DEPARTMENT OF THE INTERIOR

BULLETIN

OF THE

UNITED STATES

GEOLOGICAL SURVEY

IsTo. 176

WASHINGTON

GOVERNMENT PRINTING OFFICE 

' 1900

UNITED STATES GEOLOGICAL SURVEY

CHAJILES T>. AVALCOTT, DIIIECTOR

SOME PRINCIPLES AND METHODS

OF

EOCK ANALYSIS

WILLIAM FRANCIS HILLEBRAND

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1900

CONTENTS. .

,.w', Pago.

Part I. Introduction..................................... .................. 13

1 I. Importance of complete and thorough analyses.................. 13

II. Object and scope of the present treatise 1......................... 19

III. Statement of analyses........................................... 21

IV. Time needed for making an analysis............................. 22

V. Two useful aids in chemical manipulation........................ 23

^..j VI. Limits of allowable error in summation of results..... '. .......... 24

VII. Quality of reagents ..................:......................... 25

VIII. Preliminary qualitative analysis ................................ 26

Part II. Methods. ........................................................ 27

I. Introductory remarks ........... ........'....................... 27

II. Specific gravity ................................................ 28

By suspension in water..................................... . 28

Ordinary method.......................-...-'....-.. 28

' "" Penfield's method........ .......................... 29

Pycnometer method........................................ 29

Heavy solutions not suitable for rocks....................... 31

, III. Preparation of sample for analysis............................... 31

Quantity of rock to be crushed.............................. 31

Crushing .................................... s............. 31

Grinding .................................................. 31

Weight of ground sample.................................... 32

IV. Water hygroscopic, zeolitic, crystal ............................ 32

""> Importance of employing air-dry powder for analysis.. 32

Temperature of drying,............................. 33

Cautionary hints ................................... 33

Procedure in special cases........................... 34

Argument in favor of including hygroscopic water in

summation....................................... 35

Separate entry of hygroscopic and combined water.... 36

-< Is all true hygroscopic water expelled at 100°......... 36

Apparatus for the direct determination of water at different

temperatures............................................. 36

V. Water total or combined ...................................... 38.

Arguments against''loss on ignition'' method................ 38

Direct weighing of the water without the Use of absorption

tubes 

Penfield's methods....................................... 38

For minerals easily deprived of their water........... 38

For minerals not easily deprived of their water....... 39

Direct weighing of the water in absorption tubes.............. 40

Penfield's procedure................................ 40

Gooch's apparatus.................................. 41

Chatard's apparatus................................ 4.5

i Merits of the above three forms of apparatus......... 45

Jannasch's methods ................................ 45

5
O CONTENTS.

Part II. Methods Continued. Page.

VI. Silica, separation from alumina, etc.............................. 47 Y

Alternative methods of decomposition.... ...................^. 47

Preliminary remarks.................................... 47 -

'Decomposition of refractory silicates by hydrochloric acid

under pressure--.....----...-----..----.-....--...... 48

The boric-oxide method ................................. 49

Preparation of the boric oxide....................... 49

Treatment of easily decomposable silicates ........... 49 ._

Treatment of refractp.ry si.Hcate_s,.......... i............. 49

Further treatment after fusion....................... 50

Possible.objections to the boric oxide method........ 50

The sodium carbonate .method........................... 50

Purity of the sodium carbonate used as a flux ........ 50

Precautions in fusing ............................... 51

. Treatment after fusion.............................. 51

Subsequenttreatment.....................................-.---....... 52

. .... . Drying and.testing of silica.......................... 52

Platinum in filtrates.,..-.,............................... 54

VII. Metals precipitable by hydrogen sulphide........................ 54

VIII. Aluminum, total iron................................... ......I...... 54

Indirect method for aluminum.............................. 54

Precipitation of.aluminum, iron, etc..................... 55

Precipitation by ammonia .......................... 55 K

Precipitation by. the. basic acetate method............ 55

Ignition of the precipitate .............................. 56

Recovery of silica and possible barium................... 56

. . Estimation of iron in the precipitate of alumina, etc .......... 57

. . . Without regard to the, .pre.sen.ce of vanadium......... 57

Having regard to the presence of vanadium.......... 58

Determination of the true value for ferric iron ........... 59

. Methodsaimingat.themoreorlessdirectestimationofaluminum. 59

After first removing iron as sulphide..................... 59 ''C

..... .By.extraction., with, a fixed caustic alkali................. 59

Direct precipitation .of alumina.......................... 60

I.. Manganese, nickel, cobalt, copper, zinc .......................... 60

Manganese and zinc ........................................ 61

... Nickel, cobalt, copper ........................................ 61

X. Calcium and strontium (barium) ................................. 62

Separation from magnesium......-...-...-........---.....-. 62 >..

Precipitation and ignition of the oxalates together.... 62

. ........ . . Necessity jor.two.precipitatipns by ammonium oxalate. 62

. ...... .Separation of strontium (barium), from calcium by ether-alcohol. 63

..... .. Behaviorof barium......................................... 63

Separation of barium from strontium ......................... 63

XI. Magnesium .................................................... 64

. ....... Precipitation....................................----..---...---. 64 .

. .......Methods of collecting and igniting the precipitate............. 66

......... Contamination by and removal of barium and calcium........ 67

XII.. .Titanium, .................................................... ^. 67

........Colorimetric. estimation with hydrogen peroxide (Weller's

...... method)............,,,,.-...-..-.-..-,-.-------..--...--- 67

.... . . Alternative mode pf_ preparing the test solution.......... 69

. The colorimetric apparatus and its use ...:................... 70
CONTENTS. 7

Part II. Methods Continued. . . Pag0 

XII. Titanium Continued. . . Gooch's gravimetric method .............................. 71

Gopch's method not directly applicable to rocks containing zirconium ............I...................... 72

Superiority of the colorimetric and Gooch methods over 

the older ones ..................... J............... 73

Baskerville's method... ......^..,....^.................. 73

X-III. Barium (zirconium, total sulphur)............................. 73

 ... . Reasons for estimating barium in a.separate"portion

------- . of rock.powder ................................ 73

............... Modes-of attack and subsequent treatment......... 74

XIV.- Zirconium ....................................................... 75

 - Author's method.......................................... 75

- ..... Other methods.............................................. 76

XV. Rare earths other than-zir-conia .................... 1 .......... 77

XVI. Phosphorus.................................................. 78

Procedure when material is ample......................... 78

Procedure when material is scanty ........................ 70

XVII. Chromium................................................... 79

Gravimetric method..................................'.... 80

Colorimetric method ....................................... 80

Preparation and strength of standard solution...... 80

Preparation of the test solution.................... 80

Comparison of colors ............................. 81

A few comparative data .................................. 81

XVIII. Vanadium (chromium), molybdenum.......................... 82

Distribution of vanadium.and molybdenum................ 82

Description of method.................................... 82

Application of the method in presence of relatively much 

chromium......................................... 85

Condition of vanadium'in rocks .................'.......... 88

XIX. Ferrous iron ................................................. 88

Comparison of the sealed-tube and hydrofluoric-acid methods;

comparative worthlessness of the former in rock analysis.. 88 

The modified Mitscherlich method........................ 90

Strength of acid.................................. 90

Filling, sealing, and heating of the tube............ 90V

Reason for introducing gas and sealing as above 

directed....................................... 91

The hydrofluoric-acid method ..;......................... 92.

Pratt's modification .................................. 94

Influence of sulphides, vanadium, and carbonaceous matter 

on the determination of .ferrous iron..................... 94.

Sulphides........................................ 94

 Vanadium ........*............................... 95

Carbonaceous matter ................... 1......... 96

Uncertainties of the ferrous iron determination ............ 96

XX. Alkalies ..................................................... 96

The Lawrence Smith method ............................. 96

Treatment of the mineral pow.der.................. 97

Separation of calcium and sulphuric acid........... 98

Precipitation of potassium ........................ 98

Lithium ................................... 1............. 99

Gooch's method ..................................... 99
8 CONTENTS.

Part II. Methods Continued. Page.

XX. Alkalies Continued.

Separation of alkalies by other methods.................. 100

The mercuric-oxide method..................... 100

The ammonium-carbonate method............... 100

The amyl-alcohol method....................... 101

XXI. Carbon dioxide, carbon..:.................................. 101

XXII. Chlorine................................................... 103

XXIII. Fluorine................................................... 103

XXIV. Sulphur.....................'.............................. 105

XXV. Boron..................................................... 107

XXVI. Nitrogen...................:............................... 107

XXVII. Special operations'..............................^.......... 108

Detection of nepheline in presence of olivine.............. 108

Estimation of soluble silica.............................. 109

XXVIII. Estimation of minute traces of certain constituents............ 110
ILLUSTRATIONS.

Tagc.

. 1. Platinum-tipped crucible tongs ..................................... 23

2. .Radiator for rapid and safe evaporation ............................ 24

3. Chatard's form of drying oven for water determinations ............. 37

4. Penfield's tubes for water determination in minerals ................ 39

5. P, en field's fire brick and charcoal oven for use in determining water .. 40

6. Tube for water determinafion according to Penfield ................. 40

7. Modified form of the Gooch tubulated platinum crucible for the determination of water .............................................. 42

8. Details of Gooch crucible for determining water ................'.... 43

9. Arrangement during fusion of Gooch apparatus for determining water . 44

10. Glass tube for determination of water (Jannasch) ................... 40

11. Glass tube for determination of water in special cases (Jannasch) .... 4.6

12. Apparatus for colorimetric determinations ..... .........----..-..... 70

13. Cooke's apparatus for the determination of ferrous iron ............. 93

14. J. Lawrence Smith's crucible for alkali determinations.............. 97

15. Compact form of apparatus for estimation of carbon dioxide .......... 102

9

LETTER OE TEANSM1TTAL.

DEPARTMENT OF THE INTERIOR,

UNITED STATES GEOLOGICAL SURVEY",

 Washington, D. 0., July 13, 1900.

SIR: I herewith submit, with a request for its publication as a bulletin of the United States Geological Survey, a manuscript dealing 

in very considerable detail with the subject of silicate rock analysis, 

with special regard to the practice in the Survey laboratory. It represents, in largely rewritten and much extended form, that portion of 

Bulletin 148 which dealt with the same subject. The present publication seems fully justified l>y the demand on the part of mineral chemists 

for Bulletin 148, the supply of which available for sale has been exhausted.

Very respectfully,

W. F. HlL'LKBKAND,

Hon. CHARLES D. WALCOTT,

.Director United States Geological Survey.

SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS.

By W. F. HlLLEBRAND.

PART I. INTRODUCTION.

I. 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 this century, and for the painstaking 

care and accuracy of Berzelius, Wohler, and others the mineralogists 

and geologists of to-day have need 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 

studjr, became but a subordinate prelude to the ever-expanding study 

of the carbon compounds, whose rapid multiplication, offering an easy 

and convenient field for original research and possible profit, proved 

a more tempting opening to young chemists than the often-workedover and apparently exhausted inorganic pasture. For one student 

devoting his time to higher research on inorganic lines were perhaps 

fifty engaged in erecting the present enormous structure of carbon 

chemistry. The instruction afforded the student in mineral analysis

 13
14 SOME PRINCIPLES AND METHODS OF ROCK ANALYSES. [BUM, 176.

was confined to the ordinary separations of the commoner ingredients 

occurring in appreciable quantities, with little regard to supposed 

traces and with still less attempt to find out if the tabulated list really 

comprised all that the mineral or rock contained.

With the introduction of improved methods of examination by the 

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

heav}r 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 discovered and devised. The supposed adequacy 

of some well-established methods 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 pp. 16-17). Consequently there 

arose a feeling of distrust of much of the older work in the minds of 

those chemists and petrographers 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, is rendering the old material less and less available to meet the increasing demands of the petrographer.

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

means so exacting as they should be. Often the analysis is intrusted 

to the hands of 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
HIJXEBKAND,] IMPORTANCE OF THOROUGH ANALYSES. 15

often trying problem. Although long practice may have enabled 

one to do certain parts of it almost mechanically, one is still from time 

to time confronted with perplexing questions which require trained 

judgment to properly meet and answer, and there is still 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 should be the product 

of one competent to find his way through the intricacies of an analysis 

in which from fifteen to twenty-five different components are to be 

separated and estimated with close approach to accuracy, and this a 

beginner can not hope to do in the majority of cases. 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 of thereby enhancing his own reputation by meriting encomiums on work that has stood the test of time.

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, it is true, are entirely justifiable 

at times, and may serve the immediate purpose for which they were 

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

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

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

instances of totally inaccurate conclusions to be drawn from them have 

fallen under my own observation to fully justify this plea in favor of 

greater completeness in rock-and mineral analyses made for purely 

'scientific purposes.

The importance of the points indicated in the foregoing paragraph 

is shown by the difference between the analyses given on the f olloAving 

page. 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.
16 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

 SiO,... ...--. .......

TiO

A1A---- ------------

CrA-------------- -------

FeA -..--.-----...-.---:

FeO. ........-.-.....--.-.

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

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

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

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

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

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

Na^O. ....................

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

H20 below 110° C. ........

H20 above 110° C.........

pn

p n

o/-v

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

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

Less 0 for F ....... s ......

Earlier 

analysis.

54.42

13.37

/>.61

b 3. 52

4.38

6.37

10.73

1.60

Trace.

c 2. 76

1.82

99.58

Later 

analysis, a

53. 70

1.92

11.16

.04

3.10

1.21

.04

3.46

.19

.62

< 6.44

11.16

1.67

Trace.

.80

2.61

1.75

.06

.44

.03

100. 40 

.19

100. 21

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

that this " later analysis" is itself probably incomplete and incorrect in part incomplete because of 

the probable presence of 0.2 per cent or more of ZrO», incorrect because of the error in A1 203 resulting 

from having counted the ZrOj as AloOa, and from the fact that titanium is not fully precipitable in 

presence of zirconium by Gooch's method (the one employed). This latter error involves both the 

Ti02 and the A1203 . (See pp. 72-73.)

b 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'ln the published analysis it does.not appear whether this is total water or, as seems probable, only 

that remaining above 100° C.

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 TiO2 , 

BaO, SrO, P205 , and SO3 were present in both specimens in approximately the same amounts. In the earlier analysis determinations of 

some supposed 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.
IMPOETANCE OF THOEOUGH ANALYSES. 17

SiO,. .....................

TiO

Al O

Fe2 03 ....................

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

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

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

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

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

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

K2 0......................

Na,0. .............. ......

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

HaO below 110° C.........

H2 0 above 110° C... ......

CO.......................

p o «

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

SOS ......................

Earlier 

analysis.

44.31

Not GEt.

17.20

4.64

3.73

.10

10.40

6.57

3.64

4.45

.77

3.30

99.11

Later 

analysis.

44.65

.95

13.87

6.06

2.94

.17

9.57

a . 37

.76

5.15

4.49

5.67

Trjif'p

.95

2.10

.11

1.50

TVsi f 'p

.61

99. 92

o Not entirely free from CaO.

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, is 0.8 per cent. When the determination 

of these is neglected the error falls upon the alumina. If the latter 

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 more strongly emphasize 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 neverfailing constituents of the igneous rocks of the United States and of 

many of their derivatives. These 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 Kocky Mountain 

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

Bull. 176 2
18 SOME PRINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL. 176.

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 acid 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. Hayes, in 1875, reported its 

occurrence in a great variety of rocks apd ores. Quoting from Thorpe's 

Dictionary of Chemistry: "It is said to be diffused with titanium 

through all primitive granite rocks (Dieulafait), and has been found by 

Deville in bauxite, rutile, and many other minerals, and by Bechi and 

others in the ashes of plants and in argillaceous limestones, schists, 

and sands.'" It is further reported to comprise, as the pentoxide, up to 

0.1 per cent of many French and Australian clays, 0.02-0.03 per 

cent of some basalts, 0'.24 per cent of a coal of unknown origin, and 

0.45 per cent of one from Peru. Still later examinations in this laboratory of about 100 rocks, chiefly igneous, covering the whole 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 seriously affect 

the figures for the oxides of iron unless separately estimated and 

allowed for (see p. 96) a matter of considerable importance, since the 

petrographer \&ys great stress on accuracy in their determinations.

This 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 the writer's 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
HILLEBUAND.] OBJECT AND SCOPE OF PBESENT TKEATISE. 19

connection with the long mystifying lack of agreement between results 

for ferrous iron obtained by the Mitscherlich and the hydrofluoricacid methods, might not have been suspected. (See p. 89.)

While strongly upholding the necessity for more thorough work, 

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

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

on every analysis. But it is maintained that in general the constituents which are likely to be present in sufficient amount to admit of 

determination in the weight of sample usually taken for analysis say 

1 gram for Si02 , A12 0;! , etc., to 2 grams for certain other constituents should be sought for, qualitatively at least, in the ordinary 

course of quantitative work, and their presence or absence noted 

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

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

amount of exactly 0.02 or 0.06 per cent. In the tabulation of analyses 

a special note should be made in case of intentional or accidental neglect to look for substances which it is known are likely to be present. 

Failure to do this may subject the analyst to unfavorable criticism, 

when at some future time his work is reviewed and the omissions are 

discovered by new analyses.

Finally, whenever possible, a thorough microscopical examination 

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

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 analyt-0 

ical procedure may be employed without waste of time or labor. 1

II. OBJECT AND SCOPE OF THE PRESENT TREATISE.

The literature relating to analysis of silicates is extensive but scattered, and in no single article is there to be found a satisfactory 

exposition of the methods 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 is not intended to 

make this little volume a treatise on mineral analysis, but it is believed 

that the experience gained by the chemists of this Survey during the 

twenty years since the establishment of its first chemical laboratory

'The foregoing tables and accompanying remarks, including several sentences preceding the 

tables, have been lareely taken.from the writer's papers entitled "A plea for greater completeness in 

chemical rock analysis," published in the Journal of the American Chemical Society, Vol. XVI, pp. 

90-93, 1894; also in the Chemical News, Vol. LXIX, p. 103, 189<l! See also " Distribution and quantitative occurrence of vanadium and molybdenum in rocks of the United States," in the American 

Journal of Science, 4th series, Vol. VI, p. 209,1898, and Chemical News, Vol. LXXVIII, p. 216,1898.
20 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

in Denver may oe useful to most chemists interested in mineral and 

especially rock analysis.

The original publication of these data in Bulletin No. 148 was 

primarily intended to show the principles and methods according to 

which the major part of the very many hundreds of analyses therein 

brought together had been executed, and thus to furnish a partial 

measure of the trustworthiness of those analyses, rather than to serve 

as a practical manual of rock analysis. But the use which has been 

made by mineral chemists of that bulletin has seemed to render it 

advisable to amplify somewhat in detail and to add, besides a few new 

methods, a number of alternative ones 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 a choice from which to select in case the 

rather expensive apparatus or complicated arrangements sometimes 

preferred are not available. Where silicate analyses are very frequently made, however, it is a saving of time and of money in the end 

to set up permanent arrangements for convenience in estimating 

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

Stress will be laid on those points meriting particular attention, and 

now and then a brief discussion or criticism of methods elsewhere in 

vogue may be entered into.

In the earlier years of the existence of the Washington laboratory 

opportunity was afforded for the ^testing of novel methods and the 

devising of new ones, with most excellent results, as shown especially 

by the methods for separation of titanium, of lithium, and of boron, 

due to Prof. F. A. Gooch, to whose inventive skill chemists owe likeVise the perforated filtering crucible and the tubulated platinum crucible arrangement for the estimation of water. Of late years the press 

of routine work has been such as to more fully fill up the time of the 

much-reduced chemical force, and as a consequence it has been found 

impossible to subject to critical trial several separation methods of 

recent origin, some of which seem to be full of promise, or to follow 

out certain lines of investigation which have been suggested bty the 

observations made in this laboratory. This, then, must be offered in" 

explanation if, in the following discussion, it may seem, to some that 

any of the methods followed are too conservative. In general the 

discussion will be confined strictly to such separations as may be 

required in the analysis of an igneous, metamorphic, or sedimentary 

silicate rock of complex mineralogical composition, in which the 

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

may occur in weighable or readily discoverable.quantities:

SiO2 , Ti02 , Zr02 , A12Q3 , Fe2 03 , Cr2 03 , V2O3 , FeO, MnO, MO, 

CoO, MgO, CaO, SrO, BaO, ZnO, CuO, K2O, Na2O, Li2O, H2 0, 

P2O6 , S, 1 S03 C, 2 C02 , Fl, Cl, N.

