. REFINED METHOD.

In their elaborate study, of the thermal properties of the feldspars 0 

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 (d=l) in the third decimal place.

a Pub. Carneeic Institution of Washington, No. 31; and in less detail in Am. Jour. Sei., 4th ser., 

vol. 19, 1905. p. 93.
44 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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 stqpper 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 stopPycnometer

FIG. 7. Moore's device to remove air from mineral powders.

pering, the device of G. E. Moore" is made use of, slightly modified, 

as shown in fig. 7. 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 

warmed to 40° to 50°, in order to produce boiling within the flask, 

the -air is soon removed. During the boiling powder will usually be 

thrown up into the connecting tube; but this can be washed back by 

water from A or, after disconnecting, by boiled water from a wash 

bottle. ' Should any particles remain in the tube, they are washed into 

a tared dish and weighed, after evaporation of the water. It is absolutely essential that not the smallest grain be caught between the

a Am. Jour. Sci., 3d ser., vol. 3,1872, p. 41; Jour, prakt. Chcmie., vol. 2,1870, p. 329.
PREPARATION OF SAMPLES. 45

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 

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. 55 for remarks by Doctors Day and Alien on another source 

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

C. HEAVY SOLUTIONS NOT SUITABLE FOR 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.

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
46 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 iron .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 physical laboratory of the Carnegie Institution, which entirely obviates loss 

of material by flying fragments.

FIG. 8. Ellis's mortar for crushing coarse materials. AH parts of best chuicd and surface-hardened tool The method of operating is apsteel. A, Block, 12-J by 12J byGcm.,with depression parent from fig. 8. The block, 

in center 0.6 cm. deep; B, pestle, 20 cm. high,3.5 cm. 

dfameter at base; C, cylinder, 12A cm. high, 5 cm. 

outside diameter, .'.4 cm. insido diameter, fitting 

accurately the depression in 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.

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
PREPARATION OF SAMPLES. 47

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. The crushing must be carried to such a 

degree of fineness that after transferring the grains to the mortar the 

grinding motion of its pestle will not occasion further loss of flying 

particles, since the portions lost will, in case of all but glassy or very 

fine-grained material, not have the same composition as those retained.

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 into 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 centimeter is stretched over the open side of the 

bpx 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 practically 

no danger of contamination by metallic iron, and that any error 

resulting, from introduction of cloth fiber is negligible. This last 

will hardly^e true of the method practiced in parts of Europe (the 

German "beuteln"), which differs in essential points from the gentle 

sifting of Doctor Washington.

C. GRINDING.

Ordinarily an extrernely fine state of division is unnecessary, 

except in the case of those portions in which alkalies and ferrous iron 

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 slightly in excess of the quantity to 

be weighed off.

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. 

The grinder manufactured by the McKenna Brothers Brass Com-
48 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

pany, Limited, of Pittsburg, Pa., is shown in fig. 9, 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

FIG. 0. McKonna 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 soldervd 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 pestlo 

to be raised in removing the agate mortar. This is accomplished by loosening a set screw and dropping one of the four posts holding the mortar in place. The pestle should make about 200 revolutions 

pcr'minutn, 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 a.rm reduces the hardest ore very rapidly." Iron Age.

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 danger of copper, ziric, and
PREPAKATION OF SAMPLES. N 49

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 

tlie mortar, though its presence never became visible to the eye except 

when white materials were ground. The last contamination is prevented by the copper cylinder, A, soldered securely onto the pestle 

holder so as to form a cup large enough for the purpose intended. 

The tin shield, B, with a superposed rubber cloth, C, covering the slit 

required for the proper adjustment of the shield, greatly lessens the 

danger of metallic contamination, even with the all-steel machine. 

At first it was thought that a rubber cloth covering the mortar, with 

the pestle snugly fitting a hole in the cloth, would be an effective protection, but it was fou-nd that there was sufficient friction on the rubber itself to cause contamination of the powder beneath.

With this apparatus a large amount of work can be done in a short 

space of time, though there is much loss of fine powder if the speed of 

revolution is too high. In 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 and separate the grinders.

The abrasion of pestle and mortar becomes far more manifest with 

these machines 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 mairy iron ores, are 

as a rule softer than igneous rocks and consequently cause less 

abrasion of the grinding implements.

W. Hempel a 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 milligrams 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.

Metal sieves should never be used.

a Zcitschr. angew. Chemie, 1901, p. 843.

Bull. 305 07 4
"50 ANALYSIS OF SILICATE AND CAKBONATE BOOKS. 

D. WEIGHT OF GEOUND SAMPLE.

The sample when ground should weigh not less than 10 grams, andpreferably 20 in case i': 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 advantage over 

mineral analysis, since material is almost always available in ample 

quantity and any desired number of separate portions may be used, 

whereas with a mineral the analyst is frequently compelled to determine many or all constituents in a single, 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 HYGROSCOPIC, ZEOLITIC, CRYSTAL. 

. A. GENERAL CONSIDERATIONS.

a. IMPORTANCE OF EMPLOYING AIR-0RY 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 of course plain, namely, that of securing 

a uniform hygroscopic condition as a basis for convenient comparison 

of analytical results, since some rocks contain more hygroscopic 

moisture than others. Nothing, however, is more certain than that 

by the time the substance is weighed it has reabsorbed a certain 

amount of moisture, small indeed in most cases, but very appreciable 

in others; and further, with every opening of the tube moisture-laden 

air enters and is inclosed with the remainder of the dry powder. It 

therefore 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. Doctor Dittrich has expressed 

views similar to the above.

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 liygroscopicity 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.

b. TEMPERATURE OF DRYING.

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
DETERMINATION OF WATER. 51

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. 

In the affirmative case it may be well to repeat the drying at 100°, for 

a portion of the loss at 105° was probably due to combined water 

from a.mineral or minerals in the rock; but in that case even the loss 

at 100° may sometimes very well include combined water, in which 

case drying over -sulphuric acid alone may be desirable, or over dry 

sand.

C.. INDIRECT METHODS.

In the latter connection it is proper to point out certain pitfalls in 

the path of the unwary, which, however, are in part more likely to be 

encountered in the analysis of minerals, where their influence may be 

of far-reaching consequence. 

A-mineral which loses a great deal of water over sulphuric acid 2 or 

3 per cent, for instance may need an exposure of several days or even 

weeks for its complete extraction. If the weighings are made from 

day to d&y, 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 to1 reach it unless greater time is allowed. An experiment on 1 gram of tyrolite, made and published some years ago, seems' 

to illustrate this point in part:

Experiment of drying 1 (/ram of tyrolite.

Time 

exposed.

Hours. 

18 

26 

23 

24 

23 

24 

25

Loss.

Gram. 

0.0231 

.0083 

.0029 

.0012 

 .0008 

.0001 

.0003

Time 

exposed.

Hour.':. 

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 fifty-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 milligram per day took place for six days more, and might 

have been longer observed but for the interruption of the experiment.
52 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

Again, it is a common practice to determine the water given off by 

hydrous minerals in an air bath at temperatures at and above 100°. 

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.

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 C. 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 

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 Friedel says, the danger of accepting a loss in 

weight as an index of the amount of water lost is clearly shown, and 

thus that method of determining water is for many cases fully discredited. Just what method to adopt must be 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 b 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.

a Bull. Soc. Min., vol. 19, 1896, pp. 14, 94; Comptes rendus, vol. 122, 1896, p. 1006. 

6 Loc. cit.
DETERMINATION" OF WATE&. 53

I have shown" the importance of employing in desiccators only sulphuric acid of maximum dehydrating power. Acid that has stood long 

in desiccators that are in constant-us£_i3_by- no means so efficient as 

fresh, strong acid.

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 

4

d. DIRECT METHOD.

In general it is preferable to collect and weigh the moisture in suitable absorption tubes after its expulsion by the aid of apparatus 

described in B, page 56, even though the long time often required is 

sometimes an objection, since the absorption tube may gain weight, 

other than that of water from the mineral, sufficient to introduce an 

appreciable error. It may in such cases be necessary to run a long 

blank test for the correction to be applied.

C. ARGUMENT IN FAVOR OF INCLUDING HYGROSCOPIC WATER IN SUMMATION.

The question has been asked: "If the so-called hygroscopic water 

is not always such, but not infrequently includes combined water, why 

is not its determination and separate entry in the analysis entirely 

unnecessary? Why make a distinction, which, after all, may not be

a Am. Chem. Jour., vol. 14, 1892, pp. 6-7.
54 ANALYSIS OF SILICATE AND CAEBONATE EOCKS.

a true one?" The question involves the further consideration of the 

advisability of including in the analysis at all the loss at 100° or 110°. 

It would seem to be a reasonable desire on the part of petrographers 

to have all analyses referred to a moisture-free basis in order that 

they shall be strictly comparable. This involves the omission of the 

"hygroscopic" water from the list of constituents, which would be 

eminently proper were it always possible to be sure that the loss at 

100° to 110° truly represents mechanically held 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. 39.)

f. SEPARATE ENTRY OP HYGROSCOPIC AND COMBINED WATER.

To revert now to the primary question, it may be said that the estimation of the loss at 100° or 110° and its separate entry in the analysis 

is advisable as not infrequently affording at once to the lithologist an 

indication of the mineral character of one or more of the rock constiV 

uents, thus perhaps confirming the microscopical evidence or suggesting further examination in that line. An unusually high loss at 100° 

would be regarded as probable evidence of the presence of zeolites or 

other minerals carrying loosely combined water. It has been objected 

that the true hygroscopic moisture varies with the degree of comminution of the sample and with the condition of the air at the time ol 

weighing, and d;hat it is therefore improper to incorporate it in the 

analysis; but this variation is ordinarily not at all great. Perhaps the 

time may come when it will be the rule to ascertain by additional heating at a higher temperature whether the water lost at 100° is to be 

regarded as purely hygroscopic. In such case it would be proper to 

omit it, and a distinct advance would undoubtedly be scored.

g. IS ALL TRUE HYGROSCOPIC WATER EXPELLED AT 100°?

It has been tacitly assumed in the foregoing that true hygroscopic 

water can all be expelled at 100°, which perhaps is not to be accepted 

as universally true. Eminent authority holds that it is impossible,
DETERMINATION OF WATER. 55

in the cases of certain foliaceous minerals, notably the micas, to thus 

entirely remove it, and that a part is driven off only at higher temperatures. If this is true, a further uncertainty is introduced in its 

determination, which not only strengthens the argument in favor of 

entering all water in the tabulation, but also serves to emphasize the 

difficulties of the situation.

The following excerpt from the work of Doctors Day and Alien0 on 

the feldspars, already cited, has direct and important bearing on the 

above.

There is another error to which accurate specific-gravity determinations upon powdered 

minerals will be subject unless suitable precaution is taken. The exposure to the air during 

the period of grinding the samples gives opportunity for the condensation of sufficient atmospheric moisture upon the grains to affect the weight in air. The amount varies measurably 

with the size of the grains, as will be seen from the accompanying data, and probably with 

the degree of saturation of the atmosphere and the time of exposure.

Determination of moisture in 1 gram of powdered mineral upon exposure to ike air. 

[<=finer than. >=coarscr than.]

, Mineral.

Ahi Ana (artificial glass) ..................................................

Abi Aiii (artificial crystal) ................................................

Do....................... .........................................

Fineness (mesh).

<150.. ............

Selected, coarse... 

<100> 120... ......

<100>]20.........

<100M20.........

<150. .............

<120>150.........

<150..............

Still finer.........

>150..............

Moisture.

Gram. 

0.0001

.0000 

.0010

.0007

.0010 

.0000

.0009

.0031

.0059

.0005

.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 Bunsen b that this absorbed moisture is not altogether 

removed at temperatures only slightly above 100°, but requires 600° to 800° equivalent to 

low red heat. Several samples for which the moisture had been determined were laid away 

in corked test tubes for a number of weeks, after which redetermination gave exactly the 

former value.

It is worth noting in this connection that these measured quantities of absoi'bed 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.

« Pub. Carnegie Institution of Washington, No. 31, pp. 50-57; Am. Jour. Sci., 4th ser., vol. 19, .1905, 

p. 93. 

b Wiccl. Ann., vol. 24, 1885, p. 327.
56 ANALYSIS OF SILICATE AND CA.BBONATE BOCKS.

B. APPARATUS FOR THE DIRECT DETERMINATION OF WATER AT DIFFERENT TEMPERATURES.

GENERAL PRECAUTIONS.

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 riearly 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. 

Finally the electrifying effect of wiping a tube before placing it 011 the 

balance must not be overlooked. In my experience this has often 

amounted to as much as 1 to 2 centigrams (always an increase in 

weight) after wiping with a clean linen handkerchief. The charge 

can be removed by repeated application of the hand, but disappears 

slowly without such aid. A strongly electrified condition makes 

itself apparent by marked irregularities in the swing of the needle. 

While more pronounced in cold weather, the phenomenon is not 

peculiar to winter.

a. STEIGER'S APPLICATION OF THE TOLUENE BATH.

The apparatus devised by George Steiger consists simply of a 

U-tube of home construction and a small toluene bath, in the cover of 

which is an opening of suitable shape to receive the tube (fig. 10). 

The open space between the uprights is closed when in operation by 

a piece of asbestos board. The horizontal end of the tube is made 

long, so that in the event of much water being given off it can be readily 

driven over into the absorption tube by a low flame, which if applied 

from the first may prevent any appreciable condensation of water 

before reaching the calcium chloride. The interior of the tube having 

been first freed from adhering moisture by a current of dry air and the 

absorption tube attached, the stopper is lifted without shutting off the
WATEK-DEfERMINATION APPABATOS. 5*7

air current, and the weighed powder quickly introduced by means of the 

clean metal trough in which it has been weighed (fig. 4. p. 31). 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. 11, 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 on the top 

of the bath would suffice 

to prevent condensation 

of moisture before reaching the absorption tube, 

or to soon remove what 

might condense at first, 

but there must be no 

long rubber connections.

By employing a suitable oven this form of 

tube can "be used for 

higher temperatures, but 

the stoppers must fit airtight, for vaseline can not be employed.

h. CIIATARD'S OVEN FOR TEMPERATURES UP TO 300° AND OVER.

A form of drying oven devised by Dr. T. M. Chatard a 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. 11. The box is 

so constructed that the tube with its contents can be removed without detaching from either the drying or collecting tubes, which is a 

great advantage if it is desired to apply afterwards the direct heat

FIG. 10. Steiger's form of drying apparatus. A, Toluene bath; 

B, condcnr.er, 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.

a Am. Chcrn. Jour., vol. 13, 1891, p. 110; Bull. U. S. Oeol. Survey No. 78, 1891, p. 84.
58 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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. 

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

FIG. 11. Chatard's form of drying oven for water determinations. B, Copper box, 18 cm. long, 

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 Bull. No. 176, p. 37. 

The use of a straight tube, as shown in fig. 11, permits of a less complicated construction of box and 

stand than that'herc shown, since round holes in opposite ends of the box admit the ignition tube, 

and the roller base is then superfluous.

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, 0, after the tube is in place, but before 

closing the front.

For other forms of tubes adapted to similar determinations, see 

pages 61 and 66-67.
DETERMINATION OF WATER. 50

5. WATER TOTAL OR COMBINED. 

A. ARGUMENTS AGAINST "LOSS ON IGNITION 7 ' METHOD.

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. 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. 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.

Direct weighing of the water evolved is then imperative in most 

cases, and of the numerous methods advocated, or in general use, 

several will now be considered.

B. DIRECT WEIGHING OF THE WATER WITHOUT THE USE OF ABSORPTION TUBES PENFIELD'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. S. L. Penfield 0 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

a Am. Jour. Sci., 3d ser., vol. 48, 1804, p. 31; Zcitschr. anorg. Chemie, vol. 7, 1894, p 22.
60 ANALYSIS Otf SILICATE AtfD CARBOKATE ROCKS.

back and cracking the hot glass. A capillary glass stopper fitted in 

with rubber tubing prevents loss of water by circulating air currents. 

The tube being held horizontally, the bulb is heated to any required 

degree by the Bunsen or blast flame. Moistened filter paper or cloth 

wound about the cooler parts of the tube insures condensation of all 

water. The heated end being finally pulled off, the tube is weighed 

after cooling and external cleansing, and again after the water has 

been removed by aspiration. For most rocks, as they contain little 

water, central enlargements of the tube are hardly needed. 

Various forms of tubes used by Penfield are shown in fig. 12.

C

FIG. 12. Penfleld'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. '

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.

Few rocks, comparatively, 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.

b. FOR MINERALS NOT EASILY DEPRIVED OF THEIR WATER.

When minerals are present which 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. 13, 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,
^DETERMINATION OF WATER. 61

and the part outside by asbestos board, as well as by wet cloth or 

paper. A piece of charcoal is likewise laid on the tube, as well as 

beneath and behind, and the blast flame is given a horizontal direction, so as to play upon the side of the apparatus. In this way a 

most intense temperature can be reached.

FIG. 13. Penfield's fire-brick and charcoal oven for use in determining water.

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.

G. DIRECT WEIGHING OF THE WATER IN ABSORPTION TUBES..

a. 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 58, the determination of the hygroscopic as 

well as any other fraction of the water, is the following glass-tube 

arrangement (fig. 14) of Penfield, a whereby the brick and charcoal 

oven already referred to (fig. 13) comes again into play, but without the half brick shown in that figure.

The tube is of about 15 mm. internal diameter, and is fitted with 

two platinum cylinders at A, one inside, the other outside, where 

the heat exposure is to be most intense.

These are made from pieces of platinum foil, about 0.07 mm. in thickness and 8 by 11 

cm. in 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.

FIG. 14. Tube for water determination according to Penfield. A, Outer protecting covering of platinum foil. A second similar foii on the inside prevents the glass from collapsing when heated to 

softness, b, Cross section of platinum boat. ' '"' ^

A large platinum boat, 7 to 8cm. long and 11 to 12 mm. in diameter, with a cross section 

like bj 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

a Am. Jour. Sci., 3d ser., vol. 48, 1894, p. 37, Zeitschr. anorg. Chemie, vol. 6, 1894, p. 22.
62 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

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 asingle instance where the glass tube has broken or shown any indication of breaking. 

After heating the tube will not crack if it is left to cool slowly on the charcoal, but it can 

not be used a second time. * * * At the high temperature to which the glass is 

subjected it of course becomes very soft and the ends must be properly supported; also 

the rubber connections and absorption apparatus must be carefully screened by asbestos board. By constructing a cover for the boat no material need be lost by 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, v/hereby distortion of the boat would result 

and its withdrawal for further examination of its contents would be 

impossible.

b. GOOCU'S APPARATUS.

Of more elaborate apparatus, designed to be used with fluxes, the 

tubulated platinum crucible invented by Doctor Goochb 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. 15, 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. 15 differs from that given 

in Bulletin No. 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 figure there is absolutely no danger of their 

ends "becoming hot enough by conduction to scorch or soften the

rubber connection. >

The extra first cost 'of the platinum extension to these kibes over 

the lead-glass ends of Gooch's original and modified forms need 

hardly enter as a factor into the question of employment of this 

apparatus. The glass ends often break, and only a rich lead glass, 

not easily obtainable, can be used, since it alone will not crack at 

the joint with the platinum after cooling.

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. 16), forming at the center of the ring a secure seat

o Am. Chem. Jour., vol. 2, 1880, p. 247; Chem, News, vol. 42, 1880, p. 326.
DETERMINATION OF WATER. 63

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. 15), is there mixed with not more than 3 or 4 grams of fully 

dehydrated sodium carbonate,0 or more of lead chromate if carbon is 

to be likewise determined. The crucible is sunk in its seat, S (fig. 16), 

in the upper ring, B/, and the tubulated cap, T (fig. 15), is fitted 

on and attached to the calcium-chloride drying towers preceded by

FIG. 15. Modified form of Gooch tubulated platinum crucible for the determination of water, one-lialf 

natural size. Weight about 75 grams.

