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Full text of "Manual of the chemical analysis of rocks"

MANUAL 



OF 



THE CHEMICAL ANALYSIS 
OF ROCKS. 



v* BY 

HENRY S. WASHINGTON, Pn.D. 



FIRST EDITION. 
FIRST THOUSAND. 




NEW YORK: 

JOHN WILEY & SONS. 

LONDON: CHAPMAN & HALL, LIMITED. 

1904. 



Copyright, 1904, 

BY 

H. S. WASHINGTON. 



Entered at Stationers' Hall. 



ROBERT DRTJMMOND, PRINTER, NEW YORK. 



PEEFACE. 



THE object of this book is to present to chemists, petrol- 
ogists, mining engineers and others who have not made a par- 
ticular study of quantitative analysis, a selection of methods for 
the chemical analysis of silicate rocks, and especially those of 
igneous origin. While the publication of such a work may seem 
superfluous in view of the existence of Hillebrand's treatise on 
this special topic, yet justification may be found in the fact that 
the latter is intended, not so much for one who is not very con- 
versant with the subject, as for the practised analyst, to whom 
it is an indispensable guide. 

A further reason for its appearance is that, apart from Hille- 
brand's book and a paper by Dittrich, there does not seem to 
exist any separate modern treatise on the chemical analysis of 
rocks. The space devoted to this branch of analysis in the text- 
books is usually very small, and the various methods are widely 
scattered and often inadequately described. This is especially 
true in regard to the minutiae of manipulation and precautions 
to be observed, and to the determination of elements which, 
though usually accounted rare, have of late years been shown 
to be very common rock constituents. This neglect is rather 
striking in view of the prominence given in the last decade or so 
to the chemical composition of igneous rocks. 

There is an increasing number of geologists, petrologists, 
chemists and others, who are desirous of making chemical anal- 
yses of rocks, but who have had little or no experience in the 



iv PREFACE. 

subject, except that gained in the ordinary course of quantita- 
tive analysis, in which the study of silicates is usually confined 
to the examination of a feldspar or some such simple mineral. 
It is for the benefit of this class of students that the present 
book is written.' The general plan adopted therefore is, not to 
attempt a complete treatise on rock analysis, but to present only 
certain methods which have proved simple and reliable in the 
experience of the chemists of the U. S. Geological Survey and 
of my own. The more important of these, and some of the prin- 
cipal operations, are described with great explicitness. Many 
small details of manipulation are gone into which are omitted by 
Hillebrand and the text-books as unnecessary, a knowledge of 
them being either presupposed or their demonstration left to 
the instructor. 

In this way it is hoped that it will be possible for an intel- 
ligent student, with some knowledge of chemistry and a little 
analytical training, to be able to complete a satisfactory analysis 
of an ordinary silicate rock, without personal instruction and 
after comparatively short practice. To the expert analyst, 
therefore, the book will contain much that is superfluous, but for 
this no apology is offered. What are superfluities to him will, 
it is hoped, be welcome to the novice. 

It is assumed that silicate igneous rocks will be the most fre- 
quent objects of investigation. At the same time, the methods 
described serve equally well for most silicate metamorphic and 
sedimentary rocks. Such rocks as saline deposits, coals and 
others containing organic matter, are not considered. The 
methods are not generally adapted to the analysis of ores which, 
with such constituents as sulphides, arsenides and other com- 
pounds of the heavy metals, often call for different and more 
complex means of separation than are here given. The same 
is true of many minerals, though the methods found in the 
following pages are those appropriate to the analysis of most 
silicates. The analysis of meteorites also demands the employ- 
ment of special methods, and in most cases these bodies are of 
such character that their examination should not be undertaken 



PREFACE. . V 

by the inexperienced, especially if only a limited supply of 
material is available. 

The methods selected are, hi general, those adopted by the 
chemists of the U. S. Geological Survey, and which hi their 
essentials I have employed in my own scientific work for a 
number of years. Some modifications have been made, chiefly 
in the direction of simplification and the elimination of certain 
refinements which do not seem called for when the object of the 
volume is considered. There is no attempt at the introduction 
of new methods or the description of alternative ones which, 
either on theoretical grounds or on account of practical difficul- 
ties, are deemed to be less well adapted to the needs of students 
than those which are here given. Theoretical discussion will be 
limited to what may seem necessary to make clear the principles 
of certain methods or the reasons for their selection. 

I have also endeavored to point out to the student the 
importance of chemical analyses for the study of rocks, and their 
possible bearing on some of the broad problems which form the 
objects of the science of petrology. In other words, it has been 
sought to emphasize the fact that petrographical classifications 
and the study of textures and of minerals in thin sections are not 
the sole aims of the science, but that, supplemented by a knowl- 
edge of the chemical composition of igneous rocks, they are only 
means to broader ends. I can only express the hope that this 
little book will aid in the progress of petrology, by leading to 
an increase in the knowledge of chemical analysis among petrol- 
ogists and rendering our data in the way of rock analyses of 
superior quality more numerous. 

The great obligations under which I am to Dr. Hillebrand's 
work are evident throughout and are most gratefully acknowl- 
edged. The text-books of Fresenius, Classen, Treadwell and 
Jannasch have also been consulted, and the book is indebted 
to them in many ways. It is also a pleasure to express my 
obligations to several friends for valuable advice and assist- 
ance, and especially to Prof. S. L. Penfield and Prof. L. V. 
Pirsson, to whom my first knowledge of, and training in, quan- 



vi PREFACE. 

titative analysis are due. A number of most useful hints in 
manipulation were learned from these two analysts, all of which 
could not be specifically mentioned hi their proper places, but 
which are acknowledged here. Acknowledgments are also 
due to the Trustees of the Carnegie Institution for permission 
to publish an analysis made under their auspices. The factors 
used hi calculations are those given by Cohn hi his recent 
translation of Fresenius' Quantitative Analysis. 

All temperatures are given in centigrade degrees. The 
metric system is used generally, except in dealing with such 
pieces of apparatus as are usually sold in this country on the 
basis of English measurements. 

HENRY S. WASHINGTON. 
LOCUST, N. J., May, 1904. 



CONTENTS. 



PART I. 
INTRODUCTION. 

PAGE 

1. IMPORTANCE OF CHEMICAL ANALYSES 1 

2. GENERAL CHARACTER OF ANALYSES 3 

3. MICROSCOPICAL EXAMINATION 6 

4. CONSTITUENTS TO BE DETERMINED 8 

5. THE OCCURRENCE OF VARIOUS ELEMENTS 18 

6. SUMMATION AND ALLOWABLE ERROR 21 

7. STATEMENT OF ANALYSES 26 

PART II. 
APPARATUS AND REAGENTS. 

1. APPARATUS. 31 

2. REAGENTS 35 

PART III. 
THE SAMPLE. 

1. SELECTION IN THE FIELD 41 

2. AMOUNT OF MATERIAL 46 

3. PREPARATION OF THE SAMPLE. , 48 

PART IV. 

METHODS. 

1. PRELIMINARY OBSERVATIONS 55 

2. GENERAL COURSE OF ANALYSIS 57 

3 CHIEF SOURCES OF ERROR 61 

vii 



viii CONTENTS. 

PAGE 

4. TIME NEEDED FOR ANALYSIS , 68 

5. HYGROSCOPIC WATER 73 

6. COMBINED WATER 74 

7. SILICA -. 79 

8. ALUMINA AND To PAL IRON OXIDES 97 

9. MANGANESE AND NICKEL OXIDES -. 113 

10. LIME AND STRONTIA 115 

11. MAGNESIA 119 

12. FERROUS OXIDE 122 

13. ALKALIES 129 

14. TITANIUM DIOXIDE 142 

15. PHOSPHORIC ANHYDRIDE 151 

16. TOTAL SULPHUR, ZIRCONIA, AND BARYTA 155 

17. SULPHURIC ANHYDRIDE 159 

18. CHLORINE 160 

19. FLUORINE 162 

20. CARBON DIOXIDE 163 

21. CHROMIUM AND VANADIUM 165 

22. COPPER 166 

APPENDIX. 

1. EXAMPLE OF ANALYSIS 167 

2. TABLE OF MOLECULAR WEIGHTS 173 

3. FACTORS FOR CALCULATION 173 

INDEX.. . 175 



REFEEENCES. 



A LIST of some works which have been consulted, and some 
of which are often cited, is here given. They will be referred 
to by the author's name and page. 

CLASSEN, A. Ausgewahlte Methoden der Analytischen Chemie. Braun- 
schweig, 1901, 1903. 

DITTRICH, M. Beitrage zur Gesteinsanalyse. Mitteilungen der Badischen 
Geologischen Landesanstalt, III, pp. 75-105. Heidelberg, 1894. 

FRESENIUS, R. Quantitative Chemical Analysis. Translation of the 
sixth German edition by A. I. Cohn. New York, 1904. 

HILLEBRAND, "W. F. Some Principles and Methods of Rock Analysis. 
Bulletin of the United States Geological Survey, No. 176. Washington, 
1900. 

JANNASCH, P. Praktischer Leitfaden der Gewichtsanalyse. Leipzig, 1897. 

OSTWALD, W. The Scientific Foundations of Analytical Chemistry. Trans- 
lation by G. M'Gowan. London, 1895. 

TREADWELL, F. P. Analytical Chemistry, Vol. II. Quantitative Analy- 
sis. Translation of the second German edition by W. T. Hall. New 
York, 1904. 



THE CHEMICAL ANALYSIS OF KOCKS. 



PART I. 

INTRODUCTION. 

1. IMPORTANCE OF CHEMICAL ANALYSES. 

FOR the greater part of a century, since their study began, 
igneous 'rocks were regarded almost solely as more or less for- 
tuitous mineral aggregates, these being usually assumed to 
be due to the fusion of previously existent rock bodies or to 
the mixture of several igneous magmas. With the introduc- 
tion of the microscope, a more intimate study of their field 
relations, and especially with the improved chemical methods 
and the greatly increased number of satisfactory chemical 
analyses of the last twenty years, a decided change has come 
about in the way of regarding them. 

Various observations and theories of the order of succession 
and of crystallization of minerals, differentiation of bodies of 
magma, consanguinity and petrographic provinces, have been 
made and advanced, all tending to throw light on the origin, 
genetic relationships and mode of formation of igneous rocks. 
Briefly put, the tendency of the modern study of igneous rocks 
is toward considering them as falling under Spencer's law of 
evolution; that is, in the general line of passage from an inde- 
finite, incoherent homogeneity to a definite, coherent hetero- 
geneity. In other words, the petrologist of the present day 
does not regard them as merely inert, solidified mineral aggre- 



2 INTRODUCTION. 

gates, whose characters are largely the result of chance con- 
ditions, but as bodies which bear in themselves evidences of 
the action of physico-chemical processes, and whose charac- 
ters are determined by evolutionary laws. It is the aim of 
petrology to interpret these pieces of evidence and to ascertain 
the laws which govern their origin and formation. It is need- 
less to say that this modern point of view renders igneous 
rocks objects of far greater scientific interest than they could 
have been under the older one. 

For the proper study and understanding of these theoreti- 
cal aspects of igneous rocks, the knowledge and application 
of some of the principles of physical chemistry are necessary, 
and it is obvious that for this a detailed knowledge of their 
chemical composition, as well as of their field relations, 
is essential. Conversely, it seems probable that the study of 
igneous rocks will be of service to the sister science of physical 
chemistry, since the petrologist is dealing in fact with solidified 
masses of solutions which have been formed and acted on 
by physico-chemical forces, under conditions of temperature, 
pressure and mass which it would be impossible to reproduce 
perfectly in the laboratory. 

To the petrographer, who deals especially with the descrip- 
tive and systematic portions of the science, the s chemical anal- 
ysis of igneous rocks is assuming each year an increasing im- 
portance for their classification. Whether this is based only 
on the inherent characters of the rock-mass itself, or whether 
it takes account of genetic relationships, the chemical com- 
position is becoming more and more an essential factor, and 
one which can no longer be relegated to the background, 
behind the superficially more prominent features of mode of 
occurrence, texture and qualitative mineral composition. 

While our knowledge of metamorphic rocks is, as yet, not 
so far advanced as that of the igneous ones, their chemical com- 
position plays, likewise, a most important part in their study 
and classification, and, to a certain extent, the same is true 
of the sedimentary rocks. 



GENERAL CHARACTER OF ANALYSES. . 3 

As regards the economic side of geology, the origin and 
formation of ores and useful mineral deposits, there is accu- 
mulating evidence of the importance of a knowledge of the 
chemical composition of igneous and metamorphic rocks. 
This refers, not only to their main features, but also to the 
occurrence in them of the less abundant elements, which by 
certain processes of segregation may become commercially 
available to us. 

It is therefore evident that we possess in chemical analysis 
a means of investigation complementing, and of value fully 
commensurate with, the study of rocks in the field or with the 
microscope. That this is generally recognized is shown by 
the increasing prominence given to chemical analyses in recent 
petrological and petrographical papers, as well as in publica- 
tions of an economic character. It is also shown by the in- 
creased attention given to this study by official organizations, 
and by the growing number of those who make, or who desire 
to make, their own analyses of rocks. 

2. GENERAL CHARACTER OF ANALYSES. 

For a fuller understanding of the general subject, it will 
be as well to discuss briefly the factors which make up the 
character of a rock analysis, and which determine its value.* 

The fulfilment of two conditions is essential to the value 
of a rock analysis: the specimen analyzed must be representa- 
tive of the rock-mass, and the analysis itself must truly repre- 
sent the composition of the specimen selected. The more 
closely both of these conditions are met, the greater will be 
the value of the analysis. 

The representative character of the specimen is determined 
by the character of the rock-mass, as influencing both its 
selection and the amount of material taken for analysis. These 
points will be discussed subsequently (p. 41). 

* This and the following section are a somewhat summarized statement 
of part of the discussion published in Prof. Paper U. S. Geological Survey, 
No. 14, pp. 16-43, 1903. 



4 INTRODUCTION. 

Assuming that the sample is representative of the rock- 
mass, the degree of correspondence between the figures yielded 
by the analysis and the real chemical composition of the rock 
is dependent on the two factors of accuracy and completeness. 

By accuracy is meant the degree of precision with which 
the constituents sought for are determined, quite apart from 
whether or not all of those present have been determined 
or separated from one another. The accuracy of an analysis 
is dependent upon the methods used and upon the ability of 
the analyst to execute the various processes successfully. The 
purity of the reagents and the adequacy of the apparatus are 
also factors. 

It must be borne in mind that no method is capable of 
yielding results of absolute accuracy, any more than it is 
possible to construct a mathematically exact geometrical figure. 
Certain sources of error are inherent in all, some of a general 
nature, and others of a character dependent upon the method 
in question. The analyst must rest content with reducing 
these to a minimum, by selecting methods which have been 
shown to be reliable. In this we cannot do better than follow 
the chemists of the U. S. Geological Suryey, whose experience 
is of the widest, and who have set up a standard of analytical 
methods and practice for rocks and minerals that is beyond 
all others. 

But the selection of proper methods is not the only desidera- 
tum. They must be carried out in a proper way, which will 
not lead to errors of a purely mechanical kind, and which 
may easily vitiate the results of the theoretically most accurate 
method. In this matter the analyst himself is the most impor- 
tant factor. He should have, not only sufficient knowledge 
of the facts of chemistry and of the principles of analysis to 
work understandmgly, but also the dexterity and manipulative 
skill to enable him to carry out the various processes success- 
fully, While it may be true of some analysts that, like poets, 
they are born, not made, yet granted intelligence and chemical 
knowledge and a fair amount of dexterity and application, 



GENERAL CHARACTER OF ANALYSIS. 5 

the necessary manipulative skill will come with practice, often 
in a surprisingly short time. 

The analyst should beware of falling into careless habits 
or of allowing the analysis to become merely routine work. 
Carelessness is as fatal to obtaining good results as poor 
methods or impure reagents. During the whole progress of an 
analysis attention should be paid to every point of theory or 
manipulation, the influence of the various conditions or con- 
stituents should be considered, and indeed the analysis should 
be carried out from beginning to end with intelligent interest. 
This will turn into a pleasure what would otherwise be a dull 
and monotonous succession of precipitations, filtrations, igni- 
tions and weighings, which, as has been justly said, is not 
chemical analysis. 

That conscientiousness, a strict regard for the truth, and a 
firm determination to accept no result of doubtful character, 
are essential to the analyst, goes without saying. 

As regards completeness, the ideal analysis should show the 
percentage amount of every constituent present, as well as the 
absence of those which might be expected but which do not exist 
in the rock. This is not always attainable, and for practical 
purposes the analysis should give figures for all constituents 
which are present in sufficient amount to make their deter- 
mination a matter of interest, or whose presence or absence 
may bear on the problem for which the analysis is made. 

The number of constituents which should be sought for 
and determined depends, of course, very largely on the character 
of the rock. Thus, in most granites, quartz-porphyries and 
rhyolites, which are of simple composition, comparatively few 
constituents need be determined to make the analysis satis- 
factory. On the other hand, in such rocks as nephelite-syenites, 
diorites, basalts, tephrites, etc., the number of constituents 
which should be determined is larger, and may possibly reach 
twenty or more. 

It is to be borne in mind that neglect to seek for some of 
the rarer constituents may lead to the overlooking of important 



6 INTRODUCTION. 

features, and that an analysis complete as to the subsidiary con- 
stituents may be of great value in the future, even if this de- 
gree of completeness is not necesssary for the end immediately 
in view. The aim of the analyst should be to turn out, as the 
petrologist should be willing to accept, only results of the high- 
est character, so that it follows, as a general thing, that every 
analysis should be as complete as it is possible to make it. 

The details of the constituents to be determined will be taken 
up later, but it may be stated here in a general way that all the 
main constituents must be determined in every analysis, as well 
as those minor ones which enter into the composition of minerals 
that are present in notable amount. If the general character of 
the petrographical province indicates the probable presence of 
certain of the rarer elements, these should also be looked for 
(cf. p. 18). 

3. MICROSCOPICAL EXAMINATION. 

The chemical analysis should always be preceded by a 
microscopical examination of the rock in thin section. There 
are several reasons for this. In the first place, by a comparison 
of several specimens in thin section one is able to judge, better 
than by a merely megascopic examination, whether the speci- 
men selected may be considered as really a representative one. 
It has happened in more than one instance that specimens 
selected for analysis without such microscopic study have been 
shown later to be abnormal forms and not typical of the rock- 
mass under investigation. 

The microscope also frequently gives important indications 
to the analyst as to the presence of rare constituents which 
should be determined, or the absence of others which may there- 
fore be neglected. He will thus often avoid neglecting con- 
stituents the determination of which may be of considerable im- 
portance, or, on the other hand, may save himself much labor 
and time in searching for substances which are not present, at 
least in determinable amount, which might otherwise be better 
spent. 



MICROSCOPICAL EXAMINATION. 1 

Thus, if microscopic zircons are present in a granite, the 
amount of zirconia should be determined to render the analysis 
satisfactorily complete, while if these are absent this substance 
can be neglected without serious diminution in the value of the 
analysis. The presence of anhedra of a colorless, iso tropic 
mineral, of low refractive index, will necessitate the deter- 
mination of Cl and S0 3 , as they may be of colorless sodalite or 
haiiyne, while if none are found under the microscope in a 
holocrystalline rock these constituents may usually be con- 
sidered as absent. 

Finally, the thin section will show much more definitely 
than the hand specimen whether the rock is fresh and unaltered 
enough to justify its analysis. 

It should also be noted that the percentage amount of cer- 
tain constituents may sometimes be determined by the micro- 
scope with almost as much accuracy as by chemical analysis, 
and often with greater ease and expedition. This will be true 
for those which are present only in very small amounts and 
which occur in minerals of definite composition. 

Thus, if zirconia is present only in zircon, or fluorine in 
fluorite, or sulphur in pyrite, the amount of these minerals in 
the rock can be readily estimated by RosiwaFs method,* and the 
percentage of Zr0 2 , F or S respectively may be easily calculated. 
Though this method also applies to phosphoric anhydride in 
apatite, yet this substance is of such importance as a minor 
constituent, and its determination chemically is so easy and 
expeditious, that its amount should always be ascertained in the 
regular analytical way. In any case, except possibly for fluo- 
rine existing only in fluorite, this microscopical method is less 
satisfactory than the chemical, and if it is adopted, a note to 
that effect should be made in the statement of the analysis. 

* Roshval, Verb. Wien. Geol. Reichs-Anst. , XXXII, p. 143, 1898. Cf. 
Cross, Iddings, Pirsson, and Washington, Quant. Class. Igneous Rocks, 
Chicago, 1903, p. 204. 



8 INTRODUCTION. 



4. CONSTITUENTS TO BE DETERMINED. 

Importance of Completeness. In the earlier days of petrog- 
raphy the petrographer was quite content if the analyst re- 
ported figures for only eight or nine constituents, and he did not 
insist on the separation of the two oxides of iron. One seldom 
meets with analyses of this period in which Ti0 2 or P 2 5 are 
mentioned, to say nothing of such substances as Zr0 2 , BaO^or F. 
In the absence of exact knowledge of the mineral composition of 
rocks the presence of such rare elements was not suspected. 
Nor did neglect of them in the course of the analysis cause such 
low summations as to give rise to suspicions that something had 
been overlooked. This was partly because these rarer elements 
almost invariably occur in very small amounts, partly because 
some of them, as Ti0 2 , P 2 5 , Zr0 2 , Cr 2 3 and SrO, are precipitated 
and weighed with other constituents, and partly because the 
analyst of those days was not as accurate in his methods as at 
present, and was content with a summation which would cause 
the rejection of the analysis by a modern chemist. 

After it became possible to study rocks in thin section, and 
when the use of heavy solutions made the separation of the com- 
ponent minerals easy, it was found that the number of chemical 
constituents commonly present in rocks was far larger than had 
been supposed, although the importance of determining them 
was not recognized for many years. With the improvement of 
old methods and the adoption of new ones, the determination 
of these minor constituents was greatly facilitated, and at the 
present day analyses in which figures are reported for twenty or 
more constituents are frequent, though, unfortunately, there is 
still a tendency among many chemists to rest content with the 
estimation of only the more notable ingredients. 

At first sight it may not seem worth while to pay attention 
to constituents which are present only in amounts up to a few 
tenths of a per cent. But there are very good reasons for not 
neglecting them. 