The special problems often arising in the analysis of rocks of extra-

 : : 

1 Usually as pyrite, not infrequently as pyrrhotite. - As graphite or coaly matter.
HILLEBRAND.] STATEMENT OF ANALYSES. ' 21

terrestrial origin the more or less stony meteorites will not be considered. 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.

Thorium, cerium, and other rare earths are seldom encountered in 

quantities sufficient to warrant the expenditure of the time necessary 

for their isolation. A search for them qualitatively, even, is at present 

rarely justifiable unless 'there is microscopic or other evidence of the 

presence of minerals likely to contain them. Tantalum, columbium, 

boron, and glucinum have never been certainly rnet"with in the writer's 

experience, and yet they must be present in certain rocks, and doubtless traces have been overlooked at times, There is no reason to suppose that other elements may not be found by careful search, possibly 

all in t^e known category, and, indeed, Sandberger's researches have 

shown to what an extent this is true of a large number of those elements contributing to the filling of metalliferous veins. But those in 

the above list may usually be estimated with ease in weights of from 

one-half to 2 grams.

If the point be raised that many of the published analyses emanating 

from the Survey laboratories, even the earlier ones of the writer, 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 twenty 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, both for the geologist and the 

chemist, to turn out a limited amount of thorough work than a great 

deal of what may prove to ue of more than doubtful utility in the end.

III. STATEMENT OF ANALYSES.

Until recently it has been the practice in this laboratoiy to tabulate 

the constituents of a rock somewhat in the order of their determination, beginning with Si02 as the chief constituent- and grouping 

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

pages 16 and 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 employing the arrangement so 

valuable in stating water analyses.
22 SOME PKINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

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." 1

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

pretty closely the arrangement proposed by Pirsson and very recently 

strongly advocated by Washington (loc. cit.), namely:

Si02 , A12 03 , Fe2O3 , FeO, MgO, CaO, Na2 0,' K2O, H2O (above 105-. 

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

Fl, S (FeSj), Cr2 03 ; V2 03 , MO, CoO, CuO, MnO, SrO, BaO, Li2 0, C, 

NH,

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 recomnlends; the 

molecular ratios are calculated for these leading constituents and 

placed immediately after the corresponding oxides. The order of the 

remaining members is determined somewhat by the following considerations: C02 is placed next after H2 0, since these two are generally 

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

ZrO2 naturally follow CO2 on chemical grounds, and §O3 and Cl, being 

common constituents of the sodalite group, are conveniently placed 

together.

IV. TIME NEEDED FOR MAKING AN ANALYSIS.

The question has often been put, "How long does it take to complete an analysis of this kind?" This will depend, of course, on the 

mineral complexity of the sample and on the personal factor of the 

individual worker. If there is a opmpetent 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 

baths through the night, as to finish every three days, after the completion of the first analysis, barring accidents and delays, oneo 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. On one occasion a series of 

fourteen rocks, of comparatively simple composition, was completed 

in one month, with the help of an assistant who made the phosphorus

1 IT. S. Washington, The statement of rock analyses: Am. Jonr. Sci., 4thseries, Vol. X, p. 61,1900.
HILLEBRAND.] USEFUL AIDS IN CHEMICAL MANIPULATION. 23

and ferrous iron determinations. But such an output of work is more 

than exceptional and implies an unusual freedom from those occasional setbacks to which every chemist is exposed.

It should here be remarked that the Survey laboratory is most exceptionally well supplied with all kinds of platinum 

vessels and utensils, so that it is rare indeed for 

delay to arise through lack of dishes of even the 

largest sizes.

V. TWO USEFUL AIDS IN CHEMICAL MANIPULATION.

In connection with the foregoing remarks it is in 

place to-mention two aids to the chemist which are 

in constant use in this laboratory and have come 

to be well-nigh indispensable. Neither is novel in 

principle and both arc in use elsewhere, but they 

are not so commonly known as they deserve to be, 

hence this allusion to them.

Fig. 1 represents a form of platinum-tipped crucible tongs devised by Dr. A. A. Blair many years 

ago. With them a crucible can be securely grasped 

and brought into any desired position while still hot. 

To the contents, if in fusion over the blast flame, 

can be imparted the 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.

Fig. 2 represents a very useful adjunct to the 

Avorktable and especially to the draught cupboard, 

whereby the liquid contents of crucibles can be 

speedily evaporated at almost any desired temperature and the dehydration of many solids effected 

much more safely than on an iron plate or sand 

.bath. I do not recall who originated this form of 

air bath, but it has been in use here for over fifteen 

years and is identical in principle with the later FlQ 1 ._PlfttInuin.tlppcd 

Nickel-becher of Jannasch. Nickel undoubtedly 

has a certain advantage in not rusting as does iron, 

but the form depicted in R of fig. 2 can easily be 

made anywhere of sheet iron riveted at the joint, 

the bottom (not shown in the figure) being securely 

held by a flange at the extremity of the truncated cone. A crucible 

placed on the platinum triangle becomes uniformly heated by hot air, 

and large quantities of liquid, even sulphuric acid, can be thus volatilized in a short time A\dthout ebullition or spattering.

crucible tongs. The 

parts A B, also of heavy 

platinum, are hollow, 

to serve as sockets for 

the cheaper metal of 

the handles.
24 SOME PKINCIPLES AND METHODS OF EOCK ANALYSIS. [BULL.ITG.

VI. LIMITS OF ALLOWABLE ERROR IN SUMMATION OF ANALYTICAL RESULTS.

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, 

Avhich are eventually 

weighed in part with 

the constituents of the 

rock. The dust entering an analysis from 

first to last is very considerable, washings of 

precipitates ma}^ be incomplete, and if large 

filters are used for 

small precipitates the 

former may easily be 

insufficiently washed. 

Given the purest 

obtainable reagents, 

an ample supply of

platinum, facilities for

working, and a reasonably clean laboratory, 

there is no 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

FIG. 2. Radiator for rapid and safe evaporation. K is of sheet ln Several OI a Series

iron, also nickel (Jannasch). Various sizes. A convenient height of analyses of similar

is 7cm , width at top T010 and at bottom 5°m. , i ij r. xu nature should be the

strongest evidence that something has been overlooked. Excess above 

100.5 per cent should be good ground for repeating portions of the 

analysis in order to ascertain where the error lies, for it is not proper 

to assume that the excess is distributed over all determined constit-
HIU.EBRAND.] QUALITY OF REAGENTS. . 25

uents. 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.

\

VII. QUALITY OF RgAGENTS.

N

It is due to say that all analyses performed in the Survey laboratories 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. The best acids made in this country are of a high grade and need no redistillation except for special 

experiments. Ammonia has always been redistilled at short intervals; 

and no sodium carbonate which exceeds 2£ milligrams of total impurity 

(see p. 50) in 20 grams (0.012 per cent) is used for the main portions, in 

which silica, alumina, etc., are to be estimated. For other portions, as 

phosphoric acid, fluorine, sulphur, a poorer grade is entirely allowable, 

provided it is free from the element to be determined, and from any 

other which might interfere with its estimation.

Hydrofluoric acid was always freshly distilled with potassium permanganate until the introduction of ceresine bottles afforded an article 

sufficiently pure for all but the most exacting work. Care must be 

exercised even yet, however, that no particles of paraffin or ceresine 

are floating on the acid, and that the latter is free from traces of chlorine whenever it is to be used for attacking silicates with a view to 

estimating chlorine (p. 103).

Potassium bisulphate has usually been prepared in the laboratory

 from sulphuric acid and potassium sulphate, since it is not always to

be bo.ught of satisfactory quality. Even then the normal sulphate

had first to be examined, for it has been found to contain, on different

occasions, notable amounts of lead, calcium, and silica. '

I The phosphorus salt used for precipitating magnesium has been

j found to contain iron, and calcium is almost always a constituent of

^ ammonium oxalate. The latter has therefore to be purified or specially

prepared, as also oxalic acid, ammonium chloride (in which latter

manganese has been observed), and occasionally other reagents. Some

hydrogen peroxide contains fluorine, which renders it unfit for use as

a chemical reagent.

A "C. P." label is no guaranty whatever of the purity of a reagent; 

hence no chemicals should be taken on trust because of bearing such a 

label. Every new purchase should be examined, if it is one in which 

purity is a desideratum. In general all so-called "C. P."chemicals 

s'hould at least stand the tests laid down by Krauch. 1

Of late years the appearance upon the market of so-called guaranteed reagents promised to meet a long-felt want. But experience has

>Die Priifung clcr chemischeii Keagcntien, 3d ed., Berlin, Julius Springer, 189C.
26 SOME PEINCIPLES AND METHODS OF EOCK ANALYSIS. [BULL. 176.

shown that with the pioneer in this line at least the guaranty amounts 

to nothing, the reagents being sometimes worse than the U C. P." 

articles emanating from sources which make no claim to special purity 

for their goods, and redress being unobtainable. The "guaranteed 

reagent" needs checking as much as any .other.

VIII. 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.
PART IT. METHODS.

I. INTRODUCTORY REMARKS.

O

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 , TiO2 , MnO, NiO, CaO, SrO, 

MgO, total iron, and the combined weight of all the following: AI2 03 , 

TiO2 , P2O5 , ZrO2 , all iron as Fe2O3 , and nearly if not quite all vanadium 

as V2 05 , also perhaps rare earths if present. In a separate portion is 

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

desired as checks. The alkalies need a portion for themselves. In 

another, ZrO2 , BaO, 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 CO2 , C, H2O, Fl, Cl, are all best made in 

separate portions of substance, though 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, and zirconium may serve. Many chemists never look for the second and third 

of these, but by following the procedure given on pages 7?t-76 very 

little 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 20 can be estimated 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 por27
28 SOME PKINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

tion 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.

II. SPECIFIC GRAVITY.

o

BY SUSPENSION IN WATEE.

Ordinary method. This determination, when required, is best made l 

upon 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, andv caref ully transferred 

to a tared crucible or dish; the wire is removed and at once re weighed, 

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° C. 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; 1 but the difference will only

JIn view of the uncertainty as to what constitutes hygroscopic water (see p. 35), 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 due to loss of even all its water during ignition is quite negligible.
HILLEBBAND.] SPECIFIC GEAVITY. '29

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

unit. For instance, an undried rock of 2.775 specific gmvity 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 frag 

ments 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 pr6- 

cedure is, of course, inapplicable, unless the datum is desired for 

certain considerations in which the relative density of large rock 

masses as they occur in nature is sought, as for the comparison of 

building stones or the calculation of large known or assumed areas of 

particular rocks.

PenfielcPs method for mineral fragments. Penfield * 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 mm. 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.

PYCNOMETER 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

1 Am. Jour. Sci., 3d series, Vol. L, p. 448,1895.
30 SOME PRINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL. 176.

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

less finely divided state, the most accurate procedure is that adopted 

in this laboratory by Mr. L. G. Eakins a number of years ago. 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 capacnty of the flask filled with 

water to the zero division is then calculated for every half degree of 

temperature from 0° C. to 30° C., by making a series of careful weigh - 

. ings, in which, thecapacity of the stern being known, it is quite immaterial 

at what level the water stands provided it is within the limits of the 

scale. The exact temperature is obtained by an accurate thermometer 

placed in a companion vessel of similar shape to the pycnometer and 

containing a like amount of water, both being left in the balance case 

till its temperature has been nearly or quite assumed, as shown by a 

second thermometer. The weighing must of course be made before 

the thread of water has sunk beneath the lowest division, .which it will 

do after a time, even though at first filling the bore to the top of the 

stopper; and the correc.ted weight full of water to the zero mark is 

found by adding or subtracting the needed amount, as shown by the 

height of the thread on the scale.

For each pycnometer in use, and these are of different sizes, is prepared 

a table showing its weight, the value of each scale division in grams of 

water, and the capacity of the flask at different temperatures, as indicated above. The preparation of such a series of flasks is time saved 

in the end, for the weighing of the flask full of water each time a 

density determination is made is rendered superfluous. All that is 

necessary is to look up in the table the weight corresponding to the 

temperature.

The density of the previously weighed substance in this case is now 

determined in much the same way, 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.
HILLEBRAND.] PREPARATION OF SAMPLE. 31 

HEAVY SOLUTIONS NOT SUITABLE FOR ROCKS.

Because of their roughness, porosfty, 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.

III. PREPARATION OF SAMPLE FOR ANALYSIS. 

QUANTITY OF HOCK 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, gauged 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.

CRUSHING.

Mechanical appliances for reducing samples to fine powder are much 

in use in technical laboratories, where they answer their purpose more 

or less satisfactorily, and something similar is needed in those scientific 

laboratories where rock analysis is of daily occurrence and many samples must be reduced to fine powder in a short space of time. For 

accurate analyses the use of steel crushers and mortars is out of the 

question, because of the danger of- contamination by particles of metal 

and 'the impossibilitjr of cleansing the roughened surfaces after they 

have been in use a short time. Extraction by the aid of a magnet of 

steel particles thus introduced into the powder is quite inadmissible, 

since the rocks themselves, almost without exception, contain magnetic 

minerals. The method of rough crushing on a small scale found to be 

most satisfactory 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.

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.

GRINDING.

Of the various grinding arrangements on the market purporting to 

fulfill their purpose few, if any, observed have met the conditions
32 SOME PEINCIPLES AND METHODS OF BOCK ANALYSIS. [BULL. 176.

required by the work in hand. Either the mechanical arrangement is 

complicated or cumbersome, requiring more power or space than is 

usually at disposal or causing too much noise, or thorough cleansing 

is difficult and troublesome, or there is likelihood of contamination 

from oil or grease or lack of facility for the removal of all powder from 

the mortar. These last defects are especially prominent in those forms 

in which the mortar is fixed in its setting.

All rock samples have therefore been reduced to powder by hand, 

involving a great expenditure of time and labor. Ordinarily an extremely fine state of division is unnecessary, except in the case of those 

portions in which alkalies and ferrous iron are to be estimated 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.

The process of sifting through fine cloth, the German "Beuteln," is 

not one always to be commended, because of the"time required and, 

more especially, because of the certainty of contamination by cloth 

fiber, which in the ferrous-iron portion might affect the result.. Still 

less should metal sieves be used.

WEIGHT OF GKOUND SAMPLE.

The sample when ground should weigh not less than 10 grams, and 

preferably 20 in case it should be necessary to repeat or advisable to 

employ unusually large portions for certain determinations, notably 

carbonic acid. Rock analysis has in this respect an 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.

IV. WATER HYGROSCOPIC, ZEOLITIC, CRYSTAL.

Importance of em/ploying air-dry powder for analysis. The timehonored custom of drying a powdered specimen before bottling and 

weighing has Ipng seemed to the writer 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 r.ocks 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
HILUSBRAND.] WATEE HYGROSCOPIC, ZEOLITIC, CRYSTAL. 33

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.

It is preferable to weigh the air-dry powder and to make a special, 

determination of moisture. If all the portions necessary for an analysis are weighed out one after another, or even at different times on the 

same day, the error due to difference of hygroscopicity in dry and 

moist weather, which for most of the separate portions is an entirely 

negligible quantity, is eliminated. Only in the main portion, in which 

silica and the majority of the bases are to be estimated, can it ever be 

an appreciable factor.

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° C. For the great majority of rock specimens it is 

quite immaterial which of these temperatures is adopted, since no 

greater loss is experienced at the higher than at the lower temperature, given a sufficient time for the latter. It is the present practice 

in this laboratory to employ a toluene bath giving a temperature of 

about 105° C. 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.

Cautionary hints. In this latter cpnnection it is proper to point out 

certain pitfalls in the path of the unwary, which, however, are far 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 day, the apparent limit may be reached long before all water 

really removable has been taken up by the acid. Whenever the crucible, after weighing, is replaced in the desiccator it is no longer in a 

dry but a more or less moist atmosphere, and its contents, even when 

covered, sometimes absorb a part of this moisture and retain it so persistently that the acid is unable to bring the powder beyond its previous 

state of dryness in the next twenty-four hours. In fact, it may be 

unable even to reach it unless greater time is allowed. An experiment 

Bull. 176 3
34 -SOME PKINCIPLES AND.METHODS OF BOOK ANALYSIS. [BULL. 176.

oh 1 gram of tyrolite, made and published some years ago, seems to 

illustrate this point in part:

Hours 

exposed.

18

26

23

24 

23 

24

25

Loss.

Grain.

0. 0231

.0083

.0029

.0012 

.0008 

.0001

.0003

Hours 

exposed.

24

24

48

24

283

Loss.

Qram. ' 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.

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

hydrous minerals in an air bath at temperatures far above 100° C. To 

insure accuracy this experiment should not 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° C., 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.

Procedure in special cases. For experiments of the kind just indicated the powder should be heated in a weighed tube, through which 

a current of dry air can be passed, and allowed to cool therein, or 

else the water given off should be collected and directly weighed in 

suitable absorption tubes, even though the long time often required 

is an objection to this lattter method, since the absorption tube may
HILLEBKAND.] WATEB HYGROSCOPIC, ZEOLITIC, CRYSTAL. 35

gain weight, other than that of the water from the mineral, sufficient 

to introduce an appreciable error.

The recent important research of Friedel1 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 li per cent in weight of the partially 

dehydrated mineral mentioned on p. 34 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 (loc. cit.) 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.

Argument m 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 true one?" The question involves the further consideration of the 

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

Many petrographers desire to have all analyses referred to a moisturefree basis, in order that they shall be strictly comparable, and therefore would omit the "hygroscopic" water from the list of constituents. This would be eminently proper were it always possible to be 

sure that the loss at 100° 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 the fact of

i Bull. Soc. Min., Vol. XIX, pp. 14,94,1896; Comptes Beiidus, Vol. CXXII, p. 1006,1896.
36 SOME PKINCIPLES AND METHODS OF ROOK ANALYSIS. [BULL. 176.

the uncrushed rocks losing the same amount fully demonstrates; 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,

Separate entry of 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° C. 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 constituents, 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 loosety 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 of weighing, 

and that 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.

Is all true hygroscopic water expelled at 100° f 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, in the cases of 

certain foliaceous minerals, notably the micas, to thus entirely remove 

it, but that a part is only driven off 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.

APPARATUS FOE THE DIRECT DETERMINATION OF WATER AT DIFFERENT

TEMPERATURES.

A form of drying oven devised by Dr. T. M. Chatard* is in use in 

this laboratory for determining water at different temperatures up to 

350° C., and gives entire satisfaction. It is an asbestos-covered copper 

box B, shown in different aspects and parts in the accompanying fig. 

3. 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 afterwards apply the direct

iAin. Chem. Jour., Vol. XIII, p. 110,1891; Bull. U. S. Geol. Survey No. 78, p. 84. .
WATER HYGROSCOPIC, ZEOLITIC, CRYSTAL. 37

heat of a lamp in order to expel the water retained at 300° to 350° C. 

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 b}^ an interlaid piece of sheet copper. 

The inner rjiece of asbestos board fits snugly into the box, while the

FIG. 3. Chatard's form of drying oven for water determinations. B, copper box, 18cm. long, 

high, 9cm. wide, open in front, its sides and top covered with asbestos board; S, two slides of 

different sizes to close the 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; A, calcium chloride absorption tube.

outer one, being slightly larger, by its projecting edges hinders the 

door from falling in and helps to prevent air currents. This door is 

held in place by the metal rod R. The little slides S are made in a somewhat similar manner, and are intended to slip in from the front and 

close the two openings O after the tube is in place, but before closing 

the front.

For other forms of tubes adapted to similar determinations, see 

pages 40 and 46.
38 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

V. WATER TOTAL OR COMBINED. 

ARGUMENTS AGAINST "LOSS ON IGNITION 5 ' 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 constituents can 

the loss be accepted as the true index of the amount of water present, 

and it is rarely 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 and still upheld 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.

DIRECT WEIGHING OF THE WATER WITHOUT THE USE OF ABSORPTION 

TUBES PENFIELD'S METHODS.

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 1 

leaves nothing to be desired for accuracy. It consists simply in heating the powder in a narrow tube of hard glass, enlarged at the closed 

end and provided with one or two further enlargements in the middle 

to hold the water and prevent its running back and cracking the 

hot glass. A capillary glass stopper fitted in with rubber tubing preiAm. Jour. Sci., 3d series, Vol.-XLVIII, p. 3L, 1894; Zeitsch. fiir anorg. Chemie, Vol. VII, p. 22, 

1894.
HILLEBBAND.] WATEK TOTAL OR COMBINED.

vents 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. 4.