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. 17), on the other. Powdered sodium tungstate free from arsenic, which would soon ruin, the crucible lips is now poured into the 

flanged lip, L (fig. 15), in which the cap rests, and a metal vessel of 

cold water having been raised up by the lower ring, K" (figs. 16 and 

17),until the platinum crucible is sufficiently immersed, the flame of

a 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 fouod that 2.6 grams of it, spread out on a watch glass, gained 

only 0.0002 gram in fifteen minutes.. Pot.agsj.uxn carbonate and potassium-sodium carbonate are too 

.hygroscopic by Sax to be available,
64 ANALYSTS OF SILICATE AND CARBONATE KOCKS.

an ordinary blase 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. 66), by means of an air or toluene bath, as shown 

in fig. 16, the absorption tube, A (fig. 17), is interposed between the 

sulphuric-acid bulbs and the apparatus, and, while a slow current of

FIG. 16. 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.

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. 16 and 17). The sodium-tungstate joint is shielded from the 

flame by small pieces of asbestos board, P (fig. 17), cut out so as fc> 

fit the crucible. 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 tQ continue until the 

apparatus is cold.
DETERMINATION" OF. WATER. 65

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 

other purposes, being distorted by the alternate expansion and contraction of the carbonate.

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

FIG. 17. Arrangement, during fusion, of Gooch apparatus for determining water. E'", Blast-fed 

ring burner; P, protective asbestos shield resting on ring R"; F, asbestos-board shield; A, calciumchloride 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.

penetrating water gases is inappreciable. This hastening may be rendered safer by using rather finely powdered calcium chloride in the 

central section of the U-shaped absorption tube to avoid large air 

channels. Through this or any other apparatus based on similar principles the air current should always be forced, not drawn. A warm 

air blast directed upon the exit tube near its entrance into the 

absorption tube greatly shortens the time required and is to be 

recommended. -

Bull. 305 07 5
66 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 

(fig. 16), 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. ,

C. MERITS OF THE ABOVE FORMS OF APPARATUS.

The apparatus described in a and I 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.

d. JANNASCH'S METHODS.

This zealous deviser of methods for mineral analysis has published 

in the Zeitschrift fiir anorganische Chemie and the Berichte der 

Deutschen chemischen Gesellschaft several papers dealing with the 

problem of water determination in minerals, and in his text-book 0 

these are collected in more or less modified form.

b

FIG. 18. Glass tube for determination of water (Jannasch). b, 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. 18.

o Praktischer Leitfaden der Gewichtsanalyse, Leipzig, von Veit & Co. (1897).
DETEEMINATION OF WATEE. 67

For rocks or minerals containing not much fluorine 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 sodalime tube to the calcium-chloride tube. For one-half to 1 gram of 

silicate Jannasch uses 1 $ to 2 grams of dehydrated borax.

Regarding the borax method, its inventor 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.

n n FL n

FIG. 19. Glass tube for determination of water in special cases (Jannasch). Length from a to e, 26 

cm.; inside diameter somewhat over 1cm.; volume of bulb 6,25cm. 3 ; cd, retaining layer of lead oxide 

between plugs of glass wool. /, calcium-chloride absorption tube; g, protective tube.

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 fig. 19. Minerals, such as topaz, which is not fully decomposed by the borax 

method and which contains a large amount of fluorine, are fused at Z> 

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.
68 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

If C02 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' OE 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 

in principle, was abandoned by me after fair trial, owing to the disturbance sometimes occasioned by incomplete expulsion of fluorine 

and to a less degree by the presence of sulphates instead of chlorides. 

With the exception of a comparatively few analyses made thus, the 

sodium-carbonate method 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. 155, also footnote, p. 71), 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-fou-rths 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
METHODS Otf DECOMPOSING SILICATE' ROCKS. ()9

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 mineral to an impalpable powder, and the flux itself may need considerable hand pulverization. Once introduced, they must be removed 

before the analysis can be proceeded with, and this removal takes 

much time and is always a possible source of error.

In mineral analysis these objections are entitled to far less weight 

than in rock analysis, 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 well as to complex mixtures of them.

b. DECOMPOSITION OF REFRACTORY SILICATES BY HYDROCHLORIC ACID UNDER PRESSURE.

Jannasch0 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 partially filled with the diluted acid; seals 

the glass tube, places it in turn in an inclined position in a steel 

Mannesmann tube containing ether or benzine to equalize the pressure, and heats to any desired temperature up to 400°.

The chief drawback seems to be a somewhat incomplete decomposition, doubtless due to the necessarily inclined position of the tube, 

which causes the powder to collect at the lower end, and thus renders 

decomposition less complete than if the material were spread evenly

<*Ber. Deutsch. chem. Gesell., vol. 24,1891, p. 273; Zeit'schr. anorg. Chemic, vol. 6, 1894, p. 72.
70 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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 casoes when 

economy of material is imperative.

C. THE BORIC-OXIDE METHOD OF JANNASCH AND HEIDENREICH.«

of. Preparation of the loric 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.

J3. 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 edge of the 

crucible. When the mass has been in quiet fusion for a time in the 

covered crucible the blast flame is applied. The average duration of 

the entire operation is twenty to thirty minutes, but depends much 

on the character of the mineral.

y. Treatment of refractory silicates. For those minerals which, like 

andalusite, cyanite, and topaz, are not fully decomposable by the 

heat of the ordinary blast flame, Jannasch and Weber 6 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

aZeitschr. anorg. Chemie, vol. 12,1896, p. 208. This method of decomposing rocks with-a view to the 

determination of their contained alkali originated with Sir Humphrey Davy, as shown in his paper 

."On a method of analyzing stones containing fixed alkali by means of the boracic acid " (Phil. Trans., 

1805, p. 231;_Ann. d. chim., vol. 60, 1806, p. 294; Gilbert's 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.
METHODS OF DECOMPOSING SILICATE ROCKS. 71

are added and the oxygen blast is applied till, in ten or fifteen minutes, the fusion is as transparent as glass. a

8. Further treatment after fusion. From this point the further 

treatment is the same in both cases and, as modified by Jannasch 

and Weber b , is as follows:

The hot crucible is cooled in cold water and the contents are turned 

into a very large porcelain or platinum dish, to which, after covering 

with a glass, a saturated solution of hydrochloric-acid gas in methyl 

alcohol is added. c 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.

£. 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 the use of the oxygen 

flame when alkalies are to be estimated in the fusion, and the ability 

to so determine them is one of. Jannasch's chief claims in favor of the 

method, for it can not be doubted that at the high temperature of 

this flame alkalies are volatilized. Borax can be 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

a An interesting and important observation reported by Jannasch and Weber is that when the oxygen 

blast has been used for silicates carrying fluorine or mixed with fluorides the fluorine seems to be wholly 

expelled as boric fluoride without loss of silica. 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.

b Ber. Deutsch. chem. Gesell., vol. 32,1899, p. 1670.

"Made by passing dry hydrochloric-acid gas into cooled methyl alcohol for from one to two hours.
72 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

determined, there is no advantage in using the much recommended, 

because more fusible, double carbonate of sodium and potassium, or 

the equimolecular mixture of the normal carbonates, or of sodium 

carbonate and potassium bicarbonate. As Dittrich says, 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..

ft. 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 s,traw, which have 

sometimes been found in large amount are silica, alumina, iron, lime, 

magnesia, and sometimes phosphoric oxide, all of these going into 

aqueous solution with the carbonate. The chief of these impurities 

are usually silica, alumina, and lime. 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 sorcalled 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. 74).

y. The fusion until 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

"a Anleitung zur Gesteinsanalyse, 1905, p. 5. & Zeitschr. anal. Chemie, vol. 23,1884, p. 499.
METHODS OF DECOMPOSING SILICATE BOCKS. 73

placed over a moderately low Bunsen flame, which is gradually 

increased to the maximum and maintained there till the mass is 

quiescent. There should be no violent action. The contents of the 

crucible will then appear, in the case of highly f eldspathic 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 and 

bottom, nor should the flame be allowed to envelop the whole crucible. 

These precautions apply in all ignitions of reducible substances, and yet 

they are 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 ror 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 t>est 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,
74 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

will indicate absence of manganese when it is really present in quantity to give normally a strong coloration. Two fusions made side by 

side or successively, under apparently similar conditions, may in one 

case show little or no manganese, in the other considerable. This 

observation has been frequently made, and therefore the absence of a 

bluish-green color in the fusion is not to be taken as proof of the absence 

of manganese. This difference of behavior I can ascribe to no other 

cause than that of a reducing atmosphere in one of the crucibles and 

an oxidizing one in the other, even though the conditions were apparently alike. It is, of course, not to be expected that the green color can 

show until all other oxidizable components of the rock, like sulphides, 

ferrous iron, and organic matter have been fully oxidized, which, however, is soon the case if air has access" to the surface of the melt.

3. Fusion with sodium bicarbonate. C. Hoithof, who recommends 0 

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 maintamed 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. 28), 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. 

This is preferable to allowing the melt to form a thick cake at the bottom, since much less time is required for disintegration, and separation 

from the crucible is usually much easier.

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 approximately the amount of manganese present. The beaker is placed 

on the water bath, and when disintegration is complete, having been 

assisted by gentle pressure with a blunt glass rod, the contents are 

transferred to a large platinum dish and evaporated On the bath. It 

is permissible to dispense with the beaker and to perform the whole

a Zeitschr. anal. Chemie, vol. 23,1884, p. 499.
DETERMINATION OF SILICA. 75

- operation of solution in the platinum dish, but there will be greater 

solution of platinum in this case by reason of the action of the 

hydrochloric acid on sodium manganate, etc., in direct contact with 

platinum.

B. SUBSEQUENT TREATMENT.

From this point the treatment will ordinarily be the same whether 

the boric-oxide or the sodium-carbonate method of decomposition has 

been employed^ 

a. SEPARATION OF SILICA.

a. Reasons for adoption of accepted procedure. The once universal 

practice of employing a single evaporation with hydrochloric acid for 

the dehydration of silica has been thoroughly discredited 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 nitration) 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, 

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,6 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

"Ann. Chem. Pharm., vol. 61, 1847, p. 265.

b Xeitschr. anal. Chemie, vol. 9, 1870, p. 321.

« Eepert. anal. Chemie, vol. 7,1887, pp. 215, 757.

dChem. News, vol. 69,1894, p. 171.

« Technology Quarterly, vol. 3,1890, p. 61; Abstract in Zeitschr. anal. Chemie, vol. 29, 1890, p. 688.
6 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 a 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.& 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 c 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.

ft. 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.

The evaporating dish should be of platinum and as large as possible 

to permit considerable surface distribution of the dry mass. 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. Noth- 

. ing is gained by continuing the evaporation long beyond apparent 

dryness this first time, for the slight reduction in the soluble silica

a Chem. News, vol. 60, 1889, p. 14.

6 Common errors in the determination of silica: Jour. Arn. 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.

cZeitschr. anorg. Chemie, vol. 45, 1905, p. 411.
DETEBMESTATION OF SILICA. "77

gained by so doing is offset by a large loss of time, nor is there much 

advantage in crushing the residue to powder, whereby, moreover, the 

dish is easily scratched. The amount of silica passing into the filtrate 

will generally vary from 1 to 3 per cent of the amount present, and 

is but little less after twenty hours drying than after one-tenth of that 

time.0 Upon the seemingly dry mass is . poured enough strong 

hydrochloric acid to thoroughly drench it, then an equal bu'lkof 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 decantation,leavingnearly 

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 

matter other than silica. If the data of experiments 6 to 9 in the 

paper already cited a 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 milligrams. 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 thar.. 

the first, and if the rock is even moderately titaniferous are by no 

means pure silica.

a See Jour. Am. Chem. Soc., vol. 24,1°902, p 366.
78 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

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, a 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. 80) with highly titaniferous and ferruginous rocks and 

minerals, the operator should use discretion in his choice of a high 

drying temperature.

y. Procedure with rocks and minerals containing fluorine. This 

subject has been touched on in commenting on the boric-oxide and 

sodium-carbonate methods of fusion, b and will be considered in 

detail under the head of "Fluorine" (p. 155).

b. IGNITION OF SILICA.

The application of a strong blast c 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 these 

statements, long extant in the literature, has been disputed by 

G. Lunge and C. Millberg d 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 an 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, b«t regards the blast as unnecessary if a Teclu instead 

of a Bunsen burner is used. My experience is not in agreement with 

this.

 Although the above time limit usually suffices with a powerful blast, 

and may be materially shortened for small amounts of silica, such as

a Jour. Soc. Chem. Ind., vol. 21,1902, p. 1217.

b See a, p. 68, and footnote, p. 71.

c 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.) 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 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 platinum wire in the bedplate of the furnace was lJurned 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.

d Zeitschr. angew. Chemie, 1897, p. 425.

«Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 24, 1902, pp. 372-373.
DETERMINATION OF SILICA. 79

*

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."

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 

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.

d. ACCURACY OF THE SILICA DETERMINATION.

By observing the above rules :use of platinum, repeated evaporations and filtrations, proper blast ignition, and correction for foreign 

matter the determination of silica, from being one subject to grave 

error, has become one of the most exact of which I. have cognizance,- 

provided precautions are taken to recover, as hereinafter described, 

the portions that inevitably are to be found with the alumina. With 

careful work variations of 0.1 per cent are the exception in duplicate 

analyses.

aForthe proof see Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 24, 1902, p. 373. The duty of every 

analyst to test the efficiency of his blast or muffle can not be too strongly emphasized. The discordance 

01 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-gmm platinum crucible, showing a temperatureof probably 1,200°.
80 ANALYSIS OF SILICATE AND OAEBONATE ROCKS.

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 milligram. 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 

one-third of the total amount.

If in correcting the silica, toward the end of the evaporation, when 

the hydrofluoric acid has been driven off and the sulphates begin to 

appear in solid form, the residue has a peculiar milky or enamel-like 

appearance, it may be taken as evidence of much phosphorus and 

titanium, though possibly the appearance may be due to zirconium 

with the other elements named. Although observed in but one series 

of rocks, ° 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 

sulfates, but in my experience this is not so. Only when there is considerable excess of SO3 over BaO will any of the latter be present 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 

hydro-chloric 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 alumina, etc., precipitate (f. /?, p. 90).

Quite as rarely is calcium or magnesium ever a component of the 

residue if the decomposition of the rock powder was complete at the 

outset. I have repeatedly proved that the residue, after re-solution, 

is quantitatively precipitable by ammonia in presence of an ammonium salt.

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

a See second footnote, p. 90:
HYDROGEN-SULPHIDE PRECIPITATION. 81

mentioned by Gmelin-Kraut,0 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. 90), and to do so involves 

the reoxidation of all iron and subsequent boiling to remove or destroy 

the excess of oxidizing agent, together with the expenditure of much 

valuable time. The iron is already oxidized by the fusion, and needs 

no further help in that direction. Nevertheless, if time is not a prime 

object, its removal by hydrogen sulphide is to be recommended. In 

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.

8. ALUMINUM TOTAL IRON. 

A. INDIRECT METHOD FOR ALUMINUM. (TITANIUM.)

a. PRELIMINARY REMARKS.

The difficulties 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, 

are very great. 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 differ- 

'ence, after deducting from the precipitate produced by ammonia or

«Anorg, Chemie, 6th rev. ed., vol. 3,1875, p. 359.

Bull. 305 07 6
82 ANALYSIS OF SILICATE AND OAEBONATE EOCKS.

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. 90)., 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 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 separation of 

it from all the other admixtures, an operation which would, moreover, 

immoderately extend the time required for each analysis,

b. PRECIPITATION OP ALUMINUM, IRON, 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 the rock he is analyzing might contain. With 

extremely high, magnesian rocks a third precipitation is generally 

requisite.

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 a 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,

a Am. Jour. Sci., 3d ser., vol. 32, 1886, p. 112. . 
ALUMINUM, IKON, ETC. 83

there being no chloride to remove, both of which are excellent suggestions. a

For a reason mentioned under e (p. 87) the second precipitation 

may with advantage be made in the presence of macerated filter 

paper, as recommended by Dittrich. b

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. 0

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 Mn.j03 state and remains so 

when redissolved, being then in a fit condition for reprecipitation.

/3. The lasic-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

a 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 to 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.

6 Anleitung zur Gesteinsanalyse, 1905, pp. 10,11,14; Ber. Deutsch. chem. Gesell., vol. 37, p. 1840,1904.

c The fact must not be overlooked that certain of the rare earths may pass completely into the filtrate 

if the basic-acetate method is followed. If then, later, on rendering the combined filtrates ammoniacal 

an unexpectedly large precipitate appears, this should be carefully examined as to its nature. In an 

analysis of piedmontite from Alaryland over 2 per cent of rare earths, including cerium and others not 

identified, were quantitatively separated in this way from iron, alumina, etc.
84 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

that none of the methods of making the basic-acetate separation that 

involve the presence of notable quantities of free acetic acid are permissible, because of the solubility of aluminum hydroxide in this acid 

even when it is very dilute.

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 

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 cm3 . 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 <*, washed, 

sucked dry, and treated as in e (p. 87), after recovery as in d (p. 86) 

of the portions of aluminum and iron that may have passed into 

the filtrates.a

" 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 (Xeitschr. anal. Chemie, vol. 42,1903, p. 492), who gives the following 

directions for the use of ammonium acetate. It must be borne in mind, however, that this method is 

not applicable to aluminous materials.

The solution, containing not much free acid (hydrochloric) and preferably cool, whose volume should 

not exceed 100 cm. 3 , is neutralized in a beaker with concentrated ammonium-carbonate solution(200 

grams per liter, about double molar) till the precipitate that is formed begins to redissolve slowly, then 

with weaker solution (about one-tenth molar) till a slight precipitate persists for one or two minutes 

in spite of stirring. Next is added, according to the amount of this precipitate, 3 to 5 cm.3 of acetic 

acid (double normal) if the commercial article of ammonium acetate, which nearly corresponds to the
ALUMINUM, IKON, ETC. 85

C. PRECIPITATION OF IRON, ALUMINUM, ETC., TOGETHER WtTH MANGANESE.

ot. 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 90.

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 200cm.3 , is added enough hydrochloric acid to prevent precipitation of manganese when made ammoniacal (see b. 

a, p. 82). Heat is applied, and about 1 gram of ammonium persulphate" a free from all interfering impurities is added' When the liquid

acid salt (NH^CaHsOz.CjH^Os, is used, or 10 cm. a 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 400 cm. a 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. * 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 60°, 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 the glass with 

hydrochloric acid and reprecipitated with ammonia. If this is added to the main filter it must not 

be done till the large precipitate has been washed completely, because of the danger of precipitating, 

by the ammonia, manganese that has not yet been washed out.

The Brunck-Funk separation of iron as basic acetate from manganese, zinc, nickel, and cobalt. The 

following method of 0. Brunck (Chem. Zeit., vol. 28, 1904, p. 514), slightly modified and extended by W. 

Funk (Zeitschr. anal. Cherriie, 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 broken up 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 NaC2H3Oo.3H2O 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.

"This reagent as sold must be purified. Jannasch (Prakt. Leitfaden d. Gewichtsanalyse, 2d eel., 

1904, p. 179) accomplishes this as follows: To a saturated warm solution (not over 95° ) ammonia is
86 ANALYSIS OF SILICATE AtfD CARBONATE HOCKS.

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 

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 A12 03 , Fe2 03 , Mn3 04 , Ti02 , and P2 05 . Any 

chromium in the rock should be in the filtrates, wholly oxidized by the 

persulphate, but it will be recovered with the ungrecipitated traces of 

alumina, as detailed under d. y, page 87, and should be added to the 

main precipitate above. It is not best to attempt to determine the 

chromium colorimetrically in the filtrate.

ft. 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 OV 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.

ft. After a basic-acetate precipitation. The first filtrate is evaporated to, or nearly to, dryness, in order to get rid of the excess of

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 rapidlyas 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 (W.F. IT.) 

was found to contain no interfering impurities, though not free from alkali.
ALUMtNUM, 1EON, ETC. 87

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 «, is collected oh a small filter (7 cm.), 

and the nitrate in a flask of 150 to 200 cm.3 capacity. The second or 

ammoniacal filtrate, having been separately evaporated to small bulk, 

with the addition of a few drops of ammonia toward the end, serves as 

first wash water for the other dish and for the precipitate 011 the filter. 

 Both dishes and the filter are finally rinsed with hot water. The 

ammoniacal filtrate contains enough ammonium salts to prevent 

precipitation of magnesium in the first filtrate when the two come 

together.

If manganese peroxide has been deposited on the surface of the 

dish it is removed by hydrochloric acid and a drop or two of sulphurous acid, which mixture is then passed hot through the filter. 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.

y. After precipitation ly ammonia and ammonium- persulphate. 