CONSTITUENTS TO BE DETERMINED. 9 

For one thing, the determination or not of some of them 
may affect, and in some cases seriously, the figures for other and 
more important constituents. This is due to the fact that 
several of them are precipitated and weighed together, and then 
all except one separately determined, the figures for the final 
one thus depending on those of the others. Thus, A1 2 3 , Fe 2 3 , 
Ti0 2 , Zr0 2 and P 2 5 are thrown down and weighed together, all 
except alumina separately determined, and the A1 2 3 ascer- 
tained from the difference. It is evident that if any of these 
other oxides are neglected the figure for alumina will be too 
high, and in some cases this will give rise to serious error. A 
similar case is that of CaO and SrO, though here the error 
involved will seldom be of great moment. 

Another, and equally important, reason is that evidence is 
accumulating, as analyses of a 'high degree of completeness be- 
come more common, that much light may be thrown upon 
problems of great interest by a knowledge of the presence of the 
rarer elements. The subject has been discussed by Hillebrand,* 
whose strong plea for completeness it will be well for the student 
to read. An illustration given by Hillebrand may be cited here. 
The analyses of the U. S. Geological Survey show that BaO and 
SrO are almost invariably present in the igneous rocks of the 
United States, and that the former is uniformly in greater 
quantity than the latter. Furthermore it is made clear that, 
while never present in large amount, they are both more 
abundant in the rocks of the Rocky Mountain region than in 
those to the east and west of this. As Hillebrand says: 
' ' Surely this concentration of certain chemical elements in cer- 
tain geographical zones has a significance which future geolo- 
gists will be able to interpret, if those of to-day are not." 

Another interesting result of the determination of the rarer 
elements is the discovery that certain of them are associated 
more especially with magmas of certain characters, but are 
seldom found in rocks derived from magmas of other chemical 

* W. F. Hillebrand, Jour. Am. Chem. Soc., XVI, p. 90, 1894; Chemical 
News, LXIX, p. 209, 1894; Bull. U. S. Geol. Surv., No. 176, p. 13, 1900. 



10 INTRODUCTION. 

types. Thus it has been shown that vanadium is apt to 
occur among the more basic rocks, while it is absent, or nearly 
so, in those which are high in silica; and conversely, that mo- 
lybdenum is' apparently confined to the more siliceous rocks but 
is absent from the basic ones. It is now well known that 
zirconium is especially abundant in rocks which are high in 
soda, and also that it is a frequent ingredient of granites and 
other rocks very high in silica. On the other hand, chromium 
and nickel are seldom met with in rocks not high in magnesia 
and low in silica. Gold and platinum are occasionally found as 
apparently primary constituents of igneous rocks, but the for- 
mer is found either in granite and rhyolite or in diabase, while 
the latter seems to be confined to the peridotites. 

This leads directly to the consideration of a final point in 
favor of the present contention. This is the light that may be 
thrown on the origin and formation of ores, and the possibility of 
such chemical study of the igneous and metamorphic rocks 
leading in the future to important economic advances in the 
indication of the presence of ore bodies. The researches of 
Sandberger and others * have shown that many of the heavy 
metals, such as antimony, arsenic, bismuth, cobalt, copper, 
lead, silver, tin, uranium, and zinc, are present in the pyroxenes, 
hornblendes, biotites and olivines of some igneous rocks, and 
can be readily detected if sufficiently large amounts are taken 
for investigation. Further consideration of this topic is un- 
called for here, but, from the point of view of the mining en- 
gineer and of geological surveys, it is clear that this is a weighty 
argument in favor of completeness in the making of chemical 
analyses of rocks. 

While it follows from the above that all rock analyses should 
be as complete as it is possible to make them, yet the practical 
considerations of time and labor may set limitations on this. 
Although by judicious management a number of the minor con- 

*F. Sandberger, Zeits. Deutsch. Geol. Ges., XXXII, p. 350, 1880; Zeits. 
Prakt. Geol., 1896; cf. J. H. L. Vogt, Zeits. Prakt. Geol., 1898, pp. 225 ff. 



CONSTITUENTS TO BE DETERMINED. 11 

stituents can be determined along with the main ones, and at 
the cost of very little extra time, it is true that a thoroughly 
complete analysis will take considerably longer than a simple 
one. The analyst must judge for himself how far he can profit- 
ably go in this way, but it should always be borne in mind that 
a few complete analyses will probably be of more value in the 
end than a larger number of incomplete ones. 

While it is probable that all or nearly all of the known ele- 
ments may occasionally be present in rocks, and can be de- 
tected if sufficiently large amounts are taken for analysis, in 
practice we must, for the purposes of this volume, confine our 
attention to those which may reasonably be looked for in igneous 
and metamorphic rocks, and which may be readily estimated in 
quantities of from one-half to two grams of material. Those 
which will be considered in this book are given in the following 
list, which is substantially that of Hillebrand: * 

Si0 2 , Ti0 2 , Zr0 2 , A1 2 3 , Fe 2 3 , Cr 2 3 , V 2 3 , FeO, MnO, NiO, 
CoO, CuO, MgO, CaO, SrO, BaO, K 2 0, Na 2 0, Li 2 0, H 2 0, C0 2 , 
P 2 5 , Cl, F, S0 3 , S. 

In addition, in certain cases such rare elements as thorium, 
cerium, didymium, yttrium, zinc, glucinum, boron, nitrogen and 
carbon (as graphite or organic matter) may be present in notable 
amounts, as shown by the occurrence of certain minerals con- 
taining them, but these instances are so rare, and their deter- 
mination involves such complicated methods, that they will not 
be considered here. 

In the great majority of rocks the constituents of the list just 
given are by no means of equal importance, and it is customary 
to divide them into "main" and "minor " constituents. 

Main Constituents. Speaking generally, the main constit- 
uents are Si0 2 , A1 2 3 , Fe 2 3 , FeO, MgO, CaO, Na 2 0, K 2 0, H 2 0. 

These nine (including both oxides of iron) are almost in- 
variably present in greater or less amount in all igneous and 
metamorphic silicate rocks, and must certainly be determined 

* Hillebrand, p. 20. 



12 INTRODUCTION. 

if the analysis is to conform to even the first requirement as to 
completeness. 

The only possible exceptions would be certain rare and 
little-known types, with which the average student is not likely 
to meet. Thus, in iron ores produced by differentiation of an 
igneous magma, or in dunites, the amount of alkalies may be s 
small as to be negligible for most purposes. Or, in the case of 
very highly quartzose dikes of igneous origin, such as have been 
described by Howitt in Australia, the determination of CaO and 
especially MgO may be omitted. But even in such cases it is far 
better to prove definitely that such constituents are absent or 
present, even if only in traces. In the light of physico-chemical 
investigations of extremely dilute solutions, such knowledge 
may be of great interest and importance in the future. 

Stress must be laid on the importance of the separate de- 
termination of both oxides of iron, which are only too often 
unseparated and reported in the analysis as either Fe 2 3 or FeO. 
Neglect of this point was especially common up to twenty years 
ago, and is the cause of the relative worthlessness of many of the 
older analyses.* It is clear that, as the two oxides play different 
roles in the composition of minerals, a knowledge of the relative 
amounts of each is absolutely necessary to a thorough under- 
standing of the rock magma, the calculation of the mode (actual 
mineral composition) of the rock, or for its classification along 
chemico-mineralogical lines. Although the error involved by 
their non-separation may be small in certain highly quartzose 
or feldspathic rocks, in which they do not amount collectively 
to more than one or two per cent, yet the conscientious 
analyst should make it a point to determine them separately 
in every case. 

While the amount of water is not vital to our knowledge of 
the rock magma, except in the case of the presence of minerals 
containing water of crystallization or hydroxyl, as analcite and 
muscovite, yet it is important as giving a measure of the fresh- 

*Cf. H. S. Washington, Prof. Paper U. S. Geol. Surv., No. 14, pp. 24 
and 43, 1903; Prof. Paper U. S. Geol. Surv., No. 28, p. 15, 1904. 



CONSTITUENTS TO BE DETERMINED. 13 

ness of the rock. It is also usually present in very notable 
amount, and should therefore be reported in every rock anal- 
ysis. There is all the more reason for this on account of the 
ease and celerity of the determination, and the fact that its 
neglect will seriously affect the summation of the analysis in 
nearly all cases. It is also evident that the determination is 
essential in the investigation of many metamorphic and sedi- 
mentary rocks, and in the study of rock weathering and altera- 
tion, where hydrous minerals, as chlorite, zeolites and limonite, 
are present. 

As will be seen later, it may exist as either " hygroscopic " or 
" combined " water, which are expelled from the rock powder at 
temperatures respectively below and above about 110. There 
is considerable difference of opinion as to the advisability of the 
separate determination of these, as well as to the reporting of the 
hygroscopic water in the analysis. The arguments for and against 
their separation have been discussed by Hillebrand,* and need 
not be repeated here. It may suffice to say that the author 
coincides with the opinion of Hillebrand in recommending their 
separate determination and inclusion in the statement of the 
analysis, and the use of air-dried material for analysis. 

Apart from the constituents discussed above, there are a 
number of others (usually minor ones), which may at times as- 
sume equal importance with, or even far surpass, some of them. 
While such cases are uncommon, yet their number is rapidly 
growing with increase in our knowledge of the less well-known 
rocks of the globe, and most of them are of special interest from 
the theoretical side. As examples there may be cited titaniferous 
ores produced by differentiation, as those of the Adirondacks,' 
the apatite-syenites of Finland, such sodalite and hauyne-rich 
rocks as tawite, taimyrite, and the Italian hauynophyres, the 
eudialyte-rich lujavrites of Kola and Greenland, or the apparently 
igneous pyritiferous ores of Norway. In these, certain con- 
stituents which are usually regarded as minor, Ti0 2 , P 2 5 , Cl, 
S0 3 , Zr0 2 and S, respectively, are of an importance almost or 
* Hillebrand, p. 32. 



14 INTRODUCTION. 

fully equal to that of any of the nine mentioned above, and it is 
self-evident that an analysis of such rocks which does not take 
them into account is fatally defective. 

Minor Constituents. Turning to the minor constituents, it 
will be found that they differ much in importance. Some of 
them are precipitated and weighed with certain main constitu- 
ents (as has been mentioned above), and their weight afterward 
subtracted from that of the mixed precipitate. Therefore, if 
they are neglected, the apparent amount of the main constitu- 
ent, which is determined by difference, will be too large. This 
is the case, for instance, with Ti0 2 , Zr0 2 , Cr 2 3 , V 2 3 and P 2 5 , 
which, if disregarded, will increase the quantity of alumina by 
their weights. The resultant error may not be very large, but, 
being an avoidable one, should not be committed by the careful 
analyst. 

This is especially true of Ti0 2 and P 2 5 , which are almost 
invariably present and often in quantities sufficiently large, if 
neglected, to cause serious error in the figures for A1 2 3 . These 
two should therefore be determined in every analysis, or its 
value may be seriously diminished, as the knowledge of the exact 
amount of alumina is a very important factor in certain chemico- 
mineralogical rock classifications, as well as in the calculation of 
the mineral composition. In regard to the other three, Zr0 2 , 
Cr 2 3 and V 2 3 , they are seldom present in amount greater than 
a few tenths of a per cent and usually less, so that neglect of them 
will seldom involve appreciable error in the figures for alumina. 
Zirconia is usually the most important of them, especially in 
rocks of a certain character, and it is always well to determine 
this, as may be done for the other two, if there seems to be suf- 
ficient warrant for it. 

Falling under the same category are SrO, Li 2 and MnO. 
The first of these is precipitated along with CaO and weighed 
with it, being afterward separated from it to arrive at the true 
amount of lime. Similarly Li 2 is weighed with Na 2 0, thus 
increasing its apparent amount. But both strontia and lithia 
are present in such minute quantities, especially the latter, that 



CONSTITUENTS TO BE DETERMINED. 15 

their non-determination will not affect the figures for lime and 
soda to any great extent. They are chiefly of interest from the 
theoretical side, and this applies more especially to strontia. 

The case of MnO is somewhat complex and debatable, and 
for its discussion we must anticipate the description of some 
features of its method of determination. Under ordinary cir- 
cumstances it is sometimes precipitated in part by ammonia 
water, so that, if only this reagent is used for the precipitation of 
alumina, iron oxides, etc., some of it will probably be thrown 
down and weighed with them, and will ultimately affect the 
weight of alumina. Part of that in the filtrate is precipitated 
with the CaO as oxalate, if the manganese has not been separated 
by ammonium sulphide, and the rest will fall with the MgO as 
phosphate. It is clear, therefore, that unless the manganous 
oxide is completely separated from the alumina, etc., and if it is 
not precipitated before determination of lime and magnesia, it 
will be distributed among these three constituents. No investi- 
gation has yet been made as to the relative distribution in the 
course of these precipitations. 

On the other hand, manganese is completely separated from 
alumina and iron by the basic acetate method, but in this the 
precipitation of A1 2 3 and Fe 2 3 is apt to be not quite complete, 
unless the conditions are very exactly controlled, which is some- 
what difficult for the inexperienced analyst. The small amounts 
of A1 2 3 and Fe 2 3 left in solution will then be likely to be pre- 
cipitated later with the MnO and weighed with it, thus giving 
rise to abnormally high figures for MnO and correspondingly 
low ones for the two sesquioxides. This error seems to be a 
fairly frequent one. 

In considering this matter account must be taken of the fact 
that the total amount of MnO is almost invariably very small, 
only exceptionally over 0.50 per cent, and usually much under 
0.20 per cent, these estimates being based on the most reliable 
analyses.* Bearing this in mind, as well as the fact that these 

* J. H. L. Vogt, Zeits. Prakt. Geol., 1898, p. 235; H. S. Washington, 
Prof. Paper U. S. Geol. Surv., No. 14, p. 27, 1903. 



16 INTRODUCTION. 

small amounts are distributed among three constituents in- 
volving only slight errors in each, and the liability of the basic 
acetate method in the hands of the inexpert to serious error in 
the figures for A1 2 3 and to a less extent for Fe 2 3 , the correct 
determination of which is of great importance, it seems to the 
author that the better plan for the novice is to neglect the MnO 
altogether, using ammonia for the precipitation of alumina, and 
avoiding the basic acetate method. The analysis then will be 
admittedly less complete than if MnO is determined by the basic 
acetate method, but the figures for the alumina and ferric oxide 
will be almost certainly more correct, and, on the whole, the 
analysis will probably be better than if the other plan is 
adopted. 

Another point in this connection, though of subsidiary im- 
portance, is that determination of MnO lengthens the time 
needed for completing the analysis by at least a day, and in 
view of the comparative unimportance of this constituent, it 
would seem to be preferable to save this time and to devote 
it to other analytical work of greater interest. 

However, as the general principle of making the analysis 
as complete as possible is a good one to follow, a description 
of the basic acetate method is given later, as a part of the regular 
analysis, though the student may omit it if it seems best, with- 
out serious detriment to the character of the work. 

The second category of minor constituents consists of those 
whose determination or not does not affect the figures for any 
of the main ones. This would include NiO, CoO, CuO, BaO, 
S, S0 3 , Cl, F and C0 2 . 

Of these, the first three occur in igneous rocks as a rule 
only in minute traces, and the first two are apt to be found in 
the most basic ones, especially peridotites. In such rocks 
they may well be determined. Indeed, the determination of 
nickel is advisable in all very particular analyses of intermediate 
to basic rocks, especially if economic problems are involved, 
though neglect of it will seldom if ever lead to serious error 
in dealing with terrestrial rocks. Copper cannot be considered 



CONSTITUENTS TO BE DETERMINED. 17 

an important constituent, but it can well be looked for in 
basic rocks, as it may be of theoretical interest. 

As has been mentioned above, barium is a constant con- 
stituent of the igneous rocks of the United States, and it is 
almost certain that it will be found to be widely distributed 
elsewhere when it is systematically looked for. In view of 
its theoretical interest and the comparative ease of its deter- 
mination by the method given beyond, it will always be ad- 
visable to look for it in the course of the analysis. 

Sulphur is very frequently present as the sulphides pyrite 
and pyrrhotite, and indeed much more often than was formerly 
believed. Its amount can be readily ascertained along with 
the BaO and should enter into the statement of every analysis, 
or its absence definitely shown. 

Sulphuric anhydride and chlorine are met with in igneous 
rocks with comparative frequency, and are always to be esti- 
mated if minerals of the sodalite group are present. It is 
always well to determine them in rocks liable to carry such 
minerals, even if not visible with the microscope. In other 
cases also it can scarcely be held to be a great loss of time to 
look for them, in view of their possible theoretical interest and 
the ease of their determination. 

Fluorine is seldom present in quantities over a few tenths 
of a per cent, and, as its determination is somewhat lengthy 
and laborious, it need not generally be looked for. However, 
this may be done if the rock contains fluorine-bearing minerals, 
but even here its determination is necessary only if rich in 
these or for very accurate work. 

Carbon dioxide is often present, but, as far as is now known 
with certainty, only when the rock is not strictly fresh, as a 
component of the secondary minerals, calcite, dolomite, siderite 
and cancrinite. If it is present it should always be determined, 
as it serves to a certain extent as a measure of the freshness 
of the rock, and as the result may have a bearing on the problem 
of its occurrence as a primary constituent. 



18 INTRODUCTION. 



5. THE OCCURRENCE OF VARIOUS ELEMENTS, 

The increased number of analyses of igneous rocks, espe- 
cially of unusual types, and the more frequent determination 
of the minor constituents, with the vast mass of data obtained 
by the use of the microscope, have shown that certain of the 
rarer elements are prone to occur in rocks of certain .chemical 
characters. While our knowledge along this line is far from 
complete, a few words may be devoted to this subject, as it 
will often be of use to the analyst to know which elements should 
be especially looked for and which may safely be neglected.* 
The various minerals which carry the several elements in ques- 
tion will also be mentioned as well as the amounts in which the 
elements usually occur. 

Titanium is almost invariably present; in small amount in 
the more quartzose and feldspathic rocks, and most abundantly 
in the more basic. It is an essential component of rutile, 
ilmenite, titanite and perofskite, and is also present in many 
pyroxenes, hornblendes, biotites and garnets. Its amount may 
vary from traces to five or more per cent. 

Zirconium is present in many rocks in small amount, but 
is most apt to occur in granites, rhyolites, syenites, and in 
nephelite-syenites, phonolites, tinguaites and tephrites, and 
is most abundant in those which are high in soda, such as the 
last four. It is rarely met with in the more basic rocks, espe- 
cially those rich in lime, magnesia and iron. Zirconium is- 
usually found as the silicate zircon, especially in granites and 
syenites, but is also an ingredient of the rare minerals eudialyte, 
lavenite and rosenbuschite. Zirconium is present usually in 
amounts up to .20 per cent of Zr0 2 , but may reach 2 per cent 
or more. 

* See also F. W. Clarke, Bull. U. S. Geol. Surv., No. 78, pp. 34-42, 1891; 
J. H. L. Vogt, Zeits. Prakt. Geol., 1898, pp. 225 ff.j F. W. Clarke, Bull. 
U. S. Geol. Surv., No. 168, pp. 13-16, 1900; J. F. Kemp, Ore Deposits of the 
United States, New York, 1900, p. 35. 



OCCURRENCE OF VARIOUS ELEMENTS. 19 

Chromium is almost wholly confined to the basic rocks, 
especially those which are high in magnesia and low in silica, 
and consequently contain abundant olivine, such as peridotite 
and dunite. It occurs as chromite and picotite (chrome-spinel), 
and in some augites, biotites and oli vines. It may occur up to 
one-half of one per cent of O 2 3 . 

Vanadium, according to the investigations of Hillebrand, 
' ' predominates in the less siliceous igneous rocks and is absent, 
or nearly so, in those high in silica. " It is an ingredient 
of pyroxenes, hornblendes and biotites, but not of olivine, 
and is also found as an ingredient of ilmenite in titaniferous 
iron ores. Its amount is very small, seldom over 0.05 per 
cent. 

Manganese is uniformly present in nearly all rocks, but its 
amount is small, generally in tenths of a per cent, only excep- 
tionally one per cent or more. The high figures commonly 
reported are probably, in most cases, due to analytical error. 
It occurs hi the ferromagnesian minerals. 

Nickel and cobalt, like chromium, are most abundant in 
olivine rocks, occurring as ingredients of this mineral, as well 
as in pyrite and pyrrhotite, and in hornblende and biotite to a 
small extent. The amount of nickel in terrestrial rocks is 
seldom more than 0.10 or 0.20 per cent, while that of cobalt 
is only exceptionally more than a trace. 

Barium and strontium are very commonly present in igneous 
rocks, the latter uniformly in less amount than the former. 
There is considerable evidence, some of which is as yet un- 
published, that barium is apt to be most abundant in rocks 
which are high in potash. Barium occurs in orthoclase (as 
the hyalophane molecule) and possibly also in labradorite and 
anorthite (as celsian), as well as in a few biotites and musco- 
vites. We can, at present, form no definite conclusion as to 
the character of the magmas most likely to carry strontium. 
The amount of BaO may reach one per cent, though usually 
much less, while that of SrO may run up to 0.30 per cent, but, 
as a rule, is little more than a trace. 



20 INTRODUCTION. 

Copper is occasionally found, but as a rule merely in traces, 
in igneous rocks. It is possible that in some cases the figures 
reported for it are due to contamination during the analysis 
from the copper utensils used. It is probably most frequent 
in the more basic rocks, though sufficient data are lacking for 
deciding this point. 

Lithium is an element of very wide-spread occurrence, but 
is seldom met with in rocks in more than spectroscopic traces. 
It may naturally be expected to be most abundant in highly 
alkalic rocks, and there is reason for the belief that it is espe- 
pecially prone to occur in sodic ones. Apart from its occurrence 
as an essential constituent of such minerals as lepidolite and 
spodumene, it is also found in the alkali feldspars, muscovite, 
beryl and other minerals. 

Phosphorus is almost invariably present in igneous and 
metamorphic rocks, like titanium, and like- this element it is 
most abundant in the more basic ones, especially in those which 
are high in lime and iron rather than in magnesia. It occurs 
almost solely in apatite, or very exceptionally as xenotime or 
monazite. While the quantity of P 2 5 usually runs from 0.10 
to 1.50 per cent, it may occasionally amount to much more. 

Sulphur, as sulphides, is far more abundant in the basic 
rocks of all kinds than in the acid ones, and forms an essential 
ingredient of pyrite and pyrrhotite. As sulphuric anhydride 
(S0 3 ) it occurs only in the minerals haiiyne, noselite, and lazu- 
rite, and usually in the more basic rocks, though some haiiyne 
rocks carrying quartz are known. These last three minerals 
are most apt to occur in rocks which are high in soda. Sulphur, 
as sulphides, is present usually in tenths of a per cent, as is 
also true of S0 3 , though in certain cases the amount may be 
much higher. 