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

FIG. 4. PenflekVs tubes for water determination in minerals, a, b, c, different forms of tubes; 

cl, thistle tube for introducing the powder; e, capillary-tipped stopper.

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.

'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. 5, must be used, 

either with or without a retainer for fluorine, as circumstances demand. 

The part of the tube in the fire is to be protected by a cylinder of 

platinum foil tightly sprung about its end, and the part outside by 

asbestos board, as well as by wet cloth or paper. A piece of charcoal
40 SOME PKINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

Js 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.

In whichever way the apparatus may be used, the water found is

FIG. 5. Penfleld's fire-brick and charcoal oven for use in determining water.

the total water, from which that found separately at 105° C. may be 

deducted if desired.

DIKECT WEIGHING OF THE WATER IN ABSORPTION TUBES.

Penjidd^s procedure. The simplestof these methods as to apparatus, 

and one permitting, by the use of auxiliary arrangements such as 

are shown and described on page 37, the determination of the hygroscopic as well as any other fraction of the water, is the following glasstube arrangement (fig. 6) of Dr. Penfield's, 1 whereby the brick and 

charcoal oven already referred to (fig. 5) 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

U

FIG. 6. Tube for water determination according to Penfield. A, outer protecting covering of platinum foil. A second similar foil on the inside prevents the glass from collapsing when heated to 

softness, b, cross section of platinum boat.

a size that when applied to the combustion tubing the spring of the metal will hold 

them in place. A large platinum boat, 7 to 8 cm. long and 11 to 12 mm. in diameter, with a cross-section like b, should be used, since this will readily hold a gram 

of mineral mixed with 5 grams of sodium carbonate. * * * The tube is placed 

in the angle formed by the charcoal lining, some pieces of charcoal are placed at the 

sides in front, leaving an opening through which the flame may be directed, and an 

additional piece is laid on top. The tube can readily be brought to a full white heat,

iAm. Jour. Sci., 3d series, Vol. XLVIII, p. 37,1894; Zeitsch. fur anorg. Chemie, Vol. VI, p. 22,1894.
HOLBBBAND.] WATER TOTAL OR COMBINED. 41

and by forcing a slow current of dry air through the apparatus the carbon dioxide 

resulting from the decomposition can be removed and the water carried over into 

the weighed absorption tube. The glass fuses between the platinum casings, and 

in a number of experiments that have been tried there has not been a single instance 

where the glass tube has broken or shown any indication of breaking. After heating the tube will" not crack if it is left to cool slowly on the charcoal, but it cannot 

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, whereby distortion of the boat would result 

and its withdrawal for further examination of its contents would be 

impossible.

Q-oocKs apparatus. Of more elaborate apparatus, designed to be 

used with fluxes, the tubulated platinum crucible invented by Dr. 

Gooch 1 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 made.

Fig. 7, 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 vertical one 

being bent horizontally at right angles for convenient attachment to 

the drying towers, and the side one also bent at right angles, but 

downward, and having its end slightly drawn in at E (fig. 7) so as to 

admit of easy insertion in the rubber stopper of a U-shaped calciumchloride tube as shown in fig. 9 (p. 44). 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 stopper 

or other connection.

The extra first cost of the platinum extension to these tubes 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. In its present form the whole apparatus 

weighs approximately 88 grams.

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

i Am. Chern. Jour., Vol. IT, p. 247,1880; Chemical News, Vol. XLII, p.32G, 1880.
42 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

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

dehydrated sodium carbonate, 1 or more of lead chromate if carbon is 

to be likewise determined. The crucible is sunk in its seat S (fig. 8) in 

the upper ring K' and the tubulated cap T (fig. 7) is fitted on and attached 

to the calcium chloride drying towers preceded by one containing 

potassium hydroxide if carbon dioxide is likewise to be estimated on

FIG. 7. Modified form of the Gooch tubulated platinum crucible for the determination of water, 

one-half natural size. Weight about 88 grams.

the one side, and to a sulphuric-acid bulb tube B (fig. 9) 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. 7) in 

which the cap rests, and a metal vessel of cold water having been 

raised up by the lower ring R" (figs. 8 and 9) until the platinum crucible 

is sufficiently immersed, the flame of an ordinary blast lamp is turned 

on to melt the tungstate. As soon as this is fused the flame is removed

1 This has been heated for a length of time to near its fusing point over a free flame or in an air 

bath, to decompose the bicarbonate it usually contains, and then placed in a desiccator. Thus heated 

it is not very hygroscopic. Penfleld found that 2.5 grams of it, spread out on a watch glass, gained 

only .0002 gram in 15 minutes. Potassium carbonate and potassium-sodium carbonate are too hygroscopic by far to be available.
HILLEBBANIX] WATEE TOTAL OE COMBINED.

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° C. for two hours, more or

FIG. 8. Details of the Gooch crucible for determining water. S, seat of stout platinum wire resting 

on ring R', and serving as a support for the crucible; R'", blast-fed ring burner; R", support for air 

or toluene bath 0.

less (see below, p. 45), by means of an air or toluene bath as shown in 

figure 8, the absorption tube A (fig. 9) is interposed between the sulphuric-acid bulbs and the apparatus, being fitted to the latter by its 

stopper, which is at other times closed by a glass plug, and while a slow
44 SOME PRINCIPLES AND METHODS OF EOOK ANALYSIS. [BULL. 176.

current of a,ir continues to pass the gradual heating and subsequent 

fusion of the flux is brought about by the blast-fed sliding ring-burner 

E'" (figs. 8 and 9). The sodium-tungstate joint is shielded from the 

flame by small pieces of asbestos board P (fig. 9), cut out so as to fit 

the crucible. When fusion is complete, as shown in the case of sodiumcarbonate flux by the decided slackening of the gas current through 

the safety bulbs attached to the drying tube, the flame is extinguished 

and a current of air is allowed to continue until the apparatus is cold. 

This apparatus suffers from the drawback of being slightly permeable

FIG. 9. Arrangement during fusion of Gooch apparatus for determining water. R'", blast-fed ring 

burner; P, protective asbestos-board shield resting on ring R"; FF, board forming end of frame and 

covered with asbestos board to prevent being set on fire by the heat of the blast. This serves at the 

same time as an efficient shield for the absorption-tube A. In it there is bored a round hole at ItA, 

through which passes the outlet tube from the crucible. B, sulphuric-acid bulbs serving to show 

the rate of gas current through the absorption-tube and at the same time to prevent back entry of 

moisture from the air into A.

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, beingdistorted 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 

penetrating water gases is inappreciable. This hastening may be rendered safer by using rather finely powdered calcium chloride in the
HULEBBAND.] WATER TOTAL OR COMBINED. . 45

central section of the U-shaped absorption tube to avoid large air channels. Through this, or any apparatus based on similar principles, the 

air current should always be forced, not drawn. A warm blast directed 

upon the exit tube near its entrance into the absorption tube greatly 

shortens the time required and is to be recommended.

In this apparatus only the water expelled above 100° to 110° should 

as a rule be determined, and to effect drying of the mixed mineral 

powder and sodium carbonate, after luting the tubulated cap on the 

cylindrical crucible with sodium tungstate, the tube is sunk through a 

round hole in the cover into a small cylindrical air bath (fig. 8), 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.

ChatarcPs apparatus. The platinum apparatus devised by Dr. Chatard 1 overcomes the permeability of the metal to gases and affords 

sharp results, moreover permitting of determining by direct absorption not only the hygroscopic water, but that which may be driven off 

at any desired temperature, either with or without fluxes. It is, however, perhaps even more costly than the Gooch apparatus, and the 

supposed nonliability to injury by warping, because of the protective 

layer of borax and asbestus, can hardly be considered as proved.

Merits of the above three forms of apparatus, All of these apparatus, except the glass tube of the modified Brush method, permit of 

the estimation of other constituents besides water in the same portion 

if necessary, and by the use of lead chromate or potassium 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.

JannascKs methods. This zealous deviser of methods for mineral 

analysis has published in the Zeitschrift fur 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 2 these are collected in more or less modified form.

1 Am. Chem. Jour., Vol. X11I, p. 110,1891; Bull. U. S. Geol. Survey No. 78, p. 8-1, 1891. .

2 Praktischer Leitfadeii der Gewichtsanalyse. Leipzig, von Veit & Co., 1897.
46 SOME PKINCIPLES AND METHODS OF BOCK ANALYSIS. [BULL. 176.

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 the accompanying 

fig. 10.

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. 

Whether or not the boat is employed the borax is first introduced

FIG. 10. 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.

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 sodaFIG. 11. Glass tube for determination of water in special cases (Jannasch). Length from a to e, 

26 cm.; inside diameter somewhatover 1 cm.; volume of bulb b, 25 crn3. c d, retaining layer of lend 

oxide between plugs of glass wool; /, calcium chloride absorption tube; y, protective tube.

lime tube to the calcium-chloride tube. For one-half to 1 gram of 

silicate Jannasch uses 1£ to 2 grams of borax.

Regarding the borax method, its inventor insists upon 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.

The borax itself is prepared by heating pure crystallized borax in a 

platinum dish till a small portion has melted. That remaining unf used 

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
HILLEBEAND.] SILICA, SEPARATION FROM ALUMINA, ETC. 47

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 Jannasch for special purposes is 

shown in fig. 11. Minerals, such as topaz, which is not fully decomposed by the borax method and which contains a large amount of 

fluorine, are fused at 1) with about six times their weight of lead oxide. 

A layer of lead oxide between c d serves to retain any fluorine escaping from the fusion.

VI. SILICA, SEPARATION FROM ALUMINA, ETC. 

ALTERNATIVE METHODS OF DECOMPOSITION.

PKEUMINAKY KEMAKKS.

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 the writer 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 

exception of the comparatively few analyses made thus, the sodiumcarbonate 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 Berzelian method for fluorine estimation (see 

footnote, p. 50), but in practice it is not often necessary to resort to this 

tedious procedure, since the amount of fluorine is usually small and 

it can by no possibility cause a loss of much more than three-fourths 

its own weight of silica by volatilization as silicon fluoride when the 

sodium-carbonate fusion is evaporated directly with hydrochloric acid. 

Probably the loss is less, since some fluorine perhaps escapes as hydrofluoric acid. However this may be, the error is of comparatively 

slight importance, since it attaches to the constituent always 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 of recent years in 

this line of work, as evidenced by their numerous published papers. 

One of the advantages 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.
48 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

Another of their advantages is that with some of "them it is possible 

to estimate in one portion the alkalies, in addition to those constituents 

usually determined in the silica portion. Where the material is limited, 

as it so often is in mineral analysis, this is a most important advantage, 

sufficient to outweigh all possible objections; but in rock analysis, where 

the supply of material is usually ample, it is rarely worth considering. A still further point in their favor is that it is probably more 

easy to obtain them entirely free from fixed impurities than an alkali 

carbonate.

There are, however, objections to their use. With some of them an 

extraordinary amount of time must be devoted to grinding the 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 

fulty 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 veiy improbable that the vivid 

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.

DECOMPOSITION OF REFRACTORY SILICATES BY HYDKOCHLOKIC ACID UNDER PRESSURE.

Jannasch 1 pours upon the finely ground rock'powder contained in a 

platinum tube of about 26 cm. 3 capacity a somewhat diluted hydrochloric acid (4 acid to 1 water), places over the.open end a cap which 

does not hermetically close the tube, inserts the latter in a larger one 

of potash glass likewise partially filled with the diluted acid, seals the 

glass tube, and 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° C.

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

ifier. deutsch. chem. Gesell., Vol. XXIV, p. 273,1891, and Zeitschr. fiiranorg. Chem., Vol. VI, p. 72, 

1894.
MLLEBBASD.] SILICA, SEPARATION FKOM ALUMINA, ETC. 49

decomposition less' complete than if the material were spread evenly 

throughout the length of the tube. Further, the acid strongly attacks 

the platinum unless the air in both the platinum and the glass tubes is 

replaced by carbon dioxide. Even when this is done, several milligrams of platinum are found in the silicate solution.

Nevertheless, to those possessing the necessary platinum and steel 

tubes the method can render efficient service in special cases when 

economy of material is imperative.

THE BOEIC OXIDE METHOD OF JANNASCH AND HEIDENREICH.

Preparation of the boric oxide. This demands, if the alkalies are to 

be estimated in the same portion as silica, etc., an absolutely alkalifree boric acid, which can be prepared by two or three recrystallizations of a good commercial article. The purified ciystals are 

dehydrated and fused in a large platinum crucible. This is then suddenly cooled to cause the anhydride to crack into pieces of a size convenient for powdering, which are to be kept in a tight glass and 

powdered as needed, since the anhydrous oxide is hygroscopic.

Treatment of easily decomposable silicates. To this flux Jannasch 

and Heidenreich find that nearly all silicates readily succumb over the 

ordinary blast lamp. The fusion is made in a large crucible holding 

40-65 cm. 3 , and the proportion of flux to be used is gauged 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, which 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.

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 2 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 tox l a few grams additional of boric oxide

1 Zeitschr. fiir anorg. Cheru., Vol. XII, p. 208,189G. 

2 Ber. deutsch. chem. Gesell., XXXII, p. 1C70,1899.

Bull. 176 4
50 SOME PKINCIPLES AND METHODS OF BOCK ANALYSIS. [BULL. 176.

are added and the oxygen blast is applied till, in ten or fifteen minutes, the fusion is as transparaht as glass. 1

Further treatment after fusion. From this point the further treatment is the same in both cases, and as modified by Jannasch and 

Weber (loc. cit.) 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. 2 The cover being then removed, the liquid is heated 

to boiling over asbestos board by an inch-high flame, stirring constantly, 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° C. 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

o

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 in time. The boric ether, 

driven off in such enormous 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 in part. "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.

THE SODIUM-CARBONATE METHOD.

Purity of the sodium carbonate used as a flux. Notwithstanding the 

most earnest efforts for years, it has been impossible to procure, either

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 estimating silica in such cases, where' even its detection, 

when present in small amount, has heretofore been difficult.

2 Made by passing dry HC1 into cooled CH4O for from one to two hours.
HILLEBKAND.] SILICA, SEPARATION FEOM ALUMINA, ETC. 51

in the open market or by special arrangement with manufacturers, an 

article of sodium carbonate which can be called chemically pure. 

With special precautions small lots can be prepared in the laboratory 

that will contain less than 1 milligram total impurity in 10 grams; but 

such an article can not be purchased in the market, and rarely will the 

so-called chemically pure dry sodium carbonate contain as little as 1 

milligram in 10 grams. The invariable contaminating substances, aside 

from sand and straw, which have sometimes been found in large amount, 

are silica, alumina, iron, lime, and magnesia, 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.

Precautions infusing. Special directions with regard to the fusion 

and its first treatment are unnecessary, except to say that ordinarily 

from 4 to 6 parts of flux should be used to 1 of rock and that the flame 

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 or treatment with hydrochloric acid or 

acid potassium sulphate. In order to avoid the use of niter in case of 

pyritiferous rocks, it is well to first roast the weighed powder in the 

crucible in which the fusion is to be made.

Treatment after fusion. When fusion is complete, the crucible is 

seized with the tongs (fig. 1, p. 23) and the contents are caused to 

solidify in a thin sheet over the sides and bottom by imparting an 

appropriate rotating motion with the arm during the cooling process. 

This is far 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.

It sometimes happens that the cooled flux, and even its solution,
52 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

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. - The contents of the crucible are placed in a rather tall covered 

beaker with some water, and hydrochloric acid of 1.1 specific gravity 

is added in excess. The depth of the pink color usually produced on 

addition of the acid allows of judging approximately as to 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.

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.

Drying and testing of silica. As to the best way of rendering silica 

insoluble by evaporation, the writer's predilection is for a double 

evaporation instead of a single one on the water bath. By fusing with 

sodium carbonate in the forenoon, the silica is ready for the first filtration in the afternoon. It is quite unnecessary to carry the evaporation 

beyond approximate dryness. The filtrate is again evaporated, always 

in platinum, and is ready for final filtration the following morning, 

when approximately 1 per cent of silica is recovered and added to the 

main, portion. The writer's experience is that a better separation of 

silica is effected hereby, and in no more time than by a single long 

evaporation. That which is subsequently recovered from the precipitate of alumina, etc. (p. 56), rarely exceeds a half or, at the most, 1 

milligram.

Drying in an air bath at 110° C. or higher, or on a hot plate or sand 

bath, or over a free flame, in order to render silica insoluble, offers no 

advantage unless much magnesium is present, and then the most favorable temperature, according to Gilbert, 1 is 120° C. The presence of 

much calcium chloride seems to facilitate dehydration of the silica, 

while magnesium chloride above 120° C., on the other hand, by 

decomposing, forms a silicate which dissolves in hj^drochloric acid and

1 Technology Quarterly, Vol. Ill, p. 61,1890. Abstract in Freseuius'a Zeitschr. fiir anal. Chemie, Vol. 

XXIX, p. 088,1890.
^ HII.LEBRAND.] SILICA, SEPARATION FROM ALUMINA, ETC. 53

increases the amount of silica carried into the filtrate.' It does not 

) appear from Gilbert's paper that the blast-furnace slags, on which he 

experimented, contained titanium, phosphorus, or iron in appreciable 

amounts. Basic magnesian rocks usually do, and in such cases it is 

probable that the employment of a drying temperature of 120° would 

materially add to the large impurity always to be expected with the 

silica. In other cases he confirms the earlier belief that drying temperatures higher than that of the water bath increase the amount of 

insoluble impurity, chiefly alumina, in the silica, and that this amount 

can not be reduced by long digestion with hydrochloric acid. Further, 

he confirms Lindo's statement that evaporation with sulphuric acid till 

the appearance of white fumes gives a higher result in silica than Avith 

hydrochloric acid. But for general rock analysis the use of sulphuric 

acid at this stage must be rejected utterly.

Blasting for twenty to thirty minutes 1 is necessary to expel all 

moisture from the silica, and it is then not hygroscopic. Its weight 

should always be corrected for impurities, which are never absent, by 

evaporating with hydrofluoric and sulphuric acids and again blasting. 

If toward the end of evaporation with these acids, 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. This 

appearance is possibly due to zirconium with the phosphorus and 

titanium, 2 and is so unusual and striking that it is worth while callingattention to it. With basic rocks very rich in titanium and phosphorus the residue may amount to 2 or even 3 per cent of the rock.

The subsequent precipitate of alumina, etc., is usually ignited in 

the crucible containing the residue from the silica.

It might be supposed that this residue would contain most of the 

barium of those rocks carrying that element, together with sulphur or 

sulphates, but the reverse is true as a rule. Only when there is a considerable excess of S03 over the°BaO will much of the latter be found 

there, and in the vast majority of cases there is none at all. Should 

some be present, its removal and estimation at this stage is not necessary, as it can be more conveniently recovered later, together with the 

silica accompanying the alumina, etc., precipitate (p. 56).

The separation of silica in rocks containing fluorine has been touched 

upon in commenting on the boric-oxide and sodium-carbonate methods 

of fusion,3 and will be considered further under the head of Fluorine 

(P- 103)._____________________.______________

1 It must be borne well 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, Jour. Am. Chem.Soc., Vol. XXII,p.494,1900.)

8 See first footnote, p. 57.

3 See p. 47 and footnote, p 50.
54 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. [nuu..i7ft ^

Platinum infiltrates. The filtrates from the silica always contain 

notable amounts of platinum. This arises in very small degree from ( 

the crucible fusion, in a larger one indirectly from the action of 

hydrochloric acid on manganate, vanadate, and sometimes chromatc 

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 is little known, apparently, but is mentioned in 

Gmelin-Kraut, 1 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 second footnote, p. 57), 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.

VII. METALS PRECIPITABLE BY HYDROGEN SULPHIDE.

The presence in appreciable amounts of metals precipitable by hydrogen sulphide, except perhaps copper, is of such 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 estimation 

of these metals should be made in a separate portion of the rock broken 

up by the action of hydrofluoric and sulphuric acids.

VIII. ALUMINUM. TOTAL IRON. 

INDIRECT METHOD FOR ALUMINUM.

The common practice in this laboratory is to find alumina by difference, 

after deducting from the precipitate produced by ammonia or sodium 

acetate the sum of all other oxides this precipitate may contain. Of 

these, only ferric oxide, titanic oxide, and the trace of silica are determined in this portion (see also second footnote, p. 57), those of phosphorus, vanadium, chromium, and zirconium being looked for in other 

portions of the rock powder. This throws upon the alumina all errors 

involved in their separate determinations; but these may balance, and

1 Anorg. Chem., Vol. Ill, p. 359. Sixth revised edition.
HILLKBBAND.] ALUMINUM, TOTAL IKON. 55

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.