The filtrates are evaporated as in a. The second is carried to dryness arid the ammoniacal salts are removed by ignition. The residue / o

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 allow,ed 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 <*-aiid ft if nickel or zinc are to be looked for, otherwise 

in a large platinum dish for treatment as in 10 (p. 101).

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, page 85.

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. 79), 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
88 ANALYSIS OF SILICATE AND OAEBONATE BOOKS.

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, p. 59). 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 

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. 73).

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) and the fusion is renewed 

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.

a It will be remembered (see page 78, footnote c) 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 

empty weight at this point.

b A chief objection by many to the use of an alkali bisulphate for bringing this precipitate nto 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
ALUMINUM, IRON, ETC. 89

When all is dissolved a the melted mass is poured into a large, dry 

platinum dish, what adheres to the two crucibles is removed by 

diluted sulphuric acid, and the solution, with rinsings, is poured into 

the dish. Much more dilute sulphuric acid is added and the dish 

heated till the solid is dissolved. The solution is evaporated as far as 

can be done on the steam bath, then gradually heated higher till fumes 

of sulphuric acid come off copiously. During this heating the mass 

is apt to darken from reduction and separation of dissolved platinum 

The acid should have been used in such quantity that after cooling the 

mass is pasty and not solid, for it then dissolves readily, on heating, 

in the water, which is now to be added, the sodium salt dissolving 

much more readily than the potassium salt.

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 re weighed. 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 90, 

after filtering from barium if present (see /?, p. 90).

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 p}rrosulphate melt was taken up with

sound as applied to the bisulphate, but is swept away ifthelatteris 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 ceaees and 

white fumes begin to come off freely. If the liquid is then poured out into other dishes it cools in thin 

sheets or cakes, which can be readily broken up and bottled for future uce. 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 te 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 ol 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 pow.dered 

oxides with acid potassium fluoride (about 1 gram). The mass melts at first over a low flame, then 

solidifies. Its solution is evaporated with sulphuric acid to expel most of the fluorine, then reduced 

with hydrogen sulphide or sulphurous acid'and titrated for iron. The use of the fluorideis, 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 rnuct furthermore'be 

thorough if titanium is to bo determined in this solution.

» Should a small portion of the precipitate have escaped solution no particular harm is done. The 

further treatment is not thereby changed.

& For proof see Jour. Am. Chem. Soc., vol. 24, 1902, pp. 368-370.
90 ANALYSIS OF SILICATE ^AND CARBONATE BOCKS.

water or dilute acid as the total amount. It is, however, but a small 

portion of what the alumina held, the greater part having formed 

alkali silicate during the fusion and remaining in solution 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 elsewhere 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. a, page 85, 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,6 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 OF VANADIUM.

a. Reduction of tJie iron. Into the strongly acid and cool filtrate 

obtained in f. a, /3} pp. 88-90, held in a beaker, 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 c 

with continued passage of the gas, whereby the sulphur becomes coagulated and readily filterable. The gas current is not interrupted till

a Jour. Am. Chem. Soc., vol. 24,1902, p. 369.

6 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 TiOa and PsOs, with perhaps a little 7r02. 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. 80 

as derived from the ignited silica.

Knop (Zeitschr. Kryst., vol. 10, 1885, p. 73) seems to have obtained a similar mixture in analyzing 

minerals from the Kaiserstuhl in Baden, but its nature was not ascertained, though it was suspected 

to be, if not silica, colurnbiferous titanic acid.

c 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
DETEEMitfATlON OF IKOK. 91

the solution has cooled somewhat. This is then filtered a warm into 

a half-liter flask, hydrogen sulphide is again introduced for a few minutes, with production of slight milkiness if any iron had become 

oxidized during filtration, the flask is then connected with a carbondioxide 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.0 When this point is reached the flame is removed and "the 

flask allowed to cool without interrupting the gas current. The 

cooling is hastened by placing the flask in a basin of cold water.

ft. 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 

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

gain in platinum which may amount to a milligram. Tests have shown that this is not due to retention 

of platinum by the main AlsOs, etc., precipitate; hence, it must come from platinum mechanically loos- 

 ened from the dish during the drying and powdering of the silica preparatory to its collection on the 

filter, or to some insoluble compound of platinum formed during evaporation and drying of the. silica. 

It may also be in part or wholly due to contamination from 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. 81.)

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. A. 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. Chcm. Soc., vol. 17,1895, p. 78; Chem. News, vol. 73,1S06, p. 123.) The observation 

of A. Coppadoro (Gazz. chim. ital., vol. 31, pt. 2,1901, p. 217) that the precipitate of sulfur 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.

b The gas generated from every new lot of marble must be carefully tested for hydrogen sulphide. 

Even pure white marble is frequently not free from soluble sulphides probably pyrrhotite, sphalerite, 

or galena and the amount may be enough to 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 

a solution 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 his method of reducing the iron, without coagulating the sulphur, the filtrates are always strongly 

milky.
92 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 altogether 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 .

y. 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. 110).

b. HAVING REGARD TO THE PRESENCE OF VANADIUM.

K vanadium is present the value found for iron will be in error by the 

amount of permanganate required to oxidize V204 to V205 . 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 V2 04 , 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 may 

require the addition of a drop or 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 precipitability 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 wijJi various metals 

and gives numerous figures which show an approximation to 90 per 

cent thus thrown down under the conditions prevailing in analysis of

a Comptes rendus, vol. 104,1887, p. 1803; Zeitschr. anal. Chemie., vol.32,1893, p. 223. 

b Jour. Soc. Chcm. Industry, vol. 7,1888, p. 73.
DIEEOT DETEEMINATION OF ALUMINUM. 93

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. 138-140.)

C. METHODS AIMING AT THE MORE OR LESS DIRECT DETERMINATION OF

ALUMINUM.

a. AFTEIl 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. 88), 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 extraction with water, whereby titanium and zirconium are left on the filter

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. 6,1882, p. 246, and vol. 7, \883, p. 250.
94 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

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. 122). This is as far 

as the separation can well be carried, and the A12O3 must still be found 

by subtracting the P2 05 from the combined weights of the A12 03° and 

P2O5 . The possibility of loss of some P2 05 by volatilization 0 during 

the bisulphate fusion must be borne in mind here, for if it takes place 

the final weight of -A1 203 + P2 05 will not contain all the P205 .

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 , TiO2; P2O5 , etc., after separation of iron by ammonium 

sulphide in tartrate solution with sodium hydroxide in a silver crucible, or to boil the freshly precipitated mixture with a solution of the 

alkali, on the assumption that the oxide of titanium is hereby rendered 

wholly insoluble and thus separated from the alumina. This, however, is in part an error long since pointed out by F. A. Gooch, b 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 TiO2 , 

or about 7 per cent, determined colorimetrically. When freshly 

precipitated and boiled with the alkali the solubility was less. 

When fused with sodium carbonate but an infinitesimal trace was 

dissolved, which required strong concentration for its detection. 

When mixed with a large excess of alumina and fused with the caustic 

alkali, the solubility was still very marked, though less than when 

alumina was absent. With a large excess of ferric oxide, with or 

without alumina, no titanium could be detected in the unconcentrated filtrate.

It thus appears that fusion with caustic alkali after first removing iron involves an error in the gravimetric determination of both 

aluminum and titanium which does not appear if the iron has not 

been removed.

a H. Rose speaks of such loss when volatilizing sulphuric acid in presence of phosphoric acid (Handb. 

f. quant. Anal., Finkencr 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.

(> Proc. Am. Acad. Arts Sci., vol. 12, 1885, p. 436; Bull. U. S. Geol. Survey No. 27, 1886, pp. 16, 17-
DIEEOT DETEKMINATION OF ALUMINUM. 95

C. COMBINATION METHOD AFTER DITTRICII.

Evidently with a view to eliminating the sources of error inherent 

in the methods outlined in a and b above, Doctor Dittrich has evolved 

a procedure which is a combination of both and includes methods of 

determining titanium and zirconium. Since it involves considerably 

more work than that which has just been described in detail and has 

few compensating advantages beyond the colorimetric determination 

of titanium in absence of iron, it will be sufficient to refer the reader 

to it. a

d. DIRECT PRECIPITATION OF ALUMINUM BY PIIENYLHYDRAZINE.

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,6 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. 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 laboratory" 

and confirmed the above authors' statements in the main, finding, 

however, that two precipitations are needed to free the precipitate 

entirely from iron. "The method is excellently adapted to the 

separation of very small quantities of aluminum, such as a milligram or even less, from a large excess of iron, a point of considerable practical importance."

Although such conditions will not be met with in ordinary rock 

analysis, it will not be out of place here to give the treatment as 

slightly modified by 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 of phenylhydrazine,d 

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

a Dittrich, M., Anleitung zur Gesteinsanalyse, 1905, pp. 9-31.

6 Jour. Am. Chem. Soc., vol. 21, 1899, p. 776; Chem. News, vol. 81, 1900, p. 158.

c Jour. Am. Chenh Soc., vol. 25, 1903, p. 421.

d 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 con-- 

tain tin, which had probably been used in its preparation. ' '
96 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

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 phenylhydraidne 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 cin.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 

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.0

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 , 

FeaOg.

2.03 

9.35 

4.80 

12.71 

.58 

.98 

3.49 

l.QO

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 

Al,03) 

FejOa (by 

difference).

0.085 

'.036 

.301 

.088 

.030 

.019 

.016 

.032

CaO.

0.011 

.023 

.087 

.016 

.030 

.055 

None. 

. .101

Mg2P207 .

0.097 

.252 

.312 

.338 

.221 

.171 

None. 

.441

The results in 974 and 1130 particularly show how the manganese once precipitated tends to 

remain 'vjth the alumina, presumably by reason of its having become peroxidized,
MANGANESE, NICKEL, COBALT, COPPER, ZINC. 97

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 third footnote, 

p. 83), 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, tho absolutely 

slight, is in- rock analysis probably of more consequence than the 

latter. In regard to completeness of precipitation bromine offers 

no advantage over ammonium sulphide, and the latter has the advantage that by a single operation nickel, cobalt, copper, and zinc, if 

present, are likewise separated from the earth metals and alkalies. 

There need be no fear of overlooking nickel or copper, for under the 

conditions of the precipitation they are not retained in solution. It 

is for this reason chiefly that the ammonium-sulphide method is to 

be preferred. Most of the small amount of manganese that escapes 

precipitation is weighed later with the magnesium as pyrophosphate 

and can be readily corrected for by the colorimetric method described 

on page 99.

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 b to be 

valueless. ' '

fi. Precipitation by ammonium sulphide and separation of manganese 

and zinc from nickel, cobalt, and copper. Two or three cm.3 of ammonia are added to the flask containing manganese, the earth metals, 

etc. (8. A. d. a, fi} pp. 85, 86), 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 preferaZeitschr. anorg. Chemie, vol. 10,1895, p. 405. 

ftZeitschr- anal. Chemie,'vol. 38, 1899, p. 681.

Bull. 305 07-
98 ANALYSIS OF SILICATE AND CAEBONATE BOOKS.

ably 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. 101.)

b. MANGANESE AND ZINO.

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 sodium-carbonate 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, 

if present in some quantity, it may preferably be weighed as the sulphate, a or, finally, it may be determined colorimetrically with much 

greater certainty, as in C, page 99, 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. .

oVolhard, J., Ann. Chem., vol. 198, 1879, p. 329. Gooch, F. A., and Austin, Martha, Am. Jour, Sci., 

4th ser., vol. 5,1898, p'. 209; Zeitschr, anorg. Chemie, vol. 17,1898, p. 264.
COLORIMETRIC DETERMINATION OF MANGANESE. 99

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 tovdetermine copper in a separate portion if its presence is indicated Avith certainty. (See 7, p. 81.)

C. COLORIMETRIC DETERMINATION OF MANGANESE.

a. PRELIMINARY TREATMENT.

As has been shown above (p. 96), the gravimetric determination of 

manganese is subject to grave error, even when great care is used. 

This is due to a variety of reasons, such as incompleteness of separation from aluminum and iron, incomplete precipitation by ammonium 

sulphide, and contamination by other bodies. Because of the small 

amounts in question these errors may be relatively enormous, and 

they can not be depended on to balance each other. Therefore, it 

would be an advance if the total manganese could be determined in a 

separate portion of the sample, and in the main portion only that part 

, which is weighed with the magnesium pyrophosphate, and this only as 

a correction to the magnesia. This course is readily feasible with carbonate rocks, which can usually be brought into a fit state in a few 

minutes without a fusion or the separation of silica. With silicate 

rocks more labor is involved, but the determination itself is very 

accurately'performed by colorimetry, as in the case of carbonates.

The preliminary treatment consists in decomposing a gram or half 

a gram of the rock powder in a small platinum dish or capacious crucible (placed in the radiator shown in fig. 2, p. 29) 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 nitric acid free from chlorine is added, together with 

water, and as much of the residue is brought into solution as possible. 

What remains insoluble is usually barium and calcium sulphates. 

This is filtered off on a small filter, the filtrate is caught in a small 

beaker or flask, and the manganese determined as in the following 

paragraphs.

/ 

b. COLORIMETRIC DETERMINATION OF MANGANESE BY AMMONI0M 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

a Walters, H. E., Chem. News, vol. 84,1901, p. 239; Proc. Eng. Soc. West. Pa., vol. 17,1901, p. 257.
100 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

containing the equivalent of 2 milligrams 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 

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 of that amount, 

of the manganese solution, so that when both solutions are oxidized 

and the flasks filled the color in the standard shall be more intense 

than in the test solution. This solution is oxidized by the aid of silver salt and persulphate in the same manner as the other, cooled, filled 

to the mark, shaken, and poured into a burette. Ten cm. 3 is drawn off 

into one of the comparator cylinders shown in fig. 5 (p. 32), 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 32. If the form of colorimeter depicted in fig. 6 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 (due to deficiency of silver 

salt) have formed during the oxidation of the .standard, it is best to. 

start with a fresh portion, but in case this happens with the test solution the precipitate must be brought into solution by a little sulphurous acid, more silver salt added, and the oxidation repeated, if need 

be, after adding more persulphate.
THE ALKALINE-EAKTH GROUP. 101

10. CALCIUM AND STRONTIUM (BARIUM). 

A. SEPARATION FROM MAGNESIUM.

a. PRECIPITATION AND IGNITION OP 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. fi, p. 97). Its separation 

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.a 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, 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° 

to 160°, and the separation of strontium from calcium effected by 

ether-alcohol 6 as described below (B, p. 102).

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. 105).

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. Richards, C. T. McCaffrey, 

and H. Bisbee. 0 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

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.

& See R. Fresenius, X.eitschr. anal. Chemie, vol. 32, 1893, pp. 189,312, for the latest improvements In this 

method, in their application to considerable quantities.

cProc. Am. Acad. Arts Sci., vol. 36,1901, p. 375; Zeitschr. anorg. Chemie, vol. 28,1901, p. 71.
102 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 

milligram. 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 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 alcohol 

the method of Browning" 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.

C. BEHAVIOR OF BARIUM.

Barium, after two ammonium-oxalate precipitations, will never be 

found with the ignited calciutn and strontium in more than spectroscopic traces, unless originally present in excess of 3 or 4 milligrams, 

and very often only when in considerable excess.6 If present with 

them, however, it will be separated. with the strontium by ethero Am. Jour. Sci., 3d ser.; vol. 43,1892, pp. 50, 314.

&Hillebrancl, W. F., Jour. Am. Chem. Soc., vol. 16,1894, p. 83; Che'm. News, vol. 69,1894, p. 147.
SEPARATION OF BARIUM FROM STRONTIUM. ~L03

alcohol or amyl alcohol, and these two must then be treated by the 

ammonium-chromate method, given below, in order to arrive at the 

strontium. The barium is best estimated in a separate portion. 

(See "Barium" 13, p. 116.)

D. SEPARATION OF BARIUM FROM STRONTIUM.

Profiting by the experience of R. Fresenius and others, A. Skrabal 

and L. Neustadl 0 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 grains to the liter.

Ammonium acetate, a, 300 grams, neutralized by ammonia, to the liter.

Ammonium acetate, I, 20 cm. 3 of a diluted to 1 liter.

The reaction of the acetate solutions should be alkaline rather than 

acid.

The method for the amounts used by the authors (0.135 gram 

BaO as the chloride and the same of strontium) is as follows:

To the neutral or weakly acid solution is added ammonium acetate 

(10 cm.3 of solution a) in excess. The liquid is brought to boiling and 

while swirled about 5 cm.3 of the bichromate solution is added. 

After settling and cooling the clear liquid is decanted through a filter 

and the precipitate washed by decantation with ammonium acetate 

(solution Z>) till the filtrate is no longer perceptibly colored (100 cm.3 

of wash solution). The beaker is placed under the funnel, the precipitate on the paper dissolved by warm dilute nitric acid, and the 

paper washed. .More acid is then added to dissolve the rest of the 

precipitate, followed by ammonia till the precipitate forming again 

no longer redissolves. Ammonium acetate (10 cm. 3 of solution a) is 

now poured in, the liquid brought to boiling while kept in swirling 

motion, allowed to cool slowly, and the precipitate is washed by 

decantation with solution 5 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.

oZeitschr. anal. Cheraie, vol. 44, 1906, p. 742.
104 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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, orfiuoride. 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,a 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 

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.

oZeitschr. anal. Chemie, vol. 45,1906, p. 77.
DETEEMINATION OF MAGNESIUM. 105

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 ignited 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. 29). 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.

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 sulphate method, and in the hands of the inexperienced leads to better 

results, though he regards the sulphate method as the best in experienced hands. / 

*

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," confirmed in part and supplemented by F. A. Gooch 

and Martha Austin,6 seemed to clear the ground fairly well. NeuoZeitschr. angew. Chemie, 1896, p. 435.

6Am. Jour. Sci., 4th ser., vol. 7, 1899. p. 187; Chem. News, vol. 79,1899, pp. 233, 244, and 255; Zeitschr. 

anorg. Chemie, vol. 20,1899, p. 121.
106 ANALYSIS OF SILICATE AND CAEBONATE HOCKS. .

bauer 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 ammoniacalsalts, arid 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 

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. 108). The intense heat has caused a decomposition of the metaphosphate with volatilization of P2 05 , as follows: 

2Mg(P03) 2 = Mg2P207 + 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 MgNH4PO4 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.

a Am. Jour. Sei., 3d ser., vol. 5, 1S73, p. 114. 

6 Zeitschr. anal. Chemie, vol. 44,1905, p. 335.
DETERMINATION OF MAGNESIUM. 107

The hot magnesium solution, containing at least 2 to 3 grains of 

ammonium salts (to prevent precipitation t>f 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 dimagnesmm-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 fo.r^ our purposes.

&

b. PRECIPITATION.

of. First precipitation. This is made without special precautions in 

the filtrate from the first calcium-oxalate separation (p. 101) by sodiumammonium-hydrogen phosphate (microcosmic salt) a in indefinite 

decided excess and without the great excess of ammonia usually prescribed. It is not necessary to first remove ammoniacal salts unless 

very little magnesium is present, and then only iii 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.

ft. 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. 101), and is diluted if necessary. A few drops 

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.

° 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.
108 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

B. 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. 109), 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. 0 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. 105).

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 P205 did seem to volatilize 

slowly from Mg2P207 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

a Zeitschr. anal. Chemie, vol. 33,1894, p. 362.
CONTAMINANTS OF MAGNESIUM PYROPHOSPHATE. 109

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 appears 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 REMOVAL OF BARIUM, CALCIUM, AND

MANGANESE.

a. BARIUM.

Barium phosphate will not contaminate the second magnesian precipitate unless there are notable amounts of barium in the rock, in 

which case it must be removed by sulphuric acid prior to the final 

precipitation of the magnesium.

b. CALCIUM.

Calcium, however, is probably never absent, and has to be estimated 

and allowed for as follows:

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.° 

and not be hot, clears. It now and then happens that a little flocculent 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, p. 110). It is likely to consist, in great 

part or wholly, of phosphates of iron or manganese, or both, and shows 

often a reddish color on ignition. If an excess of acetic acid has been 

used, 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 soon shows itself, which, if fine grained and honadherent 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. Its final 

weight, averaging perhaps one-half milligram, 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

a A pink color of varying intensity almost invariably becomes apparent as the mass approaches dryness, a most delicate test for the traces of manganese which always escape precipitation by ammonium 

sulphide or bromine.
110 ANALYSIS OF SILICATE AND CAEBONATE BOOKS.

to arrive at the true figure for magnesia. This separation, to be satisfactory, requires great care.