Chlorine is present most abundantly in rocks which are 
high in soda, and especially when so low in silica that nephelite 
is present, though it is also found sometimes in nephelite-free 
rocks, and in a few cases in quartz-bearing ones. It is an 
essential component of sodalite, and is also present in scapolite 



SUMMATION. 21 

and in a few apatites. The amount of Cl is usually in tenths 
of a per cent ; but in rare cases it may be one per cent or more. 

Fluorine seems to have no special preference as to magma, 
though, on the whole, it is found more frequently in acid than in 
basic rocks. It is also, apparently, most apt to be met with as 
fluorite in rocks containing nephelite, as foyaites and tinguaites. 
It is an essential constituent of fluorite and most apatite, and 
as an integral part of the last mineral is almost universally 
present. It also occurs in biotites and other micas, in 
some hornblende and augite, as well as in tourmaline, topaz, 
chondrodite, etc. Its usual amount is very small, generally 
from traces to 0.10 per cent, only rarely getting above the 
latter figure. 

Of the other rare elements it may be of interest to the student 
to note the following. Glucinum, as a component of beryl, is 
most frequent in granites, pegmatites and quartzose gneisses. 
Tin is confined to the acid rocks, granite, quartz-porphyry and 
rhyolite, and its presence is due generally to pneumatolytic proc- 
esses. It occurs as cassiterite, and in traces in ilmenite, micas 
and feldspars. The rare earth metals occur in allanite, xeno- 
time, monazite, and other minerals of even greater rarity, and 
seem to be especially frequent in acid rocks and possibly those 
with much soda. Molybdenum, tungsten and uranium are 
almost exclusively confined to the very siliceous rocks. Zinc 
has been met with in granite, as well as in basic rocks, but no 
generalization in regard to it is possible as yet. Platinum is 
found almost exclusively in peridotites, but is occasionally met 
with in connection with gabbros. Boron, as a constituent of 
tourmaline, is most apt to occur in highly siliceous rocks. 

6. SUMMATION AND ALLOWABLE ERROR. 

In the ideally perfect analysis, of course, the summation will 
be exactly 100, but in practice, as is well known, this result is 
seldom attained, and if so must usually be regarded as due to the 
compensation of different slight errors of excess and deficiency. 
As has been already remarked, no analytical methods are wholly 



22 INTRODUCTION. 

free from sources of error, and the aim of the analyst must be to 
reduce these to as small dimensions as possible. 

As Hillebrand has stated,* l ' A complete silicate rock analysis 
which foots up less than 100 per cent is generally less satisfactory 
than one which shows a summation somewhat in excess of 100. 
This is due to several causes. Nearly all reagents, however 
carefully purified, still contain, or extract from the vessels used, 
traces of impurities, which are eventually weighed in part with 
the constituents of the rock. The dust entering an analysis 
from first to last is very considerable, washings of precipitates 
may be incomplete, and if large filters are used for small pre- 
cipitates the former may easily be insufficiently washed." 

On the other hand, deficiencies in the summation may be due 
to mechanical loss of substance through spilling of drops, etc., too 
much washing, which may result in the partial loss of slightly 
soluble precipitates, and finally to the non-determination of 
some of the constituents which are actually present. 

The limits of summation below or above 100 per cent which 
may be considered as allowable and consistent with satisfactory 
analysis are stated by Hillebrand as 99.75 and 100.50, but for 
the usual run of analytical work they may fairly be extended to 
99.50 and 100.75. If the analyst attains summations within 
these limits he may consider his results as satisfactory, pro- 
vided that there is no reason to suspect the possibility of errors 
having been made which compensate each other. If the anal- 
ysis foots up considerably under the lower limit, especially in 
several analyses of a series of similar rocks, the probability of 
some constituent having been overlooked becomes strong. If 
this is not the case, and also if the summation is much above 
100.75, the analysis should be repeated in whole or in part, to 
discover the cause of error. As Hillebrand remarks, ' ' It is not 
proper to assume that the excess (or deficiency) is distributed 
over all determined constituents. It is quite as likely, in fact 
more than likely, to affect a single determination and one which 

* Hillebrand, p. 24. 



ALLOWABLE ERROR. 23 

may be of 'mportance in a critical study o the rock from the 
petrographic side. 7 ' 

There are several special causes of high or low summations 
which are due to the determination of various constituents, and 
which therefore do not indicate inferiority in the analysis as a 
whole. If water be determined by loss on ignition the sum will 
usually be lower than it would be were the water determined 
directly. This is owing to the partial oxidation of the ferrous 
oxide in the rock, and a consequent apparent amount of water 
less than that which really is present. 

If the iron oxides are not separately determined, but are 
given as ferric oxide, the sum will be too high by one-ninth of 
the amount of ferrous oxide present, and conversely, if they are 
given as ferrous oxide alone, the sum will be too low by one- 
tenth of the ferric oxide present. This cause is, of course, elim- 
inated when both are determined. 

If the analysis shows the presence of Cl, F or S, an amount of 
oxygen equivalent to these must be deducted, or the sum of 
the analysis will be too high by that amount. The oxygen 
equivalent of chlorine is 0.22 Cl, of fluorine 0.42 F, and of sulphur 
0.43 S, if it exists only in pyrrhotite. As regards the sulphur of 
pyrite, while Hillebrand * has shown that it is attacked by sul- 
phuric and hydrofluoric acids only to a scarcely appreciable ex- 
tent in the course of the determination of ferrous oxide by the 
methods given later, yet the iron with which it is combined will 
be given in the statement of the analysis as ferric oxide. Con- 
sequently the oxygen equivalent of sulphur in pyrite is 0.375 S, 
instead of 0.25 S, as it would be were its iron content determined 
as ferrous oxide. 

To give an example of the application of these corrections, if 
the sum of an analysis is 100.28 and there is 0.54 Cl present, we 
must deduct 0.54x0.22 = 0.12 from 100.28, leaving 100.16 as 
the correct summation. 

In the earlier days of analysis chemists and petrographers 

* Hillebrand, p. 95. 



24 INTRODUCTION. 

alike were content with summations which fell below 99, or were 
above 101, and it is to be regretted that the same complacency 
has not become quite extinct at the present time. But the 
conscientious analyst should look upon such figures with the 
gravest suspicion, and reject all analyses which furnish such 
manifestly erroneous results, as they are very strong evidence 
that the analysis is faulty either in part or throughout. 

In attempting to allot the allowable limit of error for each 
constituent, regard must be had to its amount in any given case , 
Assuming that the allowable total error is 0.60, which is not 
quite correct, but near enough for the present purpose, we might 
allot this proportionately among the chief constituents some- 
what as follows. Taking, for example, the average igneous 
rock as calculated by Clarke * we would obtain these figures: 
Si0 2 0.35, A1 2 3 0.10, Fe 2 3 0.02, FeO, MgO, CaO and 
Na 2 0.03, K 2 0.02, H 2 and Ti0 2 0.01. These are 
based on the assumptions that the errors would be all in one 
direction and proportional to the amount of each constituent, 
As, however, we cannot always expect such close agreement in 
duplicate determinations of the less abundant constituents, and 
as the various errors are almost certain to compensate for each 
other to some extent, we may provisionally assume the figures 
be'ow as allowable limits of error in cases of constituents present 
in about the following amounts. The limits here given are per- 
centages of the whole rock, not of the amount of each constitu- 
ent. For Si0 2 and others which amount to 30 per cent or over, 
from 0.20 to 0.30; for A1 2 3 and others which amount to from 
10 to 30 per cent, 0.10 to 0.20; for constituents which amount 
to from 1 to 10 per cent, 0.05 to 0.10. t 

* F. W. Clarke, Bull. U. S. Geol. Surv., No. 168, p. 14, 1900. 

f An experimental examination of the amount of allowable error has 
been made by M. Dittrich (Neues Jahrbuch, 1903, II, p. 69), by the analysis 
of known mixtures of the different rock constituents. He comes to the 
conclusion that the errors for each are in general in one or the other direc- 
tion, and establishes limits of magnitude similar to those giver here. As, 
however, all the methods employed by him are not those recommended 
in this book, his figures are not appropriate for an analysis according to 
these last. 



ALLOWABLE ERROR. 25 

These figures are rough, and based on experience in analy- 
sis rather than on mathematical calculations. They merely 
indicate that duplicate determinations should not differ from 
each other by more than about these amounts, although the 
difference may sometimes be considerably greater than these 
without reflecting seriously on the character of the analysis. 
At the same time the student should not consider that the 
latitude thus granted by such allowable limits of error justifies 
him in taking advantage of them as an excuse for poor work. 
He should, on the contrary, use every endeavor to make his 
analyses so that the differences between duplicate determi- 
nations, if they are made, fall well within the limits thus 
' allowed. 

Indeed, it should be made an invariable rule by the novice 
to make duplicate analyses throughout, until he becomes 
familiar with the methods and manipulations, and by repeated 
close agreements may place justifiable confidence in single 
determinations. This will at first involve more labor and the 
turning out of fewer analyses in a given time, but the increased 
value of the results will more than compensate for this in the 
end. An analysis in which the analyst himself cannot place 
implicit confidence is not only of little use but positively dan- 
gerous for others, for whom there may be no evident reason 
for doubting the results, and such work will eventually reflect 
injuriously on its author. 

In regard to duplicate analyses, however, it must be 
remembered that close correspondence in two separate deter- 
minations is not, in itself, conclusive proof of correctness. 
Practically identical results may be obtained several times on 
repetition of poor as well as good methods, and if the same 
errors are made in duplicate analyses the figures in each may 
agree closely and yet be far from the truth. At the same time, 
the chances are decidedly against obtaining duplicate results 
so closely concordant as to be satisfactory, in the case of poor 
methods, and especially if errors of manipulation have been 
committed, so that duplicate figures which agree well with 



26 INTRODUCTION. 

each other justify, on the whole, a high degree of confidence 
in their correctness. 

7. STATEMENT OF ANALYSES. 

The results of the analysis might be stated either in terms 
of the elements present or of the metallic oxides and acid an- 
hydrides. While the former may be the more logical on purely 
theoretical grounds, yet the latter greatly facilitates calcula- 
tions based on the analytical data, and being universally in 
use, renders comparison of all rock analyses with each other 
very simple. It should therefore be adopted without question. 

The order in which the constituents are tabulated varies 
somewhat widely. In some cases the order is roughly that 
in which the constituents are determined in the course of 
the analysis. Elsewhere one finds the acid radicals placed 
first, followed by the basic oxides. Or Si0 2 is followed imme- 
diately by A1 2 3 , or sometimes by Ti0 2 , and then the more 
important basic oxides, generally including MnO, with the 
less abundant constituents following these. 

There is unanimity only in heading the list with Si0 2 . 
In regard to all the other substances reported there is very 
considerable diversity in the details of succession. Thus CaO 
sometimes precedes and sometimes follows MgO, and the same 
is true of Na 2 and K 2 0. This lack of uniformity is to be 
deplored, as it is not only extremely apt to lead to error in 
copying analyses the order of which is unfamiliar, but renders 
the comparison of two or more tabulated according to different 
systems needlessly difficult. 

A few years ago it was proposed * that petrographers and 
chemists follow a definite and uniform plan in the statement 
of the analyses of rocks, and the order then suggested with the 
reasons for its adoption are briefly given here. It may only 
be added that no cogent reason has been brought forward for 
any important modification, and that it has been adopted in 
its essentials by the chemists of the U. S. Geological Survey. 

* H. S. Washington, Am. J. Sci., X, p. 59, 1900. 



STATEMENT OF ANALYSES 27 

The general foundation for the order proposed is that analyses 
of rocks are intended primarily for the benefit of petrographers 
and petrologists, so that an arrangement along analytical or 
strictly chemical lines is neither advantageous nor appropriate. 
To them the eight oxides, Si0 2 , A1 2 3 , Fe 2 3 , FeO, MgO, CaO, 
Na 2 and K 2 0, which are present in the vast majority of 
cases in preponderating amount, are, and must always re- 
main, of prime importance. H 2 and C0 2 , which are also 
often present to a very notable extent, are of value as measures 
of the freshness of the rock. The other constituents, while of 
varying interest, are usually present in small or minute quan- 
tities, and influence the character of the rock only to a limited 
extent. The order suggested, with a few slight modifications, is: 

Si0 2 , A1 2 3 , Fe 2 3 , FeO, MgO, CaO, Na 2 0, K 2 0, H 2 0+ (igni- 
tion), H 2 0-(110), C0 2 , Ti0 2 , Zr0 2 , P 2 0,, S0 3 , C1,F, S (FeS 2 ), 
Cr 2 3 , V 2 3 , MnO, NiO, CoO, CuO, (ZnO), BaO, SrO, Li 2 0, C 
or Organic Matter. 

By putting the eight main oxides together and at the head, 
the general character of the rock is seen at a glance. Further- 
more, whether an analysis is complete or incomplete, these oxides 
are always in the same relative position, and, as they are deter- 
mined in every case, the eye finds them without trouble, thus 
immensely facilitating comparison and study. 

As regards the main portion, we start out with the chief 
acid radical and the constituent which is present in largest 
amount, and pass through successively lower orders of oxides 
to the most positive bases, the alkalies. At the same time 
they are presented in a way which brings the oxides together 
in their natural petrographic and mineralogic relations. Alumina, 
which often plays apparently an acidic role and which is usually 
the most abundant constituent next to silica, follows immediately 
after this, and is succeeded by the other main sesquioxide, 
ferric oxide. Ferrous oxide follows ferric, and magnesia is 
next to it, as the two go hand in hand in the ferromagnesian 
minerals. Lime comes next in an intermediate position be- 
tween these and the alkalies, as is proper, because it is a con- 



28 INTRODUCTION. 

stituent both of the ferromagnesian minerals and of the feld- 
spars. Soda precedes potash, as it is associated with lime in 
the plagioclases. 

Water follows immediately after the main oxides, since 
it is a highly important and generally determined constituent. 
Combined water precedes hygroscopic, being the more im- 
portant and usually present in greater amount than the latter. 
Carbon dioxide comes next, as it, with water, is a measure of 
the freshness of the rock, and this character can therefore 
be told at a glance. They also constitute together the ''loss 
on ignition " so frequently given, and may then be connected 
by a bracket in comparative statements. 

Of the minor constituents the acid radicals come first, 
following the main principle of the other division. Titanium 
and zirconium dioxides are placed at the head, as they are 
chemically similar to silica, and often replace it. Phosphoric 
anhydride comes next as being usually, next to Ti0 2 , the most 
important and most abundant of the minor constituents. Sul- 
phuric anhydride and chlorine are together, since both are 
constituents of the sodalite group of minerals. Fluorine, also a 
halogen, follows after chlorine. Sulphur completes the list 
of minor acid radicals, being less acidic than most of these, and 
being also frequently present as an apparently secondary con- 
stituent, and hence analogous to water and carbon dioxide 
among the main ones. 

The subordinate metallic oxides follow in the order R 2 3 , 
HO and R 2 0. Chromium sesquioxide precedes vanadium as 
the more important. The latter might be placed among the 
.minor acid radicals, but the position chosen seems the best. 
Manganous oxide precedes the oxides of nickel and cobalt, 
.as it is very frequently determined, and is usually present in 
greater amount. The monoxides of the other heavy metals 
when present come next, those just mentioned preceding on 
account of their greater importance and their chemical affinity 
with ferrous oxide. Of the oxides of the minor alkali-earth 
metals, which are next in order, baryta precedes strontia as 



STATEMENT OF ANALYSES. 29 

the more abundant and important. Lithia follows as the only 
representative of the alkali metals, and if carbon (graphite) 
or organic matter is present . t may appropriately close the list. 

In stating the analysis it may be recommended that the 
molecular ratios of each of the constituents, obtained by divid- 
ing the percentage amount by the molecular weight, be given 
along with the regular statement. The user of the analysis 
will thus be saved the trouble of calculating them for himself, 
and the chemical character of the rock will be more fully and 
immediately comprehended. A list of the molecular weights 
of the various chemical constituents will be found on another 
page (p. 173). 

In the statement of analyses the term "trace" is in fre- 
quent use, to indicate that a constituent is present, or supposed 
to be present, in a small but undetermined amount. The 
use of the term has been loose, and in some cases quite erro- 
neous, as more complete analyses have shown that such ' ' traces " 
may amount in reality to one-half, or possibly one or more, 
per cent. It would be better to have the meaning of the term 
more strictly defined, and it has been suggested * that it l ' should 
indicate strictly and uniformly that the constituent (to which 
it is applied) has been looked for and found, but in unweighable 
amount (0.1 milligram or less), while if it is not looked for but 
is known to be present in small amount, some such phrase 
as ' present, not determined' (p. n. d.) should be employed." 
Hillebrand suggests that, "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." For this purpose the letters "n. d." (not deter- 
mined) may be reserved. Although the adoption of some such 
definitions is advisable, yet it is scarcely to be hoped that uni- 
formity can be attained in regard to the matter, which, after 
all, is of minor importance. 

The analytical calculations should be carried to four deci- 
mals, which implies that in the statement of analyses the fig- 

* H S. Washington, Prof. Paper U. S. Geol. Surv., No. 14, p. 24, 1903. 



30 INTRODUCTION. 

ures are to be given to hundredths of a per cent. While the 
last decimal may not be of much significance in all cases, it 
represents the limit of weighing (0.0001 gram) in the quantities 
taken for the determination of the constituents of rocks, and 
gives some assurance of the value of the preceding decimal. It 
is also the almost universal practice among chemists and 
analysts. Statement in only tenths of a per cent is defective 
in that it implies correctness only in the unit column, and con- 
sequently an insufficient degree of accuracy. On the other 
hand, a statement in thousandths of a per cent implies a higher 
degree of accuracy than is possible with the limits of error 
obtaining in all but the most painstaking analytical work, and 
which is quite uncalled for in view of the variable composition 
of all rock masses from place to place, however great may be 
the apparent uniformity. It may be remarked that, in the 
course of compiling and examining thousands of rock analyses, 
I have found it to be true, almost without exception, that the 
few analyses given to thousandths of a per cent are remarkable 
chiefly for their poor quality, differing from the probable truth 
in some or all constituents by as much as one or more per cent. 
Statement in such ultra-refined terms may usually be regarded 
as evidence that the analyst has no just appreciation of the 
probable limits of error, or of the bases of accuracy in analyti- 
cal work. 

A final word must be said in regard to the recalculation of 
the analysis to an even 100 per cent. This is tantamount to 
the distribution of any error over all the constituents, which 
is not justifiable, as has been said elsewhere. Furthermore, 
as Fresenius says, "such ' doctoring ' of the analysis deprives 
other chemists of the power of judging of its accuracy. " What- 
ever the results may be, and whether the summat : on be high 
or low, the figures for the various constituents must be given 
with their summation, as they are obtained from the analysis, 
if the whole is deemed to be worthy of publication at all. Any 
other procedure would give rise to reasonable suspicion as to 
the accuracy of the analysis, which can only be judged of by 
others if the actual figures are given. 



PART II. 

APPARATUS AND REAGENTS. 

ALTHOUGH any well-equipped laboratory should have almost 
every piece of apparatus and nearly all the reagents which 
are necessary for the quantitative analysis of rocks, yet it may 
be convenient, especially for the independent worker, to give 
a list of those which should be available before an analysis is 
undertaken. Brief remarks will be made to explain certain 
points which it is especially useful for the inexperienced to 
know. The number of pieces of apparatus are those which 
it is deemed advisable to have on hand in order that the analysis 
may proceed without interruption for lack of the proper facili- 
ties. It is well to bear in mind when buying reagents that it 
is better to have a somewhat large stock on hand, as this can 
be tested for impurities once for all. This is especially true 
of sodium, potassium and calcium carbonates. 

1. APPARATUS. 

Balance. A good balance is, of course, essential. It 
should be accurate and sensitive to one-tenth of a milligram. 
The bearings should be of agate, and the arm must be gradu- 
ated for a rider. A case is necessary, and the usual accessories 
for specific-gravity work, and a support for weighing specimen 
tubes, should be provided. The set of weights (the larger ones 
preferably platinum plated) should run from 50 grams to 
1 milligram, with riders. For suggestions as to the testing of 
the balance and weights, and the process of weighing, see 

31 



32 APPARATUS AND REAGENTS. 

Fresenius. Before commencing an analysis the balance should 
be adjusted. 

Platinum. One lipped basin of about 300 c.c. capacity, 
10 cm. across the top, and weighing about 100 grams. 

Three crucibles, one of 40 c.c., and two of 30 c.c. Instead 
of one of the latter one of 20 c.c. will answer, while a 50-c.c. 
crucible also will not come amiss. 

One Gooch crucible of 20 c.c. capacity and provided with 
cap for the bottom. 

Each crucible, including the Gooch, must have its own 
cover, with which it is always to be weighed. 

Two or three triangles of 5, 6 and 7 cm. along the side. It 
is well to make a series of parallel grooves with a file at one apex 
of each, to support the cover when the crucible is heated on its 
side (p. 105). 

One spatula, about 10 cm. long and weighing about 10 grams. 

One pair of platinum-tipped crucible tongs. 

One piece of stout wire about 8 cm. long (p. 86). 

Platinum-foil and blowpipe wire. 

A small lipped platinum basin of 75 to 100 c.c., and weighing 
10 to 15 grams, will be useful for the digestion of rock powder in 
acid, but a large platinum crucible will take its place. A large 
platinum basin, holding 900 to 1000 c.c., is a great desideratum 
in the determination of alkalies, but as this is very expensive 
it may be replaced by one of silver of the same capacity (weight 
about 300 grams), or if necessary by a porcelain one. 

Especial attention should be devoted to keeping all plati- 
num utensils bright, by the use of sea-sand, and also by the 
application of fused acid potassium sulphate when needed. 
The analytical results will not only be more accurate, but the 
life of the articles will be greatly prolonged. 

Glass. Two nests of lipped beakers, from 1000 c.c. to 
50 c.c., with two or three extra of the smaller sizes. These 
are preferably of Jena glass. 

Flasks of various sizes (flat-bottomed), preferably two each 
of 50, 100, 200, and 400 c.c. These also are better of Jena glass. 



APPARATUS. 33 

Several wash-bottles, one of about 500 c.c., for general use, 
one of 1000 c.c. for boiling water in the iron determinations, 
two or three of 300 c.c., one of these reserved for ammonia 
in the determination of magnesia, another for alcohol in the 
determination of potash, and one for use with various dilute 
washing solutions. The jets should be attached by a bit of 
rubber tubing. 

Measuring-flasks, with glass stoppers. One each of 100, 200 
and 500 c.c., and two of 250 c.c. 

Pipettes. Two each of 5 and 10 c.c. 