PRECIPITATION OF ALUMINUM, IRON, ETC.

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.

Precipitation l)y the.lasic acetate method. But it will occasionally 

happen that the. separation from even very small amounts of manganese is altogether incomplete, and the uncertaintj^ of insuring this 

separation has led the writer of late 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. 1 Not more than 2, or at most 3, grams 

of sodium acetate need be used. After slight washing and sucking 

dry at the pump, the precipitate is redissolved in a large excess of 

hydrochloric acid and reprecipitated by ammonia in slight 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. Penfield and Harper 2 recommend washing with a 

dilute solution of ammonium nitrate (20 cm. 3 nitric acid, neutralized 

by ammonia, to the liter), and also the solution of the first precipitate 

in nitric instead of hydrochloric acid, in order to shorten the washing, 

there being no chloride to remove.

'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 Maryland over 2 per cent of rare earths, including cerium 

and others not identified, were quantitatively separated in this way from iron, alumina, etc.

2 Am. Jour. Sci.,3d series, Vol. XXXII, p. 112,1886.
56 SOME PRINCIPLES AND METHODS OF BOCK ANALYSIS. [BULL. 175.

The filtrates are strongly concentrated separately l in platinum, a 

drop or two of ammonia being added toward the end to the second 

one, and filtered successively through the same small filter into a flask 

of 150 to 200 cm. 3 capacity, the ammoniacal filtrate serving as wash 

water for the first dish and containing enough ammoniacal salt to prevent precipitation of magnesium in the first filtrate when mixed with 

it. If manganese has been deposited upon the surface of the dish it is 

removed by hydrochloric and a drop or two of sulphurous acids, 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 one. 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.

IGNITION OF THE PRECIPITATE.

The combined precipitates of alumina, etc., are ignited moist, in the 

paper, unless considerable iron is present, when the main one is dried, 

removed as far as possible from the paper, and the latter ignited separately to prevent partial reduction of a portion of the iron, which 

can not then be wholly reoxidized by heating or by treatment with 

nitric acid (see p. 38).

Alumina in the quantities ordinarily found can not be fully dehydrated by the full heat of the Bunseu 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 free access of air to the crucible 

(p. 51).

RECOVERY OP SILICA AND POSSIBLE BARIUM IN THE ALUMINA PRECIPITATE.

The precipitate is dissolved by fusion with acid potassium sulphate, 

an operation which is accomplished without trouble in from two to 

four hours if the temperature is kept low and the acid salt has been 

properly made free from water and excess of acid. The melt is taken 

up with hot water and considerable dilute sulphuric acid, the residue 

collected, weighed, and corrected by hydrofluoric and sulphuric acids 

for silica, which, as said before, rarely amounts to 1 milligram in 

weight, and further examined for barium (see p. 53) by dissolving any

'If, instead of sodium acetate, ammonia alone has been used to precipitate alumina, etc., it has 

sometimes happened in the experience of others than the writer that on concentration of the first 

filtrate a pale straw-colored precipitate appeared, which remained on the filter with the traces of 

alumina thatfmay also separate, although it is slowly soluble in hot water. This is said to be some 

compound of platinum, and attention is called to it here for the guidance of others who may notice 

it and be unaware of its character.
HILLEBRAND.] ALUMINUM, TOTAL IRON. 57

remaining residue in hot, strong sulphuric acid and diluting with cold 

water. 1

ESTIMATION OF IRON IN THE PRECIPITATE OF ALUMINA, ETC.

Without regard to the presence of 'vmadium. The filtrate obtained 

in the preceding paragraph is reduced, hot, by hydrogen sulphide, 

boiled to collect sulphur and the platinum sulphide 2 resulting from the 

bisulphate fusion, the hydrogen sulphide being allowed to pass for a 

short time after boiling. It is then filtered 8 hot into a flask attached 

to a carbonic-acid apparatus and brought to boiling to expel hydrogen 

sulphide. When this is fully effected the flask is cooled in water 

while the carbon dioxide still passes, and the solution is then titrated 

by potassium permanganate. 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 . 

Titanium can be conveniently estimated by adding hydrogen peroxide 

to the titrated iron solution (see p. 68).

: Somc 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 amounting to 1 to 3 per cent of the rock, 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 PaOo, with perhaps a little Zr02 . 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. 63, as derived from the ignited silica.

Knop (Zeitschr.fiir Kryst., Vol. X,p. 73,1885) seems to have obtained a similar mixture in analyzing minerals from the Kaiserstuhl in Baden, but its nature was not ascertained, though suspected to 

be, if not silica, columbiferous titanic acid.

2 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 

Avhat the latter weighed before the main silica precipitate was ignited in it; in other words, the weight 

of the platinum recovered by hydrogen sulphide should equal the loss in weight of the crucible due 

to attack by the bisulphate. In somewhat rare instances this will not be so, but the weight will be 

greater, showing a gain in platinum which may amount to a milligram. Tests have shown that this 

is not due to retention of platinum by the main A12 03 , etc., precipitate; hence, it must come from 

platinum mechanically loosened from the dish during the drying and powdering of the silica preparatory to its collection on the filter, or to some insoluble compound of platinum formed during 

evaporation and drying of the silica. It may also be in part or wholly due to contamination from 

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 p. 54).

3 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 VVells and Mitchell, and others 

before them, have pointed out. The above authors used this method of reducing ferric iron^jn titanic 

iron ores. (Jour. Am. Chem. Soc., Vol. XVII, p. 78,1895; also Chemical News, Vol. LXXIII, p. 123, 

1896.)
58 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

Having regard to the presence of vanadium. If vanadium is present 

the value found for iron will be in error by the amount of permanganate required to oxidize V2 04 to V2O5 . The amount of the correction will differ according as titration of the iron is made after reduction by hydrogen sulphide or by 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 slower-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 Carnot1 states that repeated precipitation by ammonia, ammonium carbonate, or ammonium sulphydrate, 

separates it from iron. The writer's experience with ores very rich in 

vanadium shows that precipitation along with iron and aluminum is 

only partial. Ridsdale * has determined its precipitability with various 

metals and gives numerous figures which show an approximation to 

90 per cent thus thrown down under the conditions prevailing in analysis of iron slags, the remainder passing into the filtrates and appearing 

in small part with the lime and to a greater extent with the magnesium 

phosphate. For all practical purposes it is probably safe to assume 

that the small amounts of vanadium met with in rocks are wholly in 

the alumina precipitate.

If the amount of vanadium in the rock is not known and great accuracy 

is necessary, caution requires the determination of the total iron to be 

made either in a separate portion or after reprecipitation from the 

above solution, as follows: Fuse with sodium carbonate, extract with 

water, bring the insoluble residue into sulphuric solution, reduce and 

titrate as above directed. But unless a certain precaution is here 

observed an error greater than that which it is designed to avoid will 

be committed. Contrary to general belief the aqueous extract from 

the sodium-carbonate fusion carries a small but appreciable fraction 

of a per cent of iron, as the writer has repeatedly f ou-nd 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,

iComptes Rendus, Vol. CIV, p. 1803,1887; Zeitschr' fur. anal. Chem., Vol. XXXII, p. 223, 1893. 

2 Jour. Soc. Chem. Industry, Vol. VII, p. 73, 1888.
ALUMINUM, TOTAL IRON. 59

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.

DETERMINATION OF THE TRUE VALUE FOR FERRIC IRON.

Having in one w&y or another found the total iron in the rock, 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. 

94-96.)

METHODS AIMING AT THE MORE OR LESS DIRECT ESTIMATION OF

ALUMINUM.

AFTER FIRST REMOVING IRON AS SULPHIDE.

Should it be desirable for any reason to effect an actual separation 

of aluminum, this may best be done, up to a certain point, after the 

bisulphate .fusion (p. 56), by removal of the iron 1 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 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 two last from the chromium and vanadium is 

outlined under Phosphorus, p. 79. This is as far as the separation can 

well be carried, and the A12 03 must still be found by subtracting the 

P2OB from the combined weights of the A12O3 and P2 05 . The possibility of loss of some P2O5 by volatilization 2 during the bisulphate 

fusion must be borne in mind here, for if it takes place the final weight 

of A12O3 + P2OB will not contain all the P2 05 .

Some writers recommend 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.

BY EXTRACTION WITH A FIXED CAUSTIC ALKALI.

A favorite practice in some countries of Europe is to fuse the ignited 

precipitate containing A12 03 , Fe2O3 , TiO2 , P2 05 , etc. or that of the 

A12O3 , TiO2 , P2O6 , etc., after separation of iron by ammonium sulphide 

in tartrate solution with sodium hydroxide in a silver crucible, or to

1 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. fiir Kryst, Vol. VI,p.24G, 1882, and Vol. VII,p.250,1883.)

2 H.llose speaks of such loss when volatilizing sulphuric acid in presence of phosphoric acid. 

(Handb.f. quant. Anal., Finkener edition, Vol. II, p.575, and elsewhere.)
60 SOME PRINCIPLES AND METHODS OF EOCK ANALYSIS. [BULL. 176.

boil the freshly precipitated mixture .with a solution of the alkali, on the 

assumption that the titanium oxide is hereby rendered wholly insoluble and thus separated from the alumina. This, however, is in part 

an error long since pointed out by Gooch, 1 who showed that pure 

titanic oxide is markedly soluble under both conditions of treatment. 

Experiments very recently made by the writer to test the extent of 

this error brought out the following interesting results.

When 0.045 gram of titanic oxide was fused by itself with sodium 

hydroxide, the clear aqueous extract of the fusion held 0.0031 Ti02 , or 

about 7 per cent, determined colorimetrically. When freshly precipitated and boiled with the alkali the solubility was less. When 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.

DIRECT PRECIPITATION OF ALUMINA.

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,2 but, as with the methods just considered, 

it involves finally weighing aluminum and phosphorus together, and 

the behavior of titanium has not been investigated. For this latter 

reason the details of the method will not be given. Suffice it to say 

that precipitation of the aluminum and phosphorus 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."

IX. MANGANESE, NICKEL, COBALT, COPPER, ZINC.

Ammonia is added to the flask containing manganese, the earths, etc. 

(p. 56), and hydrogen sulphide gas is introduced, whereby manganese, 

nickel, cobalt, copper, zinc, and a small part of the platinum from 

the dish are precipitated. The flask is set aside, corked, for at least 

twelve hours, and preferably twenty-four, or even longer; the preiproc. Am. Acad. Arts and Sci., Vol. XII, p. 436,1885; Bull. U. S. Geol. Survey No. 27, pp. 16 and 17. 

2 Jour. Am. Chem. Soc., Vol. XXI, p. 776,1899; Chemical News, Vol. LXXXI, p. 158,1900.
HILLEBBAND.] MANGANESE, NICKEL, COBALT, COPPER, ZINC. 61

cipitate, 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.

MANGANESE AND ZINC.

The filtrate is evaporated to dry ness, ammonium salts are destroyed 

by evaporation with a few drops of sodium-carbonate solution, hydrochloric and a drop of sulphurous acids 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 great time saver.

The precipitation of manganese in alkaline solution by hydrogen 

peroxide, as proposed by Jannasch and Cloedt, 1 a method 'which 

appeared to be simple and accurate, besides affording a separation 

from zmc, has been shown by Friedheim and Briihl 2 to be valueless, 

as also other separation methods of Jannasch based on the use of 

hydrogen peroxide.

The employment of ammonium sulphide instead of bromine for the 

separation of manganese from the alkaline earths and magnesia has the 

advantage that, by a single operation, nickel, copper, and zinc are likewise removed if present. There need be no fear of overlooking nickel 

or copper, for under the conditions of the precipitation they are not 

held in solution. Now and then a trace of alumina may be found in 

the precipitate, and magnesia, too, would contaminate it if ammonium 

salts were not present in sufficient quantity. Regard must therefore 

be had to these possibilities, and also to the rather remote possibility 

of the presence of rare earths which were not thrown out by the basic 

acetate precipitation (see footnote, p. 55).

NICKEL, COBALT, COPPER.

The paper containing these is incinerated in porcelain, dissolved in 

a few drops of aqua regia, evaporated with hydrochloric acid, the copper and platinum thrown out warm by hydrogen sulphide, and nickel 

and cobalt thrown down from the ammoniacal filtrate by hydrogen sulphide. This is then rendered faintly acid by acetic acid and allowed 

to stand. The sulphide of nickel is simply burned and weighed as

1 Zeitschr. Kit anorg. Chemic, Vol. X, p. 405,1805.

- Zeitschr. fur anal. Chemie, Vol. XXXVIII, p. 681, 1899.
62 SOME PKINCIPLES AND METHODS OF EOCK ANALYSIS. [BULL. 176.

oxide, its weight being always very small, and .is then tested for cobalt 

in the borax bead.

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 bath, or if water has been used 

which has been boiled in a copper kettle, even if tinned inside. Therefore, and because of its contamination by a little platinum, it is better 

to determine copper in a separate portion if its presence is indicated 

with certainty. (See p. 54.)

X. CALCIUM AND STRONTIUM (BARIUM). 

SEPARATION FROM MAGNESIUM.

Precipitation and ignition of the 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. 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 sodium acetate. 1 

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° C., and the separation of strontium from 

calcium effected by ether-alcohol 2 as described below.

The weight of .strontia found deducted from that of the two oxides 

gives that of the lime.

Necessity for two precipitations l)y ammonium oxalate. 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. For 

the treatment of the filtrates, see Magnesium, p. 64.

*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.

2 See Fresenius: Zeitschr. fur anal. Chemie, Vol. XXXII, pp. 189, 312,1893, for the, latest improvements in this method.
HILLEBRAND.] CALCIUM ANT) STRONTIUM (BAEIUM). 63 

SEPARATION OF STRONTIUM (BARIUM) FROM CALCIUM BY ETHER-ALCOHOL.

The thoroughly dried nitrates 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 over night in a 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 sulphuric acid and then 

alcohol is added, whereby the strontium is precipitated as sulphate, in 

which form it is weighed and then tested spectroscopically as to freedom from calcium and barium.

Because of the slight solubility of strontium nitrate in amyl alcohol 

the method of Browning 1 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.

BEHAVIOR OF BARIUM.

Barium will, after two ammonium oxalate precipitations, never be 

found with the ignited calcium and strontium in more than spectroscopic traces, unless originally present in excess of 3 or 4 milligrams, 

and very of ten only when-in considerable excess. 2 If present with 

them, however, it will be separated with the strontium by ether-alcohol 

or amyl alcohol, and these two must then be treated by the ammoniumchromate method, given below, in order to arrive at the strontium. 

The barium is best estimated in a separate portion. (See Barium, p. 73.)

SEPARATION OF BARIUM FROM STRONTIUM.

Fresenius has shown3 in what manner only a correct separation of 

barium and strontium can be made by the animonium-chromate method, 

involving double precipitation when the.amounts are at all large. This 

procedure is. here given for the amounts used by him, but a single precipitation will suffice for the small amounts met with in rock anatysis.

1 Am. Jour. Sci., 3d series, Vol. XLIII, pp. 50, 314,1892.

2 W. F. Hillebrand: Jour. Am. Chem. Soc., Vol. XVI, p. 83,1894; Chemical News, Vol. LXIX, p. 147, 

1894. 

»Zeitechr. fur aiial. Chemie, Vol. XXIX, p. 428; 1890.

i
64 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

The volumes of solutions used should be largely reduced and the 

operations otherwise shortened.

The chlorides corresponding to 0.2774 gram BaO and 0.4864 gram 

SrO were dissolved in 300 cm. 3 of water with addition of 6 drops of 

acetic acid (1.065 sp. gr.). To the hot solution was added an excess 

(10 cm. 3) of ammonium chromate solution (i cm. 3 = 0.1 gr. neutral 

chromate). After settling and cooling for an hour the precipitate was 

washed, mainly by decantation, with water holding ammonium chromate till the filtrate gave no precipitate with ammonia and ammonium 

carbonate (100 cm. 3 used). The washing was continued with warm 

water till silver nitrate gave but a very slight reddish coloration (110 

cm. 3). The precipitate was then washed into the precipitating dish, 

the filter rinsed with warm dilute nitric acid (1.2 sp. gr.), and more 

nitric acid (2 cm. 3 in all) added to the dish. The solution having been 

diluted to 200 cm. 3 and heated, 5 cm. 3 of ammonium acetate solution 

(1 cm. 3 = 0.31 gr. ammonium acetate) was very gradually added, and 

then ammonium chromate till the odor of acetic acid had wholly disappeared (10 cm. 3 ). After one hour the supernatant liquid was passed 

through the filter and the precipitate digested with hot water, which 

was then cooled; thereupon the precipitate itself was brought on the 

filter and washed with cold water till silver nitrate gave a scarcely 

perceptible reaction. The strontium was thrown down from the filtrate 

by ammonia and ammonium carbonate, after concentration in presence of a little nitric acid, and weighed as carbonate; or the carbonate 

can be redissolved, precipitated by sulphuric acid and alcohol, and 

weighed as sulphate. The barium is weighed as chromate after ignition, the filter being burned separately.

XI. MAGNESIUM. 

PRECIPITATION.

The first precipitation of magnesium is made without special precautions in the filtrate from the first calcium oxalate separation (p. 62) by 

sodium-ammonium-hydrogen phosphate (microcosmic salt) x 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 in order to hasten precipitation. Neubauer 2 has shown that precipitation is complete even in 

presence of large quantities of salts of ammonium, including the oxalate. 

He has, however, also shown that the composition of the precipitate is 

largely affected by ammonium salts, and also by the way in which the

!The objection that has been made by one writer to the use of this salt instead of disodiuru-hydrogen phosphate is, so far as our experience teaches, entirely groundless. 

2 Zeitschr. fiir angew. Chemie, 1896, p. 435.
THLLfcBRAND.] - MAGNESIUM. 65

precipitation is made. These points are only of importance when a 

single precipitation is to be made or in the final of two or more, as will 

be discussed later.

.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 calcium oxalate, and is diluted if necessary. A 

few drops of sodium-ammonium phosphate solution are now added, 

and ammonia in slight excess, with constant stirring till the crystalline 

precipitate has well formed. The large excess of ammonia of 0.96 

specific gravity (one-third the original volume) usually prescribed has 

been shown by Gooch and Austin 1 to be quite unnecessary, in fact, 

disadvantageous.

Neubauer in the above-cited paper has shown, and Gooch and Austin 

(loc. cit.) have confirmed his statements, that it is only by working 

under these conditions absence of any large excess of precipitant, of 

animoniacal salts, and of ammonia that a precipitate of normal composition is obtainable. It usually differs from the normal in containing relatively more ammonium and less magnesium for instance, an 

admixture of such a molecule as M^NHJ^POJg the result being 

that when ignited in the ordinary way too muchjuagnesiuni 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 a constant weight has been reached. The phosphate is then 

entirely pyrophosphate, which is quite unaffected by further-blasting. 

The intense heat has caused a decomposition of the metaphosphate 

with volatilization of P2 05 , as follows: 2 Mg(PO3)2 =Mg2P.!O7 +P.!Or) . 

Neubauer worked with the usual excess of ammonia, 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.

From the labors of Neubauer and of Gooch and Austin it is clear that 

the common way of adding the phosphate precipitant to the animoniacal 

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.

Gooch and Austin call attention to a modification proposed some 

years ago by Wolcott Gibbs, 2 whereby the phosphorus and magnesium

'Am.Jour.Sci., 4th series, Vol. VII,p. 187, 1899; Chemical News, Vol. LXXIX, pp.233, 244, 255,1899; 

Zeitsclir. fiir anorg. Chemie, Vol. XX, p. 121,1899. 

" Am. Jour. Sci., 3d series, Vol. V, p. 114,1873.

Bull. 176 5
66 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. {BULL. 176.

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.

METHODS OF COLLECTING AND IGNITING THE PRECIPITATE.

If the blast has not to be employed, the weight of the pyrophosphate 

can doubtless be most accurately arrived at by collecting and igniting 

the precipitate in a Gooch crucible, provided the asbestos felt is well 

constructed and not of the serpentine variety so largely on the market.