C. MANGANESE.

A separation from one another of the iron, aluminum, and manganese which the small flocculent precipitate mentioned in b may contain 

is not worth the trouble, careful prior treatment being presupposed. 

The first two constituents 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. The precipitate should therefore be brought into nitric-acid 

solution. The solution containing the magnesium is also manganiferous. It is to be evaporated to dryness, the volatile salts expelled 

by ignition, and the residue again evaporated two or three times with 

a few drops of nitric acid 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 99, and 

its amount added to that-already found, unless the total has been 

ascertained from a separate portion of the sample.

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 magnanese 

at all, is shown in the table on page 96.

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. DESCRIPTION OP THE METHOD (WELLER's). a

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.

aBer. Deutsch. chern. Gesell., vol. 15,1882, p. 2593.
DETERMINATION OF TITANIUM. Ill

Mere traces of hydrofluoric acid, in either the peroxide or the titanium solution, render this method inexact,a hence care should be exercised as to the character of the peroxide, which, as sold in the market, 

often contains fluorine. For method of testing see page. 36.

Dunnington b 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 concludes, to prevent partial reversion to metatitanic acid, which does not give a color with hydrogen 

peroxide. The standard solution of titanium sulphate, 0 holding conveniently about 1 centigram Ti02 in 10 cm. 3 , equivalent to 1 per cent 

of Ti02 in 1 gram of rock, contains, therefore, 5 per cent or more of 

sulphuric acid. Of this, 10 cm. 3 are mixed with a sufficiency of hydrogen peroxide (2 cm. 3 of most commercial brands is ample) and diluted 

to 100 cm.3 in a measuring flask.

Titanium can be determined, as a rule, most conveniently in the solution which has served for the titration of total iron (y, p. 92). This, 

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. 32) 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. 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 Ti02 in 

the rock, the amounts in the two solutions being directly as their 

volumes.

If the convenient but expensive Soleil-Duboscq colorimeter is used, 

or the modification of O. Schreiner (fig. 6, p. 33), 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 standard of the above concentration. For

aHillebrand, W. P., 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.

cPotassium-titanium fluoride.KaTiFe, best serves as the starting point for its preparation. A quantity of this is recrystallized from boiling water once 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 weighed into 

a platinum dish and evaporated several times, without bringing to dryness, with strong sulphuric acid 

till the fluorine is completely expelled. The residue is then taken up with water containing enough sulphuric acid to make 5 per cent of the latter when fully diluted. Two 50-100cm.3 portions of the prepared 

solution are then further diluted, boiled, and precipitated with ammonia. The precipitates are collected 

pn paper, washed with hot water till free from alkali, ignited moist in the filter, blasted, and. weighed. 

JDuplicates should agree ajtnpsp exactly.
112 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

the percentages of titanium found in rocks, clays, and soils, usually 

under 1 per cent, but rising to 2 or even 3 per cent or more occasionally, the colorimeter method gives results which are fully equal to 

those of the best gravimetric method, besides being a great time saver.

b. 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; then either the iron must be removed, as described under 

B.a.or, page 113, prior to making the color test, or correction should be 

applied for known amounts of ferric sulphate in solutions of the requisite dilution.

The exact correction to be applied in such cases is difficult of determination because of the impossibility of matching the colors of titanium-peroxide solutions with those of ferric sulphate; but tests made 

go to show that the coloring effect of 0.1 gram of Fe203 in 100 cm. 3 of 

5 per cent sulphuric-acid solution is about equal to 0.2 milligram of 

Ti02 in 100 cm. 3 when oxidized by hydrogen peroxide. This amounts 

to a correction of only 0.02 per cent on one gram of rock containing 

the unusual amount of 10 per cent Fe203 . W. A. Noyes a overcomes the difficulty mentioned in the last paragraph by adding 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 fig. 6 (p. 33), though practicable with Nessler tubes. 

In using the Survey colorimeter (fig. 5, p. 32), 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, then to 

make an exact determination, having added to a fresh portion of the 

standard the requisite amount of iron salt, preferably in the form of 

ferric-ammonium alum. The amount to be used is calculated as follows: Let A be the number of cubic centimeters of the test solution, 

a of the standard used, 6 of the water needed to dilute the standard 

in the preliminary test, p the weight of iron in terms of Fe2 03 in A, 

and x the weight of iron in terms of Feg03 to be added to each cubic 

centimeter of water used for diluting the standard in the final tests.

Then x = 7" p. For all practical purposes it would probably be Ac

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 former method the number possible would be limited only by the

a Jour. Anal, and Appi, Cfaem., vol. 5,1891, p. 39.
DETERMINATION OF TITANIUM. 113

stock of standard and of the prepared ferric-ammonium sulphate 

solution.

C. ALTERNATIVE MODE OP PREPARING THE TEST SOLUTION.

As said above (pp. 92, y, and 110,12. A. a), the solution that has been 

used for volumetric determination of total iron can most conveniently 

be used for the colorimetric determination of titanium, but if desired 

this can, of course, be made on some other portion of rock powder. 

At one time it was the practice in this laboratory to combine it with 

the determination of barium, as described in Bulletin No. 148, by 

decomposing the powder by sulphuric and hydrofluoric acids, a expelling the latter by- repeated evaporations with sulphuric acid, taking 

up with dilute sulphuric acid, b 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. Ill), 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.

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 

tested that of Doctor Gooch c is unequaled. With one or two minor 

modifications introduced by Dr. T. M. Chatard, d it is as follows:

Any solution of the rock freed from silica can be used, &nd 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. 6 The amount

a 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.

b 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, dissolved in dilute sulphuric acid, filtered, and the filtrate added to 

the main one. The insoluble matter will now be chiefly barium sulphate, for the further treatment of 

which see 13. A (p. 116).

c Proc. Am. Acad. Arts Sci., n. s., vol. 12, p. 435; Bull. U. S. Geol. Survey No. 27, 1886, p. 16; Chem. 

News, vol. 52, 1885, pp. 55, 68.

<* 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.

eCathrem, A., Xeitschr. f. Kryst., vol. 6, 1882, p. 243; vol. 7, 1883, p. 250.

Bull. 305 07 8
114 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

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 sulphide 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 sulphurousacid solution. '

Ammonia is then added in slight excess, followed at once hy 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, 

thenignited, fused thoroughly with sodium carbonate, and leached with 

water to remove phosphoric acid and most of the remaining alumina. 

The residue is again ignited and fused with sodium carbonate. To 

the cooled melt in the crucible strong sulphuric acid is to be added, 

wherein it dissolves readily by aid of gentle heat. This- solution is to 

be poured into a small volume of cold water and the platinum it contains precipitated by hydrogen sulphide at or near boiling temperature. After filtering and cooling, ammonia is added till the titanium 

is just precipitated, and a measured volume, containing a known 

weight of absolute sulphuric acid, is then added just enough to redissolve the precipitate. The solution is then made up with acetic acid 

in such amount that the final bulk shall contain from 7 to 11 per cent 

of absolute acid, and then enough solid sodium acetate is stirred in 

to more than take up the sulphuric acid introduced. On rapidly bringing the liquid to ebullition the titanium is precipitated in flocculent 

and easily filterable condition, and the precipitation is complete after 

a minute's boiling, provided all the prescribed .conditions have been 

followed and zirconium is absent.

The precipitate is washed first with acetic acid of 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
DETEBMLNATION OF TITANIUM. 115

actual carrying out of all these operations, when once the method is 

understood, requires much less time than the detailed description 

would indicate.

fi. 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 ZrO2 , 

and this amount was able to prevent precipitation of 0.3 per cent of 

Ti02 . 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. 118), no difficulty was experienced in precipitating all the titanium 

with the usual ease.

b. BASKERVILLE'S METHOD.

C. Baskerville a has proposed the separation of titanium from iron 

and aluminum by boiling the neutralized solution of the chlorides for 

a few minutes in presence of sulphurous acid. The test separations as 

given by him are sharp, and a single precipitation is said to suffice, the 

titanium being free from iron and easily filterable. This last statement and the ready precipitability are fully confirmed by the experiments of the writer on titaniferous iron ores, but, although the titanium 

is completely thrown out, it carries with it a little iron, for instance, 

about 0.25 per cent Fe2 03 with 8 to 10 per cent Ti02 . Zirconium 

would probably be likewise precipitated (14. B, p. 120) and phosphorus perhaps also, but this last point has not been investigated, 

neither has the applicability of the method to aluminous rocks been 

tested. . .

C. METHOD OF DITTRICH AND POHL.

Attention has. been directed (8. C. b, p. 94) to the error resulting 

from attempting to separate aluminum from titanium by either fused 

or dissolved sodium hydroxide in absence of appreciable amounts of 

iron. When iron is present, the procedure given by Dittrich b may be 

used. It involves fusion in a silver crucible of the ignited oxides of 

aluminum, iron, etc., obtained in the usual way, with sodium

a Jour. Am. Chem. Soc., vol. 16, 1894, p. 427.

bAnleitung zur Gesteinsanalyse, 1905, pp. 9-31; also Dittrich, M., and Pohl, R., Zeitschr. anorg. Chemic, 

vol. 43, 1905, p 236.
116 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

hydroxide, re-solution of the insoluble matter in hydrochloric acid, 

precipitation of the iron as sulphide from an ammoniacal tartrate 

solution, destruction of the tartrate, precipitation of titanium (and 

zirconium) by ammonia, and determination of the titanium colorimetrically after ascertaining the combined weight of the two oxides.

C. SUPERIORITY OF THE COLORIMETRIC AND GOOCH METHODS OVER

THE OLDER ONES.

In view of the good results obtainable by the colorimeter method in 

all 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. 127). It has been said above (10. C, p. 102) 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 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. 30) to prevent access of sulphur from the gas 

flame. In case sulphur is not to be regarded, the niter and disk are 

omitted. After thorough disintegration of the melt in water, to which 

a drop or two of methyl or ethyl alcohol has been added for the purpose of reducing manganate, the solution is 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.
DETERMINATION OF BARIUM, ETC. 117

(For the further treatment of the filtrate see " Sulphur," 24.B, p. 160, 

and "Chromium," 17.B, p. 124.)

The residue is washed from the paper into a small beaker without 

removing the filter from the funnel and digested with little more than 

enough warm dilute sulphuric acid to effect solution of all soluble constituents (stronger acid ma}^ 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 Erlenmeyer flask of 100 to 150 cm3 . 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. 118, and 15.A, p. 120.)

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 

chlorides .and to apply to the mixture the ammonium-chromate 

method of separation (10.D, p. 103).

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

aFor details consult Hillebrand, W. F., Jour. Am. Chem. Soc., vol. 16,1894, p. 83; Chem. News, vol. 69, 

1894, p. 147.
118 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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 a 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 A.c, p. 113, 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. 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, 6 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. 116), 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

aAm. Jour. Sci., 3d scr., vol. 43, 1892, p. 521. b Jour. Chem. Soc., vol. 49, 188G, pp. 149, 481.
BETERMlNATIOtf OF ZIRCONIUM. 119

the titanium, and then a few drops of a soluble orthophosphate solution. The flask is set aside in the cold for twenty-four to forty-eight 

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. (For the treatment of the nitrate see " Rareearth metals," 15.A, p. 120.) 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 acid potassium sulphate, 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 

fused with sodium carbonate, leached, ignited, fused with acid potassium sulphate, reprecipitated by ammonia, and weighed as Zr02 . Certainty as to its identity can be had by again bringing it into solution, 

precipitating by ammonia, dissolving in hydrochloric acid, evaporating to a drop or two, and testing with turmeric paper or by a microchemical reaction. With the very smallest amounts no color can 

be obtained by this turmeric-paper test, which, however, responds 

readily to as little as 1 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.

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, Zr2O5 , or Zr03 . a My own 

efforts as well as those of others to secure a precipitate in acid solutions of zirconium sulphate by hydrogen peroxide alone have been 

unsuccessful, except in very concentrated solutions and with 30-per 

cent peroxide. The ability to obtain the zirconium free from phosphoric acid would certainly be a great improvement on the method 

described above.

Were it not for the necessity of precipitating .the zirconium in a 

weakly 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 6 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

 aChem. News, vol. 60,1889, p. 6. . 

bJour. f. prakt. Chemie, vol. 108, 1809, p. 05.
120 ANALYSIS OP SILICATE AND CARBONATE ROCKS.

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 0 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 b 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, p. 115). 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 presumably quantitatively thrown down also, the two would have to be separated by hydrogen peroxide. No tests as to the availability of the method for separating the small amounts met with in rock analysis have been made.

The method of M. Dittrich and R. Pohl for determining zirconium 

by difference, after ascertaining gravimetrically the combined weight 

of zirconium and titanium and by colorimetry that of titanium, has 

been outlined on page 115, under c.

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.

A. USUAL METHOD.

The filtrate from the zirconium phosphate (14.A, p. 118) or, if zirconium is not to be determined, the earlier solution (13.A, p. 116), 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 hydroa Am. Chem. Jour., vol. 11,1889, p. 27.

6 Jour. Am. Chem. Soc., vol. 10, 1894, p. 475; Chcm. News, vol. 70, 1894, p. 57.
DETERMINATION OF PHOSPHORUS. 121

chloric acid, the solution evaporated to dry ness, and the residue 

heated with a few drops of a solution of oxalic acid. Anything that 

may be present except the rare earths dissolves readily, these remaining as insoluble oxalates. If there is a doubt as to the complete separation of the alkaline earths the ignited oxalates may be dissolved in 

hydrochloric or nitric acid, precipitated by ammonia, redissolved in 

whichever one of the acids may have been used, the solution evaporated to dry ness, 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 zirconium is collected on a platinum cone, washed with water acidulated 

by hydrofluoric acid, washed back into the dish or crucible, and 

evaporated with enough sulphuric acid to expel all fluorine. The 

filter is burned and 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 reevap orated with nitric acid two or three times to
122 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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.*

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 phos-" 

phorus. 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,6 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 arnmonium. 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. 108.)

B. PROCEDURE WHEN MATERIAL IS SCANTY.

The following procedure admits of determining in the same portion, 

besides phosphorus, barium, iron, vanadium, chromium, and titanium,

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 theextentof-doing away with the 

filtration of the precipitate of silicofluorides and fluoridcs before proceeding with the evaporation.

6 Am. Jour. Sci., 4th ser., VQ!. 7,1899, p. 187; Xeitschr. anorg. Chemie, vol. 20,1899, p.121; Chem. News, 

vol. 79, 1899, pp. 233, 244, 255.
DETERMINATION Otf CHROMIUM. 123

the last two either colorimetrically or gravimetrically, an.d is in large 

part extracted from a paper by Dr. T. M. Chatard.0

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 , P205 , Cr203 , Fe203 , 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 

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. 124). Afterwards, 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 filtrate 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 Am. Chem. Jour., vol. 13, 1891, p. 106; Bull. U. S. Geol. Survey No. 78,1891, p. 87; Chcni. News, 

vol. 63, 1891, p. 267.
124 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

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.

The separation of aluminum from chromium by hydrogen peroxide in ammoniacal solution, as recommended by P. Janriasch and 

E. v. Cloedt,b has been shown by C. Friedheim and E. Bruhl c to be 

valueless.

B. COLORIMETRIC METHOD.

For this very accurate and by far'the quickest method^ 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. 122) 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 milligram of chromic oxide (Cr2 03 ), in which 

condition chromium is usually reported in rocks and ores. It is 

probably inadmissible to increase the strength of the standard much 

above the figure given.

/3. 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 milligrams of chromic

« Bull. Soc. chimique, n. s., vol. 42, 1884, p. 291; Chem. News, vol. 50, 1885, p. 18. '

6 Zeitschr. anorg. Chemic, vol. 10, 1895, p. 402.

cZeitschr. anal. Chemie, vol. 38, 1899, p. 681.

dHillebrand, 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 (Ncderl Tyds. voor 

Pharm., Chem. en Tox., 1889) for the estimation of chromium in foodstuffs.
DETERMINATION OF CHEOMIUM. 125

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. 127); 

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.

y. 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 

are then diluted with water from a burette until of the same strength 

as the test solution, exactly as described on page 32. 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.a

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 (Cr203).

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 gravioD. W. Horn has studied the "Variable sensitiveness in the colorimetry of chromium." See Am. 

Chem. Jour., vol. 35, 1906, p. 253.
126 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

metric 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. 18-19), not only in 

ores and in coals, but in clays, limestones, sandstones, and igneous rocks.a I have shown6 that vanadium occurs in appreciable 

amounts in the more basic igneous and metamorphic rocks up to 

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 iip 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 less than 60 per cent of silica. The search for it even then 

will perhaps not often warrant the necessary expenditure of time, 

but in this connection it is to be remembered that neglect to determine it introduces an error in the figures for both ferrous and ferric 

oxides, which in extreme cases may be of considerable moment 

(see 7. B. b, p. 92; 19. C. c. /3, p. 140). '

B. CONDITION OF VANADIUM IN HOCKS.

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 a condition of the vanadium corresponding 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 c of western Colorado, in which it unquestionably

o Hillebrand, W. F., Distribution and quantitative occurrence of vanadium and molybdenum in 

rocks of the United States: Am. Jour. Sci., 4th ser., vol. 6, 1898, p. 209; Chem. News, vol. 78, 1898, 

p. 216; Bull. U. S. Geol. Survey No. 167, 1900, p. 49.

& Loc. cit.

cHillebrand, W. F., and Ransome, F. L., Am. Jour. Sci., 4th ser., vol. 10,1900, p. 120.
DETERMINATION" OF VANADIUM AND MOLYBDENUM. 127

occurs as trivalent vanadium (V203), has led to a decided unsettling 

of this view. It is but proper to recall that C. Czudnowicz, 0 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 (V203). 0. Lindemann's 6 

contrary conclusion with regard to certain iron ores, because the 

vanadium was extracted as V2O5 by sodium-carbonate fusion without niter, is not valid, since thisjwould probably be .the case even if 

it existed in the ore as V203 .

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. 124), the latter volumetrically, in the same solution. c

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 reinelt the residue as above, though for 

some magnetites a*nd other ores containing larger amounts of vanadium 

than the generality of rocks, this may be necessary, as Edo Claassen has 

shown. d 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 large. The use of ammonium nitrate, instead of nitric acid, for 

converting the sodium carbonate into nitrate does not seem to lessen 

the amount of chromium retained by the silica and alumina.

As a precautionary measure, therefore, and always when chromium 

is to be 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.

a Pogg. Ann., vol. 120, 1863, p. 20.

& Dissertation, Jena, 1878, thru Zeitsch. anal. Chemie, vol. 18, 1879, p. 99.

cHillebrand, 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. 

dAm. Chem. Jour., vol. 8, 1886, p. 437.
128 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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 

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. 124). 

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. ° 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 milligram of 

V205 per cubic centimeter, as calculated from the iron strength of the 

permanganate, one molecule of V205 being indicated for each one of 

Fe203 . 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.

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 dioxidej 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. Pharm., vol. 240,1887, 

p. 23; Zeitschr. anal. Chemie vol. 32,1893, p. 225.)
DETERMINATION OF VANADIUM AND MOLYBDENUM. 129

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 brownish 

tint indicates vanadium. Unless the greater part of the free sulphuric acid has been removed the appearance of this color is sometimes not immediate and pronounced, hence the above precaution. 

It is also necessary that the nitric acid shall be in considerable excess, 

since in a neutral or only faintly acid solution the color does not 

appear strongly.

The above is a surer test to apply than the following: Reduce the 

bulk to about 10 cm. 3 , add ammonia in excess, and introduce hydrogen 

sulphide to saturation. The beautiful cherry-red color of vanadium 

in ammonium - sulphide solution is much more intense than that 

caused by hydrogen peroxide in acid solution, but the action of 

ammonia is to precipitate part or all of the vanadium with the chromium or aluminum that may be present or with the manganese used 

in titrating, and ammonium sulphide is unable to extract the vanadium wholly from these combinations. Usually, however, the solution will show some coloration, and addition of an acid precipitates 

brown vanadium sulphide, which can be collected, ignited, and further 

tested if desired.