Measuring-cylinders, lipped, unstoppered. One each of 
10, 25, 100 and 500 c.c. 

Burettes. Three of 50 c.c. each, divided to tenths of a c.c., 
with glass cocks. One of these is for permanganate solution, one 
for titanium solution and one for water. 

Desiccators. Two or three of the usual form, with pipe-stem 
triangle. The bottom part is to be half filled with bits of glass 
tubing, and concentrated sulphuric acid poured in just sufficient 
to cover these. 

Watch-glasses. Half a dozen each, 2, 2J, 3, 4, 5 and 6 
inches. It will be found useful to perforate one or two of the 
larger ones by means of a mixture of hydrofluoric and sulphuric 
acids, this being retained in the center by a little ring of wax till 
.a hole is eaten through. A pair of the 3-inch glasses is to be 
taken which weigh as nearly alike as possible, and the weights 
adjusted to equality by filing or grinding off the rim of the 
heavier, the necessary amount. 

Test-tubes. A few of several small to medium sizes. 

Specimen tubes. Several each, 6X|, 5Xf and 4Xi 
inches. Appropriate smooth corks should be provided for 
these. 

Tubing. Sufficient of the usual sizes to make connections, 
etc. There should also be a supply of rather hard glass tubing, 
of an internal diameter of 6 mm., for the determination of water 
<p!45. ). 

Rods. A supply of various thicknesses for stirrers. A 



34 APPARATUS AND REAGENTS. 

number of these should be prepared, varying in length from 5 
to 10 inches. Two may be tipped with a bit of rubber tubing. 

Funnels. Two or three each, 1J, 2, 2f , and 3 inches, with one 
or two larger, 4- and 5-inch ones. Care should be taken to select 
funnels whose conical angle is exactly 60, especially for those of 
3 inches and below, as this facilitates greatly the fitting of the 
filter. It will be well to fuse onto two each of the 2 J- and 3-inch 
funnels suction-tubes of small bore, about 8 to 10 inches in length, 
and provided with a turn about half-way down. These may 
also be separate and attached by a bit of rubber tubing, though 
this method is less accurate and apt to lead to loss or contamina- 
tion of the filtrate in inexpert hands. 

A "carbon filter," of internal diameter of 1J inches, or to 
fit the Gooch crucible, provided with rubber tube to make the 
connection (Fresenius, I, p. 121). 

A stout Erlenmeyer flask with side tubulure for use with the 
Gooch crucible. 

Calcium-chloride tubes and drying-cylinders for setting up 
the apparatus for the determination of C0 2 . 

Washing-bottles or cylinders for washing gases, preferably of 
Drexel's form. Two or three will suffice. 

Apparatus for the generation of C0 2 and H 2 S. Any one of 
the usual forms. 

A pair of glasses with parallel sides, or a pair of Nessler 
tubes, for the determination of Ti0 2 (p. 145). 

Porcelain, etc. Evaporating -dishes, one or two each of 2J, 
3J and 4J inches, preferably of Berlin porcelain. 

Crucibles. Two or three of small sizes. One of about 2 
inches diameter will answer as an air-bath for the evaporation of 
sulphuric acid in platinum crucibles (p. 96). 

A square porcelain plate for use in the titration of iron. 

Steel plate and ring (p. 48). 

Diamond steel mortar (p. 51 ). This must be kept in a (cylin- 
drical) wooden box, with close-fitting cover, to prevent rusting. 

Agate mortar, about 3 inches in diameter. 

Glass box sieve for the rock powder (p. 51). 



REAGENTS. 35 

A steel plate or, preferably, polished granite slab, about 
4x3 inches, for cooling crucibles. 

Several two- and three-ring retort-stands. 

Two funnel-stands of wood. 

One burette-stand, two arms. 

Bunsen burners, and a blast-lamp, with bellows. 

Iron wire gauze, in 6-inch squares. This is preferable to 
asbestos board, though the latter may be used. 

Water-baths, preferably with porcelain rings, and a copper 
air-bath, with thermometer, reading to 200 C. 

Aspirator or suction-pump. 

Rubber tubing, a selection of sizes suitable for making con- 
nections, including some of narrow diameter for capping stirring- 
rods to be used as cleaners. 

Rubber stoppers, perforated with one and two holes, for 
making wash-bottles, etc. 

A hard rubber funnel, about 2 inches in diameter, if a plati- 
num one is not available. 

A horn spoon for weighing out alkali carbonates, etc. 

Filter-paper. Round cut filters should be used, the paper 
being of such quality as to leave only a negligible amount of ash. 
Schleicher and Schull's No. 590 are excellent. Those of 5J, 7, 
9 and 11 cm. are the most convenient sizes. While too large a 
filter is to be avoided as leading to an undue amount of wash- 
water, yet the filter must be large enough to allow all the pre- 
cipitate to be brought on it. The appropriate size in each 
operation has been indicated throughout the descriptions. 

2. REAGENTS. 

All reagents should be the purest obtainable. In general 
these can be bought sufficiently pure, especially the strong acids 
and ammonia water. They should all be tested for impurities, 
according to the tests suggested by Fresenius * or Krauch,f 

* Fresenius, Qual. Anal., pp. 52 ff., 1897; Quant. Anal., I, pp. 127 ff., 1904. 
t Krauch, Die Priifung der chemischen Reagentien, Berlin, 1896. Cf. 
Hillebrand, p. 25. 



36 APPARATUS AND REAGENTS 

and, if necessary, the salts are to be purified by recrystallization, 
etc. I must add my word of caution to that of Hillebrand in 
regard to the acceptance of C. P. reagents without proper tests, 
and especially as to the unreliability of some of those manu- 
factured abroad, and sold under a guarantee of purity. I have 
found certain samples of these last worse than reagents with an 
ordinary "C. P." label, and, as Hillebrand says, 'The 'guar- 
anteed reagent' needs checking as much as any other." In the 
subjoined list the chemicals mentioned are supposed to be 
"chemically pure/' and not of the ordinary commercial brands. 

Hydrochloric acid. 

Nitric acid. 

Sulphuric acid. 

Hydrofluoric acid, for which ceresine bottles should be used r 
not gutta-percha. 

Ammonia water. This should be fresh and must contain no- 
ammonium carbonate (p. 62). 

Ammonium chloride. This should be resublimed. 

Ammonium carbonate. The solution of this is made as 
needed (p. 134). 

Ammonium oxalate. This had best be recrystallized, as it 
frequently contains calcium oxalate. The solution is to be made 
as needed (p. 115). 

Ammonium nitrate. 

Hydrogen-ammonium-sodium phosphate (microcosmic salt). 
The solution is to be made as needed (p. 119). 

Sodium acetate. 

Sodium carbonate, dry, anhydrous. 

Acid potassium carbonate. 

These two are to be especially investigated as to impuri- 
ties, since the quantity of them which is used for an analysis 
is so large. They are to be powdered and mixed in equal parts 
for the main fusion. Acid potassium carbonate is preferable 
to the normal carbonate, as it is not as deliquescent, and the 
water and carbonic acid are driven off readily by gentle heat- 
ing (Penfield). The mixture of the two carbonates is preferable 



REAGENTS. 37 

to the use of sodium carbonate alone, as it fuses at a consider- 
ably lower temperature than either carbonate alone, and is 
equally effective as a flux. A considerable quantity of the 
mixture may be made and preserved in a glass-stoppered 
bottle. 

Acid potassium sulphate. This must be the fused salt, and 
should contain as little water and free acid as possible. 

Calcium carbonate. The ordinary precipitated carbonate 
is not well adapted for the determination of alkalies, as it is 
too fine-grained and bulky, though it can be used. It is best 
made by precipitating a boiling solution of calcium chloride 
with ammonium carbonate, which renders the precipitate dense 
and relatively coarse-grained. The precipitate is to be thor- 
oughly washed with hot water. The amount of alkalies can 
thus be reduced to very small amount, but for accurate work 
it is well to estimate them in 4 grams of the stock, so as to be 
able to apply the appropriate correction (p. 130). A suitably 
precipitated and very pure calcium carbonate is made by 
Baker and Adamson for this purpose. 

Potassium nitrate. 

Potassium chromate. The preparation of the standard 
solution of this is described on p. 165. 

Potassium permanganate. A solution of appropriate strength 
for use in rock analysis is obtained by dissolving about 1 
gram of the salt in 1 liter of water. One c.c. of this will 
correspond approximately to 0.0025 gram Fe 2 3 or to 0.00225 
gram FeO. The standardization may be effected by any of the 
methods given in Fresenius, the reagent which I prefer for 
this purpose being ammonium oxalate, which is easily obtained 
pure and dry. As the disappearance of color in this is at first 
very slow, it may be as well to note that 1 c.c. of the perman- 
ganate solution mentioned above will correspond to about 
1 c.c. of a solution of 0.57 gram of crystallized ammonium 
oxalate dissolved in 250 c.c. of water, to which some sulphuric 
acid is added. The mean should be taken of at least three or 
four determinations on 25 or 50 c.c. of the oxalate solution. 



38 APPARATUS AND REAGENTS. 

As equal amounts of permanganate are required to oxidize 
1 molecule of ammonium oxalate mol. wt. = 142) and 2 mole- 
cules of ferrous oxide (mol. wt. = 144), the weight of oxalate 
per cubic centimeter is to be multiplied by -j-ff to give the equiv- 
alent per cubic centimeter in terms of ferrous oxide. This 
divided by 0.9 (or multiplied by 1.1111) will give the value per 
cubic centimeter in terms of Fe 2 3 . The solut'on should be 
kept in the dark, and it is well to restandardize it every few 
months. 

Platinum chloride. This is usually obtained in the form of 
chloroplatinic acid, H 2 PtCl 6 +6H 2 0, which contains 37.66 per 
cent of platinum. A solution containing 0.1 gram of platinum 
per cubic centimeter is made by dissolving 1 ounce of this in 
50 c.c. of water, filtering and washing the beaker and filter 
slightly, and diluting with water to 106 c.c. 

Silver nitrate. A solution of this may be kept in a bulb for 
use in testing filtrates. 

Ammonium molybdate solution. This may be prepared 
by dissolving 100 grams of ammonium molybdate in 500 cf.c. 
of water with the aid of heat, pouring into it when cold 500 
c.c. of concentrated nitric a^id.* The mixture is to be filtered 
after standing for a couple of days. It is kept in a well stop- 
pered bottle. On long standing so much of the molybdic acid 
may separate out as a yellow precipitate that the solution 
will give little or no precipitate when phosphoric anhydride 
is present, at least in the amounts found in igneous rocks. 

Barium chloride. A solution of 10 grams in 100 c.c. of water 
will suffice. 

Magnesia mixture. This may be made as suggested by 
Fresenius (Quant. Anal., I, p. 138, 1904) by dissolving 11 grams 
of crystallized magnesium chloride and 28 grams of ammonium 
chloride in 130 c.c. of water and adding 70 c.c. of dilute ammonia 
water (sp. gr. 0.96). An alternative method is that of dissolving 
10 grams of crystallized magnesium sulphate and 20 grams of 

* The solution of ammonium molybdate should not be poured into the 
nitric acid, as a permanent precipitate will form. 



REAGENTS. 39 

ammonium chloride in 80 c.c. of water, and adding 40 c.c. of 
ammonia water. In either case the solution must be allowed 
to stand for some days, and is then filtered. 

Titanium standard solution. The preparation of this is 
described on p. 144. 

Hydrogen peroxide. A commercial brand of this which is 
usually free from fluorine is known as "Dioxogen." It should 
be fresh when used. 

Zinc oxide. A little of this may be dissolved in ammonia 
water as needed for the determination of fluorine. 

Lead oxide. A pure litharge will answer for retaining S0 3 , 
etc., in the determination of water. It must be ignited before 
use. 

Ferrous sulphide. This is used for the generation of hydro- 
gen sulphide. 

Marble. This is used for the generation of carbon dioxide. 

Acetic acid. The ordinary acid of specific gravity 1.044 
(33 per cent) will answer. 

Alcohol. Ordinary 95 per cent ethyl alcohol may be diluted 
with water to a specific gravity of 0.86 for use in the determina- 
tion of alkalies. If a hydrometer is not available, this may be 
attained approximately by mixing five volumes of the alcohol 
with one of water. 

Alcohol, absolute. 

Ether. 

Asbestos. This must be of the anhydrous, hornblende 
variety, and not the fibrous serpentine (chrysotile) which is so 
often substituted for the other. The latter, being hydrous, 
is not adapted for use in the Gooch filter. About 2 grams are 
to be boiled with dilute hydrochloric acid, thoroughly washed 
on a filter with hot water, and kept for use, mixed with 25 to 
50 c.c. of water, in a small flask, which should be covered with a 
loose glass cap. 

Litmus paper. A little of both blue and red will be useful. 

Calcium chloride. The fused, granular salt is used for 
drying-tubes in the determination of C0 2 . 



40 APPARATUS AND REAGENTS. 

Soda-lime. This is used in granular form for the absorp- 
tion of C0 2 . It should be renewed from time to time in the 
U-tube. 

Water. It is, of course, understood that only pure, dis- 
tilled water is to be used hi quantitative analysis, and that this 
is referred to whenever this substance is mentioned throughout 
this book. 



PART III. 

THE SAMPLE. 

1. SELECTION IN THE FIELD. 

SINCE the object of the chemical analysis of rocks is to as- 
certain the chemical composition of a body of rock, it is of 
fundamental importance that the specimen selected for analysis, 
and the material analyzed, be truly representative of the mass 
under investigation. Otherwise the analysis, however accurate 
and complete it may be, will be misleading and useless for the end 
in view. 

If, for instance, an igneous mass is not uniform in character, 
and the specimen is selected from some extreme phase of variation, 
it is obvious that an analysis of this will not give a just idea of 
the character of the mass as a whole. Again, in analyzing a 
diorite, for instance, the specimen may be so small or selected 
with so little care that it contains a larger proportion of horn- 
blende, let us say, than the average of the mass; or the specimen 
of a quartz-porphyry may carry only a few of the abundant 
quartz phenocrysts and a disproportionate amount of ground- 
mass. In these cases it is self-evident that the analysis made on 
such inadequate material, however skilfully it may be executed, 
cannot represent the true composition of the rock-mass. It is 
seen, therefore, that the proper selection of the material for 
analysis depends on two factors : the selection of the specimen in 
the field, and the amount of material taken for use in making the 
analysis. 

While the selection in the field is quite distinct from the 

41 



42 THE SAMPLE. 

laboratory processes, yet its importance is so vital to the proper 
analysis of rocks, that it demands some discussion here. This is 
the more called for since the petrologist will usually collect his 
own material, for analysis either by himself or by others, and, 
as has been said elsewhere, ' ' the evidence is conclusive that the 
specimen analyzed has often been collected with no reference to 
this point, this fact greatly diminishing the value of the analyti- 
cal work afterward expended on it." In selecting a representa- 
tive specimen in the field attention must be paid to two points: 
the uniformity of the mass, especially in regard to mineral com- 
position as well as to texture, and the freshness of the rock. 

Uniformity of the Rock-mass. If, as is probably true in the 
majority of cases, the igneous mass is sensibly uniform through- 
out its extent, specimens should be taken from several parts, 
when possible, in order to test the matter with the microscope. 
For an analysis representing the composition of such a uniform 
body of igneous rock, either portions of several specimens from 
different parts may be mixed, or the analysis may be made on a 
single specimen, which is considered to be representative of he 
whole in the judgment of the petrographer, both as decided on in 
the field and as confirmed by the microscope. 

As to the former procedure it may be said that no decisive 
check of one's results will be possible in the future, and that it is 
by no means certain that a mixture of several specimens really 
represents the composition of the whole better than does a single 
specimen, which has been carefully selected with this object in 
view. 

In all, or nearly all, cases therefore, it is by far the best plan to 
select a single specimen after due comparison with others from 
the same mass and consideration of its representative character. 
The specimen should be taken, if possible, from a mass of rock in 
place, and not from loose boulders or talus slopes, unless these 
are the only sources available and it is definitely known that 
they do come from the mass under investigation. 

If the mass is not uniform, but is composed of portions of 
different characters, such as a composite dike or a stock with 



FRESHNESS OF THE ROCK. 43 

marginal facies, representative specimens of the different facies 
should be collected and an analysis made of each, whether the 
differences be apparently only textural or those due to mineral 
composition. If in any way feasible, as close an estimate as the 
conditions allow should be made of the relative areas or volumes 
of each facies. While the possibility of doing this depends, to a 
large extent, on the chances of erosion and denudation, yet it is of 
such great importance in the investigation of certain theoretical 
questions of petrology that special endeavor should be made to 
arrive at the facts. 

In any case, whether the mass be uniform or composed of 
several facies, the specimens should be taken from some definite 
locality, one which can be described or named so that it can be 
readily identified by others, and also one whose accessibility is 
not likely to be lost through building or other operations. 
Quarries naturally are especially favorable spots, as fresh speci- 
mens are easily obtained, and they are of such a permanent 
nature as to be readily identified, in most cases, by future in- 
vestigators. 

Freshness of the Rock. The action of atmospheric agencies 
on rocks may vary from the changes to which Merrill * attaches 
the specific term " alteration/' in which "the rock-mass as a 
whole retains its individuality/' but is changed mineralogically, 
with the production of such minerals as chlorite, sericite, 
zeolites, serpentine, limonite, etc., to those embraced under what 
Merrill calls "weathering," "involving the destruction of the 
rock-mass/' and its ultimate resolution into sands and clays. 
The mass resulting from such changes, either of alteration or 
weathering, can be analyzed by the same methods and with 
equal facility as can a perfectly fresh rock, but it is evident that 
the results will not represent strictly the composition of the 
original magma or unaltered rock body. 

While it is in general true that for purposes of analysis only 
specimens of fresh, unaltered or unweathered rock should be 

*G. P. Merrill, Rocks, Rock-weathering and Soils, 1897, p. 174. 



44 THE SAMPLE. 

chosen, unless the study of such secondary changes is the object 
in view, yet it is at times somewhat difficult to decide whether a 
rock is fresh enough for analysis or not. In general it may be 
said that, for the study of igneous rocks, all weathered specimens 
are to be rejected, that is to say, those in which the rock-mass has 
been formally broken down. In the case of alteration, speci- 
mens should be rejected where the original color is decidedly 
changed, as where the rock is of a rusty brown through the 
abundant production of limonite, or green through that of 
chlorite. Specimens which effervesce with hydrochloric acid, 
either cold or on warming, or whose vesicles contain calcite or 
zeolites, are likewise to be shunned. 

In rocks which appear megascopically to be quite fresh, the 
microscope may reveal the presence of secondary minerals, the 
products of alteration, as sericite, chlorite, serpentine or limonite. 
Although considerable latitude must be left to the judgment of 
the petrographer in deciding this matter, yet if such minerals are 
present to any considerable extent, the rock must be regarded as 
unfit for chemical analysis, unless fresh material is absolutely 
unattainable. This last state of affairs is especially apt to be 
true of the most basic rocks, such as picrites, peridotites and 
pyroxenites, which contain a large amount of the easily oxidiz- 
able ferrous iron, and of which few perfectly fresh occurrences 
are known or have been analyzed. For lack of better material, 
one must often make analyses on specimens of such rocks that 
are far from fresh, but the results of these, while not to be 
regarded as wholly satisfactory, may yet be of some service. 

The results of alteration are usually most clearly shown in the 
analysis by the figures for H 2 or C0 2 , or both. Where these are 
high the material analyzed must be considered as having been 
more or less altered, whether this appears in the description or 
not, with the exception of certain cases mentioned below. 
While it is impossible to state in exact figures the limits of 
allowable alteration, until the subject is further studied, it may 
be held provisionally that H 2 can go up to 2 or 3 per cent 
and C0 2 to \ or 1 per cent, without seriously affecting the value 



FRESHNESS OF THE ROCK. 45 

of the analysis. It must also be borne in mind that a rock can 
be more or less profoundly altered, and yet show comparatively 
low figures for these two constituents, though this is not often 
to be expected. 

The exceptional cases just referred to consist of rocks com- 
posed in part of primary minerals which contain either hydroxyl 
(as muscovite and biotite), water of crystallization (analcite) 
or carbon dioxide (cancrinite). With rocks carrying analcite, 
which is the only zeolite that apparently may exist as a primary 
mineral, the H 2 may amount to 3 or 4 per cent, and yet the 
mass be to all appearances perfectly fresh, and often presumably 
so, as Pirsson has shown in the case of the monchiquites. Can- 
crinite-bearing rocks may have more than 1 per cent of C0 2 and 
yet be quite unaltered, as far as one may judge from the micro- 
scope, so that it is entirely possible, if not probable, that this 
mineral is a primary constituent in some cases. No well- 
established cases of the existence of calcite as an undoubtedly 
primary mineral are known as yet, though instances have been 
brought forward where its occurrence as such seems to be 
possible. 

In discussing the subject of analyses of altered rocks we 
may advert to a phase of the matter which is of some importance. 
When a rock is not fresh it is sometimes assumed that the 
original composition can be arrived at by deducting the amounts 
of H 2 and C0 2 and calculating the remainder to 100 per cent. 
This assumption is quite unwarranted in the great majority 
of cases, since the processes of alteration are usually by no 
means simple and the result of the simple addition of the two 
substances mentioned. On the contrary, they are very com- 
plex and produce changes of greater or less magnitude in the 
proportions of some or all of the other constituents. These 
may be additive, as when calcite is deposited in rocks by means 
of percolating waters carrying calcium bicarbonate in solution, 
or they may be subtractive, as when kaolinization of a feldspar 
takes place with resultant loss of alkalies or lime. In any 
case it is almost universally true that the processes of rock 



46 THE SAMPLE. 

degeneration affect all or nearly all of the chemical constit- 
uents,* and that the assumption that such is not the case is 
quite unwarranted by the known facts. 

2. AMOUNT OF MATERIAL. 

As has been said above, the representative character of the 
specimen depends, after proper selection in the field supple- 
mented by the use of the microscope, upon the amount of 
material which is taken for pulverization in preparation for 
the analysis. The weight of the sample which will adequately 
represent the average of the rock-mass varies with the texture 
of the rock, and especially with its granularity, that is, the size 
of its component mineral particles. 

It may first be noted that at least 10 grams of rock powder 
must be available for the purpose of analysis, and this amount 
should be increased to 20 or 30 grams if the analysis is to be 
very complete, since the determination of some of the rarer 
constituents demands the use of two or more grams of powder. 
Indeed, it is always a wise precaution to have 20 or 30 grams 
on hand, in view of the possible necessity for the duplicate 
determination of some of the constituents, or even the making 
of a second complete analysis. In the case of many minerals 
and meteorites it is often impossible to obtain anything like 
this amount of material, and the analyst must be content with 
far smaller quantities, sometimes even less than a gram for the 
whole analysis. With rocks, on the other hand, there is usually 
an ample supply, so that the analyst has generally no reason 
for stinting himself. In this way a number of constituents 
can be easily determined in separate portions, which could 
only be accomplished by the use of longer and much more com- 
plex methods if it were necessary to determine them in a single 
portion. 