Neubauer ignites slowly in platinum after drying, without removing 

from the paper, applying the blast only when the carbon has been 

wholly burned off. 1

Almost as exact are the two modifications of the method in use for 

phosphate analyses at the agricultural experiment stations at Danzig 

and Lisbon, described by Schmoeger 2 and Mastbaurn. 3 According to 

the former the precipitate after drying is detached from the paper and 

placed in a platinum crucible, followed by the folded filter. To the 

covered crucible the full flame of a burner is applied, and after a short 

time the burning off of the carbon is accomplished with the crucible 

open. A short blasting follows. In a number of experiments on quantities ranging from 0.06 to 0.28 gram of pyrophosphate the results 

were, with a few exceptions, naturally lower than those obtained on 

duplicates by the ordinary method of igniting, but only by 0.0013 

gram in maximum. 

Mastbaum, to shorten time, applies the. full flame to the moist precipitate wrapped in its filter. Later, when most of the carbon is 

burned off, he moistens the residue with two or three drops of strong 

nitric acid, evaporates this carefully, heats with full burner for a few 

minutes, then blasts for half a minute. He describes the results as 

irreproachable. In this laboratoiy only the Mastbaum modification 

has been tried, and it certainly seems to be satisfactory when the extreme of accuracy is not required.

At one time the procedure first recommended by Ulbricht, later by 

Broockmann, and also by L. L. de Koninck, was used. It consists in 

dissolving the ammonium-magnesium phosphate off the filter with 

nitric acid, collecting the filtrate in a weighed crucible, evaporating 

the contents to dryness, 4 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 comi Zeitschr. fur anal. Chemie, Vol. XXXIII, p. 3C'2,1894. 

. 2 Ibid., Vol. XXXVII, p. 308j 1898.. ... .'. .. ......................_.................

3 Ibid., p. 581,1898.

4 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.
HILLEBRAND.] MAGNESIUM, TITANIUM. 67

pletely 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,

CONTAMINATION BY AND KEMOVAL OF BAKIUM AND CALCIUM.

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. 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 

Itydrochloric acid, is added ammonia to alkalinity, and then acetic acid, 

drop by drop, till the solution, which should not be hot, clears. It 

now and then happens that a little flocculcnt matter fails to dissolve. 

This is to be removed, ignited, and subtracted from the original -weight. 

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 finegrained and nonadherent 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 from that of the magnesium pyrophosphate in 

order to arrive at the true figure for magnesia. This separation, to be 

satisfactoiy, requires great care.

XII. TITANIUM. '

 COLORIMETRIC ESTIMATION WITH HTDEOGEN PEROXIDE (WELLEft'S

METHOD). 1

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

JBer. deutsch. cheni. Gesell., Vol. XV, p. 2593,1882.
68 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

of the peroxide should be approximately measured by titration with 

permanganate on opening a fresh bottle, and again after a few weeks, 

otherwise very serious error may arise through its deterioration.

Mere traces of hydrofluoric acid, either in the peroxide or the titanium solution, render this method inexact, 1 hence care should be exercised as to the character of the peroxide, which, as sold in the market, 

often contains fluorine.

Dunnington 2 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, holding conveniently about 1 centigram TiO3 in 10 cm. 3 , equivalent to 1 per cent 

of TiOjj in 1 gram of rock, contains, therefore, 5 per cent or more of 

sulphuric acid. Of this, 10 cm. 8 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 estimated, as a rule, most conveniently in the solution which has served for the titration of total iron (p. 57). 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 described below 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 TiO2 in the rock.

If the convenient but expensive Soleil-Duboscq colorimeter is used, 

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 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

IHillebrand: Jour. Am.Chem. Soc.,Vol. XVII, p. 718,1895; Chemical News, Vol. LXXII, p. 158,1895; 

Bull. U. S. Geol. Survey No. 167, p. 56. 

2 Jour. Am. Chem. Soc., Vol. XIII, p. 210,1891.
HILLEBKAND.] TITANIUM. 69

saver. The error introduced by iron, in consequence of the yellowish 

color of its sulphate solution, is practically negligible unless its percentage is very high; then either the iron must be removed 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 Fe2 03 in 100 cm. 8 5 per cent 

sulphuric-acid solution is about equal to 0.2 milligram of TiO2 in 100 cm. 3 

when oxidized by hydrogen peroxide. This amounts to a correction of 

only 0.02 per cent on 1 .gram of rock containing the unusual amounts of 

10 per cent Fe2O3 . It will be more satisfactory, when much iron is 

present, to remove this as described on page 71 and to colorimetrically 

estimate the titanium thus freed from iron.

ALTERNATIVE MODE OF PREPARING THE TEST SOLUTION.

As said above (pp. 57 and 68), the solution that has been used for 

volumetric estimation 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 148 of the United States Geological 

Survey, by decomposing the powder by sulphuric and hydrofluoric 

acids, 1 expelling the latter by repeated evaporations with sulphuric 

acid, taking up with dilute sulphuric acid, 2 filtering from barium 

sulphate, etc., and estimating the titanium colorimetrically in the 

nitrate. The expulsion of fluorine must be thorough, or else the 

titanium result will be low, as already'stated (p. 68),"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.

!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.

2 With acid rocks solution is very complete, and it can be made nearly so with' the most basic by 

transference to asmall'beaker and gentle boiling. The residue thus obtained may contaih, 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, 

fusee} with potassium bisulphate, 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 page 74,
70 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

THE COLORIMETKIC APPARATUS AND ITS USE.

The glasses G (fig. 12) may be of square or rectangular section, 8 to. 

12 cm. high and 3 to 3£ cm. inside measurement between those sides 

through which the liquid is to be observed. 1 These sides should, of 

course, be exactly parallel; the others need not be, but should be 

blackened externally. In order to further exclude the effect of side

FIG. 12. Apparatus for colorimetric determinations, in different aspects. G, one of two glasses of 

square or rectangular section, 8 to 12 cm. higfi 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 o'pen, 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 between partition and glasses, so as to shut 

off all light above the lowest surface of the liquid in the glasses.

light in this and other similar methods (chromium, for instance, p. 8.0), 

it is very convenient to have a simple light box (B, fig. 12) that can 

be easily held in one hand, about 35 cm. long and 12 cm. square, stained 

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

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

1 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 seems to be a disinclination or inability 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. 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.

A pair of entirely satisfactory glasses can be made from a couple of square or rectangular 3 to 4 ounce 

bottles by cutting off one pair of sides from each and grinding down till the calipers show that 

agreement is perfect. The tops are then to be sawed off and pieces of plate glass cemented on the 

sides.
HILLEBRAND.] TITANIUM. 71

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

 ) trate around their sides or between them. Immediately back of the 

glasses is a partition P, with openings of appropriate size cut in it.

"* A stiffly sliding black cardboard shutter S is movable up and down

^ immediately back of the partition, so that all light can be cut off except 

that which comes through the liquid.

' 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 the writer's experience 

goes, to expensive instruments like the colorimeter of Soleil-Duboscq, 

etc. In making the color comparisons the box is best held close to a 

window, so as to get a full, strong light. Daylight is far preferable to 

artificial light.

GOOCH'S GEAVIMETRIC METHOD. '1

] 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 Dr. Gooch 1 is 

unequaled. With one or two minor modifications introduced by Dr. 

T. M. Chatard, 8 it is as follows:

Any solution of the rock freed from silica can be used, and the first 

step is to remove the iron. This is best done, after adding tartaric 

acid and reducing the iron by means of hydrogen sulphide to the ferj rous condition, by rendering the solution amnioniacal and introducing 

more hydrogen sulphide. If the iron is not thus reduced before precipitation, titanium will be in part thrown down also. 3 The amount of 

tartaric acid is to be gauged 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

i Proc. Am. Acad. Arts Sci., n. s., Vol. XII, p. 435; Bull. U. S. Geol. Survey, No. 27, p. 16,1886; Chemical 

\ News, Vol. LII, pp. 55 and 68,1885.

, \ 2 Am. Chem. Jour., Vol. XIII, p. 106,1891; Bull. U. S. Geol. Survey, No. 78, p. 87; Chemical News, Vol. 

\ LXIII, p. 267, 1891. 

' scathrein: Zeitschr., fur Kryst., Vol. VI, p. 243,1882; Vol. VII, p. 250,1883.
72 SOME PKINC1PLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

been fully broken up, and the precipitated manganese is to be redissolved by a few drops of ammonium bisulphite or of sulphurous acid 

solution.

Ammonia is then added in slight excess, followed at once by acetic 

acid in considerable excess, and the boiling is continued for a few 

minutes. Thereby the titanium is freed from most of the alumina, and 

from lime and magnesia if they had not been earlier removed, also 

from most of the manganese introduced. The precipitate is filtered 

and washed with water containing acetic and sulphurous acids, then 

ignited, fused thoroughly with sodium carbonate, and leached with 

water to remove phosphoric acid and most of the remaining alumina. 

The residue is again ignited and fused wi^h sodium carbonate. To 

the cooled melt in the crucible strong sulpuric 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. Upon 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 15 to 20 minutes' ignition over a good 

burner it is in condition for weighing and will lose no more weight 

over the blast lamp. For large amounts of titanium a repetition of 

the sodium carbonate fusion, etc., should be made. The actual carrying out of all these operations, when once the method is understood, 

requires much less time than the detailed description would indicate.

GOOCH'S METHOD NOT DIRECTLY APPLICABLE TO KOCKS CONTAINING ZIRCONIUM.

Prior to the adoption of the colorimetric method, Dr. 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
HILLEBKAND.] BABIUM (ZIRCONIUM, TOTAL SULPHUR). 73

TiOa . 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 in the manner to be hereafter described (p. 75), however,

no difficulty was experienced in precipitating all the titanium with the

k, usual ease.

SUPERIORITY OF THE COLOIUMET1UC AND GOOCH METHODS OVER, THE OLDEU 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 

incomprehensible 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.

Attention has been directed (p. 60) to the error resulting from 

attempting to separate aluminum from titanium by either fused or 

w 'dissolved sodium hydroxide.

J BASKEKVILLE'S METHOD. a

Baskerville 1 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 Fe 2 03 with 8 to 10 per cent TiO2 . Zirconium would 

probably be likewise precipitated (see p. 77) and phosphorus perhaps also, but this last point has not been investigated, neither has the

J applicability of the method to aluminous rocks been tested.

XIII. BARIUM (ZIRCONIUM, TOTAL SULPHUR).

Reasons for estimating barium in a separate 2)ortion of rock powder. 

It has been said above (p. 63) 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 armnoniacal salts. Addition of some alcohol insures

N also the recovery of traces of strontium if. the rocks are very rich in

^ it. But it is unsafe to regard the amount thus separated from the

, / Muagnesium as representing the total amount of barium in the rock. It

\ ' Jour. Am. Chem. Soc., Vol. XVI; p. 427,1894.
74 SOME PRINCIPLES AND METHODS OF EOCK ANALYSIS. [BULL.ITC.

will almost always be found lower than the truth, probably for the 

reason that there are opportunities during the analysis for slight losses. 

It is best to estimate it in a separate 2-gram portion, which may also 

serve with advantage for the estimation of zirconium and total sulphur.

Modes of attack and subsequent treatment, If zirconium and sulphur 

are not to be looked for, the simplest procedure is to decompose the 

powder by sulphuric and hydrofluoric acids (seep. 69, under Titanium), 

and to complete the purification of the barium sulphate thus obtained 

in the manner, described in the third paragraph below.

If zirconium and sulphur are both to be likewise determined, decomposition is.effected by fusing over the Bunsen flame and then over the 

blast with sulphur-free sodium carbonate and insufficient niter to 

injure the crucible, first fitting the latter snugly into a hole in asbestos 

board (Lunge) to prevent access of sulphur from the gas flame. In 

case sulphur is not to be regarded, the niter and asbestos board 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 x manganese, 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.

For the further treatment of the filtrate see Sulphur, p. 106, and 

Chromium (colon-metric method), p. 80.

The residue is dissolved in quite dilute warm sulphuric acid (stronger 

acid may be used if barium only is sought) and filtered through the 

original filter. This, with its contents, is ignited, evaporated with hydrofluoric and sulphuric acid, and taken up with hot dilute sulphuric acid. 

The filtrate, added to the former one, now contains all the zirconium 

(see pp. 75-76 for its further treatment). The residue contains all the 

barium, besides some of the strontium, and perhaps a good deal of

calcium. It is fused with sodium carbonate, leached with water, the 7 \ '

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 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 (p. 63).

Barium and strontium sulphates can be brought into a condition for j 

testing spectroscopically by reducing for a very few moments the/ 

whole or part of the precipitate on a platinum wire in the luminous
HILLEBBAND.] ZIECONIUM. {)

tip of a Bunsen burner, and then moistening with hydrochloric acid. 

This should be known to everyone, but probably is not.

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. 1 Even where 

 no attempt is made to separate contaminating traces of SrO and BaO 

one from the other, the error is usually of no great consequence, for 

an absolute error of 25 per cent, even, in a substance constituting only 

one or two tenths per cent of a rock is ordinarily of small moment 

compared with the ability to certify to its presence with approximate 

correctness. . With such ^mall amounts of barium as are usually found in rocks it 

is doubtful if Mar's 2 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.

XIV. 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 of and a chemical test rendered almost unnecessary; but 

sometimes it occurs in other minerals, and is then unrecognizable under 

the microscope. It may rarely be present up to a few tenths of 1 per 

cent of the rock.

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 

by G. H. Bailey, 3 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 (p. 74), where the separation from barium has been 

described and also the concentration of the zirconia m oa 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

1 For details consult W. F. Hillebrand: Jour. Am. Chem. Soc., Vol. XVI, p. 83,1894; Chemical News. 

I Vol. LXIX, p. 147,1894. 

\ 2Am. Jour. Scl., 3d ser., Vol. XLIII, p. 521,1892.

3Jour.Cliem.Soc., Vol. XLIX, pp. 149,481,1886.
76 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176.

should be in a small flask, is now added hydrogen peroxide to oxidize 

the titanium, and then a few drops of a soluble orthophosphate solution. 

The flask is set aside in the cold for twenty-four to 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. 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 of"about 20 cm. 3 capacity, a few 

drops of hydrogen peroxide and of sodium phosphate added, and the 

flask set aside. Titanium is now almost never present, and the zirconium appears after a time as a white 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 ZrOa (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 ZrO2 . 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 ZrOg. 1 My own 

efforts to secure a precipitate' in acid solutions of zirconium sulphate 

by hydrogen peroxide alone were unsuccessful, perhaps for lack of a 

sufficiently strong 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 working in a weakly acid solution, 

the separation of zirconium could be made in the same portion in which 

the titanium is colorimetrically determined.

OTHER METHODS OF SEPARATING ZIRCONIUM.

Streit and Franz 2 claim to secure complete separation of titanium 

from iron and zirconium by boiling the neutralized solutions of the

1 Bailey, Chemical News, Vol. LX, p. 6,1889.

2 Jour, f iir prakt. Chemie, Vol. C VIII. p. 65,1869.
HILLEBRAND.] BARE EARTHS OTHER THAN ZIRCONIA. 77

sulphates with a large excess (50 per cent) of acetic acid. The method 

has been from time to time recommended, but without any data showing its value. The single separation made by Streit and Franz was 

far from perfect.

Davis 1 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.

Baskerville 2 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 (p. 73). It is based on the profitability 

of Zr02 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.

XV. RARE EARTHS OTHER THAN ZIRCONIA.

For the few cases in which it may be necessary to look for rare earths 

other than zirconia, the following procedure is suggested as likely to 

prove satisfactory.

The rock powder is thoroughly decomposed by several partial evaporations with hydrofluoric acid, the fluorides of all earth metals except 

zirconium are collected on a platinum, cone, washed with "water acidulated by hydrofluoric acid, and the precipitate 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 separated by ammonia, washed, redissolved in hydrochloric 

acid, and evaporated to dry ness, then taken up with water and a drop 

of hydrochloric acid, and onty 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 have been found when working on not more than 2 grams 

of materials.

This method eliminates at once most of the aluminum, all the iron, 

phosphorus, titanium, and zirconium, and has the further advantage of 

collecting with the earthy fluorides, as UF4 , any uranous uranium that 

the rock might have held.

An alternative method would be to fuse with sodium carbonate,, leach 

with water to get rid of phosphorus as far as possible, dissolve the

1 Am. Chem. Jour., Vol. XI, p. 27,1889.

2 Jour. Am. Chem. Soc., Vol. XVI, p. 475,1804; Chemical News, Vol. LXX, p. 67,1894.
78 SOME PRINCIPLES AND METHODS OF EOCK ANALYSIS. [BULL.176.

residue in hydrochloric acid, separate silica as usual, precipitate alumina, etc., by ammonia, dissolve the precipitate again in hydrochloric 

acid, evaporate, and proceed as by the former method, which in most 

cases would undoubtedly give better results than this one.

XVI. PHOSPHORUS.

It is sometimes possible to extract all phosphorus from a rock by 

simple digestion Avith 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.

PROCEDURE WHEN MATERIAL IS AMPLE.

When material is ample it is best to use one portion for phosphorus 

only and to proceed as follows:

Fuse with sodium carbonate, separate silica by a single evaporation 

with nitric acid, treat the ignited silica with hydrofluoric and a drop 

or two of sulphuric acids, evaporate to expel hydrofluoric acid, bring 

the small residue into solution by boiling with nitric acid and add it 

to the main portion, in which, after addition of considerable ammonium nitrate, precipitate the phosphorus by molybdate solution.

The turbidity often observed on dissolving the precipitated and 

washed phospho-molybdate in ammonia is due to a compound of phosphorus. If the addition of a small fragment of a crystal of citric or 

tartaric acid fails to dissolve it, this should always be re-fused with 

sodium carbonate, extracted with water and the filtrate otherwise 

treated as above, in order to secure the phosphorus in it.

According to Gooch and Austin, 1 in order to secure a magnesiumammonium phosphate of normal composition, the procedure at this 

point should be as follows: To the phosphate solution, containing not 

more than 5 to 10 per cent of ammonium chloride and a slight excess 

of magnesia mixture, a little ammonia is added, and the precipitate is 

washed in due time with weak ammonia water. In general, however, 

as these conditions can seldom be fulfilled, they recommend to decant 

the supernatant liquid through the filter which is later to receive the 

precipitate, to dissolve this in as little hydrochloric acid as possible, to 

reprecipitate by dilute ammonia without further addition of magnesia 

mixture, and to wash finally with weakly ammoniacal water. Excess 

of ammonia, of ammonium salts, and of precipitant are all objectionable. In rock analysis the second precipitation will seldom be necessary. For ignition, etc., of the precipitate, see this subject under 

Magnesium (p. 66.)

1 Am. Jour. Sci., 4th series, Vol. VII, p. 187, 1899; Zeitschr. fur anorg. Chemie, Vol. XX, p. 121, 

1899; Chemical News, Vol. LXXIX, pp. 233, 244, 255, 1899.
^ HILLEBBAND.] - PHOSPHORUS, CHROMIUM. 79 

PROCEDURE WHEN MATERIAL IS SCANTY.

The following procedure admits of determining in the same portion, 

besides phosphorus, barium, iron, vanadium, chromium, and titanium, 

the last two either colorimetrically or gravimetrically, and is in large 

part extracted from a paper by Dr. T. M. Chatard. 1

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 und 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 precipated A12O3 , P2O6 , CraO3 , Fe2O3 , and TiO2 is 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 chro- 

/ rnium can be determined colorimetrically if present in sufficient 

amount to give a pronounced color (see p. 80). 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, containing chromium and vanadium, can be 

treated as detailed in the next following sections.

XVII. CHROMIUM.

If vanadium is absent, or nearly so, as is apt to be the case in those 

highly magnesian rocks (peridotites) usually carrying a good deal of 

chromium, the following separation and gravimetric method for chror 

mium gives good and concordant results, but in presence of vanadium, 

and it is best generally to assume its presence, the coloriinetric method 

should always be adopted.

i Am. Chem. Jour. Vol. XIII, p. 10C, 1891; Bull. U. S. Gcol. Survey No. 78, p. 87; Chemical News, 

Vol. LXIII, p. 267,1891.
80 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BOLL. 176. ^ 

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 Baubigny l by dissolving 

in nitric acid, evaporating to near 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 and reprecipitated to free from alkali, and weighed.

The separation of aluminum from chromium by hydrogen peroxide 

in ainmoniacal solution, as recommended by Jannasch and Cloedt, 2 has 

been shown by Friedheim and Bruhl, 3 together with most of the other 

separations of Jannasch based on the use of hydrogen peroxide and 

from which so much was hoped, to be valueless.

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, 

p. 79) in order to compare its color with that of a standard solution.