C. APPLICATION OF THE METHOD IN PRESENCE OF 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 cliromium 

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 milligrams of vanadium pentoxide can be made in presence of as much as 

30 milligrams 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.

Bull. 305 07 9
130 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

C. H. Ridsdale a titrated the cold solution to avoid oxidation of chromium and'obtained accurate results, but in my experience the end 

reaction is then uncertain.

The following tables contain the results of a considerable number of 

tests, those in Table 2 being- tabulated separately in order to show the 

degree of accuracy attainable with a large excess of chromium by 

applying the correction mentioned above and also the amount of this 

correction:

TABLE 1. Tests for vanadium in the presence of chromium.

No.

1

2

3

4

5

6

7

Chromic 

oxide.

Milligrams

1

1

1.5

2

3

3

3.5

Vanadium 

pontoxide.

Milligrams

9.87

.94

5.25

5.62

4.68

5.62

18.74

Vanadium 

pentoxide 

found.

Milligrams

9.22

1.04

.98

5.49

5.43

5.5

5.5

4.78

4.78

4.83

.5.58

5.58

18.89

Error.

Mg.

-0. 15

+ .10

+ .04

+ .24

+ .19

- .12

- .12

+ .10

+ .10

+ .15

- .04

- .04

+ .15

No.

7

8

9

10

11

12

13

14

15

Chromic 

oxide.

Milligrams

3.5

6

6

6

10

10

10

25

87.5

Vanadium 

pentoxide.

Milligrams

18.74

5.6

4.68

5.62

5.62

23.52

46.85

23.52

23.52

Vanadium 

pentoxide 

found.

Milligrams

18. 97

6.1

4.78

5.58

5.58

23.81

23.71

46.98

47.20

23.65

23.75

23.71

Error.

Mg.

+ .23

+v .50

+ .10

- .04

- .04

+ .29

+ .19

+ .13

+ .35

+ .13

+ .23

+ .19

TABLE 2. Application of correction for larger amounts of chromium, obtained by adding 

potassium permanganate to an equal bulk of solution containing a like amount of chromic 

svlphate.

No.

16

17

18

19

20

21

Chromic 

oxide.

Milligrams.

20

20

20

30

30

62

Vanadium 

pentoxide.

Milligrams.

0.94

1.87

18.74

1.87

1.87

46. 85

Vanadium pentoxide 

found.

Uncorrected.

1.59

2.69

2.39

2.59

19.4

19.3

19.3

2.99

2.79

2.79

2.69

2.69

2.69

2.89

2.89

2.79

48.60

Corrected.

0.99

2.09

1.79

1.99

18.73

18. 63

18. 63

2.14

1.94

1.94

1.84

1.84

1.79

2.09

2.09

' 1.99

47.60

Error.

Milligram.

+0.05

' + .22

- .08

+ .12

- .01

- .11

- .11

+ .27

+ .07"

+ .07.

- .03

- .03

- .08

+ .22

+ .22

+ .12

+ ."75

Volume of solution.

50 to 100 cm. 3

50 to 100 cm.a

50 to 100 cm. a

About 100 cm.3

200 cm. 3

200 cm. 3

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.

Jour. Chem. Soc., vol. 7,1888, p. 73.
FERROUS-IRON DETERMINATION. 131

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 

Fischer, while the other lead salts are wholly decomposed, but the 

applicability of this method to the separation of the minute amounts 

often found in rocks and ores has not been tested. The object has 

been in the present case to reach satisfactory results with the greatest 

expedition, and when chromium is not present in considerable amount 

this is accomplished.

Fortunately, chromium is almost never a prominent constituent of 

clays, coals, iron ores, and those rocks in which vanadium has thus far 

been reported, for although it is usually certain of the most basic of 

the silicate rocks that are highest in chromium as the peridotites 

yet in these, so far as present experience teaches, vanadium is lacking, 

a fact doubtless connected with the simultaneous absence from them 

of ferric aluminous silicates. , \

D. COLORIMETRIC METHOD FOR VANADIUM.

In the paper already cited b' the possibility of a colorimetric method 

for vanadium, based on its behavior toward hydrogen peroxide, was 

suggested. L. Maillard c has since developed such a method, though 

it has not been tested in the Survey laboratory.

19. FERROUS IRON.

A. 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 

rMitscherlich method with sulphuric acid, for a long time the only 

available one, is in theory perfect, since complete exclusion of oxygen 

is easily attainable. Its earliest recognized defect lies in the inability 

to secure always complete decomposition of the iron-bearing minerals, 

and even to ascertain, oftentimes, whether or not the decomposition 

has been complete. The addition of hydrofluoric acid to the sulphuric in the tube, in order to insure this breaking up, is to be 

regarded as of very doubtful utility in most cases, since the glass may 

be so strongly attacked as to add an appreciable amount of iron to the

» Inaugural Dissertation, Rostock, 1894.

6 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. 

c Bull. Soc. chim., vol. 23,1900, p. 559.
132 ANALYSIS OF SILICATE .AND CARBONATE ROCKS.

solution, and the hydrofluoric acid may have exhausted itself in 

attacking the glass before the more refractory minerals succumb! 

Nevertheless, if decomposition can be effected by sulphuric acid alone 

the results obtained are sharp and concordant; but they are in rock 

analysis usually higher than' when made by any of the modifications 

of the hydrofluoric-acid method now so extensively practised. 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 Koninck 6 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,d 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,, of ten in 

considerable amount, often in traces only. Sulphur can almost always 

be detected in 2 grams of rock powder.

Experiment has shown (C. c. a, p. 138) that with the amounts of 

sulphides usually found in igneous ,rocks their effect on the estimation of ferrous iron by the hydrofluoric-acid method at atmospheric 

pressure and boiling heat is negligible, though by increasing the amount 

of sulphide the effect becomes more and more apparent, because of 

the greater surface of pyrite exp'osed to the action of the ferric iron of 

the rock.

«Ber. Deutsch. chem. Gesell., vol. 32,1899, p. 2217, footnote.

6 Ann. Soc. g6ol. Belgique, vol. 10,1882T83, p. 101; Zeitschr. anorg: Chemie, vol. 26,1901, p. 123. 

cBull. U. S. Gcol. Survey No. 186, 1901; Am. Jour. Sci., 4th ser., vol. 12, 1901, p. 414. 

dZeitschr. prakt. Geol., 1899, pp. 250-251.
FEBROUS-IEOK DETERMINATION. 133

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 become 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 p.er 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.®

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.

B. THE MODIFIED MITSCHERLICH METHOD.

of. Strength of acid. The method in its original and usual application calls for a mixture of 3 parts of sulphuric acid and 1 of water by 

weight, or about 3 to 2 by volume, though a still stronger acid is sometimes used. In some cases, however, perhaps in most, much better 

decomposition of the silicates is effected by reversing the proportions 

of water and acid, or at any rate by diluting considerably beyond the

a 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.
134 ANALYSIS OF SILICATE AND OAEBONATE BOOKS.

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.

ft. 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 linger 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.

y. Reason for introducing gas and sealing as above directed. The 

usual practise 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 

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,

oUllmann, C., Zeitschr. fur angew. Chemie, 1893, p. 274; Zeitschr. anal. Chemic, vol. 33, 1894, p. 582. 

6 Bull. U. S. Geol. Survey No. 78,1891, p. 50; Chem. News, vol. 64,1891, p. 232
FEEEOUS-IBON DETEKMINATION. 135

whereas after filling the tube with gas from a generator there was 

found

32.11, 31.90, 32.15, 32.12, 32.06, 32.17, 32.28,

the average error of the former series being 1.78 per cent. The percentage error would, of course, be reduced by increasing the weight 

of mineral operated on. An average error equal to the above when 

employing 1 gram of ferrous minerals would make the percentage for 

FeO about 0.3 per cent too low. While the absolute error might be 

the same in all cases, the relative error would increase with minerals 

low in ferrous iron.

C. THE HYDROFLUORIC-ACID METHOD.

a.. PRINCIPLE OF THE METHOD.

This method consists simply in securing complete decomposition of 

the very fine 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 hitherto 

employed is the original one devised by J. P. Cooke a (fig. 20, p. 141). 

This does not permit driving off the superfluous hydrofluoric acid, as 

does that of Treadwell (fig. 21, p. 143) 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.

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.

b. DEFECTS OF THE METHOD.

a. Oxidizability of divalent manganese ly 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

o Am. Jour. Sci., 2d ser., vol. 44 1867, p. 347.
136 ANALYSIS OF SILICATE ANB CAEBOI^ATE BOCKS.

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 terrous iron, and consequently the manganous salt formed, increases.

E. Deussen, a 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 manganous 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 

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

o Zeitschr. anorg. Chemie, vol. 44,1905, p. 425.
VERROUS-IRON DETERMINATION. 137

differences, but it is possible that they resulted from his 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 TreadwelFs apparatus accomplishes this, but, as 

the experiments show, its complete expulsion is unnecessary.

ft. Extreme oxidizability of divalent iron lyfree 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 with hydrofluoric acid in addition 

in the other, a minus error was in all cases observed when the latter 

acid was present. An observation made by E. Peters," 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.

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 Treadwell apparatus involves long contact of the mineral with the acids, and as the experiments last mentioned were favorable in their results, it seemed as if the simple method of J. H. Pratt 6 

might be modified in the same sense. He avoided the use of all apparatus other than a capacious platinum crucible fitted with a perfoa-Zeitschr. phys. Chemie, vol. 26,1898, p. 193. 

6 Am. Jour. Sci., 3d ser., vol. 48,1894, p; 149.
138 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

rated 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 not yet 

been tested on rocks in comparison with that of Cooke, so that it would 

be premature to assert that this is the one to employ in preference to 

the other or to that of Treadwell, but the indications are so favorable 

that extended tests will be carried out in the regular course of Survey 

work.

C. INFLUENCE OF SULPHIDES, VANADIUM, AND CARBONACEOUS MATTER ON THE DETERMINATION OF FERROUS IRON BY THE HYDROFLUORIC-ACID METHOD.

A dark color of the undissolved residue 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
FERROUS-IKON DETERMINATION. 139

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.

B. b, p. 160, 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 0 that the oxidizing effect 

of ferric salts on pyrite and other sulphides is vastly greater than seems 

to have been suspected (see p. 132), 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 horn blende schist, free from sulphur and carrying 10.09 per 

cent FeO as the mean of several determinations and 4.00 per cent Fe203 , 

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

a Bull. U. S. Geol. Survey No. 180,1901; Am. Jour. Sci., 4th ser., vol. 12,1901, p. 414.
140 ANALYSIS OF SILICATE AND CAEBONATE BOCKS.

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.

ft. 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 V3 03 

(150.8) in oxidizing to V2 05 requires as much oxygen, as four molecules 

of FeO (288) when oxidized to Fe2 03 . The proportion, 150.8 : 288 : : 

V2 03 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 KMnO4 to .13 V203.

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 V2O3.

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 Fe2p3 in the rock.

Failure to correct for the vanadium in both cases would have made 

the figures for FeO and Fe2 03 , respectively, 2.50 and 2.22 instead of 

2.25 and 2.36 as shown above.

y. Carbonaceous matter. As said before (c, p. 138), matter of 

organic origin other than graphitic carbon renders the results of the 

ferrous-iron determination altogether unreliable. 

d. THE METHOD IN ITS VARIOUS MODIFICATIONS.

a. According to Coolce. a The apparatus, as shown in fig. 20, 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 th<? 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 6 , p. 91.)

a Am. J our. Sci., 2d ser., vol. 44,1867, p. 347.
FERROUS-IRON DETERMINATION. 141

A gram of the finely ground powder 0 is placed in a platinum crucible of 80 to 100 cm. 3 capacity and stirred up therein.with water 

enough to moisten and about 10 cm. 3 of dilute sulphuric acid (1 acid 

to 4 to 6 water by volume). If the rock contains carbonates there 

will be effervescence, hence the acid must be added cautiously and the

FIG. 20. Cooke's apparatus for ferrous-iron determination.

cover placed on till action is over. There need be no fear of oxidation 

of ferrous iron at this stage, should any go into solution. Thereover 

is rinsed if need be and the 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

« 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.
142 ANALYSIS OF SILICATE AND CARBONATE ROCKS

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 'measurecj, 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 

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 ), which is 

already under the burette, the contents of the crucible quickly follow 

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. 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.

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. .

ft. According to Pratt (modified). One gram of the finely ground 

powdel* is treated in a capacious crucible, as in a} with water enough 

to moisten and about 10 cm. 3 of dilute sulphuric acid, and 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.
FERROUS-IRON DETERMINATION. 143

CO*-

Then from a small platinum crucible a measured quantity of strong 

hydrofluoric acid (5 to 7 cm. 3 ) is poured in with one hand, while the 

other draws the lid a little to one side. A second 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. 28) to the titration dish and the operation is concluded as in 

a. The method should first be tested, by the novice with ferroussulphate 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 may come into play.

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 undecomposed portion are certainly different from those 

in the part dissolved.

y. According to Treadwell, 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. 21. After covering the box with its leaden cover there is introduced through A a rapid current of carbon dioxide b until the air is displaced. 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

FIG. 21. 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.

. Jour. Sci., 3d ser., vol. 48,1894, p. 150. 6 See footnote 6, p. 91.
144 ANALYSIS OF SILICATE AND CAEBONATE EOCKS.

cool, the contents of the dish are titrated, as in a, in presence of an 

additional few cubic centimeters of sulphuric acid.

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 

obtained than with the variations of the hydrofluoric-acid method 

described in a and fi, by reason of greater oxidation of ferrous iron.

D. UNCERTAINTIES OF THE FERROUS-IKON 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 can the 

result be regarded as above suspicion.

20. ALKALIES.

A. THE J. LAWRENCE SMITH METHOD.

a. ITS ADVANTAGES.

The various methods for 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 1 method of J. Lawrence 

Smith," 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

a Am. Jour. Sci., 2d ser., vol. 50,1871, p. 269; Am. Chemist, vol. 1,1871; Annalea Chem. und Pharm., 

vol. 159,1871, p. 82.
DETERMINATION OF ALKALIES. 145

entirely the sodium salt, but the amount has been brought down to 

half the above by very long washing. This correction may be 

admitted at once to be a defect of the method, but it is one easily 

applied with safety. It is not at all certain that all the alkali found 

in the blank test comes from the carbonate. Much hot water is used 

for the analysis and a hot-water bottle, even of 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 dull 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. ° 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, of 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. 

22) 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.

FIG. 22. The J. Lawrence Smith crucible for 

alkali determinations. For dimensions see 

text.

Perfectly satisfactory results are 

to be obtained with but half a gram 

of rock powder. This is weighed out, ground down somewhat finer 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 trans--

a U. L. Steinlen (Chem. Zeit., vol. 29, 1905, p. 264) 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. < Bull 305 07 10
146 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

ferred 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. 22) or through a hole in a 

piece of stout asbestos board clamped in a vertical position, and 

heated for about ten minutes by a low, flat flame placed at considerable distance beneath. As soon as the odor of ammonia is no longer 

perceptible the nearly full flame of two Bunsen burners is substituted, 

and continued for forty to fifty minutes. The sintered cake a 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. 30). 

From the aqueous solution of the residue but a few cubic centimeters 

in bulk the rest of the calcium is thrown out by ammonia and 

ammonium oxalate, the last being more effective than the carbonate. 

The filtrate, caught in an untared platinum crucible or small dish, is 

evaporated to dryness and gently ignited; the residue is moistened 

with hydrochloric acid to decompose any alkali carbonate that may 

have been formed, 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. 

I 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.

a 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 

this 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.3 

of water at first.
DETERMINATION OF ALKALIES. 147

C. PRECIPITATION OF POTASSIUM.

To the solution of the chlorides in a small porcelain a dish an excess 

of platinic. chloride solution is added. The dilution should be such 

that when heated on the water bath any precipitate that may form 

wholly redissolves. Evaporation is then carried on till the residue 

solidifies on cooling. It is then drenched with absolute alcohol b or 

with that 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 resultant loss sometimes takes place if this is not done. With 

rocks low in potash drying at 100° suffices fully to expel all water. The 

factor used for reduction of K2PtCl6 to 2KC1 is 0.307 and of 2KC1 to 

K20, 0.632. It does not seem necessary with the relatively small 

amounts of potassium in rocks to make use in place or the first of 

these of the slightly different empirical factor given in some textbooks, a factor based on the analysis of commercial potassium salts. 

If thought desirable the potassium salts can be tested spectroscopically for C£esium 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,0 

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 

sojution may be examined directly. Lithium is almost invariably

a Preferred to platinum because of the possibility, under certain rare and ill-understood conditions, of 

the formation of an insoluble platinous compound, probably by reaction between the platinum of the 

dish and that of the salt. (See also Bolm, F., Zeitschr. anal. Chemie, vol. 38, 1899, p. 349).

&H. Precht (Zeitschr. anal. Chemie, vol. 18, 1879, p. 513.) claims that this is to be preferred to 80 per 

cent alcohol, especially if evaporation has been carried to dehydration of the sodium salt. A. Atterberg disputes this final statement and says that 80 per cent alcohol gives better results.

cWhen 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'inercury, then heating to expulsion of the excess of mercury and 

of its chloride (Sonstadt, E., Jour. Chem Soc., vol. 67,1895, p. 984, who thus reduces potassium chloroplatinate in order to weigh its platinum). . °
148 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

present, but almost never in amount to warrant quantitative estimation. Should it be so, however, the very excellent Gooch method 

(summarized below), of separation by amyl alcohol is to be followed. 

In rock analysis there need be no fear of enough lithium falling with 

the potassium to cause any concern.

If ammonium carbonate alone has been relied on to separate all 

calcium (see d., p. 146) 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® for separating lithium. To the concentrated solution of the chlorides 

amyl alcohol is added and heat is applied, gently at first, to avoid danger of bumping, until 

the water disappearing from solution and the point of ebullition rising and becoming constant for some minutes at a temperature which is approximately that at which the alcohol 

boils by itself, the chlorides of sodium and potassium are deposited and lithium chloride is 

dehydrated and taken into solution. At this stage in the operation the liquid is cooled and 

a drop or two of strong hydrochloric acid added to reconvert traces of lithium hydrate in 

the deposit, and the boiling continued until the alcohol is again free from water. If the 

amount of lithium chloride present is small, it will now be found in solution and the chlorides of sodium and potassium will be in the residue, excepting the traces, for which correction will be made subsequently. If, however, the weight of lithium chloride present exceeds 

10 or 20 milligrams, 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 0.00050 

gram is to be made if sodium chloride constitutes the precipitate, 0.00059 gram if potassium 

chloride alone is present in the residue, and 0.00109 gram if both these chlorides are present, 

for every 10 cm.3 of filtrate, exclusive of washings.

Amyl alcohol is not costly, the manipulations of the process are easy, and the only objectionable feature the development of the fumes of amyl alcohol is one which is insignificant when good ventilation is available.

The process has been used for some months frequently and successfully, by others as well 

as by myself, for the estimation of lithium in waters and minerals.

B. SEPARATION OF ALKALIES BY OTHER METHODS.

When, as may happen in rare instances, it is necessary to 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.

oProc. 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,$9, 40, 56, 78; Am. Chem. Jour., vol. 9, 1887, p. 33.
DETERMINATION OF ALKALIES. 149

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 ] 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.® 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.

C. THE AMYL-ALCOHOL METHOD.

Under certain circumstances, notably absence of lithium, the 

method of Gooch developed by Riggs 6 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. 148) 

in the description of Gooch's method. Riggs's summary is as follows:

Evaporate the solution nearly or quite to dryness. Dissolve the residue in as little 

water as possible and add a few drops of hydrochloric acid. Then add 30 to 40 cm.3 of 

amyl alcohol and expel the water by bringing the alcohol to boiling. Continue the boiling 

until the volume of the solution is reduced to 10 cm.3 , or even considerably less. In filtering, it is of great advantage to use a perforated crucible and an asbestos felt and to filter 

under pressure. In case the total chlorides exceed 0.2 gram it may be advisable to decant 

the liquid, wash the residue, redissolve, and repeat the precipitation. If this be not done, 

the precipitate should be redissolved with the least possible quantity of water, a few drops 

of hydrochloric acid added, and the precipitation repeated in the original solution. The 

filtrate is transferred to a weighed platinum dish and evaporated. Water is added before 

the alcohol has been expelled, and the evaporation continued. The residue is dissolved

aW.ulfing, E. A., Ber. Deutsch. chem. Gesell., vol. 32,1899, p. 2214. The neutral carbonate is prepared 

by dissolving 230 grams of ammonium carbonate in 180 cm.3 of ammonia of 0.92 specific gravity and 

enough water to make 1 liter. This is sometimes called Schaffgotsch's solution.