The texture of rocks varies within such wide limits that it 

is difficult to give exact figures, and much must be left to the 

, - ____ 

* Cf. Merrill, op. cit., especially pp. 234 to 240. 



AMOUNT OF MATERIAL. 47 

judgment of the petrographer or analyst. Speaking generally, 
and almost without exception, the finer grained and less porphy- 
ritic the rock is the smaller will be the amount of material 
necessary to be representative. 

Ten or twenty* grams of chips or fragments will be ample 
for very fine-grained, aphanitic or glassy rocks, as many basalts, 
trachytes, and obsidians, especially if non-porphyritic, or very 
finely so. With more coarsely granular rocks, such as granites, 
syenites and diorites, a larger quantity must be taken, de- 
pending on the coarseness of the grain. This amount may vary 
from 30 to 50 grams of a medium-grained rock to 100 or even 
more if the grain is coarse. In some cases, as in pegmatites, 
the grain may be so large that only a whole hand specimen, or 
even several pounds, will adequately represent the true compo- 
sition. Very exceptionally the crystals may be of such gigan- 
tic size that the relative proportions of the various minerals 
must be estimated from a flat exposure and corresponding 
portions of the^several minerals weighed out and mixed. Fortu- 
nately this last will be necessary only in rare instances, as 
results obtained thus could be "regarded as but approximations 
to the truth. 

If the rock is porphyritic this feature involves the taking 
of a larger quantity than would be necessary if the grain of the 
whole were that of the ground-mass. If the phenocrysts are 
very small, only a few millimeters in diameter, and close together, 
as in many andesites and basalts, only 20 or 30 grams will be 
sufficient. As they get larger, and if more widely scattered, 
more must be taken, from 50 or 100 grams to larger quantities. 
With porphyritic rocks also care must be taken that brittle 
or loosely attached phenocrysts, as of feldspar or quartz, do 
not fall out, so as to yield a disproportionate amount of ground- 
mass in the material for analysis. 



48 THE SAMPLE. 



3. PREPARATION OF THE SAMPLE. 

For the purpose of analysis it is necessary that the sample 
of rock be reduced to powder in order that 'it may be readily 
and completely attacked by the reagents used for its decom- 
position. To accomplish this one of two methods may be 
followed. 

The first is that advocated by Hillebrand * and employed 
in the laboratory of the United States Geological Survey. It 
consists in first crushing the rock fragments by means of a 
hardened steel hammer on a hardened steel plate. The plate 
used by Hillebrand is 4J cm. thick and 10 cm. square, and the 
rock fragments are surrounded by a steel ring 2 cm. thick and 
6 cm. internal diameter to prevent the flying and loss of small 
rock fragments. After reduction in this way to very small 
particles and powder, the whole is ground down by hand in an 
agate mortar in small portions at a time. 

In the second method the rock is broken into small pieces, 
and these crushed in a steel mortar. The resultant mixture 
of small fragments and powder is sifted through a silk-gauze 
sieve, the part which does not pass through being once more 
crushed in the steel mortar and again sifted, and this operation 
repeated till only a very small portion is left, which is pul- 
verized by hand in an agate mortar. 

Of these two methods it may be said that neither is perfect, 
since both are open to rather serious objections, while, on the 
other hand, each possesses certain advantages over the other. 

In favor of the first are the facts that the preliminary rough 
crushing is quickly accomplished and with a minimum possibility 
of contamination by metallic iron, and that, the final pulveriza- 
tion being carried out in agate, the chance of contamination is 
here also very slight. Against it may be urged that in the prelimi- 
nary crushing on the steel plate, which must necessarily be car- 

* HUlebrand, p. 31. 



PREPARATION OF THE SAMPLE. 49 

ried pretty far to prepare the material for grinding in an agate 
mortar, there is considerable flying of fragments, which the 
steel ring cannot wholly prevent. This will be still more marked 
during the grinding in the agate mortar, in which it is almost 
impossible to avoid very considerable loss, unless the material is 
already very finely crushed and there are no particles of any con- 
siderable size. The fragments thus lost may be of the same 
average composition as that of the rock, which will be true of 
aphanitic rocks or obsidians. But if the rock is medium- or 
coarse-grained, or contains phenocrysts of any considerable size, 
the chances are largely against this, since the more tough and 
resistant minerals, as pyroxene and hornblende, will be the most 
apt to fly off. They will be accompanied, it is true, by some 
adhering feldspar, but in less amount than in the rock itself. 
The result of this would be that the powder finally obtained 
would not quite correspond in composition to that of the rock, 
though the error thus introduced would probably be com- 
pensated for to a certain extent by the loss of fine dust during 
the grinding, which would contain more of the brittle quartz and 
feldspathic constituents. 

Another, and very serious, objection against this method is the 
great amount of time and labor involved in grinding down the 
crushed material in the agate mortar, if the presence of coarse 
particles is to be avoided, as is essential for proper attack by 
the reagents used. 

The advantages of the second method are the great saving of 
time over that needed for the first, and the avoidance of loss 
by flying fragments which is incident to the other, though 
it must be confessed that this is partially counterbalanced by a 
somewhat greater loss of fine dust. This will not, however, be 
very great or lead to serious error if the operation is conducted 
with care and in a place free from draughts, and anyway it seems 
to be unavoidable by either method. 

The most serious objection that can be brought against this 
method is the danger of contamination by particles of steel de- 
rived from the mortar. These cannot, of course, be removed by 



50 THE SAMPLE. 

a magnet, as magnetite, pyrrhotite, and some pyroxenes, horn- 
blendes, biotites and olivines are magnetic, and hence would also 
be extracted, and there are few rocks which do not contain some 
of these minerals. 

While this objection is entitled to great weight and would 
indeed be fatal if the contamination thus possibly introduced 
were of serious dimensions, yet experience goes to show that it is 
by no means as formidable as it appears at first sight. If a steel 
mortar of the best quality, and properly hardened, is selected, 
the wear involved by crushing the material for any one ana 1 y sis 
is so extremely small as to be entirely negligible. This is evi- 
dent from the very slight total wear in such a mortar that has- 
been in use for eight years. Furthermore, although it would be 
expected that the small pieces of steel which may be torn off from 
the mortar would be caught in and not pass through the fine silk 
gauze, on account of their size and jaggedness, I have not found 
any present, although search has often been made for them with 
a lens. Another bit of evidence showing that the contamination, 
if any, must be very slight, is that in rocks which are entirely 
free from carbon dioxide there is absolutely no visible evolution 
of gas (hydrogen) on treating the rock powder with acid, as 
might be expected to occur if metallic iron were present to any 
considerable extent. 

The objection which Hillebrand raises against the use of a 
silk sieve can scarcely be held to be of great moment. The dan- 
ger of contamination by particles of silk, and hence, error in the 
determination of the ferrous iron, is more theoretical than reaL 
Only an almost infinitesimal weight of silk would pass into the 
rock powder, a milligram or so at the very most, and this would 
be distributed among twenty or more grams of rock powder, of 
which but half a gram is taken for the ferrous iron determination. 
It is certain that the reducing action of the small amount of 
organic matter thus introduced would be very much less than that 
necessary to decolorize a single drop of the permanganate solu- 
tion, and hence would be entirely negligible, even for the most 
accurate work. As Hillebrand says, however, it is obvious that 



PREPARATION OF THE SAMPLE. 51 

metal sieves should never be used, as there would be in this case 
almost certain contamination of serious importance. 

While, after all, there is little to choose between the two 
methods, and while the fact that the first is adopted by the 
chemists in Washington is a very strong point in its favor, yet, 
taking all things into consideration. I have adopted in my own 
work, and can recommend, the second method, of which some 
details follow. 

The " diamond" steel mortar is preferably of Plattner's form,* 
though one made of only two parts may also be used. In this 
case it is well to have the bottom of the cavity hemispherical for 
greater ease in cleaning, the end of the pestle being similar so as 
to fit snugly (Penfield). The sieve consists of a cylindrical 
glass box, which may be 3.5 cm. deep, 7.5 cm. internal diameter 
and the walls about 2 mm. thick. With this is a brass ring, 1 cm. 
in height, and of such a diameter as to fit snugly over the mouth 
of the box. The gauze used is the best silk bolting-cloth, with 
about 25 meshes to a centimeter. An agate mortar about 7.5 
cm. in diameter will be found a convenient size. 

The whole amount of the sample which is deemed to be 
representative of the rock-mass is reduced to small frag- 
ments, either on a steel plate with a ring, as in the first 
method, or if the amount of material is small, by breaking up 
with a hardened hammer on the top of the steel pestle which is 
placed in position in the mortar. Care must be taken in either 
case to avoid the flying off of fragments.f If the pieces of rock 
are broken on the pestle-head they can be held in the dry fingers 
and cracked by a sharp, quick blow, and the pieces so obtained 
cracked again. The largest of the fragments finally obtained 
must be small enough to drop easily into the mortar, and all of 
them, with any resulting small grains and powder, are placed on 
a clean sheet of white, glazed paper. 

* Fresenius, I, p. 52, Fig. 25. 

f Wrapping the rock in paper for the first breaking up, as is sometimes 
done, is not to be recommended, as it is almost impossible to free the frag- 
ments entirely from adhering paper, and the considerable organic matter 
thus introduced may lead to serious error. 



52 THE SAMPLE. 

One of the small fragments of rock is then placed in the steel 
mortar, which rests on a firm, solid support, and is partially 
crushed by a dozen or so sharp blows of a light (one-half pound) 
hammer. The pestle is removed and placed on the sheet of 
paper, and the contents of the mortar dropped into the glass 
box, from which the gauze and brass ring have been removed. 
A few gentle taps of the base of the mortar against the cylindrical 
portion assist in removing the last portions of adhering powder. 
It is well to break up any coherent lumps of fine powder in the 
glass box by gentle pressure with the pestle, as this will aid 
materially in the subsequent sifting. 

The whole of the fragments and powder resulting from the 
first crushing are to be thus passed through the mortar and placed 
in the box. The mortar should not be filled more than a third 
full at a time, and it is not necessary, nor possible, to crush all 
of the rock to a fine powder at this stage. Care should be taken 
that the cylinder is placed vertically in the base before any fresh 
material is placed in it, and that the pestle is also inserted in a 
strictly vertical direction. Lack of attention to these points 
gives rise to the danger of small shavings or chips of steel being 
cut off and falling into the rock powder. 

When all the sample taken has been thus partially pulver- 
ized and placed in the glass box, a piece of the silk gauze, about 
10 or 12 cm. square, is stretched over its mouth and held firmly hi 
place by the brass ring which is slipped over it. The sieve is 
then held upside down over another sheet of white, glazed paper,* 
about 300 by 400 cm. (12 X 16 inches), a short distance above it, 
and gently shaken from side to side. This operation should be 
conducted as gently as is consistent with proper efficiency, and 
in a place free from draughts, so as to avoid undue loss of dust. 

When no more powder falls through, the brass ring and the 
gauze are removed, and the contents of the box poured out on 
the first sheet of paper. The whole process of crushing in the 
steel mortar is then gone through with on this material, exactly 
as before, and it is again sifted. The residue from the second 
* The sheets used by botanists for herbaria will be found convenient. 



PREPARATION OF THE SAMPLE. 53 

sifting is again treated, and if necessary the process is repeated 
till only a small amount of powder is left in the glass box, too 
coarse to pass through the gauze. This may then be ground 
down by hand in the agate mortar in small portions at a time, the 
different portions as they are ground being scattered over dif- 
ferent parts of the low heap of powder on the sheet of paper. 
Unless the amount of material to be crushed is very large, or the 
rock extremely tough, three or four successive crushings will be 
all that will be needed. The final grinding of the last small lot of 
powder should never be omitted, as this consists of the tougher 
minerals of the rock, and if it were thrown away, the corre- 
spondence between the sample and the rock would be incomplete. 

When the whole is thus brought upon the large sheet of paper, 
the powder is very thoroughly mixed. This is best accomplished 
by tilting up successively the ends and the sides of the paper 
until the mass is in the center. One end of the sheet is then 
raised gently until the heap of powder is lifted and turned over 
and slid toward the other end. It is essential to proper mixing 
that the mass of powder should not only slide down, but that it 
should actually be turned over. This is repeated many times, 
not only from end to end but from side to side, with an occa- 
sional oblique roll. A platinum spatula may also be used to mix 
the powder, care being taken that none of the paper surface be 
rubbed off, but the process described above is to be preferred. 
When it is considered that the powder is thoroughly mixed, it is 
not an undue precaution to roll it over hi different directions 
several times more. The powder may also be mixed by putting 
it again in the box and sifting it through a somewhat coarser 
gauze. 

After thorough mixing, the powder is poured into a specimen 
tube. For amounts of 20 to 30 grams one 6X| or 5Xf inches 
will answer, while one of 4xi inches will hold about 10 grams of 
rock powder. The tube used must be carefully cleaned, inside 
and out, by washing with distilled water, and thoroughly dried. 
This is best accomplished by the application of a gentle heat, the 
moist air being at the same time sucked out with a piece of glass 



54 THE SAMPLE. 

tubing attached to a suction-pump. The tube must be per- 
fectly cool before the powder is introduced, and is closed 
with a smooth, well-fitting cork, on the top of which the number 
of the specimen is written in ink. 

If the amount of rock to be taken is so large as to render 
crushing in small portions at a time in the steel mortar very 
laborious, that is, if it is 100 or more grams, and especially 
if a whole hand specimen or several pounds need be taken, 
it is best to crush the whole rather fine on an iron plate with a 
surrounding ring, and take out a portion by quarter ing. For 
this the crushed mass is poured on a large sheet of paper and 
well mixed. With a clean steel spatula portions are removed 
from different parts of the mass, care being taken that they do 
not include undue proportions of either the coarse fragments or 
the more finely powdered material. These selected portions, 
amounting to about 50 grams, are placed on another sheet of 
paper, and the operation of crushing hi the steel mortar con- 
ducted on this, exactly as described above. 

It is of the utmost importance to note that the whole of the 
sample which is prepared for the steel mortar, either the chips if 
the amount of material be small or that obtained by quartering if 
it be large, should be pulverized and passed through the sieve or 
ground in the agate mortar. If it is only partially pulverized 
and the last portions rejected, it is clear that the powder ob- 
tained will not represent the average composition of the rock. 
The rock-forming minerals differ widely in brittleness, so that 
the portions pulverized first will have a content higher than the 
average in particles of the more easily pulverizable minerals, as 
quartz, feldspars and feldspathoids, while the last portions will 
be especially rich in the tougher minerals, pyroxene, hornblende 
and the micas. The micas, above all, are difficult to pulverize 
completely either in the steel or agate mortar, on account of 
their ready cleavage and flexibility, but the thinness of their 
flakes renders these quite easy of attack by the reagents used. 
If they are present in any quantity it is necessary to see that 
the flakes are well distributed. 






PART IV. 

METHODS. 

1. PRELIMINARY OBSERVATIONS. 

To ensure satisfactory results the analyst must be scrupu- 
lously particular about the freedom from dust of the laboratory 
and the cleanliness of his apparatus. No matter how clean the 
laboratory may be, all vessels whose contents must stand for 
more than a short time, and especially overnight, are to be kept 
covered to avoid the entrance of dust. These are to be 
labelled with a paper containing the number of the specimen 
and the constituent to be determined laid on the cover. In 
prolonged evaporations it is well to hold a large pane of glass 
horizontally at some distance above the liquid, which may be 
done with a clamp and support devoted to this purpose. 

It is well to make it a rule to wash and wipe dry all glassware 
and other apparatus as soon as possible after use. Soiled 
vessels will then not accumulate, nor will there be danger that 
they be put away and used by mistake for clean ones. A clean 
beaker is to be used to collect a filtrate, even if it is to be re- 
jected, to permit the recovery of the precipitate in case part of 
it passes through the filter or the breaking of the latter. Before 
using a clean beaker or flask, it is best to rinse it out once or 
twice with a little water, and in volumetric or colorimetric work 
the burette should always be rinsed out with a little of the solu- 
tion before rilling it, even if it is apparently dry. If it is moist, 
the drops of water present will dilute, and hence change the 
strength of, the standard solution. 

55 



56 METHODS. 

If a good grade of filter-paper be used, such as that recom- 
mended elsewhere, the weight of filter ash may be neglected in 
the calculations, as it will fall within the other limits of error. 
The only general exception would be in the case of the precipitate 
by ammonia, for alumina, etc., when three or more 11 -cm. 
filters are used and ignited. The combined weight of their 
ashes may not be negligible in accurate work, and should be 
deducted from the weight of the ignited precipitate. 

In regard to the weight of the portions which it is recom- 
mended to take for the various determinations, it should be 
borne in mind that they are intended for the great majority of 
rocks, and that in exceptional cases they are to be departed from 
according to the judgment of the analyst. For instance, in the 
analysis of iron ores, if a gram be taken for the main portion the 
bulk of the voluminous precipitate of ferric hydroxide will be so 
great that it cannot all be brought on one filter, and possibly not 
on two. In such cases, therefore, only half a gram of material 
need be taken, even though extra care must be paid to the de- 
termination of other constituents. On the other hand, for the 
determination of alkalies in peridotites and other rocks in which 
their amount is extremely small, a whole gram of powder should 
be taken, instead of the half gram which is usually sufficient. 

The beginner should take full notes during the progress of 
the analysis, until the various methods become familiar, and 
even then all occurrences or manifestations out of the ordinary 
are to be noted and not left to memory. The details of all the 
calculations are to be recorded in the note-book for future refer- 
ence. It may sometimes happen that an apparent analytical 
error is merely due to a slip in arithmetic, and a reexamination 
of the recorded weights and calculations may obviate the neces- 
sity of a duplicate analysis. 

In rock analysis a preliminary qualitative examination is 
seldom, if ever, necessary. The microscope will often serve the 
purpose. But if not, and the presence of some unusual substance 
is suspected, it is better, as Hillebrand remarks, to assume its 
presence and conduct the quantitative analysis on this assump- 



GENERAL COURSE OF ANALYSIS. 57 

tion. This will be time saved in the end, even if the result is 
merely to prove the absence of the suspected body. One should 
always test by qualitative methods the character of the weighed 
precipitate in such cases, to see whether it is really the sub- 
stance in question or not. 

Finally, before beginning an analysis the student should see 
that the balance is correctly adjusted, and that all the necessary 
apparatus and reagents are at hand, so that the work may pro- 
ceed without interruption. It will be well to read the whole of 
the description of each of the various methods before beginning 
their execution, as some information may be given at the end 
which is essential to the proper performance. Thus, in the 
determination of combined water, if the rock which is being 
analyzed contains haiiyne or sodalite, and the whole description of 
the method has not been read, the student may be unaware of the 
necessity for binding the chlorine or sulphuric anhydride with 
lead oxide, and so obtain erroneous results. 



2. GENERAL COURSE OF ANALYSIS. 

Before beginning the detailed description of the methods for 
determining the various constituents, it will be advisable to state 
in a concise way what the course of analysis is, in what separate 
portions the different constituents are determined, and the plan 
of separation, in order to obtain a general survey, and so that 
the details may be considered later with greater intelligence and 
knowledge of their relations to the whole analysis. In this sum- 
mary, if there are several alternative methods which are de- 
scribed subsequently, only that one will be mentioned which 
especially recommends itself for the use of students, and which, 
in general, I have adopted for my own work. 

a. In a portion of about 1 gram, hygroscopic water is de- 
termined by heating at a temperature of 110. This portion 
may also be used afterward for the determination of other con- 
stituents, as P 2 5 , or S, Zr0 2 and BaO. 



58 METHODS. 

b. In a portion of J to 1 gram, combined water is to be 
determined by Penfield's method. The powder is ignited in a 
dry glass tube sealed at one end, and the water driven to. the 
cool portion of the tube, the end containing the powder drawn 
off, and the water weighed in the remaining portion. The 
amount of hygroscopic water is deducted. 

c. In a portion of 1 gram, silica, alumina, total iron as ferric 
oxide, manganese, lime, strontia, magnesia and titanium di- 
oxide are determined. The powder is fused with five times its- 
weight of mixed sodium and potassium carbonates, the melt 
dissolved in hydrochloric acid and evaporated to dryness, thus 
rendering the silica insoluble. The silica is filtered off and in the 
filtrate alumina, ferric oxide, titanium dioxide and phosphoric 
anhydride are precipitated, first by sodium acetate if manganous 
oxide is to be determined, or by ammonia water if this is to be 
neglected. After filtration the precipitate is dissolved in nitric 
acid and reprecipitated by ammonia, and this repeated if there 
is much magnesia present. The precipitate is ignitecl and 
weighed, and then brought into solution by fusion with acid 
potassium sulphate. This is dissolved in water, the ferric iron 
reduced by hydrogen sulphide, the excess of this boiled off, and 
the total iron determined by titration with potassium perman- 
ganate. Titanium dioxide is determined in the same liquid by 
the colorimetric method, which consists in comparing the in- 
tensity of color of a known volume of the titrated fluid after 
oxidation by hydrogen peroxide, with that of a standard solu- 
tion of titanium colored in the same way. 

If manganous oxide is to be determined, the filtrates from the 
sodium acetate and ammonia precipitations are evaporated to 
small bulk, ammonia added, and then hydrogen sulphide. After 
standing, the precipitate of manganous sulphide (containing 
sulphides of nickel, etc., if present) is filtered off, and the man- 
ganese weighed as oxide, after solution and precipitation as 
carbonate. 

If manganese is neglected the filtrate from the ammonia pre- 
cipitate, or ; if it has been determined, the filtrate from the man- 



GENERAL COURSE OF ANALYSIS. 59 

ganous sulphide, is precipitated with ammonium oxalate, the 
precipitate of calcium oxalate dissolved and reprecipitated, and 
the lime determined as such by ignition of the oxalate. 

Strontia is determined in the weighed lime, obtained as above, 
by solution in nitric acid, evaporation to dryness, solution of the 
calcium nitrate by a mixture of ether and absolute alcohol, solu- 
tion of the insoluble strontium nitrate in water and precipitation 
as sulphate after addition of alcohol. 