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 one liter of water made alkaline by 

a little sodium carbonate. Each cubic centimeter then corresponds to 

one-tenth milligram or two-tenths milligram of chromic oxide (Cr2O3), 

in which condition chromium is usually reported in rocks and ores. It > 

is probably inadmissible to increase the strength of the standard much 

above the figure given.

Preparation of the test solution. :Before filtering the aqueous 

extract of the sodium-carbonate fusion a few drops of alcohol (ethyl or 

methyl) are added to destroy the .color of sodium manganate. If the 

yellow color of the filtrate is very faint, concentration by evaporation

'Bull. Soc. Chimique (u. s.) Vol. XLII, p. 291, 1884; Chemical News, Vol. L, p. 18,1885.

"Zeitschr. fiiranorg. Chemie, Vol. X, p. 402,1895.

3 Zeitschr. fur anal. Chemie, Vol. XXXVIII, p. 681,1899. ,

" W. F. Hillebrand, Jour. Am. Chern. Soc., Vol. XX, p. 454,1898; Chemical News, Vol.LXXVIII.pp. 

227,239,1898; Bull. U. S. Geol. Survey No. 167, p. 37; First applied by L. de Koniugh (Nederl. Tyds. voor 

Pharm. Chem. and Tox., 1889) for the estimation of chromium in foodstuffs.
HIU.EBHAND.] CHROMIUM. 81

will strengthen it, and less than 2 milligrams of chromic oxide in 1 

gram of rock can then be exactly measured. For smaller amounts it 

is best to employ from 3 to 5 grams of powder and then to concentrate the chromium by precipitation by rnercurous nitrate, as detailed 

in the next section under Vanadium (p. 83); 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 temperatur,4 of the blast should fiver be high enough to permit the crucible to 

be attacked.

/ Comparison of coloi^s. 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 68 for the colorimetric 

estimation of titanium. For very minute amounts it is necessary to 

use Nessler tubes, as in ammonia estimations, instead of the glasses 

and apparatus described and depicted under Titanium (p. 70).

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 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.

Gravimetric 

per cent Cr20a.

Trace.

0.05

.14

.08

Trace.

None.

None.

' Colorimctric 

per cent Cr303 .

0.018

.051

.12

. 033

.013

.0086

.0067

The outcome was somewhat surprising, for it was hardly to be 

expected that the long and laborious quantitative separations should 

Bull. 176 6
82 SOME PRINCIPLES AND METHODS OF BOCK ANALYSIS. [BULL. 176.

have resulted so well as they are shown to have done. It should be ' 

mentioned that for the gravimetric tests but one or two 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.

XVIII. VANADIUM (CHROMIUM) AND MOLYBDENUM. 

DISTRIBUTION OF VANADIUM AND MOLYBDENUM.

The wide distribution of vanadium thoughout the earth's crust has 

in recent years been clearly established (see ante, p. 18), not only in ores 

and in coals, but in clays, limestones, sandstones, and igneous rocks. 1 

The writer has shown (loc. cit.) that vanadium occurs in quite appre- x 

ciable 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 up to 0.13 

per cent V8 03 in a biotite separated from a pyroxenic gneiss. Motybdenum, 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 estimate it introduces an 

error in the figures for both ferrous and ferric oxides, which in extreme cases met with may be of considerable moment. (See p. 58, and 

also pp. 95-96.)

DESCRIPTION OF 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 

(p. 80), the latter volumetrically, in the same solution. 2

Five grams of the rock are thoroughly fused over the blast with: 

20 of sodium carbonate and 3 of sodium nitrate. After extracting 

with water and reducing manganese with alcohol it is probably quite 

unnecessary, if the fusion has been thorough, to remelt the residue

1 W. F. Hillebrand, Distribution and quantitative occurrence of vanadium and molybdenum in rocks 

of the United States: Am. Jour. Sci., 4th series, Vol. VI, p. 209, 1898; Chemical News, Vol. LXXVIII, 

p. 216,1898; Bull. U. S. Geol. Survey No. 167, p. 49.

2\V. F. Hillebrand: Jour. Am. Chem. Soc., Vol. XX, p. 461,1898; Chemical News, Vol. LXXVIII, 

p. 295,1898; Bull. U. S. Geol. Surv., No. 167, p. 44. . '
HII.LEBRAND.] VANADIUM (cHKOMIUM) AND MOLYBDENUM. 83

as above, though for some magnetites and other ores containing larger 

amounts of. vanadium than the generality of rocks, this m&y be necessaiy, as Edo Claassen has shown. 1 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.

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 or more cubic centimeters capacity. The 

chromium is then estimated accurately in .a few minutes by comparing 

with a standard alkaline solution of potassium monochromate (p. 80). 

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

lAm. Chem. Jour., Vol. VIII, p. 437, 1880.
84 SOME PRINCIPLES AND METHODS OF ROOK ANALYSIS. [BULL. 176.

in a small pressure bottle. 1 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 vola: 

tilized. 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° C. with a 

very dilute solution of permanganate representing about 1 mg. of 

V2O5 per cubic centimeter as calculated from the iron strength of the 

permanganate, one molecule of V2 05 being indicated for each one of 

Fe2O3 . 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, 8 

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.

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 

two or three cubic centimeters 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 cubic centimeters, 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

iFrom a sulphuric solution the separation of platinum and molybdenum by hydrogen sulphide is 

much more rapid and satisfactory than from a hydrochloric solution.

2The direct use of a solution of sulphur dioxide or of an alkali sulphite is inadmissible unless these 

have been freshly prepared, since after a lapse of time they contain other oxidizable bodies than sulphurous acid or a sulphite. The sulphur dioxide is best obtained as wanted by heating a flask containing a solution of sulphur dioxide, or of a sulphite to which sulphuric acid has been added.

The expulsion of the last traces of sulphur dioxide is said to be more effectively accomplished by 

boiling with simultaneous passage of a rapid current of carbon dioxide for a few minutes at the last 

than by boiling alone. Because of the small amount of air carried with it, long passage of the gas is 

said to result in slight oxidation of the vanadium (Manasse, Ann. Chem, u. Pharm., Vol. CCXL, p. 

23,1887; Zeitschr. fiir anal. Chemie, Vol. XXXII, p. 225,1893).
HILLEBUAND.] VANADIUM (CHKOMIUM) AND MOLYBDENUM. ' 85

solution will show some coloration, and addition of an acid precipitates 

brown vanadium sulphide, which can be collected, ignited, and further 

tested if desired.

. APPLICATION OP 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 chromium 

itself takes place so rapidly that a very large excess of the reagent 

may be added before a pronounced end reaction is obtained. Nevertheless, quite satisfactory determinations of as little as one or two 

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.

Kidsdale 1 titrated the cold solution to avoid oxidation of chromium, 

and obtained accurate results, but in the writer's experience the end 

reaction is then uncertain.

i Jour. Chem. Soc., Vol. VII, p. 73,1888.
86 SOME PRINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL. 176.

The following tables contain the results of a considerable number 

of tests, those in Table II being tabulated separately in order to show 

the degree of accuracy attainable with a large excess of chromium by 

applying the correction above mentioned and also the amount of this

correction:

TABLE I.

Tests for vanadium in the presence of chromium.

No.

1

2

3

4

5

6

7

'8

9

10

11

12

13

14

15

Chromic 

oxide.

Milligrams.

1

1

1.5

2

3

3

3.5

6

6

6

10

10

10

25

87.5

Vanadium 

pentoxide.

Milligrams.

9.87

.94 .

5.25

5.62

4.68

5.62

18.74

5.6

4.68

5.62

5.62

23. 52

46.85

23.52

23.52

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

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.

Milligram,.

-0.15

+ .10

+ .04

+ .24

+ .19

- .12

- .12

+ .10

+ .10

+ .15

- .04

" - .04

+ .15

-1- .23

+ .50

+ .10

- .04

- .04

+ .29

+ -19

+ .13

+ .35

-f .13

+ .23

+ .19
VANADIUM (CHEOMIUM) AND MOLYBDENUM. 87

TABLE II.

Shouting application of correction for larger amounts of chromium, obtained by adding 

potassium permanganate to an equal bulk of solution containing a like amount of chromic sulphate.

No.

16

17

.18

19

20 

21

Chromic 

oxide.

Mttliynvnis.

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

Vanadium 

pentoxide 

found.

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.

50-100 cm. 3

50-100 urn. 8

50-100 cm. 3

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.

The method of T. Fischer1 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 meta-vanadate remaining quite unattacked, according to 

the author, 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

1 Inaugural Dissertation, Kostock, 1894.
88 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL.HO.

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.

CONDITION OF VANADIUM IN ROCKS.

The above and elsewhere mentioned connection 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 V203 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 the writer's opinion until recently, that it should then be 

regarded as in the pentavalent state (V2OB), but his work upon certain 

remarkable vanadiferous sandstones1 of western Colorado, in which it 

unquestionably occurs as trivalent vanadium (V2O3), has led to a 

decided unsettling of this view. It is but proper to recall that 

Czudnowicz, 2 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 (V2O3). 

Lindemann's 3 contrary conclusion with regard to certain iron ores, 

because the vanadium was extracted as V2 06 by sodium-carbonate 

fusion without niter, is not valid, since this would probably be the 

case even if it existed in the ore as V2O3 .

XIX. FERROUS IRON.

COMPARISON OF SEALED-TUBE AND HYDROFLUORIC-ACID METHODS 

COMPARATIVE WORTHLESSNESS OF THE FORMER IN ROCK ANALYSIS.

No point in rock analysis has been the cause of greater solicitude to 

the chemist, and especially to the mineralogist and petrographer, than 

the determination of iron in ferrous condition. The sealed-tube or 

Mitscherlich method .with sulphuric acid, for a long time the only 

available one, is in theory perfect, since complete exclusion of oxygen 

is easily attainable. Its chief hitherto recognized defect lies in the 

inability to always secure complete decomposition of the %iron-bearing 

minerals, and even to ascertain, oftentimes, whether or not the decom1 Hillebrand and Ransome: Am. Jour. Sci., 4th series, Vol. X, p. 120,1900.

2 Pogg. Ann., Vol. CXX, p. 20, 1863.

3 Dissertation, Jena. 1878, through Zeitsch. fiir anal. Chemie, Vol. XVIII, p. 99,1879.
HILI.EBBAND.] FERROUS IRON. 89

position has been complete. The addition of hydrofluoric acid to the 

sulphuric in the tube, in order to insure this breaking up, is to be 

regarded as of very doubtful utility in most' cases, since the glass may 

be so strongly attacked as to add an appreciable amount of iron to the 

solution, and the hydrofluoric acid may have exhausted itself in attacking the glass before the more refractory minerals succumb. Nevertheless, if decomposition can be effected by sulphuric acid alone the 

results obtained are sharp and concordant, and what has seemed 

especially remarkable, and up to almost the present moment without 

a satisfactory explanation, they are in rock analysis usually higher 

than when made by any of the modifications of the hydrofluoric-acid 

method now so extensively practiced. This difference is not very 

marked with rocks containing but 1 or 2 per cent of ferrous iron, but 

it increases with rising percentage to such an extent that where the 

sealed-tube method will show 12 per cent FeO the other may indicate 

no more than 10 per cent. This is a fact of which the writer has long 

been cognizant, but it does not seem to be known to chemists or petrographers at large, though Wiilfing 1 has 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.

In spite of several attempts to find a solution to the problem, none 

presented itself until very recently, when, as a result of observations 

made in this laboratory by Dr. H. N. Stokes in a pending investigation 

on the action of ferric salts on pyrite and other sulphides, the clue 

was given. Dr. Stokes found that ferric salts exercise a most marked 

oxidizing effect on pyrite and probably other sulphides. The reaction 

is not new (see J. H. L. Vogt in Zeitschr. fur prakt. Geol., 1899, pp. 

250-251), but 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, were entirely unexpected. 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.

However, experiment has shown (p. 95) that with the amounts of 

sulphides usually found in igneous rocks their effect upon 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 moVe and more apparent, because of the greater 

surface of pyrite exposed to the action of the ferric iron of the rock.

Under the conditions of the Mitscherlich method, on the other hand 

a temperature of 150 to 200° C., and even higher, high pressure, much 

longer time of action, and impossibility of escape of any hydrogen suli Ber. deutscb. chem. Gesell., Vol. XXXII, p. 2217, footnote, 1899.
90 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [uuLi..l7G.

phide 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. 

Now, rocks with hardly an exception, and many minerals, carry pyrite 

or pyrrhotite, or both, often in considerable amount, often in traces 

only. My own experience has been that sulphur can almost always 

be detected in 2 grams of rock powder.

Let us now see what the effect of these traces when fully oxidized 

amounts to. One atom of sulphur (32) requires for its complete conversion to trioxide the oxygen of three molecules of ferric oxide (480), 

which then becomes six molecules of ferrous oxide (432). In other 

words, 0.01 per cent of sulphur may cause the ferrous oxide to appear 

too high by 0.135 per cent, and 0.10 per cent of sulphur may bring 

about an error of 1.35 per cent in ferrous oxide. The case is still 

worse if the sulphur is set free as hydrogen sulphide from a soluble 

sulphide, for then the above percentages of sulphur produce errors of 

0.18 and 1.8 per cent, respectively, in the ferrous oxide determination.

The error caused by sulphides tends to become greater the more 

there is present of either or both sulphide and ferric salt. Now, the 

highly ferruginous rocks usually carry more ferric iron than the less 

ferruginous ones, and they are often relatively high in pyrite and 

pyrrhotite; hence the increasing discrepancy between the results by 

the two methods as the iron contents of the rocks rise is fully in accord 

with the above explanation. 1

Notwithstanding that the Mitscherlich method' has thus been discredited in its general applicability to rocks and minerals, it is still 

capable of affording valuable assistance with those which are totally 

free from sulphides. Hence the conditions under which success can 

best be achieved by it are set forth in the following paragraphs.

THE MODIFIED MITSCHERLICH.METHOD.

Strength of acid. The method in its original and usual application 

calls for a mixture of three parts of sulphuric acid and one of water 

by weight, or about three to two by volume, though a still stronger 

acid is sometimes used. In som'e 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 b,y diluting considerably 

beyond the above proportion. Hereby the separation of salts difficultly soluble in the stronger acid is avoided and the actual solvent 

effect on the minerals seems to be in no wise diminished.

1 For details of experiments showing the worthlessness of the Mitscherlich method for rocks and 

minerals which contain even a trace of free sulphur or sulphides, see Hillebrand and Stokes, in an 

as yet unpublished paper in Jour. Am. Chem. Soc., Vol. XXII, and Zeitschr. fiiranorg. Chem., Vol. 

XXV, 1900, entitled, Relative value of the Mitscherlich and hydrofluoric-acid methods for ferrous iron 

determinations.
HILLEBKAND.] FEEEOUS IEON. 91

Filling, sealing, andlwating of the fade. The very finely powdered 

mineral having been introduced into a tube of resistant .glass free from 

ferrous iron, the open end is drawn out, so as to leave a funnel for the 

introduction of the acid. A very little water is then introduced and 

carefully heated to boiling for a moment to expel all air from the 

powder. The diluted acid which has just been boiled down from a 

state of greater dilution in order to have it free from air is then 

poured in until the tube is about three-fourths filled. Carbon dioxide 

is then introduced from a generator which has been in active operation for some time, through a narrow glass tube drawn out of the 

same kind of glass as that of which the decomposing tube consists. 

In a few moments the air is expelled, and the small tube is then sealed 

into the large one over the blast lamp without interrupting the gas current until the very last instant, when to prolong it would perhaps cause 

a blowing out of the softened glass. The interruption of the current 

at the proper moment is easily effected by the pressure of the thumb 

and finger holding the small tube at the point where it enters the 

rubber tube leading from the gas generator. No breakage in the oven 

ever occurs as a consequence of thus fusing one tube into the other.

The heating is done in a bomb oven at any desired temperature up 

to, say, 200° C., 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* 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.

JReason for introducing gas and sealing as above directed. The 

usual practice in employing the above method has been to expel air 

before sealing by introducing a few crystals or lumps of an alkali carbonate or bicarbonate, the gas set free on their contact with the acid 

being supposed to effectively expel all air. That this is not accomplished the following series of comparative results long since published elsewhere 2 fully show. The material used was the oxide of 

uranium U3Og , requiring by theory 32.07 per cent of UO2 . Operating 

as just above described on from 0.3 to 0.5 gram, the results were

31.06, 31.07, 29.72, 29.33, 29.89, 30.69,

whereas after filling the tube with gas from a generator there was 

found

32.11, 31.90, 32.15, 32.12, 32.06, 32.17, 32.28,

the average error of the former series being 1.78 per cent. The percentage error would, of course, be reduced by increasing the weight

'UHmann, Zeitecbr. fiir angew. Chemie, 1893, p. 274; Zeit. fur anal. Chemic, Vol. XXXIII, p. 582, 

1894. 

2Bull. U. S. Geol. Survey, No. 78, p. 50; Chemical News, Vol. LXIV, p. 232,1891.
92 SOME PEINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL. 176.

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.

THE HYDROFLUORIC-ACID METHOD.

This method is the one which has been almost exclusively used since 

the earliest years of the Survey's existence.

The specially ground powder, in a capacious crucible, is placed, 

after stirring up with dilute sulphuric acid, on a small water bath of 

a single opening (fig. 13) and covered with a glass funnel, the stem of 

which has been cut off near the flare, resting in a depression of the 

specially made cover, into which water constantly drops from a tubulated bottle, thus securing a perfect water joint and serving to keep 

the bath full. Through a small metal pipe carbonic-acid gas flows into 

the bath above the surface of the water, and rising through orifices 

in the cover fills the funnel and crucible. 1 The lamp under the bath is 

lighted and hj^drofluoric 'acid is poured into the crucible through a 

platinum funnel, which is left in place to serve as an occasional stirrer, 

for which a rod or wire may be substituted. After boiling commences 

the rapid gas current can be safely interrupted, to be restored when 

the lamp is extinguished after one-half to one or more hours. A full 

stream of cold water is then caused to flow from the tubulated bottle 

into the bath, the overflow from the outlet tube being caught in a 

receiver. As soon as cool the contents of the crucible are emptied 

into a platinum dish containing cold water, and titrated till the first 

permanent color appears, which usually will last for only a few seconds. Duplicate determinations are to be advised whenever possible, 

since even with the utmost care the results will occasionally differ 

more than is allowable.

In absence of a suitable water bath an ordinary one can be used 

covered with a beaker, through a hole in the bottom of which a strong 

current of carbon dioxide is introduced, or the crucible may be set 

in a sand bath and covered in the same way with a broken beaker 

(Doelter).

The cause of the rapid disappearance of the first pink blush when 

titrating in hydrofluoric-sulphuric solution appears to be the ready 

oxidizability of manganous fluoride by permanganate. The latter 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 blush. The solution, however, takes on in 

ever-increasing intensity the red-brown color characteristic of mani J. P. Cooke, Am. Jour. Sci., 2d series, Vol. XLIV, p. 347,1867.
HILLEBRAND.] FERROUS IRON.

ganic salts. The decolorization due to this cause is hence much more 

pronounced in the case of rocks high in ferrous iron than of those low 

in this constituent, because of the greater amount of manganous salt

FIG. 13. Cookc's apparatus for the determination of ferrous iron.

resulting from reduction of a correspondingly larger amount of permanganate.

When pyrite is present the bleaching is in part due to its action on 

any permanganate added in excess of the requirements of the ferrous
94 SOME PRINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL.ITG.

oxide. But this action is not so immediate as to affect the ferrous 

oxide determination if the end point in the latter has been properly 

observed.

PRATT'S MODIFICATION OP THE HYDROFLUORIC-ACID METHOD.

J. H. Pratt 1 has shown that very satisfactory ferrous iron determinations can be secured by simple boiling of the rock powder with hydrofluoric and sulphuric acids in a large crucible fitted with a cover and 

platinum tube for introduction of carbon dioxide. His test experiments 

on ferrous sulphate show that there need be practically no oxidation, 

even if the heating lasts several hours. The directions given on page 

150 of his paper, with reference'to the treatment of very refractory 

minerals which are not fully decomposed by this treatment, must be 

understood as referring 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.

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 estimation of ferrous iron.

Sulphides. Pyrite, in the quantities usually met with in igneous 

rocks, is probably without serious effect on the ferrous-iron determination by any of the hydrofluoric-acid methods. This sulphide is very 

resistant toward attack in the absence of oxygen, as is shown by the 

fact that if present in any quantity it can be readily recognized in the 

residue after titration. In any case it is impossible to allow for an 

error introduced by its possible decomposition, and the result of titration must count as ferrous iron. In the case of soluble sulphides two 

sources of error are introduced that of reduction of ferric iron by 

hydrogen sulphide evolved, and that due to the ferrous iron which the 

sulphides themselves may contain, especially if pyrrhotite is present. 