&Am. Jour. SCL, 3d ser., vol. 44 1892, p. 103.
150 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

in water. Sulphuric acid is added in slight excess. This solution is evaporated to dryness, 

the residue ignited and weighed, and the treatment with sulphuric acid is repeated. The 

residue of insoluble chlorides may be transferred to the weighed perforated crucible and 

dried at a temperature below their melting points, or it may be dissolved and the solution 

transferred to a weighed platinum dish, evaporated, and the residue dried as above and 

weighed.

As with the Gooch method for lithium, the numerous test results 

are good.

21. CARBON DIOXIDE, CARBON. 

A. x 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. 23 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 CO2-free air with which

o For a simple and convenient form, see Treadwell's Quantitative Analysis, American edition, p. 298.
DETERMINATION OF CARBON DIOXIDE.

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: Plot 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

FIG. 23. Compact form of apparatus for determination of carbon dioxide. A, Protective calciumchloride tube, frequently refilled, to retain most of the moisture from the condenser. B, Double Utube, 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 bqcomes less and less effective as it takes up the water set free from 

the soda lime in C during its conversion to carbonate. E, Observation bulbs containing sulphuric 

acid to show the rate of gas flow.

absorption tubes, until the original air has been displaced, the observation bulbs E being attached directly to the drying system, B. The 

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,
152 ANALYSIS OF SILICATE AND CARBONATE BOOKS.

rapidly if there is but little. When effervescence diminishes in the 

former case, at once in the latter, the lamp is .lighted and the flow of 

water through the condenser started. The flame is kept low, so as to 

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 

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 152.

It has already been shown under "Water" (5 C. c, p. 

66) 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. Kreider0 

(fig. 24) 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.

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 drawn 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-holed stopper, through which passes a short glass tube

FIG. 24. Kreider's 

apparatus for indirect determination of volatile 

substances.

a Am. Jour. Sci., 4th ser., vol. 19,1905, p. 188;-Zeitschr. anorg. Chemie, vol. 44,1905, p. 154.
bETERMlNATION OF CHLORINE. 155

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 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 Band 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. 150), 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 ,a 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 groupi 

and sometimes apatite; in the last chiefly in the scapolites. Where

a Jour. Chem. Soc., vol. 85,1904, p. 1001.
154 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

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.

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 OF ACID-SOLUBLE CHLORINE.

a. BY NITRIC ACID.

If nitric acid will decompose the chlorine-bearing minerals, or if it 

is desired to distinguish between the chlorine in soluble and in insoluble minerals, the rock powder may be boiled for a few minutes with 

dilute chlorine-free nitric acid. The acid should be very dilute in 

order to cause no loss of chlorine and the boiling should be as brief 

as possible for the same reason, and also to prevent gelatinization of 

the silica from soluble silicates. Acid as dilute as 1:40 will readily 

decompose apatite and probably the minerals of the sodalite group, 

but it is doubtful if anything like this dilution is called for.
DETERMINATION OF FLUORINE. 155

The filtrate does not require evaporation for the removal of dissolved silica, but may be precipitated at once with silver nitrate. 

The precipitate is treated as in B, or if at all appreciable in amount 

may be collected on a Gooch crucible.

b. BY NITRIC AND HYDROFLUORIC ACIDS.

In many cases in order to obta.in all the chlorine it is sufficient to 

attack the powder 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 fluoride 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 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.

B. QUANTITATIVE DETERMINATION OF FLUORINE.

a. THE METHOD.

For the reason that the fluorine minerals occurring in rocks are' 

mostly attacked but partially, if at all, by strong hot sulphuric acid, 

none of the.methods depending on the volatilization of silicon fluoride 

can be used. There is the further reason that even with decomposable
156 ANALYSIS OF SILICATE AND CARBONATE EOCKS.

fluorides it is impossible to obtain quantitative results -in presence of 

amorphous silica or silicates." Only with quartz powder is volatilization perfect. The method to follow is that of Berzelius, which, 

though not difficult, requires great attention to details and even then 

affords low results (see 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 to 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. 6 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

2 

are repeated till it requires but 1 to 1$ cm. 3 of ^ acid to discharge the

color. There is now added 1 to 2 cm. 3 of an ammoniacal solution of 

zinc oxide, c and the liquid is boiled till the ammonia is wholly expelled. 

The precipitate, containing the last of the silica and some pliosphorus, 

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

a See Daniel, K., Zeitschr. anorg. Chemie, vol. 38,1904, pp. 257-306.

& The use of ammonium nitrate or chloride, instead of carbonate, for throwing out the silica and 

alumina is not to be recommended because of loss of fluorine on subsequent evaporation (H. Rose).

.c 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. 149, 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.' of this reagent are to be used. The solution is then to De evaporated to complete dryness, the 

residue taken up with water, filtered and washed, the filtrate again neutralized with hydrochloric acid 

[nitric in rockanalysis W.-F. H.j. and again evaporated to remove the last oi 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 nood) yields at once silica. Its use is manifestly allowable 

in rock analysis only after the alumina has first been separated by ammonium carbonate.
DETERMINATION OF FLUORINE. 157

almost invariably present, and chromium must still be removed, and 

this can be done only from a nitric solution, as follows: To the still 

alkaline solution silver nitrate is added in excess, whereby phosphate, 

chromate, chloride if chlorine is present, and carbonate of silver are 

precipitated. The last serves to correct any acidity resulting from 

the reaction between the alkaline phosphate and the silver salt, thus 

producing the neutral solution needed for complete precipitation of 

the phosphate and chromate. After slight heating and filtering, the

2

excess of silver is removed by sodium chloride and 1 cm. 3 of ^ 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 filtration 

of the latter. The precipitate is collected on paper and washed with hot 

water, dried, and ignited separately from the filter as far as possible. 

If the dish used for the precipitation was of platinum it is not necessary to cleanse it from adhering precipitate, but the contents of the 

filter are washed back into the dish, the liquid in this is evaporated 

away, the ash of the filter added, and the dish heated over a free flame 

to faint redness for a few moments.

Dilute acetic acid is now poured upon the 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 b take the next to the last weight as 

correct.

b. TESTING OP THE CALCIUM FLUORIDE.

The well-washed and gently ignited calcium fluoride finally obtained 

in the course of this method should be converted to sulphate &s 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

a Am. Jour. Sci., 3d ser., vol. 47, 1894, p. 389. & Zeitschr. anal. Chemie, vol. 43,1904, p. 469.
158 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

correspond to that of the fluoride, the former should be dissolved in 

hot nitric acid and tested for phosphorus by ammonium molybdate 

solution. If phosphate is absent the impurity may have been silica 

or calcium silicate which of these it would be difficult to decide. In 

the former case the fluorine might be safely deduced from 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.

CaS(X-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 it possible to detect additional fluorine by repeating the precipitation with calcium chloride in presence of sodium carbonate, and the 

total errors to be such that for 5 milligrams 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 b 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 

based on volatilization of the fluorine as silicon fluoride, by reason of

oZeitschr. anal. Chemie, vol. 43,1904, p. 469. & Zeitsclir. anal. Chemie, vol. 44,1905, p. 343.
DETERMINATION OF SULPHUR. 159

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, refusion of the 

residue left after leaching the alkali-carbonate melt, including in the 

same refusion 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 aceticacid solutions of the precipitated calcium carbonate.

C. DETERMINATION OF 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 68. These may be greatly simp/ified, 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. a, page 88.

24. SULPHUR. 

A. DETERMINATION OF ITS CONDITION.

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 splution 

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.

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.
160 ANALYSIS OF SILICATE AND CARBONATE ROCKS. 

B. QUANTITATIVE DETEEMINATION.

a. TOTAL SULPHUR.

Although the sulphur of sulphides may sometimes be correctly determined by extraction with aqua regia or some other powerful oxidizer, 

in the wet way, this is not aways so. Therefore it is 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. 30), 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. 116). After thorough disintegration of the fusion in 

water, to which a drop or two of alcohol ha.s 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.

Owing to the small amount of sulphur in rocks, special purification of 

the barium sulphate obtained is hardly ever needful, especially as it 

has been precipitated in the absence of iron. 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.6

b. FRACTIONAL DETERMINATIONS.

If traces of water-soluble sulphates are present, they can be removed 

when desired by boiling water.

For the quantitative extraction of the sulphur of all soluble sulphates, simple boiling with hydrochloric acid suffices, which should be 

done in an atmosphere of carbonic acid if pyrites or other oxidizable 

sulphides are present, and should be finished as quickly as possible in 

order to minimize the error resulting from oxidation to sulphuric acid

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 Dy 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.

b In Jour. Soc. Chem. Ind., vol. 24, 1905, p. 10, and Chem. Zeit., vol. 29, 1905, p. 29, I. Pattinson and 

J. T. Dunn call attention to certain sources of error in the determination of the sulphate ion as the 

presence of sulphides in some barium chloride and the use of red rubber stoppers.
DETERMINATION OF BORON. 161

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.0 In the residue the sulphur of the insoluble 

sulphides 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 set 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 these separate 

determinations may be carried out, the final figures for ferrous and 

ferric oxides can hardly be regarded as more than approximations 

 when much sulphide is present (see p. 138, c. «).

25. BORON.

To the best of my belief it has never been found necessary in this 

laboratory to determine boron quantitatively in a silicate rock. 

Should this determination be required it would be necessary, since 

most borosilicates are insoluble minerals, to fuse with sodium carbonate and apply in one of its modifications the Kosenbladt-Gooch 

method,6 depending on expelling the boron as methyl ester by distila 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.

6 Th. Rosenbladt (Zeitschr. anal. Chemie, vol. 26,1887, 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. 64; 

Chem. News, vol. 55,1887 p. 7) preferred lime, as more active and reliable. Gooch and L. C. Jones have 

later (Am. Jour. Sci., 4th ser., vol. 7, 1899, p. 34, Chem. News, vol. 79,1899, pp. 99, 111) upheld the use of 

lime and proposed as a convenient though perhaps not quite so perfect substitute, sodium tungstate containing an excess of tungstic oxide. In this article they likewise indicate the precautions now used 

to insure complete collection and retention of the boron.

For a useful modification in the way of collecting the boric ether in ammonia before bringing in contact with the lime, see S. L. Penfield and E. S. Sperry (Am. Jour. Sci., 3d ser., vol. 34,1887, p. 222); also 

H. Moissan (Comptes rendus, vol. 116,1893, p. 1087; Bull. Soc. chim., vol. 12,1894, p. 955), who modifies 

the Gooch distilling apparatus in certain respects.

G. W. Sargent (Jour. Am. Chem. Soc., vol. 21,1899, p. 858) obtained satisfactory results with tourmaline by collecting the boron in sodium-hydroxide solution, neutralizing the alkali with hydrochloric acid 

by the aid of methyl orange, then titrating the freed boric acid by sodium hydroxide in presence of 

glycerin, using phenolphthalein as indicator (method of Thompson, Jour. Soc. Chem. Ind., vol. 12, 

1893, p. 432).

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(BOs)2. and by Wilson H. Low (Jour. Am. Chem! Soc., vol. 28,1906, p. 807) who modifies 

the distillation feature, with much apparent advantage, by the addition of dry granulated calcium 

chloride, and perfects the turmeric-paper qualitative test.

Bull. 305 07 11
162 ANALYSIS OF SILICATE AND' CARBONATE ROCKS.

lation with methyl alcohol from an acid solution and collecting this in 

some suitable manner. For simple borates, natural or artificial, this 

method gives entire satisfaction when all needful precautions are carefully observed, but its application to borosilicates yet needs investigation, in view of the as yet unexplained very discordant results obtained 

some years ago by J. E. Whitfield in this laboratory on the mineral 

warwickite, a borotitanate of magnesium and iron. Perhaps bis difficulty arose from the fact that a single fusion with an alkali carbonate 

does not remove all the boron from a borosilicate, as shown by G. W. 

Sargent 0 and W. E. Ford, 6 a cause which would doubtless be inoperative in the case of rocks, by reason of the small amounts of boron 

involved. For this last reason it is quite possible also that the accurate determination of but a few milligrams at most of boric oxide 

would not be feasible by any one of the proposed modifications of collecting and weighing or titrating it. In any case fluorine, if present, 

would have to be first removed by calcium nitrate or acetate before 

freeing the boron.

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 c " Ueber den Gang und die Ausf iihrung der chemischen Untersuchung," folio whig Sandberger's own paper d in the general report " Untersuchungen der Nebengesteine dsr Pribramer 

Gange." I have published a few data as to gold, silver, lead, zinc, 

etc., e in S. F. Emmons's report on "The Geology and Mining Industry of Leadville;" J. S. Curtis/ in his report on "The Silver-Lead

o Jour. Am. Chem. Soc., vol. 21,1899, p. 858.

6 Am. Jour. ScU, 4th ser.. vol. 14,1903, p. 195.

e Jahrbuch der Bergakademie, Leoben u. Pribram, 1887, p. 363.

d 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 strikiag tact 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. 138.)

« Mon. U. S. Geol. Survey, vol. 12,1886, Appendix B, pp. 592-596.

/Mon. U. S. Geol. Survey, vol. 7,1884, pp. 120-138.
GASES AND VAPORS. . 163

Deposits of Eureka, N.ev.," 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* and L. Dieulafait, b 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 

exteiit, sometimes a large extent, especially as to carbon dioxide, the 

source of these is entrapped fluid inclusions, Avhose origin was contemporaneous with that of the containing minerals. A further portion 

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, c A. Gautier, d and K. Hiittner,6 

it is very evident that the gases are often produced by chemical 

changes resulting from the heat used for their expulsion. Thus, 

hydrogen may be due to reduction of water by minerals susceptible 

of oxidation at high temperatures, as ferrous silicates; the' carbon 

monoxide to reduction of carbon dioxide in a like manner or by the 

hydrogen formed by the first reaction; the methane might arise from 

interaction between water and traces of metallic carbides, etc/

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 9 says that pitchstone gives off ammoniacal 

water on heating; A. Delesse h found ammonia in rocks, and A. Gautier

a. Pogg. Ann., vol. 95, 1855, p. 60.

6 Ann. chim. phys., vols.,.15, 17, 18, 21, 1878-1880. , 

cProc. Roy. Soc., vol. 64,1899, p. 130.

d Comptes rendus, vol. 131, 1900, p. 647; vol. 132, 1901, pp. 58 and; 189; vol. 136, 1903, p. 16; Ann. chim. 

phys., 7th ser., vol. 22,1901, p. 97; Ann. des Mines, 10th ser., vol. 9, 1900, p. 316.

e Zeitschr. anorg. Chemie, vol. 43,1905, p. 8.

/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, Comptes rendus, 

vol. 142, 1906, p. 44.

a Quantitative Analyse, Finkener ed., p. 673.

h Ann. des mines, vol. 18,1860, p. 151. 
164 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

later made quantitative tests; H. Erdmann 0 found that ammonia was 

obtained by acting on various minerals of ancient igneous rocks with a 

caustic alkali; C. Luedeking and H. A. Wheeler 6 found ammonium 

sulphate in a barite from Missouri, the presence of which I was able to 

confirm.

It has been noted in this laboratory on three separate occasions, 

when series of ores, roofing slates, and eruptive rocks were analyzed, 

that ammonia, either in the form of chloride or sulphate, or even as free 

ammonia, was given off on heating. Its appearance was not limited 

to one or a few specimens of a series, but seemed to be characteristic 

of all and to be afforded by the unbroken rock as well as by the powdered sample. The precise conditions under which the specimens 

were collected not being known, it is impossible to affirm positively 

that the ammonia may not have been due to recent organic contamination of some sort, especially in the case of the slates, but it is believed that a more critical collection of material will not alter the general result. Its amount was sometimes readily determinable by Nesslerization, being as high as 0.04 per cent in some slates. Carbonaceous 

organic matter was absent from most of these, but doubtless existed 

in them in their early history. In their case the ammonia was, in part 

at least, evolved as such, imparting a strong alkaline reaction-to the 

water in the upper part of the tube. The presence of sulphides, 

fluorides, or chlorides in the rock might cause the ammonia to appear 

as a sublimate of sulphate, fluoride, or chloride. It has been suggested 

that ammonia might result from the action of water on metallic 

nitrides, 0. Silvestri c 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 the length of time it is exposed to the action of the 

reagent.

A. DETECTION OF NEPHELINE IN ERESENCE OF OLIVINE.

For confirmation of the microscopic diagnosis, Prof. L. V. Pirsson d 

has indicated a means of detecting nepheline in presence of olivine, as 

in nepheline basalts, based on the very ready solubility of nepheline, as

«Ber. Deutsch'. chera. Gescll., vol. 29, 1896, p. 1710. c Gazz. chim. ital., vol. 5,1875, p. 301. . 

b Am. Jour. Sci., 3d ser., vol. 42,1891, p. 495. <* Am. Jour. Sci., 4th ser., vol. 2,1896, p. 142.
DETERMINATION OF SOLUBLE SILICA. 165

compared with olivine, when boiled for but one miniite 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 discriminate 

between soluble and insoluble silica already existing together. Usually a boiling solution of sodium carbonate has been employed for this 

purpose, though the caustic alkalies have found advocates.

G. Lunge and C. Millberg 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 abovementioned 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

a Zeitschr. angcw. Chemie, 1897, pp. 393, 425.
166 ANALYSIS OF SILICATE AND CARBONATE. EOCKS.

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 coris'tituerits 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 a 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 CK65 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.

o Jour, landw. Chemic, 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 metamiorphism 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

167
168 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

rocks differ qualitatively in no essential respect from their silicate 

associates except as to the more common occurrence of carbonaceous 

matter; and a complete analysis of one of them involves most of the 

determinations and separations described in the first part of this 

work. The analytical procedure differs, however, in some respects, 

owing to the great preponderance in most cases of components easily 

soluble in the common mineral acids, which either renders it unnecessary to use an alkaline flux or enables the analyst to reduce its amount 

very materially, thereby simplifying subsequent operations. ' The 

analysis is further simplified by the occurrence in reduced amounts, as 

a rule, of those elements which most complicate the analysis of a silicate rock. Only in the very purest carbonate rocks are some of them 

nearly or entirely lacking, as silicon, aluminum, and the alkalies, but 

the minor constituents zirconium, barium, and strontium are often 

not present in readily determinable amount.

In the following pages the descriptions will apply especially to 

those large deposits of carbonate materials denominated limestones, 

magnesian or dolomitic limestones, and dolomites, many of which 

are of great and growing economic importance. For the purpose of 

the analyst an exact definition of these terms is of minor significance. 

Indeed, among geologists there has been no uniform rule for 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 (CO3 ) 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. Ries 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.

It has seldom been considered necessary to analyze the carbonate 

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 eitlier to calculate its supposed amount on

a Bull. New York State Mus. No. 44,1901, p. 644.
MINEEAL COMPOSITION. 169

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 Fe2 03; 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 gaming 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 times from carbonaceous matter.
170 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

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 even then sometimes 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 is 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.
DISTINGUISHING DIFFERENT OABBONATES. 171

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 has 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 magnesiaii 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.
172 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

a. DIFFERING SOLUBILITY IN TAKTAKIC 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.& 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. Jannettaz,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 solubilit}7 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 6 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 aragonite reaction, but 

that formed at 0° affords the calcite reaction.

A. .Hutchinson^ 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.

a 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; Chem. 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.

& Jour. Am. Chem. Soc., vol. 22,1900, p. 117.

cComptes rendus, 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.
DISTINGUISHING DIFFERENT CAKBONATES. 173

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 

magiiesian 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'dololnitic 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 Jake.

F. Hinden b 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.

oZeitschr. Deutsch. geol. Gesell., vol. 40,1888, p. 357. 

6 Verb. Naturforsch. Gesell. Basel, vol. 15,1905, p. 1.
174 ANALYSIS OF SILICATE AND CARBONATE KOCKS.

PART.IT. REFINED METHODS OF ANALYSIS.