In the nitrate from the calcium oxalate the magnesia is de- 
termined by precipitation as ammonium-magnesium phosphate, 
which, after solution and reprecipitation, is ignited and the 
magnesia weighed as pyrophosphate. The filtrate from this last 
operation is rejected. 

d. Ferrous oxide is determined in ^a portion of specially 
ground powder of half a gram by solution in a mixture of 
hydrofluoric and sulphuric acids at a boiling heat, the operation 
being conducted hi a well-closed platinum crucible. The con- 
tents of the crucible are transferred to water and titrated with 
potassium permanganate. 

e. A portion of half a gram of specially ground powder serves 
for the determination of the alkalies, which is effected by the 
Lawrence Smith method. The powder is intimately mixed with 
ammonium chloride and calcium carbonate, and fused. After 
thorough leaching the filtrate is precipitated with ammonium 
carbonate, and the filtrate from this is evaporated to dryness. 
The ammonium chloride is driven off from the alkali chlorides by 
cautious heating, and the mixed chlorides of sodium and po- 
tassium weighed. The potassium is separated by the use of 
hydrochloroplatinic acid, and the potassium weighed as plat- 
inichloride, the soda being determined by difference, from the 
weight of the mixed chlorides. 

/. In a portion of about 1 gram, phosphoric anhydride is 
determined by digestion with nitric and hydrofluoric acids, 
removal of silica by evaporation, and subsequent precipita- 
tion as ammonium phosphomolybdate. The precipitate of this 
substance is dissolved in ammonia water, the phosphorus is 



60 . METHODS. 

thrown down by magnesia mixture as ammonium-magnesium 
phosphate, and weighed as magnesium pyrophosphate. 

g. In a portion of 1 gram, total sulphur, zirconia and baryta 
may be determined. The rock powder is fused with alkali car- 
bonates, and the melt leached with water. After acidification of 
the filtrate with hydrochloric acid the sulphur is precipitated 
and weighed as barium sulphate. The zirconia is dissolved 
out of the residue insoluble in water by very dilute sulphuric 
acid, and, after addition of hydrogen peroxide, is thrown down 
and weighed as basic phosphate by the addition of sodium 
phosphate. The barium remains as sulphate after solution of 
the zirconia. It is brought into solution by fusion with alkali 
carbonate, which converts it into carbonate, leaching out the 
melt with hot water, and solution of the hydrochloric residue in 
acid. It is precipitated as sulphate, in which form it is weighed. 

h. Sulphuric anhydride is determined in a portion of about 
1 gram by digestion with hydrochloric acid and precipitation 
as barium sulphate. 

i. For chlorine a portion of 1 gram is digested with chlorine- 
free nitric acid, and the chlorine precipitated in the filtrate by 
silver nitrate. 

j. Fluorine is determined in a portion of 2 grams by fusion 
with alkali carbonates, leaching with water, precipitation of the 
filtrate with ammonium carbonate, the filtrate from which is 
precipitated with an ammoniacal solution of zinc oxide. In the 
filtrate from this a mixture of calcium carbonate and fluoride is 
precipitated by calcium chloride, and the calcium carbonate dis- 
solved out by acetic acid, leaving the calcium fluoride, in which 
form the fluorine is weighed. 

k. A portion of from 2 to 5 grams is used for the determina- 
tion of carbon dioxide. The rock powder is decomposed by 
hydrochloric acid in a small flask, and the carbon dioxide ab- 
sorbed in a weighed U-tube containing soda-lime, precautions 
being taken to keep the apparatus full of a current of air free 
from carbon dioxide, and to properly dry and purify the gas 
given off from the rock. 



CHIEF SOURCES OF ERROR. 61 

I. For chromium a gram of rock powder will suffice, though 
2 grams are preferable. After fusion with alkali carbonate and 
a little potassium nitrate, and subsequent leaching with water, 
the chromium is determined as chromate in the filtrate, if nec- 
essary after concentration by evaporation, by a colorimetric 
comparison of a known volume of the solution with a standard 
solution of potassium chromate. 

m. For copper a portion of 2 grams is decomposed by a mix- 
ture of nitric and hydrofluoric acids, filtered, evaporated to dry- 
ness, the residue taken up with dilute hydrochloric acid, and the 
copper precipitated in the acid filtrate by H 2 S, and weighed 
as CuO. 

3. CHIEF SOURCES OF ERROR. 

It may be found useful by the student to have pointed out 
those portions of the various methods where error is liable to 
occur, and in regard to which especial care should be taken. 
The list is not intended to be complete, and general sources of 
error, such as incomplete washing or entrance of dust, are 
omitted. Certain small corrections are also not mentioned, as 
being refinements beyond the needs of the average student. 
Hillebrand 's book abounds in these, and it is therefore espe- 
cially valuable to the practised analyst. 

Silica. Hillebrand * has shown that a double evaporation to 
approximate dryness yields more accurate results than the older 
and more usual method of a single evaporation and subsequent 
heating at 110 or 120. By the first method practically all the 
silica is rendered insoluble, only a minute amount being found hi 
the alumina precipitate. Prolonged heating at 110 or 120 is 
apt to increase the amount of impurity in the silica, and also 
allow more silica to be dissolved in the treatment with HC1. 
The silica thus dissolved is shown by Hillebrand to be not 
wholly precipitated along with alumina, etc., and he also shows 
that silica is not perfectly insoluble in melted potassium pyrosul- 
phate. Blasting of the silica for at least twenty minutes is es- 

* Hillebrand, p. 52. 



62 METHODS. 

sential for the complete expulsion of water. The weight of the 
silica must always be checked by evaporation with hydro- 
fluoric and sulphuric acids, whatever the rock may be, as it is 
never pure. 

Alumina. In precipitating this, if ammonium salts are not 
present in sufficient amount, some magnesia falls down with the 
alumina, thus increasing the apparent quantity of this and 
diminishing that of magnesia by the same amount. This is an 
extremely frequent source of error, especially in basic rocks con- 
taining considerable magnesia, and it should be carefully guarded 
against by the analyst. It has undoubtedly caused more trouble 
and has rendered worthless more rock and mineral analyses, 
than any other single special source of error, and possibly more 
than all others combined. 

The analyst must, therefore, be sure of an abundance of am- 
monium salts (preferably chloride), in the liquid, and also make 
it a rule to dissolve the first precipitate and reprecipitate with 
ammonia once at least, and twice or thrice in basic rocks^ 
whether ammonia alone or sodium acetate has been employed 
for the first precipitation. 

If the ammonia water used is not fresh and contains am- 
monium carbonate, some calcium carbonate will be thrown down 
with the alumina, and will, of course, increase its amount and 
diminish that of the lime of the rock by the same amount. In 
case of doubt the ammonia water should be tested with CaCl 2 
before using, and if a precipitate is formed it should be rejected, 
or boiled till the ammonium carbonate is entirely decomposed. 

Another precaution to be observed in regard to the use of 
ammonia water is that if the bottle has been in use for hold- 
ing it for a long time, the interior is apt to be acted on by the 
alkaline liquid, with the result that, besides impurities going into 
solution, the liquid will contain small flakes of silica or partially 
decomposed glass, which will increase the apparent weight of 
alumina or appear with the extra silica separated later. In such 
cases a new bottle must be taken for holding the ammonia 
water. 



CHIEF SOURCES OF ERROR. 63 

Prolonged boiling or standing of the liquid after addition of 
the ammonia is to be avoided, as this will not only render the 
precipitate slimy and hard to filter, but will also lead to the pre- 
cipitation of some lime through the action of the atmospheric 
carbon dioxide. 

The final precipitate by ammonia must be washed absolutely 
free of all traces of chlorine, since any of this, if present, will com- 
bine with the aluminum and iron on ignition, forming aluminum 
and ferric chlorides, which will volatilize and lead to loss of 
alumina and ferric oxide. For this reason the first and second 
precipitates should be dissolved in nitric acid, rather than in 
hydrochloric, thus rendering complete washing from chlorine far 
more easy (Penfield). 

If the basic acetate method is employed for the first precipita- 
tion, regard must be had to the probability of some alumina and 
ferric oxide not being precipitated and passing through with the 
filtrate, unless the conditions as to acidity and the amount of 
free acetic acid are very exactly adjusted. The only way to 
guard against this is by care and strict attention to the condi- 
tions as laid down in the description of the method. But even 
under favorable circumstances, and in the hands of experienced 
analysts, a little, alumina especially is liable to be found in the 
filtrate. This should always be recovered before precipitation 
of the manganous oxide, though this precaution is frequently 
neglected, apparently through ignorance of its necessity. The 
amount of the error is usually not very large, but may reach as 
high as 2 per cent of the rock, judging from some analyses 
with abnormally, and otherwise inexplicably, high percentages 
of MnO. As, however, it affects to a very notable extent the 
figure for the highly important alumina, the use of the basic 
acetate method is to be avoided by the inexperienced student, 
or if adopted should be carried out with the greatest caution. 
It may be noted that, chiefly on account of this source of error, 
Jannasch * rejects this method altogether. 

* Jannasch, p. 215. Cf. the remarks in Fresenius, I., p. 647; and Hille- 
brand, p. 55. 



64 METHODS. 

Alumina is always determined by difference, and therefore all 
the errors are thrown upon it which may be involved in the de- 
termination of Fe 2 3 , Ti0 2 , Zr0 2 , P 2 5 , Cr 2 3 and V 2 3 . As 
Hillebrand says, however, these may balance, and anyway there 
seems to be at present no escape from this mode of procedure, 
since as yet no satisfactory method has been devised for its 
separation and direct determination, at least without the ex- 
penditure of an inordinate amount of time. This fact, as well 
as the numerous possible sources of error noted above and the 
importance of alumina from the chemical and mineralogical 
points of view in the application of the analysis, emphasize the' 
necessity for extreme care in the separate determination of the 
various constituents weighed with it. 

The method of separation from iron which is sometimes 
employed in Europe, by fusion of the ignited precipitate with 
sodium hydroxide in a silver crucible, should never be used, as it 
is open to very grave objections.* 

Ferric Oxide. A not infrequent source of error in the deter- 
mination of this is incomplete reduction to the ferrous condition 
before titration with permanganate. The current of H 2 S, which 
is the best reducing agent and which should always be used, 
must therefore be allowed to pass for at least ten or fifteen 
minutes, and until considerable sulphur has separated out. 
Care should also be taken that the air in the flask, in which the 
expulsion of the excess of H 2 S takes place by boiling, be re- 
placed by C0 2 , and that the boiling be not carried out to a very 
small volume of liquid, when the strong sulphuric acid is liable 
to oxidize part of the ferrous iron. 

Zinc is to be avoided as a reducing agent, partly because 
perfectly pure and iron-free zinc is difficult to procure, partly 
because of the difficulty of ascertaining when reduction is com- 
plete, and still more on account of the reducing effect of nascent 
hydrogen on Ti0 2 , which is always present, and on V 2 5 , the 
lower oxides of which would affect the permanganate and thus 
appear as ferric oxide. 

* Cf . Hillebrand, p. 59. 



CHIEF SOURCES OF ERROR. 65 

Ferrous Oxide. Hillebrand * has discussed the reliability of 
the Mitscherlich method by decomposition by sulphuric acid in 
a sealed tube, which is widely adopted in Europe, and shown 
that it tends to too high values, owing to the oxidizing effect of 
ferric sulphate on the pyrite present in the rock under the con- 
ditions of decomposition, and the consequent reduction of part 
of the ferric iron of the rock to the ferrous condition. This is 
especially marked in basic rocks, which are high in iron, and 
which are those where pyrite is most frequently met with. This 
method should therefore be abandoned, and replaced by that 
of decomposition by hydrofluoric and sulphuric acids in an 
atmosphere of steam, or of steam and carbon dioxide. 

In this there is liability to error hi the hands of the inex- 
perienced through partial oxidation of the ferrous iron. This is, 
however, very largely a matter of manipulation, and should not 
noticeably affect the results after some practice. It is always 
the wisest plan in particular analyses, when possible, to make 
duplicate determinations of ferrous oxide. 

Since a solution of potassium permanganate, though quite 
stable, is liable to suffer decomposition on long standing, care 
should be taken, in the determination of both ferric and ferrous 
oxides, that its assumed strength is unchanged, the tendency 
being to too high values for iron owing to weakening of the 
solution. The solution should therefore be standardized from 
time to time, say every two or three months. This is a precaution 
which is not always sufficiently well observed. 

Magnesia. The chief source of error here is that already 
mentioned in connection with alumina, namely, the tendency 
to partial precipitation as hydroxide by ammonia along with 
alumina. This must be prevented by the presence of sufficient 
ammonium salts and repeated precipitations, as already de- 
scribed. 

An error of less magnitude and importance, but which should 
be taken into account, is that involved in the precipitation of 
the ammonium-magnesium phosphate. If there be present 
* Hillebrand, p. 88. 



66 METHODS. 

excess of ammonia, ammonium salts and precipitant, the am- 
monium-magnesium phosphate, and hence the magnesium pyro- 
phosphate, will not be normal in composition, owing to the 
presence of extra P 2 5 , as pointed out by Neubauer * and by 
Gooch and Austin, f This must be corrected by solution of the 
first precipitate and reprecipitation from the acid solution by 
a slight excess of ammonia. This error will not affect the other 
constituents, but will raise the figures for MgO only, and hence 
the summation of the analysis. 

The magnesia will be low if the precipitate of calcium oxalate 
is not precipitated twice, as mentioned below. 

Lime. The only serious source of error in regard to this is the 
possible presence of ammonium carbonate in the ammonia water 
used for precipitating the alumina, etc., which will render the 
apparent amount of CaO too low, as has been already described. 

The first precipitate of calcium oxalate invariably contains 
some soda and magnesia, and it should therefore be dissolved 
and reprecipitated. 

Alkalies. The Lawrence Smith method is so much superior 
to all others, both as to accuracy and saving of time, that it 
should always be employed. Its only inherent serious source 
of error lies in the fact that the calcium carbonate usually con- 
tains a very small amount of alkalies, chiefly sodium salts. But 
the amount of these can be determined once for all in a weighed 
portion of the stock of calcium carbonate, and the small constant 
correction is easily and safely applied. If the carbonate is well 
prepared and thoroughly washed, the error involved by neglect 
of applying this correction will seldom be serious. 

The other methods of decomposition, involving the separa- 
tion of alumina, iron oxides, lime and magnesia by the usual 
methods, introduce a large element of uncertainty through 
impurities in the reagents used and through the possibility of the 
introduction of alkalies from the glass vessels. They are also 
far more laborious and much longer in point of time. 

* Neubauer, Zeits. Angew. Chemie, 1896, p. 435. 
t Gooch and Austin, Am. J. Sci., VII, p. 187, 1899. 



CHIEF SOURCES OF ERROR. 67 

It must be mentioned that in a recently published * com- 
parison of the Lawrence Smith with the usual European method 
for determining alkalies, Dittrich comes to the conclusion that 
the one is as accurate as the other, but favors the use of the 
former on account of its greater expedition. It may well be 
doubted, however, if in the hands of less expert analysts the 
second method would compare as favorably as it does according 
to the figures given by him. But even if so, the point of labor 
and time saved should certainly decide analysts in favor of the 
former. 

Titanium Dioxide. There are few sources of error of serious 
importance in the determination of this by the colorimetric 
method, which is the one to be employed in almost every case. 
If the hydrogen peroxide contains fluorine, as occasionally hap- 
pens, the results will be too low (Hillebrand), and this reagent 
should therefore be tested for this impurity before use. 

Use of the method of determining Ti0 2 by prolonged boiling 
in a dilute acid solution with S0 2 is to be discouraged. Pre- 
cipitation of metatitanic acid is by no means complete in all 
cases, and that which is precipitated is almost always contami- 
nated by alumina and ferric oxide. It is also extremely liable to 
adhere very firmly to the sides of the beaker, whence it is re- 
moved with great difficulty. After thorough trial, with various 
modifications, I have rejected this method entirely. 

A drop or two of H 2 S0 4 must always be added to the hydro- 
fluoric acid before evaporation of the silica with this, as other- 
wise the whole of the titanium present in the silica will not be 
retained but will be partially vaporized as fluoride. The as- 
sumption is sometimes made that the residue from evaporation of 
the silica represents the amount of Ti0 2 in the rock. This is 
quite unwarranted, as the residue contains only part of the Ti0 2 , 
as well as A1 2 3 , Fe 2 3 , P 2 5 , etc. 

Phosphoric Anhydride. The liability to the formation of 
ammonium-magnesium phosphate of abnormal composition 
through excess of ammonium salts or magnesia mixture, similar 

* M. Dittrich, Neues Jahrbuch, 1903, II, p. 80. 



68 METHODS. 

to that spoken of under magnesia, also affects this constituent. 
But for the small quantities of this substance ordinarily found in 
rocks this error is of no great moment. 

Manganous Oxide. The error involved in the separation of 
this by the basic acetate method has already been discussed 
(p. 63), so that it need not be enlarged on here. 

In the determination of the other minor constituents the 
possible errors are of such slight absolute importance that special 
mention of them here is uncalled for. They will be spoken of when 
necessary in their respective places in the descriptive part, and 
should be guarded against in accurate work, of course. As 
Hillebrand remarks, however, in regard to the rarer elements, 
"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." 

4. TIME NEEDED FOR ANALYSIS. 

While the time necessary for most of the separate parts of 
the various analytical operations is conditioned by the circum- 
stances of these in a more or less fixed way, yet the actual time in 
which the whole rock analysis can be finished depends within 
limits very largely upon the skill and judgment of the analyst. 
Thus, it will take a definite, minimum time to evaporate a given 
bulk of liquid, or to allow a precipitate, as that of ammonium 
phosphomolybdate, to stand. But an expert analyst will be 
able to complete many operations in much less time than can a 
novice. For example, the time needed for filtering and com- 
pletely washing a precipitate can be reduced very materially 
with care and experience, and likewise the quantity of washing- 
water needed, which, in turn, will shorten the subsequent opera- 
tions with the filtrate. 

Again, while some of the operations are proceeding auto- 
matically the analyst can be carrying out others, and thus make 
use of time which would otherwise be wasted for the purposes of 
analysis. Or, the skilful chemist can carry out two filtrations 



TIME NEEDED FOR ANALYSIS. 69 

simultaneously, while the attention of the novice will be fully 
occupied with one. 

The analyst, therefore, should not be content to sit still and 
wait for such partial operations to be terminated before begin- 
ning others, but should avail himself of all the opportunities 
which present themselves for carrying on simultaneously as 
many separate operations as it is possible to do with success. 
The ability to do this naturally grows with experience in regard 
to the purely mechanical execution, and also with judgment as 
to the best way of economizing time. It is not to be recom- 
mended that the novice should attempt very much in this way, 
and he will probably find that one or two operations at once are 
all that he can cope with successfuly at the start. But he 
should constantly bear in mind the manifold possibilities in 
this direction, and, with growing experience, avail himself of 
the various opportunities that present themselves. 

With some practice, the number of different operations, both 
active and passive, which may be conducted simultaneously or 
nearly so, may easily reach six or more. Thus, while filtering 
the first precipitate of ammonium-magnesium phosphate, the 
solution of alkali chlorides can be evaporating, the reduced 
iron solution be boiling down to expel H 2 S, the precipitate of 
calcium oxalate ignited, ferrous oxide or water be determined, 
and the precipitates by which phosphoric anhydride, sulphur, 
baryta and zirconia are determined can be standing and fil- 
tered successively. Any such combination implies, of course, a 
sufficiently liberal supply of apparatus so as not to be kept wait- 
ing for lack of the necessary utensils, and it also implies the 
ability of the analyst to devote several hours continuously at a 
time to the analysis. 

To come down to concrete figures,* it is easily possible to 
finish an analysis involving the determination of eighteen or 
twenty constituents in five days, not necessarily consecutive, of 
eight or ten hours each, and even in less time. Such an analysis 

* Cf. Hillebrand, p. 22. 



70 METHODS. 

can surely be made in six days without any special effort at 
economizing time. Indeed, a comparatively simple analysis, 
in which a dozen constituents are to be determined, may be 
completed readily in four, or even in three, days without any 
sacrifice of accuracy, but this last is possible only in the hands of 
a quick and experienced worker. 

In the present section some suggestions are made of the possi- 
bilities in the way of shortening the time of analysis. They are 
not intended to be final, but will serve merely as guides in laying 
out the plan of analytical work, and are subject to modification 
to suit the exigencies of each particular case. In connection 
with them some estimates are given of the amount of time which 
is needed for the several operations and determinations. These, 
again, must be regarded as only rough approximations, which 
will vary with differing laboratory facilities and according to the 
skill and experience of the operator. They will have to be 
extended somewhat when conducted by a novice. 

Assuming that we start one morning at eight o'clock, 
with about 50 grams of rock chips, these can be reduced to 
powder ready for analysis in about an hour. The main fusion 
with alkali carbonates is then begun, the time needed for the 
fusion and cooling being about an hour. After this, the solution 
of the cake in hydrochloric acid and preparation for evaporation 
are carried out, which may be completed in half an hour or so, 
when the first evaporation is commenced. In the meanwhile, 
during the fusion with carbonate, the portion for phosphoric 
anhydride may be weighed out, digested with acid, filtered, and 
the filtrate evaporated, so as to free the platinum basin for the 
silica evaporation. This first evaporation for silica will be over 
by three o'clock, and during its continuance the precipitation of 
phosphoric anhydride by ammonium molybdate and the fusion 
of the portion for total sulphur, zirconia and baryta, and some of 
the succeeding operations can be done. The filtration of the 
silica will take nearly an hour, after which the filtrate is placed 
on the water-bath and the second evaporation continued till 
dark, or overnight if possible and necessary, so as to be ready 



TIME NEEDED FOR ANALYSIS. 71 

for filtration the next morning. Time will usually be found in 
the afternoon for the determination of hygroscopic water. 

The second day begins with the second filtration of silica, and 
its washing, which will take in all an hour and a half or less. 
While the silica is being dried in the crucible and ignited, which 
lasts an hour or more, the precipitations of alumina, etc., may be 
made, three of which will consume nearly two hours, bringing us 
to lunch- time. During this the weighed silica may be evapo- 
rating with hydrofluoric acid, so as to be ready for the ignition 
and weighing of the crucible and residue after lunch. The 
filters and moist precipitate of alumina, etc., are next dried and 
ignited, for which nearly two hours are required. While this is 
going on, the filtrate can be precipitated twice with ammonium 
oxalate, and the ammonium-sodium phosphate added to the 
filtrate, to stand overnight for complete precipitation. After 
the ignition of the ammonia precipitate, its fusion with acid 
potassium sulphate can be begun and continued during the rest 
of the afternoon, by the end of which it may generally be con- 
cluded. If not, it may be continued for an hour or so the next 
morning to completion, but the fusion should not be continued 
overnight. Ignition of the calcium oxalate and weighing of 
the lime may finish the day's work. 