The first of these is perhaps negligible, since most of the hydrogen sulphide would probably be expelled without reducing iron. The second 

is approximately measurable if it is known that pyrrhotite is the only 

soluble sulphide present, and its amount has been ascertained by determining the hydrogen sulphide set free on boiling with hydrochloric 

acid in a current of carbon dioxide. .In this case a correction is to be

1 Am. Jour. Sci., 3d series, Vol. XLVI1I, p. 149, 1894.
HILLEBRAND.] FERROUS IRON. 95

applied to the result of titration for total ferrous iron. (See also p. 106, 

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 recently made: Pare 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 in a pending investigation that the* oxidizing effect of ferric salts on pyrite and other sulphides is vastly greater than seems to have been suspected (see p. 89), 

the following tests were made in order to ascertain the probable error 

due to this action under the conditions prevailing in rock analysis: 

Successive portions of 1 gram each of a hornblende-schist, free from 

sulphur and carrying 10.09 per cent FeO as the mean of several determinations and 4.00 per cent Fe2 03 , were mixed in a large (50 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 pemanganate, the solution was filtered as above and in the clear filtrate the titration was 

carried to completion. The results were 10.02, 10.16, and 10.70. 

Inasmuch as the smallest of these three charges of pyrite was several 

times greater than what may be considered an unusually high amount 

for an igneous rock, it is very evident that for all practical purposes 

the influence of pyrite on the ferrous estimation 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 undoubtedly influenced 

by the degree of fineness of the pyrite powder.

Vcmadium. 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. Knowing the amount of vanadium 

a correction can be applied as follows: One molecule of V2 03 (150.8)
96 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS. [BULL. 176;

in oxidizing to V2O5 requires as much oxygen as four molecules of 

FeO (288) when oxidized to Fe2 03 . The proportion, 150.8 : 288 :: V2O3 

present : a?, 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 RMn04 to .13 V2 0S.

Leaving 2.25 per cent FeO corrected.

Found 5.00 per cent apparent total iron as Fe2 03 in the same rock.

Deduct .14 per cent Fe203 corresponding to .13 per cent V203 .

Leaving 4.86 per cent corrected total iron as Fe2 03 .

Deduct "2.50 per cent Fe20s equivalent to 2.25 per cent FeO.

Leaving 2.36 per cent Fe203 in the rock.

Failure to correct for the vanadium in both cases would have made 

the figures for FeO and Fe3O3 , respectively, 2.50 and 2.22 instead of 

2.25 and 2.36 as shown above.

Carbonaceous matter.-. As said before (p. 94), mattej of organic 

origin other than graphitic carbon renders the results of the ferrous 

iron determination altogether unreliable.

UNCERTAINTIES OF THE FEEEOUS IEON DETERMINATION.

From the foregoing it is apparent that, despite the utmost care in 

practical manipulation, the exact estimation of ferrous iron in rocks 

is one fraught with extraordinary difficulties and uncertainties. Only 

in absence of decomposable sulphides, and when the amount and condition of vanadium are known, can the result be regarded as above 

suspicion.

XX. ALKALIES. 

THE LAWRENCE SMITH METHOD.

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 method of J. Lawrence Smith, 1 

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.

Decomposition of the powder is effected by heating it with its own

'Am.Jour.Sci.,2d series, Vol. L,p.269,1871; Am! Chemist, Vol. I, 1871; Annalen Chem. und Pharm., 

.Vol. CLIX, p. 82,1871.'
HILLEBKAND.] ALKALIES. 97

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 contain usually from 0.0012 to 0.0016 gram of alkali chlorides, 

almost entirely the sodium salt, but the amount has been brought 

down to half the above by very long washing. This correction may 

be admitted at once to be a defect of the method, but it is one easily 

applied with safety.

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. 14) for one-half gram of rock powder and 4 

grams calcium carbonate is 8 cm. long, 1.8 cm. wide at the mouth, and 

1.5 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.

Treatment of the minei^al poivder. Perfectly satisfactory results are 

to be obtained with but a half 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 transferred to the long crucible, the rest 

of the carbonate being used for rinsing off mortar and pestle. The 

crucible is then capped and placed in a clay cylinder (fig. 14), or through 

Bull. 176 7

FIG. 14. The J. Lawrence Smith crucihlc for alkali determinations. For dimensions sec text..
98 SOME PRINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL. 176.

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 

applied, and continued for forty to fifty-minutes. The sintered cake 1 

detaches readily from the crucible as a rule; if not, it is softened up in 

a few minutes by hot water and digested in a dish until thoroughly 

disintegrated. It is first washed by decantation, and any lumps are 

broken up by a pestle, then thrown on the filter and well washed with 

hot water. The residue should dissolve completely in hydrochloric 

acid without showing the least trace of unattacked mineral, not even 

of quartz.

Separation of calcium and sulphuric acid. All but a trilling 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. 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, this 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.

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-platinic chloride carrying sodium 

sulphate. A faint reaction for sulphate can usualty be obtained, 

anyway, if the evaporations have been made on a water bath heated 

by gas.

Precipitation of potassium. To the solution of the chlorides in a 

small porcelain 2 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

'To avoid the formation of a melted cake with silicates very high in iron it is advisable to increase 

the proportion of calcium carbonate.

2 Preferred to platinum because of the possibility, under certain rare and ill-understood conditions, 

of the formation of an insoluble subchloride of platinum, probably by reaction between the platinum 

of the dish and that of the salt. (See also Bohn, Zeitschr. fur anal. Chemie, Vol. XXXVIII, p. 349,1899.)
HILLEBRAND.] ALKALIES. 99

with absolute alcohol 1 or with that of 80 per cent strength, filtered 

by decantatioh 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 water bath and afterwards heated to 135° C. in an air bath. 

The factor used for reduction of KaPtCl6 to 2 KC1 is 0.307 and of 

2KCltoK2O, 0.632.

LITHIUM.

After separation of the potassium platinic chloride, the alcoholic 

filtrate is evaporated and tested spectroscopically for lithium. This 

element is almost invariably present, but almost never in amount to 

warrant quantitative estimation. Should it be so, however, the very 

excellent Gooch method (summarized below) of separation by ainyl 

alchohol is to be followed, after removal of the platinum by hydrogen 

gas. 2 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 (ante, p. 98) the few tenths of a milligram of calcium chloride 

that escaped precipitation can now be found with the sodium.

GOOCH'S METHOD 8 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,

JPrecht (Zeitschr. fur anal. Chemie, Vol. XVIII, p. 513,1879) claims that this is to be preferred to 

80 per cent alcohol, especially if evaporation has been carried to dehydration of the sodium salt. 

Atterberg disputes this final statement and says that 80 per cent alcohol gives better results.

"When haste is not an object, this way of Bunsen's for removing platinum from the chlorides of 

the alkalies is by far the neatest and most satisfactory. The small flask containing the solution is 

placed in a water bath and attached to a hydrogen generator. After expelling all air the flask is 

closed, without breaking connection with the generator, and left to itself, except for occasional light 

shaking up, till reduction is accomplished. A more expeditious and very satisfactory reduction is 

effected by evaporating the solution to dryness with metallic mercury, then heating to expulsion of 

the excess of mercury and of its chloride (Sonstadt, Jour. Chem. Soc., LXVII, p. 984,1895), who thus 

reduces potassium-platinie chloride in order to weigh its platinum.

aProc. Am. Acad. Arts Sci., p. 177,1886; Bull. U. S. Geol. Survey No. 42, p. 73, 1887; Chemical News, 

Vol. LV, pp. 18, 29, 40, 56, 78, 1887; Am. Chem. Jour., Vol. IX, p. 33,1887.
100 SOME PBINCIPLES AND METHODS OF KOCK ANALYSIS. [BULL. 176.

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 

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.

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.

The mercuric oxide method. The old barium-hydroxide method is 

not to be recommended. The mercuric oxide method of Zimmermann, 

whereby the magnesia is precipitated from solution of the chlorides 

by moist, freshly precipitated, and alkali-free mercuric oxide, can give 

satisfactory results. The oxide is added in excess to the solution in a 

platinum crucible and evaporated to dryness. Then the mercuric 

chloride and most or all of the excess of oxide are expelled by cautious 

heating. On leaching with water the magnesia remains on the filter. 

With more than 1 per cent of magnesia the operation must be repeated 

(Dittrich).

The mnrnonium carbonate method. Lately the once favored method 

of precipitating the magnesium by neutral ammonium carbonate in 

concentrated solution has been again recommended. 1 The magnesium 

solution must be as strongly concentrated as possible, and a great 

excess of ammonium carbonate solution must be used. A voluminous

1 Wolfing: Bor. deutsch. ehem. Gesell., Vol. XXXII, p. 2214, 1899. The neutral carbonate is prepared by dissolving 230 grams of ammonium carbonate in 180 cubic centimeters of ammonia of 0.92 

specific gravity and enough water to make 1 liter.
HILLEBRANB.] ALKALIES, CAEBON DIOXIDE, CAEBON. 101

precipitate forms, which dissolves on vigorous stirring if enough of 

the precipitant was used. After a time a crystalline precipitate falls 

a doujble carbonate of magnesium and ammonium which is insoluble 

in a concentrated solution of ammonium carbonate. Allow to stand 

for six to twenty-four hours. Wash with the concentrated ammonium 

carbonate solution. It is probably no exercise of undue caution to 

redissolve and reprecipitate, to make sure of getting all alkali in the 

filtrate.

The amyl alcohol method. Under certain circumstances, notably 

absence of lithium, the method of Gooch developed by Riggs 1 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 

(p. 100) in the description of Gooch's method. Riggs's summary is as 

follows:

Evaporate the solution nearly or quite to dryness. Dissolve theoresidue in as little 

water as possible and add a few drops of hydrochloric acid. Then add 30-40 cubic 

centimeters 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 cubic centimeters, 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 grams 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 hydrychloricacid 

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 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.

XXI. CARBON DIOXIDE, CARBON.

For this estimation an apparatus (fig. 15) permanently set up is used, 

of which several forms have been described by different writers. The 

rock powder is boiled with dilute hydrochloric acid in a small Erlenmej^er 

flask, attached to an upward-inclined condenser, whence, after passing 

through a compact arrangement of drying tubes first, one of calcium 

chloride, then one of anlrydrous copper sulphate to retain hydrogen 

sulphide from decomposable sulphides and any hydrochloric acid that 

may pass over, and finally a second calcium chloride tube the carbon 

dioxide is retained by absorption tubes filled with soda-lime followed

i Am. Jour. Sci., 3d series, Vol. XLIV, p. 103, 1892.
102 SOME PEINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

by calcium chloride. Of course arrangement is made for a current of 

CO2 -f ree air with which to sweep out the apparatus before and after 

the experiment, and for a slow current during its continuance. t The

FIG. 15. Compact form of apparatus for estimation of carbon dioxide.

results are very accurate and the determination can be quickly carried out.

In the preliminary qualitative test for carbon dioxide, it must be 

remembered that while calcite gives off its carbon dioxide on treat 

ment with cold acid, dolomite and siderite do not, and hence warming
HFLLKBBAND.] CHLORINE, FLUORINE. 103

should not be omitted; otherwise, a few tenths per cent of carbon 

dioxide can very well be overlooked. Moreover, the powder should 

first be stirred up with a little hot water, to remove all entangled air 

which might otherwise be mistaken for carbon dioxide.

It has been already shown under Water (p. 45) how, in case of need, 

the determination of carbon dioxide can be combined with that of water 

by fusion with lead chromate or potassium chromate. This latter 

method must always be resorted to when the carbon of graphite or 

carbonaceous matter has to be estimated. If carbonates are present 

at the same time the result of the test includes the carbon from both 

sources, and a separate determination by the wet way of that of the 

carbonates is necessary.

XXII. CHLORINE.

To make sure of getting all the chlorine, it is best to fuse with 

chlorine-free sodium-potassium carbonate, or even sodium carbonate 

alone, iirst over the full burner, then for a moment or two over the 

blast, leach with water, acidify with nitric acid, and precipitate by 

silver nitrate without preliminary separation of silica. If 1 gram of 

material has been used no precipitation of silica need be feared on 

acidifying or on standing.

In many-cases it is quite sufficient to attack the powder by chlorinefree hydrofluoric acid and a little nitric acid, with occasional stirring, 

and after filtering through paper fitted into a large platinum cone or 

rubber funnel, to throw down the chlorine by silver nitrate. The 

presence of nitric acid is necessary, since otherwise ferrous fiuoride 

reduces silver nitrate with deposition of crystallized silver. When 

coagulated b}^ heating and stirring, the precipitate is collected on the 

filter, washed, dissolved by a little ammonia, and reprecipitated by 

nitric acid, when it can be collected in a Gooch crucible and weighed, 

or, if very small in quantity, on a small paper filter, which is then dried, 

wound up in a tared platinum wire, and carefully ignited. The increased weight of the wire is due to the metallic silver of the chloride 

which has alloyed with it.

XXIII. FLUORINE.

Fluorine can only be estimated by the method of Rose, care being 

taken to use sodium-potassium carbonate as a flux, and to avoid use 

of the blast if possible. For minerals rich in fluorine and low .in silica 

it may be necessary to add pure silica before "the fusion in order to 

effect complete decomposition of the fluoride just as with the alkalineearth phosphates. To the hot aqueous extract several grams of 

ammonium carbonate are added and more on cooling. After twelve
104 SOME PBINCIPLES AND METHODS OF EOCK ANALYSIS. [BOLL. 176.

hours the solution is filtered, ammonium carbonate is expelled, and an 

ammoniacal solution of zinc oxide added, whereupon evaporation is 

carried on till the odor of ammonia is entirely gone. After filtering, 

add nitric acid in insufficient quantity to fully neutralize.

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 evaporation (Rose). Jf the rocks are very basic 

it may happen that the amount of silica in the alkaline solution is so 

small that ammonium carbonate may be dispensed with and the ammoniacal zinc oxide solution added at once.

By whatever modification of the method the silica and alumina may 

have been separated, the alkali carbonate must be converted into 

nitrate and not chloride if phosphorus or chromium, or both, are 

present. " To remove the chromium and the last of the phosphorus, 

silver nitrate in excess is added to the solution containing still enough 

alkali carbonate to cause a copious precipitate of silver carbonate, which 

shall take up the acid set free and thus insure a neutral solution and 

consequent complete precipitation of phosphorus and chromium. 

After heating and filtering, the excess of silver is to be removed by 

sodium or potassium chloride, and sodium carbonate is to be added, in 

order to furnish by ^addition of calcium chloride in excess to the hot 

solution a sufficient admixture of calcium carbonate with the fluoride. 

At this stage there must be no ammoniacal salts in solution^ otherwise 

calcium fluoride may be held up.

The next operation is perhaps best conducted as recommended by 

Fenfield and Minor. 1 To the gently ignited precipitate ot carbonate 

and fluorideof calcium at most i-2 cm. 3 of acetic acid are added in the 

crucible, which is then placed for a time on the water bath and afterwards its contents are evaporated to dryness. They are then taken 

up; with hot water, the solution is decanted through a small filter, 

likewise the washings. The filter is burned in the same crucible, more 

acetic acid is added and the various operations are repeated until all 

calcium oxide and carbonate have been extracted. The above authors 

find that if a great excess of acetic acid is used at the start, the results 

are low. While their experiments related to the determination of 

fluorine in a mineral rich in that element topaz their precautions 

are probabty not needless with the small amounts of fluorine met with 

in rocks.

 The well-washed and gently ignited calcium fluoride finally obtained 

in the course of this method should be converted to sulphate as a check 

upon its.purity, and at the same time as a qualitative test to ascertain 

if it really is calcium fluoride by the characteristic odor of the gas 

given off. - Should fluorine be found, and the weight of sulphate not 

correspond to that of the fluoride, the former should be dissolved in

' 'Am.Jour. Sci.', 3d scries, Vol. XLVII, p. 389, 1894
HILLEBRAND.] FLUORINE, SULPHUR. .. 105

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, b}^ the formula:

CaSO, 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.

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 riot to be 

relied on in all cases. 'While as little as one-tenth of 1 per cent of 

fluorine can sometimes be thus detected with ease, much larger amounts 

in another class of rocks may fail to show.

XXIV. SULPHUR.

Before proceeding to the estimation of sulphur, its condition, if present, should be ascertained.

Evolution of hydrogen sulphide on boiling with hydrochloric acid is 

evidence of a soluble sulphide, usually pyrrhotite, but possibly lazurite. 

Extraction of magnetic particles reacting for sulphur shows pyrrhotite 

to have been in part at least the source of the hydrogen sulphide. A 

reaction for sulphuric acid in the filtered solution indicates a soluble 

sulphate, usually 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.

For the quantitative extraction of the sulphur of soluble sulphates, 

simple boiling with hydrochloric acid suffices, which should be done in 

an atmosphere of carbonic acid if pyrites or other oxidizable sulphides are present, and should be finished as quickly as possible in 

order to minimize the error resulting from oxidation to sulphuric acid 

of the sulphur of sulphides, if- present, by any ferric salts that may 

have been dissolved.
106 SOME PKINCIPLES AND METHODS OF BOOK ANALYSIS. [BOLL. 176.

The sulphur of sulphides may sometimes be correctly determined 

by extraction with aqua regia or some other powerful oxidizer, but 

not always; so that 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, fitting the crucible into a hole in 

asbestos board (Lunge) to prevent access of sulphur from the flame. 

After thorough disintegration of the fusion in water, to which a 

drop or two of alcohol has been added for the purpose of reducing 

manganese, the solution is filtered and the residue washed with a 

dilute solution of sodium carbonate. In the filtrate (100-250 cm. 3 in 

bulk) the sulphur is precipitated at boiling heat by barium chloride 

in excess after slightly acidifying b}^ 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 the water 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.

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 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.

This, of course, gives the total sulphur in the rock. If soluble sulphates and sulphides as well as insoluble sulphates and sulphides are 

present together, the sulphur of the first is found in solution after 

extraction by hydrochloric acid in a carbon-dioxide atmosphere, and 

that of the decomposable sulphides by collecting the hydrogen sulphide 

evolved. 1 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 Fe7 S8 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 pp. 94-95.)

1 With pyrrhotite a small fraction of its sulphur one-eighth if the formula Fe7Sg is adopted is 

liberated as free sulphur and not as hydrogen sulphide.
HILLEBIUND.] BOROTST, NITROGEN. 107

XXV. BORON.

To the best of the writer's belief, it has never been found necessary 

in this laboratory to estimate boron in a .silicate rock. Should the 

determination be required, since most silico-borates are insoluble minerals, it would probably be necessary to fuse with sodium carbonate, 

extract with water, faintly acidify with nitric or acetic acid, expel the 

boron by distillation with methyl alcohol, and collect the boric ether 

in a suitable manner. For simple borates, artificial or native, this 

method, 1 first devised by Rosenbladt and Gooch independently, gives 

entire satisfaction when all needful precautions are carefully observed, 

but its application to boro-silicates yet needs investigation, in view of 

the as yet unexplained very discordant results obtained some years 

ago by J. E. Whitfield in this laboratoiy on the mineral warwickite, a 

boro-titanate of magnesium and iron.

It is also quite possible that the accurate estimation of but a few 

milligrams or even less of boric oxide by the use of a large excess of 

lime as a retainer would not be feasible. Fluorine would have to be 

first removed by calcium nitrate or acetate before freeing the boron.