32. SILICA, ITS SEPARATION FROM ALUMINA, ETC. 

A. METHODS OF DECOMPOSING' THE HOCK.

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, p}Tite, 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. 71 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. 29). 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 178.

If the original residue is small, and accurate knowledge of its composition is desired,.several grams of the rock may be dissolved and the
SEPARATION OF SILICA FROM ALUMINA. 175

whole filtrate best treated for dissolved iron, aluminum, and manganese, as in 33. A. a, page 178, 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 arid 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 1NOKGANIC BESIDUE IS NOT TO HE 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 a 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 

pf visible redness.
176 ANALYSIS .OF SILICATE AND CAEBONATE BOCKS.

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.* 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.

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

the siliceous components are in such amount as not to permit the 

formation of a wholly soluble product by strong ignition, it is necessary to mix sodium carbonate with the powder and decompose the 

silicates by its aid over the blast lamp. This procedure may be 

^adopted with all siliceous limestones if desired. The amount of flux 

to be used is but a fraction of that needed for a silicate analysis. 

One-fourth to one-half gram for 1 gram of limestone suffices,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 magnesian 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 ft, page 76, 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. <*, and /?, takes little time as compared with 

a silicate analysis. When dry, or nearly so, on the steam bath, the 

dish may be placed in an air bath or (covered) on a platinum triangle resting on a hot plate, and heated to 200° for an hour if a 

limestone is under treatment, but for a highly magnesian limestone

o The changes that take place during the ignition comprise loss of all carbon dioxide, water, and 

carbonaceous matter; oxidation of all pyrite, with retention of the whole of the sulphur as calcium 

sulphate. Prolonged heating will gradually expel all the sulphur trioxide from the calcium sulphate and 

later the alkalies, which can be wholly volatilized in an hour or less by a powerful blast. With an 

inclined blast the alkalies condense in part on the under side of the lid as a soluble and powerfully 

alkaline deposit, sometimes weighing several milligrams, but in the time above set no loss of alkali 

appears to occur.

6 Shimer, P. W., in Meade, R. K., The Chemist's Pocket Manual, p. 1C2.

<= Personal communication from R. K. Meade.
ALUMINUM, IBON, TITANIUM, ETC. 177

the temperature should not exceed 120°, according to J. P. Gilbert,06 

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 dryness, the residue extracted with 

hydrochloric acid as before, but with allowance of only a few minutes' 

time, and the solution filtered once more through a second and smaller 

paper. The two papers with their contents are slowly dried, charred, 

and ignited in platinum, finally over the blast for 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. 79). 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, ETC.c

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

« Technology Quart., vol. 3, 1890, p. 61; abstract in Zeitschr. anal. Chemle, vol. 29,1890, p. 688. 

» Jour. Soc. Chem. Ind., vol. 21,1902, p. 1217. 

« Sec also 8, p. 81.

Bull. 305 07 12
178 ANALYSIS OF SILICATE AND OAEBONATE BOCKS.

follow. Nor in the following are all methods of separation that may 

be capable of affording good results noticed. There are some that 

seem promising but that have not yet been studied sufficiently in 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 OF 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. 176), 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. 183.)

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 A12O3 , 

Fe203 , Mn3 04 , TiO2 , and P2 05 . (For the separation of these, see C,. 

p. 180.)

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.
TREATMENT OF THE FILTRATES FROM ALUMINA, ETC. 179

b. PRECIPITATION OF 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 hydrochloric 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 

hot and moderately strong hydrochloric acid, the solution is boiled to 

drive out the trace of chlorine derived from solution of any precipitated manganese dioxide, and the precipitation is repeated 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 Fe2O3 , A12 03 , TiO2 , and P2O5 . (For separation of 

the ignited oxides see C, p. 180.)

C. PRECIPITATION OF ALUMINUM, IRON, TITANIUM, AND PHOSPHORUS BY THE BASIC-ACETATE

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 then- more ready separation by ammonia from 

appreciable quantities of manganese. (For its application, see A. b. 

ft, p. 83, 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

1 .
180 ANALYSIS OF SILICATE AND CAKBONATE BOOKS.

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 veiy small beaker.. If need be the precipitation is to be again 

repeated, but this will seldom be the case. A first precipitation is, 

however, called for in order to separate a little calcium carbonate that 

may have precipitated during the evaporation of the original ammoniacal filtrate. The alumina and perhaps trace of iron oxide thus 

obtained are added to that already found (A. b, c, p. 179). (For treatment of the filtrate,.see 34, p. 181.)

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 178-179, 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 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. .. . .

" For its preparation sec p. 35.
DETERMINATION OF MANGANESE. 181

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 90. 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 92.

0. TITANIUM.

After titration of the iron the solution is treated exactly as prescribed under 8. B. a. y, page 92, and the titanium is determined 

colorimetrically (p. 110).

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. 184), 

and further the rnanganoso-manganic oxide, if this had intentionally 

been precipitated along with the iron and aluminum as in A. a, page 178. 

(For the discussion of the relative merits of this indirect and the 

direct methods for arriving at the aluminum, see 8. A. a, p. 81, and 

C, p. 93.)

34. MANGANESE. 

A. IN THE FILTRATES FROM 33. B (p. 179).

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 sulphide0) is collected on a 7-cm. filter and washed with 

a dilute solution of ammonium chloride carrying a little ammonium 

sulphide.5 (For treatment of the filtrate, see 35, p. 182.)

If the manganese is not to be determined in a separate portion of 

the rock, the flask is then cleaned from possibly adhering sulphide 

with a solution of half-strength hydrochloric acid diluted with five 

times its volume of hydrogen-sulphide water, which is then passed 

through the filter in order to dissolve the manganese sulphide. The 

fitlrateis treated exactly as under 9. B. b, page 98, if the gravimetric 

method of determination is chosen. In view of the relatively enoro 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 inacids and the method of direct solution has been employedj it may very 

well happen that some iron (aluminum likewise) will fail of precipitation by ammonia. The former will 

then appear at this stage. Hence, prior ignition of the limestone is imperative'in such cases.

6 This is best prepared by considerably overneutralizing a little hydrochloric acid in a small beaker, 

and then adding hydrogen-sulphide water or introducing hydrogen-sulphide gas for a few moments, 

and further diluting if need be.
182 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

mous errors affecting this method when small amounts are in. question 

(see 9. A, p. 96), 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. 99).

If the manganese is to be determined in a separate portion, the sulphide precipitate is discarded; indeed, if it is known that but a few 

hundredths of 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 99. 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 99.

35. COPPER/ NICKEL, COBALT, 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 126; 

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 178, 

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
CALCIUM, STRONTIUM, BAEIUM, MAGNESIUM. 183

neutral solution by oxalic acid, ignited, and weighed. They can then 

be tested as to their character by methods to be found in special 

treatises on the rare earths. The filtrates are to be freed from oxalic 

acid by evaporation and gentle ignition and the residue redissolved 

and tested for nickel, cobalt, zinc, chromium, vanadium, and molybdenum by approved methods. It must not be forgotten 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 127.

36. CALCIUM, STRONTIUM, BARIUM, MAGNESIUM (MANGANESE).

 The filtrate obtained in 33. A. a, page 178, or 34. A, page 181, is 

treated for the most part as in silicate analysis (pp. 101-110).

With dolomitic, limestones and dolomites it will be usually impossible to obtain a correction by the method given in C.b, page 109, for the 

small amount of calcium with the magnesium pyrophosphate. Possibly a better result might be had by adding to the nearly neutral solution of the pyrophosphate a few drops of sulphuric acid and a volume 

of alcohol equal to that of the solution, in order to precipitate calcium sulphate, but this has not been put to the test in presence of phosphoric acid, though it works well in its absence.

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
184 ANALYSIS OF SILICATE AND CABBONATE BOOKS.

 - - . . ' . '

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 in the manner 

elsewhere detailed (p. 107).

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 maybe mixed with 

half its weight of sodium carbonate and strongly blasted. The nitricacid 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 ammoniummolybdate 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 determiriation 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 CARBONACEOUS 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 j 

air is excelled. While still boiling dilute sulphuric acid is added a
FEEROUS IEON. 185

little at a time/till effervescence ceases, an"d"then a further amount. 

Calcium sulphate precipitates, but the iron will remain in solution. 

The flame is then removed and a stopper tightly inserted through 

which passes a small stopcock funnel. When cool or nearly so, cold 

water is poured into the funnel, the cock cautiously opened, and the 

water drawn into the flask, more water being poured into the funnel as 

fast as it empties, till the solution amounts to 100 or 150 cm. 3 . Such 

precaution to exclude air is hardly necessary in most cases, however, 

for in presence of sulphuric acid the oxidation of ferrous iron is exceedingly slow. It is ordinarily quite sufficient to equalize the internal 

and external pressures by opening the cock, removing the stopper, and 

pouring in cold water. The flask is then brought under a burette containing dilute permanganate solution and the iron titrated without 

delay. With a carbonate which is wholly decomposable without the 

aid of heat, this may be accomplished in a flask filled with carbon 

dioxide, whereby the danger of attack of silicates is lessened. If the 

preference is for the potassium-bichromate method of titration, hydrochloric acid may be used instead of sulphuric, in absence of manganese 

peroxide. In this case there is of course no separation of an insoluble 

calcium salt, a fact which renders easier the 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. C. d, page 140.

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. C. d, page 140, together 

with 5 cm. 3 of hydrofluoric acid, the decomposition of the silicates 

is effected in an atmosphere of carbon dioxide, and the titration is 

made as there directed.
186 ANALYSIS OF SILICATE AND CARBONATE KOCKS. 

B. IN PEESENOE 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.

As in A. a, page 184, 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 

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. 144). 

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 an'd 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 150. 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
DETERMINATION OF CAEBON. 187

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 

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 OP 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. 15, p. 63), collecting 

the water and the carbon dioxide asinB. 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. 186) 

gives the data for calculating the carbon of the organic matter.

According to G. T. Morgan0 the two conditions of carbon can be 

successively determined on the same portion of sample by first finding

. a Jour. Chem. Soc., vol. 85,1904, p. 1001.
188 ANALYSIS OF SILICATE AND CAKBONATE BOOKS.

the'carbon dioxide as in A,'bat with substitution of orthophosphoric 

for hydrochloric acid, whereupon, after weighing and replacing the 

absorption tubes, chromic acid is added and the boiling renewed 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 G, pp. 153-154.)

If the rock is likely to contain chlorine-bearing silicates, it is decom- 

 posed 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 

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 157. 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 155.

43. SULPHUR.

A. TESTS AS TO ITS CONDITION. DETEKMINATION 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
DETERMINATION OF SULPHUR. 189

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 OF CONVEKTING SULPHIDES TO SULPHATES.

a. 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.

The platinum crucible containing 1 or 2 grams of the rock powder 

is placed in the perforated disk (fig. 3, p. 30) 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. 175.)

ft. 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 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.
190 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

Evaporation to dryness to separate the dissolved silica is quite 

unnecessary. After decomposition with acid the solution should never 

be permitted to gelatinize, and it needs but little practice on the part 

of the operator to insure unfailing success in preventing this. If it 

should happen, however, it is generally best to begin over, but the 

difficulty may be overcome if but little free acid is present by dissolving the gelatinized silica in sulphur-free fixed alkali and reacidifying in 

the cold with hydrochloric acid.

44. WATER. 

A. HYGROSCOPIC WATER.

From 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 

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 by heating 

in a tube of combustion glass and collecting the water in a calciumchloride 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. b, p. 62) or with anhydrous borax according to 

Jannasch (5. C. d, p. 66). 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.
CONDENSED ANALYSIS. 191 

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, and moistened 

with a few cubic centimeters of water. The crucible is cleaned with 

dilute hydrochloric acid, the solution poured into the dish, which is to 

be kept covered if sodium carbonate was used, and more acid added. 

Solution of the mass may be aided by gentle pressure with the flattened end of a glass rod. The solution is then evaporated to 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.

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. 29), 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.
192 ANALYSIS OF SILICATE AND CARBONATE BOCKS.

47. A.LUJVIINUM, IRON, ETC.

The filtrate, which need not exceed 100 cm. 3 in bulk with fairly 

pure limestones, is brought to boiling in a bea^apj 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 

the filtrate, the precipitated oxides may be washed with water containing in the liter 20 cm. 3 of nitric acid that has been neutralized 

with ammonia.

The paper containing the final precipitate is placed in a platinum 

crucible, slowly charred, then ignited over a gradually increased 

flame, and finally over the blast for two to five minutes. The weight 

found represents the oxides of ferric'iron, aluminum, titanium, phosphorus, and manganese, the last presumably Mn3 04 .

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. 180. The phosphorus and manganese, having 

been determined in different portions (37, p. 184, and 34. B, p. 182), 

the aluminum oxide is found by subtracting all these oxides from 

the original weight of the mixture. Of ten the percentage reported 

as alumina includes in reality the titanium, phosphorus, and some 

of the manganese, where no attempt has been made to separately 

determine these.

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
IGNITION LOSS. 193

and treated with the main quantity of iron and aluminum oxides, 

and the nitrates 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 permanganate.

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 considerable excess. After several hours, twelve or fifteen if the precipitate is very slight, the solution is filtered, the precipitate redissolved in hydrocloric 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. 186.

51. CARBON DIOXIDE.

See 40, p. 186.

52. SULPHUR.

See 43, p. 188.

53. WATER.

See 44, p. 190.

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 laboratories, some space will be devoted to it.

Loss on ignition with carbonate rocks represents, as with those of 

a silicate nature, the algebraic sum of a number of chemical changes 

involving both losses and gains, and its amount will depend largely 

on the temperature employed. At the temperature of a moderate

Bull. 305 07 -13
194 ANALYSIS OF SILICATE AND CARBONATE ROCKS.

blast, with crucible covered, carbon dioxide, water, and carbonaceous matter escape wholly. Sulphides are oxidized to sulphates and 

all the sulphur is retained as sulphate by the calcium. With a powerful blast the sulphate is decomposed gradually, with eventual loss of 

the entire sulphur. At this point the alkalies begin to escape as 

oxides, the potassium relatively faster than the sodium, and they 

may be found in part condensed on the lid of the crucible. If the 

heating is long continued they can be wholly volatilized. As a 

small offset to these losses the iron of pyrite. and the iron and manganese of ferrous and manganous carbonates take up oxygen and 

unite with the lime. By proper 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. 30), 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 repetitiono 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.

Absorption tubes, use of, in water determination ....................... 61-68

Acids, quality of............................ 35

Acknowledgments to those aiding.......... 13

Alkalies, determination of............ 144-150,186

determination of, apparatus for, figure

showing........................ 145

Alien, E. T., cited.......................... 95-96

Alien, K. T., and Day, A. L., cited......... 55

pycnometer method of................. 43-45

Aluminum, concealment of, by manganese. 96 

direct determination of................. 93-96

indirect determination of... 81-90,177-181,192 

ignition of precipitate of oxide of....... 87-88

precipitation of.......... 82-86,95,178-179,192

recovery of, from filtrates...... 86-87,179-180

separation of, from iron................ 93-95

Aluminum chloride, loss of......... 83 (.footnote)

Ammonia, occurrence of, in rocks........ 163-164

Ammonium chloride, reagent, preparation

of.............................. 82,144

Ammonium oxalate, reagent, quality of.... 36

Analysis, allowable error in................ 25-26

completeness and thoroughness of, importance of.................. 14-20,38

crushing of rock for.................... 45-47

diversity of, for same rock............. 16-17

grinding rock for....................... 47-50

methods of............................. 12

neglect of certain factors in, consequences of...................... 17-19

preparation of sample fo r.............. 45-50

quantity of rock required for.. 20,37-38,45,50 

statement of............................ 27

time required for...... 1................ 28

See. also Carbonate rocks; Silicate rocks. 

Analysis, qualitative, usefulness of......... 34

Appliances and apparatus, descriptions and

figures of....................... 28-34

Aragonite, tests for........................ 72

Atterberg, A., cited.........:.... 147 (footnote)

Austin, M., and Gooch, F. A., cited. 98^105-106,122

B. 

Bailey, G. H., cited....................... 118-119

Barium, determination of. 102-103,116-118,180,183 

ignited silica free from ................. 80

precipitability of, by ammonium persulphate ........................ 85

occurrence of, in rocks........... 18,23-24,159

recovery of, from alumina precipitate.. 90 

removal of, from magnesium pyrophosphate........................... 109

separation of, from strontium.......... 103

Page. 

Baskerville, C., method of, in determination

 of titanium...................... 115

method of, in determination of xirconium............................ 120

Baubigny, H., method of. in determination

of chromium ................... 124

Bibliography of rock analysis.............. > 11-12

Bisbee, H., Richards, T. W., and McCaffrey,

C. T., cited..................... 101

Blair, A. A., crucible tongs of............... 28

Blast, temperature of, test of...... 79 (footnote)

Blount, B., cited.......................... 78,177

Bolm, P., cited.................... 147 (footnote)

Bolton, H. C., cited..-....................... 172

Boric oxide, reagent, preparation of..'...... 70

Boron, determination of.................. 161-162

occurrence of, in rocks.................. 25

Broockmann, K., cited..................... 108

Browning, P. E.,cited..................... 102

Briihl, E,,.and.Friedheim. C., cited........ 97,124

Brunck, 0., cited......................... 104,105

basic-acetate method of, in separation of

iron, manganese, etc... 85 (footnote) 

Brush, G. J., method of, in wa'ter determination............................. 59-60

Buckley, E. R., method of, for determination of porosity................. 40-41

Bunsen, R., cited........................... 55,75

C. . 

Calcite, tests for...................... 150,172,173

Calcium, determination of.... 101,105,183,192-193

ignition of oxalate of................. 101-102

occurrence of, in rocks................ 169-170

precipitability of, by ammonium persulphate ........................ 85

removal of, from magnesium pyrophosphate......................... 109-110

in alkali determination............. 146

separation of strontium from.......... 102

Calcium chloride, reagent, deterioration of. 56 

Calcium fluoride, testing of precipitate of. 157-158 

Calcium oxalate, solubility of........: ...... 101

Cameron, A., cited.......................... 75

Campbell, E. D.. and Hess, W. H., cited... 95 

Carbon, determination of............. 153,186-188

effect of, on ferrous-iron determination. 138,

140,184,186 

occurrence of, in rocks.................. 171

Carbonate rocks, analysis of............. 167-194

analysis of, defects of, as usually made 168-170 

condensed forms of............... 190-194

detailed methods of.............. 174-190

causes of color of....................... 170
196 INDEX.

Page. 

Carbonate rocks, ignition loss of.......... 193-194

importance of ......................... 12

impurities in.......................... 167-168

mineral composition of............... 169-171

qualitative comparison of silicate rocks

and........................... 167-168

qualitative tests of................... 171-173

Carbonates, qualitative tests of.......... 171-173

Carbon dioxide, direct determination of.... 150-

152,186 

direct determination of, apparatus for,

figure showing.................. 151

expulsion of, by heat................... 163

indirect determination of............. 152-153

Carbon monoxide, evolution of, on heating

rocks........................... 163

Carnot, A., cited............................ 92

Cathrein, A, cited.. 93 (footnote), 113 (footnote) 

Cerium, detection of.. ..................... 121

occurrence of, in piedmontite... 83 (footnote) 

Chalcopy rite, occurrence of, in rocks........ 24

Chatard, T. M., cited..................... 113,123

dryingovenof, description and figureof. 57-58 

Chlorine, condition of, in rocks............. 154

determination of................. 153-155,188

occurrence of, in rocks. J................ 24

Chromium, colorimetric determination of. 116- 

117,123-125,127-131,182-183 

colorimetric determination of, comparisonofgravimetricmethodand. 125-126 

effect of vanadium on............... 123

gravimetric determination of........... 124

occurrence of, in rocks................. 22,131

Citric acid, relative solubility of carbonatesin.......................;....... .172

Claasen, Edo, cited......................... 127

Clarke, F. W., cited........................ 18

Classen, A., cited......'..................... 36

Cloedt, E. v., and Jannasch, P., cited...... 97,124

Cobalt, detection of........................ 97-98

determination of.................. 98,182-183

occurrence of, in rocks.................. 23

Colorimeters, description of and figures

showing. ...................... 31-34

Colorimetric methods, for determination

of chromium.......... 124-125,127-129

for determination of chromium, comparison of gravimetric method 

and........................... 125-126

for determination of manganese....... 99-100

of titanium................... 110-112,116

of vanadium........................ 131

Columbium, occurrence of, in rocks......... 25

Cooke, J. P., method of, for determination

of ferrous iron............ 135,140-142

method of, apparatus for, figure showing.............................. 141

Coppadoro, A., cited............... 90 (footnote)

Copper, determination of........... 98-99,182-183

occurrence of, in rocks.................. 23

Cramer, E., cited........................... 42

Cross, VV., and others, cited................ 38

Crucible, disk for, description and figure of. 30-31 

tongs for, description and figure of...... 28-29

Crucibles, platinum, loss of weight of.. 78 (footnote), 88 (footnote)

Page. 