If manganese is to be determined, the precipitation of this 
by hydrogen sulphide will take the place of the determination of 
lime, and, as the precipitate must stand for at least twelve hours, 
the determination of lime and magnesia are postponed for a day 
at least. 

On the third day the determination of the alkalies is begun, 
the grinding, mixing and subsequent fusion taking up about 
two hours. While this fusion is in progress, the fusion of the 
ammonia precipitate with acid potassium sulphate being com- 
plete, the cold pake is dissolved in water, filtered for the trace of 
silica, the solution reduced with H 2 S, and the boiling off of the 
.excess of this begun, which can usually be accomplished in less 
than two hours. This interval is occupied with the solution 
of the fusion for alkalies in water, and the precipitation of the 



72 METHODS. 

filtrate with ammonium carbonate, which may take up the rest 
of the morning till lunch-time. During the first of the morning 
a liter of water may be boiled and allowed to cool, so as -to be 
ready for the iron determinations in the afternoon. The evapora- 
tion of the filtrate containing the alkali chlorides may be begun 
before lunch, or immediately after it, and will usually last several 
hours. By afternoon the solution in the flask is boiled down 
sufficiently, cooled in water, and the total iron determined. The 
cooling may take half an hour, and the titration only a few min- 
utes, after which the solution is evaporated on the water-bath, 
in preparation for the titanium determination next day. As a 
supply of cold, boiled water is now available, the determination 
of ferrous iron may follow immediately after that of total iron, 
and will be completed in less than half an hour by the simple 
method given elsewhere. A duplicate determination may also 
be made if desired. Assuming that manganese is neglected, 
during this afternoon the magnesia precipitate is dissolved and 
reprecipitated, and then filtered through the Gooch crucible, 
ignited and weighed. Finally, the dried alkali chlorides are 
freed from ammonium chloride by heating, brought into solution, 
filtered, and the evaporation in a weighed platinum crucible 
begun, which may be advantageously carried on overnight. 

The fourth day is taken up with the determination of potas- 
sium, titanium and combined water, the finishing off of the 
operations for phosphorus, barium, etc., if these have not been 
done before in appropriate intervals. If manganese is deter- 
mined, the determination of lime is carried out on the third day, 
and that of magnesia on the fourth. The extra time needed 
may cause the analysis to be prolonged into a fifth day, though 
skilful working will avoid this. 

The above is an outline of my usual procedure, and it must be 
noted that a working day of nine or ten hours, with an hour's 
intermission for lunch, is postulated to allow some leisure, but 
with skill and application days of eight hours will suffice. It will 
be found that there are plenty of enforced pauses in the course of 
the main operations, during which the various portions of the 



HYGROSCOPIC WATER. 73 

determinations of phosphorus, barium, chlorine and the other 
minor constituents can be easily carried out. The volumes of 
liquid used for these are so small as a rule that the filtrations and 
other operations involved will each consume little time. 

5. HYGROSCOPIC WATER. 

By this term is meant the moisture which is absorbed by the 
rock powder from the atmosphere, or which may come from that 
enclosed in microscopic cavities, although a part of the more 
loosely combined water of crystallization of some zeolites and 
other hydrous minerals may also be included under this head. 
It is all, or practically all, expelled from the rock at a tempera- 
ture of about 110. Although it is usually present only in very 
small amount, and has no important bearing on the constitution 
of fresh igneous rocks, yet it should always be determined 
separately from the combined water. The reasons for this have 
been fully discussed by Hillebrand * and need not be gone into 
here. 

About 1 gram of the rock powder is weighed out into a 
previously ignited and cooled platinum crucible of 30 or 40 cc. 
capacity (cf. p. 80), and this is heated in an air-bath at a tem- 
perature a little above that of boiling water. The exact tem- 
perature is of no great importance, as long as it is only slightly 
above 100. In the U. S. Geological Survey laboratory a toluene 
bath is used, giving a temperature of 105 (Hillebrand), while my 
practice has been to use an ordinary copper air-bath, with single 
walls, and the flame so regulated as to maintain the temperature 
constantly at 110, which is readily accomplished. The crucible 
is preferably covered during the heating with a 7-cm. filter-paper, 
the platinum cover being removed. It will usually be found 
that half an hour's heating, and often less, will be sufficient to 
arrive at a constant weight. After heating, the crucible is 
allowed to cool in a desiccator and weighed, heated again for a 
quarter of an hour, and if the weight is constant, the loss in 

* Hillebrand, p. 32. 



74 METHODS. 

weight, divided by the weight of rock powder taken, gives the 
percentage of hygroscopic water, which may be conveniently 
tabulated as H 2 - . 

6. COMBINED WATER. 

Under this head is included all the water in a rock which is 
chemically combined in mineral molecules, either as water of 
crystallization (as in analcite) or hydroxyl (as in muscovite or 
biotite). 

Loss on Ignition. The early method, and a very frequent 
one even at the present day, for the determination of this con- 
stituent, was that of simple ignition in a platinum crucible, the 
assumption being that this ''loss on ignition" represents only 
the total water in the rock. A little consideration shows that 
the results under these circumstances will only be accurate when 
the rock contains neither substances which are easily volatilizable 
at the temperature of ignition (as carbon dioxide, carbon and 
organic matter, sulphur, chlorine and fluorine) nor oxidizable 
constituents (as ferrous oxide). In the former case the apparent 
amount of water will be too great, owing to the partial or entire 
loss of the volatilizable ingredients, and in the latter it will be too 
small, on account of the gain in weight through the oxidation of 
ferrous oxide to ferric.* 

It is held by many that the error due to the latter cause may 
be corrected by calculation of the gain in weight which the fer- 
rous oxide present in the rock, and which is separately deter- 
mined, would undergo if completely oxidized to ferric oxide. 
This assumption, however, is by no means valid under the cir- 
cumstances obtaining in the process of ignition, as is shown, for 
example, by the difficulty of completely oxidizing magnetite by 
ordinary ignition, even after roasting with nitric acid. 

In the case of volatilizable constituents, also, there can 
scarcely ever be a certainty that their loss in this way will be 
complete, so that appropriate corrections may be made with 

* This may be so great that if little water is present, the powder may 
weigh more after ignition than before. 



COMBINED WATER. 75 

safety after their separate determination. This would only be 
true of carbon dioxide when derived from calcite, magnesite or 
dolomite, and then only after prolonged blasting. 

This being so, and it being also a fact that there are only rare 
instances of rocks which contain no such disturbing constituents 
(especially FeO), it follows that in the great majority of cases the 
combined water should not be determined by loss on ignition. 

As, however, the determination of combined water is not 
always of vital importance for the chemical study of rocks, it 
happens that this simple method may be used in certain cases. 
These would include very fresh igneous rocks, containing but 
a small amount of water, no other volatilizable ingredients, 
and only a small amount of ferromagnesian minerals, say up 
to 5 per cent, and consequently only 1 or 2 per cent of ferrous 
iron. Many granites, porphyries, syenites, trachytes, bostonites 
and anorthosites fall under this description. For such rocks 
the minute error due to the very small amount of ferrous oxide 
present (amounting at most to one-ninth of its weight) may be 
deemed to be negligible, and the results of such a determination 
regarded as acceptable. 

If the method of "loss on ignition" is to be employed, the 
crucible and its contents, which have previously been used for the 
determination of hygroscopic water, are ignited (covered) at a 
bright-red heat for about half an hour, or to constant weight, 
cooled in the desiccator and weighed. The loss in weight repre- 
sents the amount of combined water. The fact must, however, 
be recognized that this method of procedure is not strictly accu- 
rate, and for all high-class work, and in all cases where the 
amount of ferrous oxide is at all considerable, or volatilizable 
substances are present, the combined water must be determined 
directly. 

Penfield's Method. For the direct determination of water 
the extremely easy and simple method of Penfield is to be used.* 
This consists essentially in igniting the rock powder in a narrow 

* S. L. Penfield, Am. Jour. Sci., XL VIII, p. 31, 1894. 



76 METHODS. 

tube of hard glass, closed at one end and with or without enlarge- 
ments in the middle, pulling off the heated end containing the 
powder and leaving the balance of the tube closed, weighing the 
portion of the tube which contains the expelled water, and finally 
weighing this portion of the tube after thorough drying. This 
gives the total amount of water, hygroscopic and combined, 
from which the amount of the former, as previously obtained, 
is to be deducted to obtain the latter. For illustrations of the 
apparatus used the reader is referred to the paper cited above. 

In the case of most fresh igneous rocks a simple tube of hard 
glass may be used, closed at one end, and without any enlarge- 
ment. The dimensions recommended by Penfield are 20 to 25 
cm. long,* and with an internal diameter of about 6 mm. If the 
rock contains more than a fraction of a per cent of water it is 
better to have a bulb or enlargement blown about midway in the 
tube. Indeed, this is always advisable, to guard against drops of 
water rolling back on the heated portion. A single bulb is 
sufficient for nearly all rocks, and the more complicated forms 
illustrated by Penfield will seldom be found necessary in rock 
analysis. 

It is of the utmost importance to have the tube thoroughly 
dry, and this ' ' is best accomplished by heating and aspirating a 
current of air through it (while hot) by means of a glass tube 
reaching to the bottom." This must always be done, even if 
the tube is apparently dry. After cooling, the tube is weighed, 
its weight including that of the brass-tube support which is used 
to support it on the balance-pan. 

From one-half to one gram of the rock powder is then in- 
troduced, filling the tube about 2 or 3 cm. from the closed end. 
This must be done without soiling the upper portion of the tube, 
and is accomplished by means of a small thistle-tube, of diameter 
small enough to slip easily into the bulbed tube, and long enough 

* The tube must not be too long to go in the balance-case, and so inter- 
fere with weighing, nor too short, so as to give rise to the danger of loss of 
water through lack of sufficient cooling surface and heating of the cooler 
portion. 



COMBINED WATER. 77 

to reach the end. Such a filling-tube can be readily constructed 
from a 5-c.c. pipette by cracking the bulb in two and reducing 
the length of the tube to 25 cm. The filling-tube, of course, 
must be thoroughly dry also.* After the powder is introduced 
the tube is weighed again, tp obtain the weight of substance 
used, the manipulation being delicate and gentle to avoid any 
rolling of the powder toward the bulb. 

After a few gentle taps so as to form a free passage above the 
powder for the heated air, which might otherwise drive the 
powder toward the bulb and -so necessitate refilling and reweigh- 
ing, the tube is held in a clamp horizontally, or very slightly 
sloping toward the mouth. A strip of filter-paper or cloth, 
moistened with cold water and kept moist, is wrapped around 
the bulb and farther end of the tube, so as to ensure condensa- 
tion of the expelled water, care being taken that it is not so 
near the mouth as to allow any water dropped on it to enter 
the tube. 

A gentle heat is then applied to the closed end, and gradu- 
ally increased to the full heat of the Bunsen burner. The blast 
may be used if minerals are known to be present which only 
give off their water with difficulty, but this will not be needed in 
most rocks. If the strip of cloth or filter-paper be kept moist, 
there is scarcely need for a screen of asbestos board, nor is it 
often necessary to partially close the tube with another short 
piece of tube drawn out to a capillary and connected by rubber 
tubing. If the heated end of the tube tends to sink, this should 
be prevented by gently turning it round from time to time 
parallel to its axis, the clamp being adjusted so as to allow of 
this being done. 

After the whole extent of the powder has been ignited and the 
water completely expelled, which will take at least a quarter of an 
hour, a short piece of narrow tubing is melted onto the closed tip, 
to serve as a handle. The flame is then lowered and the water 

* The thistle- tube can be easily cleaned "by drawing through it a bit 
of cotton attached to a wire," or, if the analyst be a smoker, a fresh pipe- 
cleaner will be found useful. 



78 METHODS. 

is very gently and gradually driven into the bulb. This must be 
carried out with caution and patience to avoid cracking the tube. 
When the water has been driven into the bulb and to a safe dis- 
tance, the portion of the tube immediately in front of the powder 
is heated to softness all around, and the end containing the 
powder drawn off and the other part sealed without allowing the 
flame to enter. This last procedure is not strictly necessary in 
all cases, but is always advisable, so as to obviate the possibility 
of loss of powder during the subsequent drying and aspiration. * 

The upper portion of the tube containing the water is allowed 
to cool in the clamp in a horizontal position, wiped clean and dry 
on the outside and weighed. It is then placed again in the clamp 
and gently heated, the moist air and steam being sucked out by 
means of a small tube extending to the bottom and connected 
with a suction-pump. After thorough drying in this way it is 
allowed to cool and is again weighed. 

The loss in weight is the amount of total water, which is re- 
duced to percentage figures by division by the amount of sub- 
stance taken, and the percentage of hygroscopic water already 
determined is subtracted. 

In nearly all cases the simple method described above will be 
quite sufficient and will yield very accurate results. But when 
rocks, such as some metamorphic ones, contain minerals like 
topaz, chondrodite, or staurolite, whose water is not completely 
driven off over the blast, it becomes necessary to use a more 
intense method of heating. For a description of this, reference 
may be made to Penfield's article. 

If the rock contains constituents like S0 3 , Cl or F in appre- 
ciable amount, which are volatile and which will add to the 
weight of the water driven off and condensed, it is necessary to 
use a retainer for these during the ignition. This may be either 
CaO or PbO, previously ignited and cooled. A little of either of 
these is introduced by means of the thistle-tube into the bulbed 
tube, after the rock powder has been weighed, and mixed ' ' by 
means of a fine wire, bent into a corkscrew coil at the end." A 
decigram or two will be ample for most rocks. In ordinary 



SILICA. 79 

rock analysis the correction for C0 2 , described by Penfield, will 
not be necessary. 

With the usual run- of rock analyses the more complicated 
apparatus of Penfield or Gooch, involving the use of absorption- 
tubes, will seldom be called for. For a description of them the 
references below had best be consulted if their use be deemed 
desirable.* 

7. SILICA. 

Fusion with Alkali Carbonate. A number of minerals, as 
leucite, nephelite and olivine, are easily and completely decom- 
posed by hydrochloric acid, and their analysis may be affected 
after such a simple preliminary solution. Others again, as 
quartz, orthoclase, albite, pyroxene and hornblende, are either 
quite unattacked or only partially decomposed by this medium. 
Since practically no igneous rocks, so far as we know, are com- 
posed entirely of the first class of minerals and are completely 
soluble in hydrochloric acid, it is necessary to bring their con- 
stituents into soluble form by other means, as a preliminary to 
their analysis. 

A number of methods have been proposed for this purpose, 
some of them based on the use of hydrochloric, sulphuric or 
hydrofluoric acids, and others involving the use of various fluxes, 
as alkali carbonates, calcium carbonate, lead or bismuth oxide 
and boric acid. A description and discussion of some of these 
is given by Hillebrand,t but it is unnecessary to enter into this 
phase of the matter here. It will suffice to describe only those 
methods which commend themselves to the author and to the 
chemists of the U. S. Geological Survey. 

In order to determine the different constituents of a rock 
different methods of decomposition are found to be appro- 
priate, depending on the constituents to be determined in a 

* S. L. Penfield, Am. Jour. Sci., XL VIII, p. 37, 1894; F. A. Gooch, Am. 
Chem. Jour., II, p. 247, 1880; Hillebrand, pp. 40-47. 
t Hillebrand, pp. 47-52. 



80 METHODS. 

given portion. Those with which we shall have to deal most 
are: fusion with alkali carbonate for the determination of all 
the main constituents except ferrous iron and alkalies, as well 
as for zirconia, baryta, etc.; fusion with calcium carbonate 
and ammonium chloride for the alkalies; solution in a mixture 
of sulphuric and hydrofluoric acids for ferrous iron; and simple 
digestion with hydrochloric or nitric acid for sulphuric anhy- 
dride and chlorine respectively. 

The method of fusion with alkali carbonate depends upon 
the fact that this reagent at the temperature of fusion decom- 
poses the minerals present, forming silicate, aluminate, titan- 
ate, phosphate and zirconate of sodium and potassium, and 
carbonates of iron, manganese, magnesium, calcium and barium, 
all of which are readily decomposed by and soluble in hydro- 
chloric acid. 

About 1 gram of rock powder is needed for this operation. 
A platinum crucible of 40 or 50 c.c. capacity is selected. A 
smaller one is less appropriate, on account of danger of loss 
through bubbling of the melted mass, as well as on account of 
greater difficulty in loosening the solid cake. It is cleaned, 
ignited to bright redness, and allowed to cool in the desiccator. 
When perfectly cold, it is weighed with the cover on, the weighing 
being carried to tenths of a milligram by means of the rider,* 
and the weight noted. 

A gram is then added to the weights in the pan (usually 
the right-hand one), and the crucible placed on the weighing- 
table with the cover off, the forceps being used to handle it. 
Some of the rock powder is poured into the crucible from the 
specimen tube and the covered crucible replaced on the balance- 
pan. If not enough powder has been poured in to balance 
the extra gram the operation is repeated, very small portions 
being added at a time from the specimen tube, till the weights 
in the right-hand pan are just about balanced. One very 
soon judges from the movements of the pointer whether the 

* It is to be understood that in all weighings, except for the rough ones of 
fluxes, the weighing is to be carried out to tenths of a milligram. 



SILICA. 81 

difference is large or not. If too much is added, small por- 
tions are removed from the crucible by a small platinum spatula 
or the handle of the forceps, and replaced in the specimen 
tube. The correct weight is then carefully taken, also to 
tenths of a milligram, and the result noted in the line above 
that of the empty crucible as Cruc. + Subst. The difference 
will be the weight of substance taken. 

An alternative method of weighing consists in weighing 
the uncorked specimen tube with the rock powder, pouring 
out carefully about a gram into the (unweighed) crucible, 
and then weighing the tube a second time. The loss in weight 
will be the weight of substance taken.* Of the two, the former 
is to be preferred here, as rather the more convenient, though 
either may be used. 

In either case, care must be taken that no rock dust falls 
on the crucible cover, and in the second method that every 
particle of powder from the tube falls into the crucible. None 
of the rock powder should be allowed to fall on and adhere to 
the sides of the crucible, as this will not be acted on by the flux. 

It is not necessary, indeed it is better not, to weigh out 
exactly 1 gram, which will take considerable time, but an 
amount varying from 0.9 to 1.1 gram should be taken, prefer- 
ably a little more than a little less than a gram. With some 
practice it will be found simple to estimate with the eye when 
one has about the right amount. 

The crucible (covered) and the weights being removed 
from the balance, one of a pair of balanced 3-inch watch- 
glasses (p. 33) is placed on the right-hand pan, and a 5-gram 
weight placed on it. On the other watch-glass a mixture of- 
dry, powdered anhydrous sodium carbonate and potassium 
bicarbonate (p. 36) is placed by means of a dry horn spoon, 
which is kept for this purpose in the balance-case drawer, 
and which must be carefully wiped off at the end of the opera- 
tion. Enough is added or subtracted to balance the other 

* This method is described in detail under the alkali determination (p. 129). 



82 METHODS. 

watch-glass and the 5-gram weight. It is not necessary to 
weigh this accurately, but the difference should not be, more 
than a few decigrams either way. It is usually stated that 
the amount of carbonate should be four times that of the sub- 
stance taken, but it is found that a somewhat larger amount 
is advisable for proper fusion. 

The crucible is placed on a clean sheet of paper, the cover 
laid to one side, and the greater part of the alkali carbonates 
transferred to the crucible by means of the platinum spatula, 
care being taken that none of the rock powder is thrown 
out. About half a gram of carbonate should be left on the 
watch-glass. The rock powder and the flux are carefully and 
thoroughly mixed in the crucible with the spatula, attention 
being paid to getting the carbonate well down at the bottom, 
and that no patches of rock powder are left at the angles or 
remain unmixed. After this thorough mixing, the surface is 
levelled down with the spatula, and this is well rubbed and 
cleaned off against the carbonate in the watch-glass, which is 
gently transferred to the crucible. 

The covered platinum crucible is placed on a platinum 
triangle and heated over a low flame for about ten minutes, in 
order to decompose gently the acid potassium carbonate and 
drive off moisture. The heat is then increased till the mass 
sinters, so that the C0 2 may pass off without spattering, allowed 
to stay so for ten minutes or more, and finally brought to 
complete fusion at a bright-red heat. The cover should be kept 
on during the operation, except when examining the contents, 
to catch any drops spattered from the molten mass, though none 
of these should be found on the under side of the cover if the 
operation has been done with care and the heat applied gradu- 
ally.* As Hillebrand suggests, it is better to have the flame 
play obliquely against the bottom and lower sides of the cru- 
cible, and it is important that the flame does not envelop the 
whole crucible, to ensure an oxidizing atmosphere within it, 

* If any such are found they should be fused by heating the cover upside 
down over the flame for a few minutes. 



SILICA. 83 

and guard against any possible reduction by the gas. An 
occasional removal of the cover is advisable in order to effect 
this object, though not necessary. 

The operation is at an end when the whole mass is in a state 
of quiet fusion, and no more bubbles are given off. The liquid 
will seldom be perfectly clear and transparent, as the carbon- 
ates of iron, magnesium and calcium will form cloudy masses 
within it, so that any such appearances need cause no concern. 
Indeed, with very basic rocks the mass may seem to be com- 
pletely fused only around the edges, owing to the abundance 
of these infusible substances, although the rock is completely 
decomposed. 

The crucible is taken from the flame and placed on a cool, 
flat surface of iron or polished stone. Such methods for quick 
cooling as using a blast of air, or dipping into water, are to be 
avoided, as they tend to injure the crucible and greatly shorten 
its life. Hillebrand recommends giving the crucible a quick, 
rotary motion before placing on the slab, so as to spread the 
melt over the sides in a thin sheet. This certainly has the 
advantage of rendering the subsequent disintegration in water 
more rapid, and also to some extent facilitates the separation 
of the cake from the crucible. It is not, however, necessary, 
and in general I am content to cool the crucible quickly but 
quietly on a slab of polished granite. 

During the first moments of cooling the melt should be 
watched, and if it is seen to bubble or form miniature craters, it 
may be taken as evidence that the decomposition and expulsion 
of C0 2 is not complete. In this case the. whole should be re- 
melted and kept at a bright-red heat for another ten minutes. 