XXVI. NITROGEN.

Nitrogen has been found in igneous rocks or the minerals occurring 

in them by several observers. Thus, H. Rose 2 says that pitchstone 

gives off ammoniacal water on heating; Silvestri 3 mentions a nitride 

of iron in lavas from Etna; Sandberger finds ammonium carbonate to 

be given off from certain rocks of Pribram; the writer has shown 

nitrogen to exist in uraninite; Ramsay and others have noted it in 

traces with or without helium, etc., in numerous minerals; and later 

Erdmann 4 found it to be given off as ammonia on treating various 

minerals of "ancient igneous rocks" witlra caustic alkali. Luedeking 

also found ammonium sulphate in a barite from Missouri, the presence 

of which the writer 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

1 Rosenbladt (Zeitschr. fiir anal. Chemie, Vol. XXVJ, p. 21,1887) used magnesia for binding the boron, 

while Gooch (Proc. Am. Acad. Arts and Sci., p. 167,188C; Bull: U. S. Geol. Survey No. 42, p. C4; Chemical News, Vol. LV, p. 7, 1887) preferred lime, as more active and reliable. Gooch and Jones have 

later (Am. Journ. Sci., 4th series, Vol. VII, p. 34,1899; Chemical News, Vol. LXXIX, pp. 99, 111, 1899) 

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 

prccautions'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 Penfleld and Sperry (Am. Journ. Sci., 3d series, Vol. XXXIV, p. 222,1887); 

also Moissan (Comptes Rendues, Vol. CXVI, p. 1087,1893, and Bull. Soc. Chim., Vol. XII, p. 955,1894), 

who modifies the Gooch distilling apparatus in certain respects.

2 Quantitative Analyse, p. G73. Flnkener edition.

3Qazz. chim. ital., Vol. V, p. 303,1875.

«Ber. Deutsch. chem. Gesell., Vol. XXIX, p. 1710,1896.
108 SOME PRINCIPLES AND METHODS OF BOOK ANALYSIS. [BULL. 176.

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 readity 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. Speculation on this 

matter would be altogether premature, but attention is called to it in 

the hope .that other observers may be led to look for and investigate 

similar appearances. It should be borne in mind that the nitrogen 

present would not necessarily appear as ammonia or ammonium salts, 

since it might be given off in the elemental condition, as with the gases 

obtained from uraninite.

XXVII. 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.

DETECTION OF NEPIIEIJNE IN PKESENCE OF OLIVINE.

For confirmation of the microscopic diagnosis, Prof L. V. Pirsson l 

has indicated a means of detecting nepheline in presence of olivine, as in 

nepheline basalts, based on the very ready solubility of nepheline, as 

compared with olivine, Avhen boiled for but one minute with a sufficiency 

of veiy dilute nitric acid (1:40). Gelatinizatipn of the filtrate on evaporation is taken as evidence of the presence of nepheline. If olivine

' i Am. Jour. Sci., 4th series, Vol. II, p. 142,1896.
HILLEBBANJX] SPECIAL OPERATIONS. ' 109

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 gelatin izatioii 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.

ESTIMATION OF SOLUBLE SILICA. .

Very often in treatment by acids silica is separated in gelatinous or 

granular form mixed Avith the unattached 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.

Lunge & Millberg 1 have lately conclusively ishown 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 15 minutes with 5 per cent solution of sodium carbonate is the only way to 

secure exact separation of unignited precipitated silica from quartz, 

and then only when the finest flour has been removed by levigation. 

The authors say:

If, however, no more of such flour is present than is produced in the ordinary 

operations of powdering and sifting through cloth of the finest mesh, the error arising from the above mentioned treatment is so slight that it can generally be neglected; 

it reaches 0.1 to at the most 0.2 per cent of the total silica, by which amount the 

quartz will appear too low, the amorphous silica too high.

The above authors also show, however, that the solvent action of 

the caustic alkalies on quartz becomes very apparent only when the 

material has been reduced to such an utterly impalpable degree of 

fineness as is practically never reached in the preparation of samples 

for rock analysis. For this reason I have no hesitation in recommending the employment of a dilute solution of sodium hydroxide when

1 Zeitschr. fur angewandte Chemie, 1897, pp. 393, 425.
110 SOME PRINCIPLES AND METHODS OF BOCK ANALYSIS. [BULL. 176.

the silica separated by acid from one of several mineral constituents 

of a rock is to be estimated. Even when dilution is considerable, 

solution is almost immediate, and as soon as this is accomplished 

the point being known by the change in appearance of the residue 

the solution should be diluted with cold water and filtered at once. 

The difficulty met with in filtration may often be overcome by faintly 

acidifying, which has the added advantage of at once arresting any 

further action of the alkali. If the dilution is sufficient no separation 

of silica results from so doing. Veiy 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.

XXVIII. ESTIMATION OF MINUTE TRACES OF CERTAIN CONSTITUENTS.

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 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 purhty 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 the writer is as yet unacquainted with the report 

by Von Foullon "Ueberden Gang und die Ausfiihruug der chemischen Untersuchung," l following Sandberger's own paper in the general 

report "Untersuchungen der Nebengesteine der Pribramer Gauge." 2 

The present writer has published a few data as to gold, silver, lead, 

zinc, etc., 3 in Mr. S. F. Emnions's report on " The Geology and Mining 

Industry of Leadville;" and Mr. J. S. Curtis, 4 in his report on "The 

Silver-Lead Deposits of Eureka, Nevada," has given his method of 

assaying rocks for traces of gold and silver.

To Prof. F. W. Clarke and Dr. H. N. Stokes the writer's thanks are 

due for friendly suggestions in the preparation of the foregoing work.

'Jahrbuch der Bergnl^dcmie, Leoben u. Pribrum, 1887, p. 3C3.

£ From Sandberger's report it appears that the rocks were treated successively with water, acetic 

acid, boiling dilute hydrochloric acid for two days, and iinally hydrofluoric acid, the several extracts 

nnd final residue of fluorides (and pyrite) being separately examined for heavy metals. The products 

of distillation were also examined. A striking fact observed in all cases was the complete insolubility of the pyrite, even after the severe treatment mentioned. This speaks strongly iu 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 p. 95.)

3 Mon. U. S. Geol. Survey, Vol. XII, Appendix B, pp. 592-596, 1886.

*Mon. U. S. Geol. Survey, Vol. VII, pp. 120-138,1884.
INDEX.

Page. 

Alkalies, contamination of, by traces of

calcium ............................ 99

determination of...................... 96-101

Aluminum, direct method for determining ................................. 59-CO

ignition of precipitate of............... 50

indirect method for determining ...... 54-57

methods of determining............... 54-60

modes of precipitation of............... 55-56

Ammonia in rocks, occurrence of.......... 108

Analyses, ingredients sought in............ 20

limit of allowable error in.............. 24

mode of crushing or grinding rock for. 31-32 

mode of statement of................... 21-22

number of portions of powder needed

for.................................. 27

quantity of rock needed for............ 31,32

tables showing errors arising from incomplete ........................... 16,17

time needed for making ............... 22-23

unadvisability of qualitative........... 26

weight of ground sample needed for.. 32 

weights of portions of powder needed

for.................................. 27,28

Austin and Gooch, cited ................... 65,78

Bailey,G.H.,cited......................... 75,76

Barium, contamination of magnesium

phosphate by....................... 67

estimation of........................... 73-75

ignited silica free from................. 53

percentage of rock content of.......... 17-18

preliminary procedure when material

is scanty............................ 79

recovery from alumina precipitate of

possible amounts of ................ 56-57

separation of strontium, from........... 63-64

Basic acetate method of precipitating aluminum, iron, etc ................... 55-56

Baskerville, C., method of separating titanium from iron and aluminum devised by ............................ 73

method of separating zirconium devised

by .................................. 77

Baubigny, H., cited......................... 80

" Beuteln " in preparing rock sample, objections to ............................. 32

Blair, A. A., platinum-tipped crucible tongs

devised by.......................... 23

Bohu, C., cited..................... 98 (footnote)

Boric-oxide method for decomposing silicates, description of................ 49-50

possible objections to................... 50

Boron, estimation of........................ 107

rare occurrence of...................... 21

Pago. 

Broockmann, K., cited...................... 66

Browning, P. E., cited ...................... 63

Briihl and Friedhcim, cited ................ 61,80

Brush, G. J., method of water determination

devised by.......................... 38

Bunsen, R., cited................... 99 (footnote)

Calcium, contamination of, in weighed alkali chlorides ...................... 99

contamination of magnesium phosphate by............................ 67

determination of....................... 62-04

separation of strontium from.......... 63

Campbell and Hess, cited ................... 60

Carbon, determination of................ 101-103

Carbon dioxide, determination of........ 101-103

figure showing apparatus for estimation of.............................. 102

Carbonaceous matter, determination of ferrous iron as affected by............. 94,96

Carnot,A.,cited............................ 58

Cathrein, A., cited............... 59,71 (footnote)

Cerium, determination of .................. 77

rare occurrence of...................... 21

Chatard, T. M., cited........................ 79

description and figure of drying oven

devised by.......................... 36-37

Gooch gravimetric method of estimating titanium as modified by........ 71-72

method of water determination devised 

..by .................................. 45

Chlorine, determination of................. 103

Chromium, determination of............ 79-S2,83

preliminary procedure when material

is scanty............................ 79

tables showing results of tests for ...... 86,87

Claassen, E., cited.......................... 83

Clarke, F. W., acknowledgments to ........ 110

cited.................................... 17

Cloedt and Jannasch, ci ted................. 61,80

Cobalt, determination of................... 61-02

Coloriinetric apparatus for estimating titanium, descriptions and figures of... 70-71 

Colorirnetic method for determining chromium............................... 80-81

comparison of gravimetric method

with................................ 81-82

Columbium, rare occurrence of ............ 21

Cooke, J. P., cited........................... 92

figure of apparatus for determining

ferrous iron devised by............. 93

Copper, determination of................... 61-62

Crucible tongs, description and figure of... 23 

Crushing rock, mode of.................... 31

Curtis, J. S., cited .......................... 110

111
112 INDEX.

Pago. 

C/udriowicz, C., cited........................ 88

Davis, J. Thomas, method of separating zirconium devised by ................. 77

Dittrich, M., cited .......................... 100

Dpelter, C., modification in method devised . 

. by .................................. 92

Drying _oven for water determinations, description and figure of.............. 30-37

Drying temperatures in moisture determinations ............................. 33

Dumiingtoii, F. P., cited.................... 08

Eakins, L. G., pyciiometer method of ....... 30

Earths, rare, cautions regarding, in basic

acetate method ............ 57 (footnote)

estimation of.............:............. 77-78

Erdmann, H., cited ......................... 107

Evaporation, description and figure of radi-.

ator for............................. 23-24

Feldspars, error in calculations of .based on

incomplete analyses................ 17

Ferric iron, determination of............... 59

partial reduction of, by faulty ignition.. 38,50 

Ferrous iron, determination of............. 88-90

figure showing Cooke's apparatus for 

. determining........................ 93

uncertainties in estimation of.......... 90

Fischer, T., cited............................ 87

Fluorine, determination of............... 103-105

qualitative detection of ................ 105

Foullon, H. von, cited ...................... 110

Franz and Streit, cited...................... 7G

method of separating zirconium devised

by.................................. 70-77

Fresenius, R., cited.............. 02 (footnote), 63

Friedel, C., cited on water determinations.. 35 

Friedheim and Briihl, cited................ 01,80

Ceiith and Penfield, cited 011 precipitation of

aluminum, iron, etc., by ammonia.. 55 

Gibbs, Wolcott, cited........................ 65

Gilbert, J.P., cited on silica determination. 52-53 

Glucimim, rare occurrence of .............. 21

Gooch,F.A.,auiyl-akohol method of separating lithium devised by.......... 101

apparatus devised by................... 20

cited ....................... 60,107 (footnote)

gravimetric method of estimating titanium devised by.................... 71-73

method of estimating boron devised by. 107 

methods of separating lithium devised

by................................. 99-100

method of water determination devised

by.................................. 41-45

Gooch and Austin, cited.................... 65,78

Gooch and Jones, cited............ 107 (footnote)

Gravimetric method for determining chro-

, mium............................... SO

comparison of colorimetric method with 81-82 

Grinding rock, mode of..................... 31-32

Harper and Penfield, cited on washing of

precipitated alumina............... 55

Hayes, A. A., cited.......................... 18

Heidenreich and .Tannasch, boric-oxide 

method of decomposing silicates 

devised by.......................... 49-50

Hess and Campbell, cited................... 60

Hillebrand, W. F., cited..........19,63 (footnote),

68,75,80 (footnote),82,91 (footnote), 110

Page. 

Hillebrand and Ransome, cited.... 88 (footnote)

Hillebrand and Stokes, cited....... 90 (footnote)

Hydrofluoric acid, cautions concerning

quality of........................... 25

Hydrofluoric-acid method of determining

ferrous iron......................... 92L94

Hydrogen peroxide, impurities of.......... 25

Hydrogen sulphide, metals precipitable by. . 54 

Hygroscopic water, importance of determining ............................. 35-36

modes of determining.................. 32-3?:-

Iron, estimation of ......................... 57-59

ferrous, estimation of................... 88-90

 ignition of precipitate of............... 56

methods of determining................ 54-60

preliminary procedure when material

is scanty............................ 79

solution by sodium carbonate fusion of

traces of............................ 58-59

Jannasch, P., methods of water determination devised by..................... 45-47

modes of silica determination devised

by .................................. 48-50

Jannasch and Cloedt, cited ................ 61,80

Jannasch and Heidenreich, boric-oxide 

method of decomposing silicates 

devised by.......................... 49-50

Jannasch and Weber, boric-oxide method 

for decomposing silicates devised 

by ..............................'.... 50

use of oxygen blast in treatment of refractory silicates by the boric-oxide 

method................. I........... 49-50

Jones and Gooch, cited ............107 (footnote)

Knop,A.,cited ..................... 57 (footnote)

Koninck,L. L. de,cited . '................... 66

Koningh, L. de, colorimetric method of determining chromium, devised by.. 80 

Krauch, C., cited on tests for purity of

chemical reagents.................. 25

Linderaann, Otto, cited .................... 88

Lithium, determination of................ 99-100

Luedeking, C., cited ........................ 107

Lunge, G.,cited ............................ 106

Lunge and Millberg, cited.................. 109

Magnesium, collection and ignition of precipitated phosphate of.............. 66

1 contamination by barium of precipitated phosphate of ................. 67

contamination by calcium of precipitated phosphate of.................. 67

determination of....................... 64-67

separation of calcium, and strontium

from................................ 62

Manasse, O., cited.................. 84 (footnote)

Manganese, determination of.............. 60-61

Mar, F. W., cited ........................... 75

Mastbaum, Hugo, cited..................... 66

Metals precipitable by hydrogen sulphide. 54 

Microcosmic salt, cautions concerning quality of................................ 25

Millberg and Lunge, cited.................. 109

Mitchell and W.ells, cited .......... 57 (footnote)

Mitscherlich method for determining ferrous iron, defects of.......... 88-89,89-90

modification of......................... 90-92

Moissan, H., cited ................. 107 (footnote)
INDEX. 113

Moisture, modes of determining............ 32-37

Molybdenum, distribution of............... 18,82

determination of....................... 82-84

precipitation of, by hydrogen sulphide. .....'................. 8-1 (footnote)

qualitative test for..................... 84

Nepheline, detection of................... 108-109

Neubauer, Hugo, eited................... 04,05,06

Nickel, determination of................... C1-G2

.JJitrogen, estimation of.......'............ 107-108

.Oven for water determinatiori,'dcscriptkm

and figure of........................ 87

Penfleld, S. L., cited......................... 42

methods of water determination used

by .................................. 38-41

mode of determining specific gravity

recommended by.....'.............. .29

Peufleld and Genth, cited on precipitation of

aluminum, iron, etc., by ammonia. 55 

Pen field and Harper, cited on washing of

precipitated alumina............... 55

Peniield and Minor, cited.................. 104

Penfleld and Sperry, cited........ 107 (footnote)

Phosphoric and titanic oxides, combined

average of,inrocks of earth's crust. 17 

in alumina precipitate, peculiar occurrence of.................... 57 (footnote)

Phosphorus, determination of............. 78-79

Pirsson, L. V., jirrangementof analyses proposed by............................ 22

cited on detection of nepheline ....... 108

Platinum, presence of, infiltrates from silica 54 

removal of, from filtrates... 54, 57 (footnote) 

Platinum-crucibles, loss in weight of, on

blasting.................... 53 (footnote)

Potassium bisulphate, cautions concerning

mode of preparation of............. 25

Prutt, J. H., modification in method for determining ferrous iron devised by.. 94 

Precht, H., cited.................... 99 (footnote)

Pycnometer method of determining specific

gravity, description of.............. 29-80

Pyrite, determinations of ferrous iron as

affected by ......................... 94-95

Qualitative analyses, unadvisability of..... 26

Radiator for evaporation, description of... 23 

figure of................................ 24

Ramsay, William, cited..................... 107

Ransome and Hillebrand, cited.... 88 (footnote)

Reagents, quality of........................ 25-26

Ridsdale, C. H., cited ....................... 58,85

Riggs, R. B., development of Gooch amylalcohol method of separating alkalies from magnesium by............ 101

Rose, H., cited ................. 59 (footnote), 107

- method of estimating fluorine devised

by................................ 103-105

Rosenbladt, T., method of estimating

boron devised by................... 107

Saudb'erger, F., cited.................. 21,107,110

Schmocger, M., cited........................ 06

Silica, method of separating alumina, etc.,

from................................ 47-54

mode of drying and testing ............ 52-53

. modes of determining.................. 47-54

recovery from, alumina precipitate of

amounts of......................... 50-57

Bull. 176 8

Pago. 

Silica, separation of, in rocks containing

fluorine ............. 47,50 (footnote), 103

soluble, estimation of ......'.......... 109-110

Silicates, modes of decomposition of....... 48-49

Silvestri, .cited ......................... 107

Smith, J. Lawrence, figure showing cruci-' . 

ble for alkali determinations devised by............................ 97 . method of determining alk'alies devised 

by.................................... 90-99

Sodium carbonate, limit of impurity of.... 25,51

Sodium carbonate'method for decomposing

silicates, description of.'............ 50-52

Sonstadt, E.,cited.................. 99 (footnote)

Specific gravity, modes of determining ...'. 28-31 

Sperry and Penfleld, cited ........ 107 (footnote)

Stokes, H. N., acknowledgments to........ 110

cited................................. 76,89,'95-

Stokes and Hillebrand, cited....... 90 (footnote)

Streit and Franz, method of separating zirconium devised by ................. 70-77

Strontium, determination of................ 02-64

percentage of rock content of.......... 17-18

separation of barium from.............. 63-64

separation of calcium from............. 63

Sulphides, determinations of ferrous iron

as affected by....................... 94-95

methods of distinguishing ............. 105

nearly constant presence of, in rocks... 18-19 

Sulphur, determination of................ 105-106

Tantalum, rare occurrence of.............. 21

Thorium, determination of................. 77

rare occurrence of...................... 21

Titanic and phosphoric oxides, combined

average of, in rocks of earth's crust. 17 

in alumina precipitate, peculiar occurrence of.................... 57 (footnote)

Titanium, estimation of.................... 67-73

loss of, by evaporation with hydrofluoric

acid alone.................. 69 (footnote)

preliminary procedure when material

is scanty............................ 79

solubility in caustic alkal ies of oxide of. 60 

Tongs for handling crucibles, description

and figure of........................ 23

Ulbricht, 11.,cited .......................... 66

Ullmann, C., cited.................. 91 "(footnote)

Uranium, determination of................. 77

Vanadium, condition of.................... 88

determination of....................... 82-88

determinations of ferrous iron as affected by ........................ 94,95,96

distribution of.......................... 82

effect of, in estimation of total iron ..... 58

occurrence of........................... 18

precipitation of, with iron, etc ......... 58

preliminary procedure when material

is scanty............................ 79

qualitative tests for..................... 84-85

tables showing results of tests for ...... 86,87

Vogt.J.H.L.,cited ......................... 89

Washington, H. S.,arrangement of analyses

advocated by....................... 22

Water,methods of determining ............ 32-47

Water determination, drying oven for...... 37

dryiii'gtemperatures in................. 33

figures of Jannasch's glass tubes for.... 46
114 INDEX.

Page

Water determination, figures showing 

' Gooch tubulated platinum crucible 

for............................... 42,43,44

figure showing Penfield's fire-brick and

charcoal oven for. .................. 40

figures showing Penfield's tubes for.... 39,40

Weber and Januasch, boric-oxide method 

for decomposing silicates devised 

by .................................. 50

use of oxygen blast in treatment of refractory silicates by the boric-oxide 

method............................. 49-50

Page.

Weller, A., colorimetric estimation of titanium by method of................. 07-69

Wells and Mitchell, cited .......... 57 (footnote)

Whitfield.J.E.,cited ....................... 107

Wulfing,E. A.,-cited ............ 89,100 (footnote)

Ziuc, determination of...................... 60-61

Zimmermann, C., mercuric oxK'e method

of separating alkalies devised by .. 100 

Zirconium, disturbing effect of, in gravimetric estimation of titanium.......... 72-73

estimation of........................... 73-77

o