Crushing, methods of....................... 45-47

Crystal water. See Water.

Curtis, J. S., cited...............:.......... 162

Czudnowitz, C., cited....................... 127

D. 

Daniel, K., cited................... 156 (footnote)

Davis, J. F., cited.......................... 120

Davy, Humphrey, cited.................... 70

Day, A. L., and Alien, E. T., cited.......... 55

pycnometer method of.................. 43-45

Delesse, A., cited........................... 163

Desiccators, use of.................... 51,52,53,56

Determinations, importance of order of.... 37

Deussen7E., cited............. 89 (footnote), 136

Dieulafait, L., cited........ 18, 20 (footnote), 163

Dittrich, Max, cited....................... 11,26,

50,67,72,83,88,95,149

method of, in determination of titanium.. ........................ 115-110

Dittrich, Max, and Pohl, R., cited ....... 115,120

Dolomite, definition of..................... 168

tests for................................ 173

Drying before analysis, uselessness of...... 50

Drying for hygroscopic tests, process of..... 50-52

Dunn, J. F., cited................. 160 (footnote)

Dunnington, F. P., cited................... Ill

E. 

Eakins, L. G., cited........................ 42-43

Electrification of glass tubes, influence of,

on weight....................... 56

Ellis, C. W. H., mortar of, description and

figure of........................ 46

Erdmann, H., cited......................... 164

Error in analysis, allowable limits of....... 25-26

F.

Feldspars, error in calculation of .......... 18

Ferric iron, calculation of.................. 93

See also Iron. 

Ferrous iron, determination of ... 131-144,184-180

determination of, hydrofluoric-acid

method of.................... 135-144

sealed tube method of............ 133-135

See also Iron. 

Fischer, T., cited........................... 331

Fluid inclusions, volatilization of........... 163

Fluorine, determination of............ 155-159,188

influence of, in silica determination..... 68, 

71 (footnote)

occurrence of, in rocks................... 24-25

qualitative tests for.................... 155

Forchhammer, J. G., cited.................. 163

Ford, W.E.,cited.......................... 162

Foullon, H. von, cited...................... 162

Frantz, B., and Streit, G., cited.......... 119-120

Fresenius, R., cited.......... 101 (foot note), 103

Friedel, C., cited............................ 52

Friedheim, C., cited........................ 70

Friedheim, C., and Bruhl, E., cited........ 97,124

Funk, W., basic-acetate method of, for 

separation of iron, manganese, 

etc...................... 85 (footnote)

G.

Galena, occurrence of, in carbonate rocks... 170 

Gases, evolution of, on heating rocks...... 163-164
INDEX. 197

PageGautier, A., cited........................... 103

Gibbs, Wolcott, cited...................... 106

Gilbert, J. P., cited..................... 75-70,177

Glassware, inferiority of........ 31 (footnote), 35

Glucinum, occurrence of, in rocks.......... 25

Gold, occurrence of, in rocks............... 25

Gooch, F. A., apparatus of, for water determination, description and figures of.......................... 62-05

cited....................... 93,101 (footnote)

method of, in determination of lithium. 148 

in determination of titanium..... 113-115

Gooch, F. A., and Austin, M., cited. 98,105-lOfi, 122 

Gooch, F. A., and Jones, L. C., cited

101 (footnote) 

Grinding, fineness of........................ 14V

methods of............................. 47-49

H. 

Hall, R. W., cited.......................... 78

Harper, D. N., and Penfield, S. L., cited.... 82

Harrington, B. J., cited.................... 171

Harrison, J. B., cited.......................23, 25

Hauynite, evidence as to presence of....... 159

occurrence of, in rocks.................. 24

Hayes, A. A., cited.......................... 18

Heidenreich, 0., and Jannasch, P., boricoxide method of, for decomposing silicates..................... 70

Hempel, W., cited........................... 49

Hewett, Foster, cited....................... 23

Hess, W. H., and Campbell, E. D., cited ... 95 

Hinden, F., cited........................... 173

Holthof, C., cited........................... 72,74

Horn, D. W., cited......................... .125

Hutchinson, A., cited...................... 172

Huttner, K. cited ........................... 103

Hydrofluoric acid, reagent, quality of...... 35

Hydrofluoric-acid method of determining

ferrous iron................... 135-144

Hydrogen, evolution of, on heating rocks .. 103 

Hydrogen peroxide, reagent, quality of ... 36, 111 

Hydrogen sulphide, occurrence of, in carbonate rocks....................... 171

Hygroscopic water, determination of. 50-58,66,190 

See also Water.

I.

Iddings, J. P., and others, cited............ 38

Ignition, loss by carbonate rocks on...... 193-194

loss on, inaccuracy of water determination by......................... 59

temperature of, variations in (footnote) 79 

Iron, correction of titanium determination

for............................ 112-113

determination of.... 90-93,131-144,177-181,192

effect of carbonaceous matter on.... 138,

140, 184, 186

effect of sulphides on.. 132-133,138-140, 161 

effect of vanadium on.......... 91-93,140

ignition of precipitate of oxide of....... 87-88

occurrence of, in carbonate rocks..... 169,170

oxidizabiiity of divalent, by free oxygen,

in presence of a fluoride......... 137

precipitation of............. 82-86,178r179,192

recovery of, from filtrate............... 8S-87

reduction of............................ 90-91

Page. 

Iron, separation of, from aluminum........ 93-95

in titanium determination........ 113-114

solution of oxide of, by alkali fusion.... 93

titration of............. 91-92,142-144,181,184

See also Ferric iron; Ferrous iron. 

Iron oxides, error in determination of...... 19,

131-133,135,138-140,144

Jannasch, P., Nickel-becher of.............. 29

silicate decomposition methods of...... 9-70

water determinations of, apparatus for,

figure of........................ 67

method of.......................... 66-08

work of.................................. 68

Jannasch, P., and Cloedt, E. v., cited..... 97,124

Jannasch, P., and Heidenreich, 0., boricoxide method of................ 70-71

Jannasch, P., and Weber, H., cited

71 (footnote) 

Jannettaz, E., cited........................ 172

Jarvinen, K. K., cited.................... 106,108

Jones, L. C., and Gooch, F. A., cited

101 (footnote)

Knop, A., cited..................... 90 (footnote)

Koch, A. A., and Treadwell, F. P., cited.. 157,158 

Koninck, L. L. de, cited.................. 108,132

Koningh, L. de, cited............. 124 (footnote)

Krauch, C., cited........................... 35

Kreider, J. L., apparatus of, for determination of volatile substance, description and figure of........ 152-153

L.

Lang, W. R., and Manning, R. J., cited

161 (footnote) 

Lazurite, evidence of presence of, in rocks.. 159

occurrence of, in rocks.................. 24

Lead, occurrence of, in rocks............... 25

Lemberg, J., cited.......................... 173

Limestones, causes of color in.............. 170

minor constituents of.................. 169

Limestones, dolomitic, definition of........ 168

Limestones, magnesian, definition of....... 168

Lindemann, O., cited....................... 127

Lindo, D., cited............................ 76

Literature of analysis...................... 11-12

Lithium, determination of............... 147-148

occurrence of, in rocks.................. 24

Low, W. H., cited............... 161 (footnote)

L6 we, J., clay disks of...................... 31

Ludwig, F,., cited........................... 75

Luedeking, C. ', cited........................ 164

Lunge, G., cited............................ 31

Lunge, G., and Millberg, C.,'cited...... 78,165-166

M.

McCaffrey, C. T., Bisbee, H., and Richards,

T. W., cited.................... 101

McKenna Brothers Brass Co., ore grinder

of, description and figure of .... 47-48

Magnesium, determination of..... 105-110,183,193 

occurrence of, in carbonate rocks....... 169
198 INDEX.

Page. 

Magnesium, precipitate of, ignition of.... 108-109

precipitate of, contaminants of, removal

of............................. 109-110

precipitation of......................... 107

essentials of...................... 105-107

separation of, in alkali determination .. 147,

148-150 

Maillard, L. C., cited....................... 131

Manasse, 0., cited.......................... 138

Manganese, determination of.............. 96-100,

110,181-182,192 

occurrence of, in rocks................. 23,169

oxidizability of divalent, in presence of

hydrofluoric acid............. 135-137

precipitation of............ 85-86,97-99,178-179

removal of, from magnesium pyrophosphate........................... 110

Manning, R. J., and Lang, W. R., cited.... 161

Mar, F. W., cited........................... 118

Marble, contamination of, by sulphides

91 (footnote) 

Meade, R. K., cited......................... 176«

Mechanical separation, literature of........ 12-13

Meigen, W., cited........................... 172

Meineke, C., cited........................... 75

Meteorites, analysis of...................... 12

Microscopic examination, value of.......... 19-20

Millberg, C., and Lunge, G., cited........ 78,165-166

Minerals, specific gravity of fragments of ... 42 

Mingaye, J. C.IL,cited............. 19 (footnote)

Minor, J. C., and Penfield, S. L., cited....... 157

Mitchell, W. L., and Wells, H. A., cited

91 (footnote)

Mitscherlich method of ferrous-iron determination. ................. 131,133-135

objections to.......... 131,133,133 (footnote)

Mittasch, A., basic-acetate method of. 

for separation of manganese

84-85 (footnote) 

Moissan, H., cited'.......................... 161

Molybdenum, determination of....... 128,182,183

occurrence of, in rocks.......... 19,25,126,170

Moore, E. G., device of, to remove air from 

mineral powders, description 

and figure of.................... 44-45

Morgan, G. T., cited.................. 153,187-188

Morley, E. W., cited............... 145 (footnote)

Moureu, C., cited............................ 163

N.

Nepheline, detection of, in presence of

olivine........................ 164-165

Neubauer, H., cited................... 105-106,108

Neustadl, J,., and Skrabal, A., cited......... 103

Nickel, determination of............... 98,182-183

occurrence of, in rocks................. 23,170

precipitation of......................... 97-99

Nickel-becher, description of................ 29

Nitrogen, occurrence of, in rocks............ 163

Noselite, evidence as to presence of.......... 159

occurrence of, in rocks.................. 24

Noyes, W. A., cited....................... 112-113

0.

Organic matter, removal of................. 175

Oxidation, incompleteness of, on ignition of

ferrous compounds............. 59

P. 

Panebianco, G., cited....................... 172

Pattinson, I., cited ......................... 160

Penfield, S. L., cited........................ 42,82

' method of, for water determination..... 59-62

apparatus for, figures showing...... 60,61

Penfield, S. L., and Harper, D. N., cited.... 82

Penfield, S. L., and Minor, J. C., cited....... 157

Penfield, S. L., and Sperry, C. S., cited

161 (footnote) 

Peters. R., cited ............................ 137

Phenylhydrax.ine, reagent, contamination

of ..................... 95 (footnote)

Phosphorus, determination of.... 121-123,184,192

loss of, by volatization.................. 94

occurrence of, in rocks................. 24,171

precipitation of....................... 178-179

Phosphorus salt, reagent, quality of........ 36

Piedmontite, rare earths in........ 83 (footnote)

Pinagel, A., cited ........................... 76

Pirsson, L. V., cited................... 27,164-165

Pirsson, T,. V., and others, cited............ 38

Platinum, occurrence of, in rocks........ 25.80-81

precipitation of.......... 81,90-91 (footnote)

reduction of, from solution.... 147 (footnote)

Platinum crucibles, loss of weight in

78 (footnote),88 (footnote) 

Pohl, R., and Dittrich, Max, cited....... 115,120

Porosity, determination of .............. 38; 40-42

Potassium, determination of ............... 147

Potassium bisulphate, reagent, conversion

of, to pyrosulphate............. 36

objections to use of ............ 88 (footnote)

quality of............................... 35-36

relative solubility of carbonates in...... 172

Potassium pyrosulphate, reagent, advantages n use of....... 88-89 (footnote)

Powell, N. S., and Richards, J. W., cited.... 172

Pratt, J. H., method of, in ferrous-iron

determination............ 137,142-143

Precht, H., cited.................. 147 (footnote)

Pycnometer method of specific-gravity determinations. ................... 42-45

Pyrite, effect of, on ferrous-iron determination........................... 138-140

occurrence of, in carbonate rocks........ 170

Pyrrhotite, evidence as to presence of, in

rocks............................ 159

R.

Radiators for evaporating solutions........ 29

Ransome, F. L., cited...................... 22,126

Rare earths, caution against overlooking

of................... 83 (footnote),97

determination of.. ] 16-117,119,120-121,182-183 

occurrence of, in rocks.................. 25

Reagents, quality of........................ 34-37

testing of............................... 35

Richards, J. W., and Powell, N. S., cited.... 172

Richards, T. W., McCaflrey, C. T., and

Bisbee, H., cited................ 101

Ridsdale, 0. H., cited...................... 92,130

Ries, H., cited .............................. 168

Riggs, R. B., method of, for separation of

magnesium from alkalies...... 149-150

Robertson, J. D., cited.. ................... 163

Rose, H.,cited.. 94 (footnote), 156'(footrrtp), 163 

Rosenblatt, Th.,cited............. 161 (footnote)
INDEX. 199

s.

Sandberger, F., cited........... 20 (footnote), 162

Sargent, G. W., cited......... 161 (footnote), 162

Schaffgotsch's solution, character of

149 (footnote) 

use of. ........................ 156 (footnote)

Schaller, W. T., cited. ............ 146 (footnote)

Schreiner, Oswald, colorimeter of, description and figure of............... 33-34

Scoop. See Weighing, scoop for.

Seemann, F., cited......... 156 (footnote), 158-159

Seger, H., cited ............................. 42

Separation, mechanical, literature of........ 12-13

Shimer, P. W., cited........................ 176

Sieves, metal, unavailability of............. 49

Silica, dehydration of....................... 75-78

determination of...................... 68-81,

88-90,159,174-177,180,191 

accuracy of.......................... 79,89

impurities in, correction for............. 79

precipitate of, ignition of............... 78-79

recovery of, from alumina precipitate.. 88-90

removal of, in fluorine determination... 156

in sulphur determination ........... 160

residue from, composition of........... 80

separation of, from alumina, etc. 68-81,176-177 

fluxes used in....................... 68-75

methods of...................... 68,75-78

Silica, soluble, determination of .......... 165-166

Silicate rocks, analysis of.................. 14-166

analysis of, methods of................ 37-166

constituents in......................... 20-25

literature of............................ 11

methods of decomposition of........... 69-74

Siliceous limestones, character of........... 170

Silver, occurrence of, in rocks.............. 25

Silvestri, 0., cited.......................... 164

Sjollema, B., cited.......................... 166

Skrabal, A., and Neustadl, L., cited........ 103

Smith, J. Lawrence, cited.......... 89 (footnote)

method of, for alkali determination.. 144-145 

apparatus for, figure'showing...... 145

Sodium, determination of.................. 147

Sodium bisulphate, objections to .. .88 (footnote) 

quality of ............................... 35

Sodium carbonate, reagent, quality ~of..... 36,72

Sodium hydroxids, reagent, quality of..... 36

Sodium-potassium carbonate, comparison

of sodium carbonate and....... 71-72

Sodium pyrosulphate, reagent, preparation

of ............................... 36

use of, advantages.......... 88-89 (footnote)

Solutions, heavy, unavailability of, in specific gravity determinations of 

rocks............................ 45

Sonstadt, E., cited................ 147 (footnote)

Specific gravity, determination of.......... 38-45

Sperry, E. S., and Penfield, S. L., cited..... 161

(footnote)

Sphalerite, occurrence of, in carbonate rocks. 170 

Steiger, George,cited. 96 (footnote),146.(footnote) 

drying apparatus of, description and

figure of........................ 56-57

Steinlen, R. L., cited.............. 145 (footnote)

Stoddart, C. W.,- cited............ 160 (footnote)

Stokes, H. N., cited.............. 119,132,133,139

Streit, G., and Franz, B., cited........... 119-120

Page. 

Strontium, determination of............... 102

occurrence of, in rocks............... 18,23-24

separation of, from calcium............ . 102

from magnesium................. 101-102

Sulphides, conversion of, to sulphates in

limestones ..................... 189

Sulphur, condition of,determination of. 159,188-89 

determination of...... 116-117,159-161,189-190

failure to determine, error arising from. 19 

occurrence of, in rocks.................. 19,24

removal of, in alkali determination..... 146

Sulphur dioxide, reagent, quality of ...!.... 128

(footnote)

Tantalum, occurrence of, in rocks..........

Tartaric acid, relative solubility of carbonates in..........................

removal of, in titanium determination..

25

172

114

Tho'rner, T. W., cited....................... 42

Thorpe, T. E., cited........................ 18

Titanic oxide, solubility of, in alkalies...... .94

Titanium, colorimetric determination of... 110-

113,181

colorimetric determination of, superiority of........................... 116

gravimetric determination of.. 94,113-116,192 

loss of......................... 113 (footnote)

occurrence of, in rocks.................. 21-22

precipitation of... 81,90 (footnote), 93,178-179 

Titanium sulphate, reagent, preparation of. Ill

(footnote)- 

Toluene bath, description and use of....... 51,56

Trace, definition of......................... 27

Travers, M. W., cited....................... 163

Treadwell, F. P., cited...................... 78

method of, for ferrous-iron determination ........................ 135,143-144 '

apparatus for, figure showing...... 143

Treadwell, F. P., and Koch, A. A., cited.. 157-158 

Tungsten, occurrence of, in rocks........... 25

Tyrolite, drying of, experiment on......... 51-52

U. 

Ulbricht, R., cited........................ 108-109

Ullmann, C., cited.......................... 134

Uranium, occurrence of, in rocks........... 25

V.

Vanadium, colorimetric determination of.. 131 

effect of, on iron determination. 92-93,126,140 

failure to determine, error from......... 19

gravimetric determination of........... 123,

127-131,182,183 

occurrence of, in rocks.... 18-19,22-23,126,171

Vogt, J. H. L., cited........................ 132

Volatile substances, determination of, apparatus for, description and figure of......................... 152-153

Volhard, J., cited.................. 98 (footnote)

W. 

Walters, H'. E., cited............... 99 (footnote)

Warwickite, analyses of, discordancy of.... 162

Washington, H. S., cited .................. 11-12,

15 (footnote), 16 (footnote), 20, 21, 23, 

26, 27, 47, 91 (footnote), 96 (footnote)
200 INDEX.

Page.

Washington, H. S., method of. in determination of phosphorus......... 121-122

Washington, H. S., and others, cited....... 38

Water, direct determination of..... 50-68,187,190

direct determination of, apparatus for,

description and figures of........ 56-68

precautions to be observed in...... 56

indirect determination of......... 51-53,59-66

porosity and, determination of......... 40-42

suspension in, determination of specific

gravity by...................... 39-40

Weber, H., boric-oxide method of, for decomposing silicates............. 70-71

Weighing scoop, description and figure of. 31 

Weller, A., method of, for determination of

titanium...................... 110-112

Wells, H. A., and Mitchell, W. L., cited....

91 (footnote) 

Wheeler, H. A., cited'....................... 164

Whitfleld, J. E., cited...................... 162

Page. 

Williamson, J. A., cited.................... 35

Wiilflng, E. A., cited...................... 132,149

Zeolitic minerals, dehydration of........... 52

occurrence of, in rocks......... 39 (footnote)

Zeolitic water. See Water.

Zimmerman, 0., method of, for separation

of magnesia..................... 149.

Zinc, determination of................. 98,182-183

occurrence of, in rocks.................. 25

precipitation of......................... 97-99

Zinc-oxide solution, preparation and use of.

156 (footnote)

Zirconium, determination of. .. 94,116-117,118-120 

difficulty with, in gravimetric titanium

determination.................. 115

occurrence of, in rocks............"...... 22