When the crucible is finally cold, it is best to place it again 
over the full flame and heat it till the edges are melted, when it is 
to be removed and placed again on the slab till cold. This renders 
the removal of the cake from the crucible far easier, as a rule. 
A very important point to be borne in mind is that the crucible 
and its contents must be thoroughly cold before the process of re- 
moval is begun. The contents must be so cold that they sepa- 



84 METHODS. 

rate either wholly or partially from the metal walls. If water is 
poured into the crucible before this happens the removal of the 
cake will probably be a difficult and lengthy proceeding. It is 
always better and time saved in the end to be patient during the 
cooling process and to allow the crucible to stand more time 
than may be actually needed, than to incur the possible annoy- 
ance of a cake that obstinately refuses to be extricated whole. 

When a considerable amount of pyrite is present in the rock r 
it is necessary to oxidize the sulphur, to avoid attacking the 
crucible and the formation of an alloy between the iron and 
platinum. This may be done by adding a very little KN0 3 to "the 
carbonates. But even a small quantity of this gives rise to 
effervescence, through reaction with the carbonates, and hence 
increases the possibility of loss through spattering. There is 
also- danger of attacking the crucible through the action of the 
nitrate. It is therefore better in such cases, after weigh- 
ing the rock powder and before the addition of the alkali car- 
bonate, to roast the rock powder in the crucible at a low red 
heat, insufficient to sinter, and far less to fuse, the rock. The 
mass can then be mixed with the carbonates and the fusion 
proceeded with, as described above. 

As a general rule the cooled cake will be of a bluish-green color, 
due to the formation of sodium manganate. If no reducing 
agents were present during fusion, and regularity in the forma- 
tion of the color could be counted on, the depth of this color 
would serve as an excellent basis for estimating the amount of 
manganese. This might be made very precise by the preparation 
of standard cakes of sodium carbonate, fused with varying 
amounts of MnO, and preserved in glass tubes for reference. 
The possibility of the adoption of such a method, however, is 
seriously interfered with by the usual presence of ferrous oxide, 
which, by its reducing action, introduces serious irregularities 
in the depth of color. It often happens that rocks high in fer- 
rous oxide, and containing considerable manganese, show in the 
cooled melt not a trace of the characteristic green, but only a 
muddy-brown color, due to the disseminated ferric carbonate. 



SILICA. 85 

Hillebrand also attributes certain irregularities to the occa- 
sional presence of a reducing atmosphere within the crucible, 
under conditions which are little understood. Thus it may 
happen that "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." It is probable 
that all analysts have had similar experiences. 

These causes of irregularity might be removed by the addition 
of nitre, although the serious disadvantages of this have been 
mentioned. Possibly some other oxidizing agent may be found 
suitable, and it is greatly to be desired that some such method be 
devised, which would allow of an easy and rapid estimation of 
the amount of manganese, as this entails at present considerable 
extra labor, time and liability to error. 

Before describing the removal of the cake from the crucible, 
one or two points in regard to the crucible itself may be touched 
on. From a new or little-used platinum crucible, with the ordi- 
nary amount of flare, the extraction of the cake usually offers no 
special difficulties, if attention be paid to the small points men- 
tioned above and given below. But after a platinum crucible 
has been in use for some time, especially when often heated 
over the blast, the bottom tends to drop, and so alters the shape 
of the lower part. The smooth, single, interior concave curve 
becomes a double, ogee-like one, and, being slightly convex 
inwardly, frequently gives rise to difficulty in removing the cake 
When the crucible which is used for the carbonate fusion gets 
into this condition, it is well to return it to the maker and 
have it re-formed. 

As all dents and other irregularities are apt to give rise to 
difficulty, the platinum crucible should never be allowed to fall 
or become dented. Above all,, any squeezing or other violent 
pressure should be avoided in attempting to loosen the melt, as 
any such deformations will greatly decrease the usefulness and 
value of the crucible. Caution on these points may seem super- 
fluous, but one sees so often battered crucibles in use in labora- 



86 METHODS. 

tories, especially in the hands of students, that the reference to 
them may not be amiss. 

The thoroughly cold crucible containing the cake is placed on 
a platinum triangle and nearly half filled with water. It is 
gently heated over a small flame, that of an ordinary glass 
alcohol lamp being convenient, as it is not too intense. The 
flame is cautiously applied, especially around the edges of the 
cake, all boiling being avoided, as likely to lead to loss. After 
the edges are freed, the bottom is gently heated, when, under 
favorable circumstances, the cake loosens. This may be aided 
very materially by gently prying it up with a piece of thick 
platinum wire, one end of which has been hammered or filed to a 
wedge, and which serves as a miniature crowbar. 

If this first operation is not successful, the fluid is carefully 
poured out into the j)latinum basin, any drops running over the 
edge being washed into the basin with a few drops of water from 
the wash-bottle. The crucible is then again half filled with 
water, and the operation repeated. Two or three repetitions 
will usually be sufficient to attain the object. When the cake is 
loosened it is transferred to the platinum basin" and the crucible 
washed slightly, so as to transfer any loose particles to the basin. 
Small fragments of the melt adhering to the sides of the crucible 
may be allowed to remain, and the crucible is covered and laid to 
one side for treatment later. The platinum basin containing the 
cake, and not more than one-third filled with water, is heated on 
the water-bath, or over a low flame, so as to avoid boiling, until 
the cake is easily broken up with the spatula, and it is finally dis- 
solved as far as possible. This is indicated by the absence of 
any hard portions of the cake. The presence of small, hard, 
black grains need not cause uneasiness, as magnetite and ilmenite 
are only attacked with difficulty by sodium carbonate, and these 
will be dissolved later. 

If the cake should prove obstinate and refuse to loosen from 
the crucible, one of two plans may be followed. The one pre- 
ferred is to dissolve the cake in the crucible itself over a low flame 
or on the water-bath. The liquid in the platinum basin may be 



SILICA. 87 

used for this, in small portions at a time, the crucible being 
emptied back into this each time. The other consists in placing 
the crucible on its side in the basin, filling this with water about 
one-third full, and heating gently till the cake is dissolved. The 
crucible is then lifted out of the basin by means of a stirring-rod, 
and thoroughly washed, inside and out, the washings failing, of 
course, into the basin. This method involves the use of rather 
more water, and is somewhat more likely to lead to loss of 
substance. 

If the cake is colored a deep green, on the addition of hy- 
drochloric acid chlorine will be evolved, through reaction with 
the manganate, and will attack the platinum. To avoid this 
a few drops of alcohol are to be added to destroy the man- 
ganate. 

When the cake is qui^hissolved, the platinum spatula is 
removed and washed with a little water, and laid aside in a 
clean place. The basin is removed from the flame and covered 
with a watch-glass which should project about an inch on all 
sides. This is, of course, placed with the convex side down. 
Ten or fifteen c.c. of concentrated hydrochloric acid are meas- 
ured off in a 25-c.c. measuring-cylinder with lip, and poured 
very gradually into the basin through a small funnel, the end 
of which has been somewhat drawn out and bent at an angle 
of 45, so as to project into the basin through the lip-opening. 
This addition of acid should be very gradual, by a few drops 
at a time at first, so as to allow the effervescence to be as gentle 
as possible. It is also well to let the acid flow down the side of 
the basin below the lip, so that the drops thrown up by the 
first, somewhat violent, effervescence may be directed away 
from the lip-opening. If carefully conducted, there need be 
no danger of loss on this score. 

When all the acid has been added, except 1 or 2 c.c., the 
funnel is withdrawn, and the tip washed into the crucible 
with a little water. A few drops of acid are poured on the 
under side of the crucible cover, to dissolve any drops spat- 
tered from the fusion, and washed into the crucible with a 



88 METHODS. 

very little water. The rest of the acid is then poured into the 
crucible, to dissolve any adhering portions of th carbonate, 
and slightly warmed, the crucible being kept well covered. 

When all effervescence has ceased in the basin, the drops 
on the watch-glass cover are rinsed down into it, the glass 
being held vertically, with the part which has been next the 
lip downward and near the surface of the liquid in the basin, 
The rinsing is to be repeated several times, the stream 
being so directed as to let the water flow over all the wetted 
surface from top to bottom. The watch-glass is laid aside, 
and the sides of the basin above the liquid are washed down 
by a gentle stream from the wash-bottle, the basin being slowly 
revolved to facilitate the operation. One complete washing 
down all around will be sufficient. The contents of the crucible 
are then added, and this and th08over rinsed several times 
into the basin. When complete, if care has been used to avoid 
an inordinate amount of wash-water, the basin will be little 
more than half full. 

The platinum spatula is then put in the basin, and this 
placed on the water-bath for evaporation. The fluid should 
be clear, and contain no solid except some light, floating flakes 
of silica. There may be a few small black particles of mag- 
netite or ilmenite present, which will dissolve in the hot acid. 
But if many small, hard, gritty particles are felt at the bottom, 
it is evidence that the fusion has not been successfully carried 
out to complete decomposition of the rock, and the contents 
of the basin should be rejected, another portion of rock powder 
weighed out, and the whole operation of fusion with alkali 
carbonate gone through with as before. 

Separation of Silica. The fluid in the basin now contains 
all the rock constituents in solution as chlorides, except the 
silica, which is for the most part in solution as a soluble silicic 
acid, and partly as insoluble flakes. Our first object then is 
to separate the silica from the other constituents, so that it 
may be weighed. This is effected by evaporation to dry ness, 
when the silica is rendered insoluble in water. 



SILICA. 89 

Hillebrand* has shown that a single evaporation will not 
attain this end perfectly, even with a subsequent heating at 110 
to 120, which is the method usually employed, but that a 
small amount of silica will go into solution and will not be 
wholly recovered in the later processes. He therefore recom- 
mends a double evaporation as conducive to the most accurate 
results, and his suggestion is followed here. 

The first evaporation is continued, on the water-bath, until 
no more fumes of HC1 are given off and the mass appears 
quite dry, the dark-yellow color of the moist salts changing to 
a pale-brown shade. During the last stages it is well every now 
and then to break up the gelatinous mass with the platinum 
spatula, which is kept in the basin, so that the water and hydro- 
chloric acid may pass off more readily. When the mass be- 
comes crystalline, the lumps may likewise be broken up, but 
this should be done with caution to avoid loss by flying off 
of particles of the salts. 

It is not necessary to heat the dried salts at a temperature 
of 110 or 120, as is usually done. Indeed this is distinctly 
disadvantageous, since silicates (especially of magnesium) are 
liable to be formed, which dissolve in the hydrochloric acid 
added later, and thus lead to loss of silica. At the same time 
the heating at such a temperature will probably add consid- 
erably to the impurities in the silica after evaporation with 
hydrofluoric acid (Hillebrand). 

As soon as the mass is quite dry and free from all odor 
of hydrochloric acid, the basin is removed from the water-bath 
and the contents moistened to a paste with concentrated hydro- 
chloric acid, to dissolve the basic salts and magnesia which are 
invariably formed during the evaporation. The small amount 
of salts adhering to the spatula must not be neglected. It is 
important here not to use a large quantity of acid, as this will 
tend to prolong the filtration, probably through reaction of the 
strong acid on the paper and consequent swelling and clogging 



* Hillebrand, p. 52. 



90 METHODS. 

of the pores. About 5 c.c. will be ample to moisten the whole 
thoroughly. The pasty mass should be thoroughly mixed 
with the spatula, some of it being rubbed around the line mark- 
ing the original border of the liquid, where a band of some- 
what strongly adherent silica is apt to form. 

After standing and warming for a few minutes, the whole 
is diluted with water from the wash-bottle, the stream washing 
down the sides of the basin. The spatula should be well rinsed 
off and laid aside, leaning its broad end against the granite 
slab, as a little silica adheres to it persistently which is recov- 
ered later. A glass stirring-rod, about 2 inches longer than 
the diameter of the basin, is placed in this, which should be 
about one-third full of liquid. The basin with its contents 
is next heated on the water-bath or over a low flame, with 
occasional stirring, until the chlorides are entirely dissolved 
and only insoluble silica remains, as is indicated by the absence 
of gritty particles under the rod. 

While the solution of the chlorides is being effected at a gentle 
heat, the filter may be made ready for the silica. A dry, clean 
2^-inch (6.5 cm.) funnel is selected, preferably one with a 
suction-tube fused on (p. 34). A suction-tube may be con- 
nected by a short length of rubber tubing, but there is great lia- 
bility to loss of liquid in the crevice between the glass and rubber, 
unless care is taken to wash this out later. A 9-cm. filter-paper 
is folded in the usual way, first along a diameter and then into a 
quadrant, opened out and placed in the funnel. If the apical 
angle of the funnel is 60 it will fit snugly. If not, the filter 
must be refolded the second time, not quite evenly, so as to form 
a trifle more than a quadrant, and opened out either on the 
larger or the smaller half, according as the filter was found 
before to be too narrow or too broad. 

The paper is then moistened with water and pressed snugly 
home, air-bubbles being squeezed out gently with the finger, 
and the lines on either side made by the folds being well pressed 
down, especially at the rim, as they are liable to form air-channels 
and thus retard filtration, as well as possibly cause loss of silica 



SILICA. 91 

if the filter happens to be filled above the rim. The funnel is 
then placed in a funnel-stand, and beneath it a 400-c.c. lipped 
beaker. The end of the suction tube should reach to within 
an inch or two of the bottom to avoid loss by splashing, and 
preferably near one side of the beaker. 

When the salts are entirely dissolved, the heated liquid in the 
basin is passed through the filter. The stream is directed by the 
stirring-rod held against the lip to the side of the filter, not the 
bottom, which it is liable to break. The filter should not be 
allowed to fill more than to within 2 or 3 mm. of the edge, or par- 
ticles of precipitate may be carried between it and the funnel, 
and there will also be a tendency of the liquid to creep up the 
glass sides. At first the clear, supernatant liquid is poured into 
the filter, which should not be allowed to quite empty. Finally 
the silica itself is poured in with the liquid, as washing by de- 
cantation is not necessary here. 

It is highly important in all filtering operations to keep th? 
tube part of the funnel, or the suction-tube, if there be one 
attached, full of liquid, so as to take advantage of the increased 
suction due to the column of liquid. This may usually be accom- 
plished by care and attention to several points, the chief of which, 
are: to moisten the interior of the tube before fitting the filter 
(the suction-tube will not need this) ; to see that the filter fits 
tight to the funnel, and especially that there is no passage for the 
air along the lines of folds at either side; * to keep the filter from 
emptying, once the suction has been established, till all of the 
liquid has been filtered off, and the washing is to begin. 

The ease with which this may be accomplished depends on 
the liquid, the funnel and the filter, all of which vary in this 
respect, but with practice the correct filling of the tube can be 
accomplished in nearly all cases with great readiness, and will 
reduce the time needed for filtering very greatly. 

When all the liquid and silica that will flow readily have been 

* If bubbles begin to pass along these, the open ends should be gently 
pressed down and closed with the tip of the stirring-rod, and without break- 
ing the paper. 



92 METHODS. 

brought on the filter, the basin is gently rinsed with a little cold 
water from the wash-bottle, the silica adhering to the sides being 
washed down to the bottom/and the liquid and as much of the 
silica as possible poured into the filter as before. When the 
filter is empty, the basin is held in the left hand, above the filter, 
with the stirring-rod across it and resting on the lip, the end of 
the rod an inch or so beyond. A gentle stream of water is then 
directed against the upper part of the basin, so as to wash the 
silica into the filter, and at the same time rinse the basin. When 
the filter is nearly full the liquid is allowed to empty and the 
operation repeated two or three times. It is not necessary here 
to wash thoroughly, or to bring all the silica into the filter at 
this stage, though this should be done as far as possible without 
too many rinsings. 

In regard to the washing of silica it is of very great importance 
to note that only cold water should be used, as hot solutions of 
iron, unless strongly acid, have a tendency to throw down basic 
salts, which will contaminate the silica. It sometimes happens 
that the silica in the filter is colored a brick-red through this 
cause, when hot water has been used for washing. 

When the liquid has about ceased dropping from the last 
washing, the platinum basin is substituted for the beaker be- 
neath the funnel- or suction-tube, taking care to lose no drops 
from the latter during the change. The contents of the beaker are 
poured into the basin, and the beaker itself rinsed once or twice, 
the rinsings going also into the basin. They are then inter- 
changed once more, and the stirring-rod is placed in the beaker 
set beneath the funnel. The basin, with the platinum spatula 
in it, is once more placed on the water-bath for the second 
evaporation. It- is better to cover the funnel with a watch- 
glass, and the beaker as well, for which purpose a perforated 
watch-glass (p. 33) is very convenient, as it allows the suction- 
tube to remain in place inside the beaker. 

When the second evaporation is complete and the salts are 
reduced to dryness and free from HC1, occasional stirring with 
the spatula hastening the process, the mass is again moistened 



SILICA. 93 

with a little (3 to 5 c.c.) hydrochloric acid, and, after standing 
a short time, about 50 c.c. of water are added, and the whole 
gently heated to complete solution (except for particles of silica). 

This liquid is then filtered through the filter which holds 
the bulk of the silica, the funnel not being allowed to empty 
till all is through. The basin is rinsed as before, and all particles 
of silica washed into the filter by small jets of water. If any 
adhere, and indeed in any case, the interior of the basin should be 
gently rubbed all over with a rubber-tipped stirring-rod (p. 35), 
so as to free any strongly adhering particles, the zone of the upper 
border of the original liquid being especially attended to. The 
rubber tip should be slightly washed afterward by a jet of 
water. Cold water must be used throughout the washing process. 

In washing, the filter must be allowed to empty before the 
addition of another portion of wash-water, so as to leave as 
little as possible of the soluble salts in the precipitate or funnel. 
This is highly important for facilitating the washing and reduc- 
ing the bulk of water needed. Given the same bulk of washing 
liquid the removal of the soluble salts will be more complete if a 
number of additions of small volume are used rather than a few 
of large volume.* 

When the basin has been rinsed out several times and all 
the silica is in the filter, the contents of this must be well washed. 
This is best done by stirring up the silica with the first few 
portions of wash-water, and afterward washing down the sides 
of the filter, so as to bring all the silica toward the bottom. 
Here the suggestion as to the addition of only small quantities 
of water at a time, and allowing the filter to empty after each, 
should be followed, so as to keep down the bulk of liquid. 

This washing is to be carried out till a few drops from the 
end of the funnel give no chlorine reaction with solution of 
silver nitrate in a small watch-glass. In making this test, 
and in all similar cases, the end of the funnel or suction-tube 
should be washed off with a small jet of water, before collecting 

* Cf. Ostwald, pp. 18 to 21; Treadwell, p. 16. 



94 METHODS. 

the drops for testing, as some of the fluid which has previously 
passed may have crept up the side, and by mingling with the 
drop may give a chlorine reaction, when the last portions of 
the liquid are, in reality, quite free from chlorides. 

When washing is complete the bulk of liquid, including all 
the washings, in the 400-c.c. beaker will be from 150 to 200 
c.c., which ought to be sufficient for complete washing if the 
operation has been conducted with care and due avoidance 
of excessive use of liquid. 

Ignition of Silica. A platinum crucible of 30- or 40-c.c. 
capacity is selected, preferably the latter if the rock contains 
much alumina or iron, ignited, cooled in the desiccator and 
weighed. The free edges of the filter in the funnel containing 
the silica are then folded down upon the silica, so as to com- 
pletely enclose it, the platinum spatula being used for this purpose. 
The little package is then removed from the funnel and' placed 
in the crucible by means of the spatula, preferably with the side 
uppermost which has three thicknesses of paper. It is gently 
pressed down toward the bottom of the crucible, but the paper 
should not be torn, nor should all egress for steam from below 
be shut off. With a small piece of filter any particles of silica 
adhering to the spatula are rubbed off, and also any which may 
be on the funnel above the edge of the filter, and the piece of 
paper is also placed in the crucible. 

In this way the silica can be dried in the crucible and ignited, 
with no danger of loss from whirling up of the light powder. 
This is preferable to the method recommended by Fresenius * 
of drying the filter and silica prior to ignition. In this latter 
method the danger of loss by handling the filter when the 
powder is dry is far greater. Incineration of the filter will 
be equally complete in either case. 

The covered crucible is then heated at some distance above a 
low flame, to avoid boiling of the pasty mass, and probable loss 
of substance or spattering of it on the sides of the crucible. This 



* Fresenius, I, p. 510. 



SILICA. 95 

is continued till the contents are dry and the filter begins to 
char. As the water is driven off the crucible may be gradually 
lowered, but this must be done with great caution, and the flame 
kept small. Also a filter which is carbonized at a low tempera- 
ture is more easily incinerated than one' which is carbonized 
rapidly and at a high temperature. The crucible is finally 
brought close to the flame and heated till no more smoke is given 
off. The escaping vapors should never be allowed to ignite, and 
consequently the flame should be kept low and the bottom of the 
crucible not brought to a red heat till carbonization is complete. 

The full, or almost full, flame is then turned on and the 
crucible heated to a bright-red heat, being kept vertical and with 
the cover very slightly moved to one side, so as to allow the 
entrance of some air, but not enough to give rise to danger- 
ous draughts. The flame, of course, should not be allowed to 
envelop the crucible, as an oxidizing atmosphere within it is 
essential. When the carbon is entirely consumed,* or almost so, 
the cover is put in place, a blast substituted for the Bunsen 
burner, and the crucible blasted for at least twenty minutes. 
This is necessary in order to effect complete dehydration of the 
silica, the last portions of water being retained with great obsti- 
nacy. It also has the advantage of rendering the silica non- 
hygroscopic (Hillebrand). If the blast is not available, the 
crucible must be heated several times to constant weight at the 
highest heat of the Bunsen burner. But in this case the expul- 
sion of water is probably never quite complete, and the results 
for silica will therefore be a trifle high. The time needed for 
ignition will also be much longer. The cover should be examined 
to see if it carries any adhering carbon, and if so this is to be burnt 
off by heating in the flame. 

The crucible and its contents are then cooled in the desiccator 
and weighed, reheating to constant weight not being necessary 
when the blast has been used. The result is to be noted as 

* If the carbon of a filter-paper burns with difficulty, it will be well to 
remove the flame and allow the air to penetrate the cold carbon. On reheat- 
ing combustion will usually be rapid. 



96 METHODS. 

Cruc. + Si0 2 +x above the weight of the empty crucible, and also 
in a place to the right of it. 

The silica as thus obtained is never pure, but contains small 
amounts of Fe 2 3 , Ti0 2 , P 2 5 , and possibly other substances, and 
in basic rocks these may amount to several per cent. After weigh- 
ing, therefore, the crucible is placed on a sheet of paper and the 
silica mixed with 5 c.c. of water. In doing this the tip of the 
wash-bottle should be filled with water by blowing before insert- 
ing in the crucible, to avoid blowing out any of the light silica 
by the first puff of air from the empty tip. Three or four drops of 
dilute sulphuric acid are then added, the presence of this being 
necessary to retain the Ti0 2 , some of which would be vaporized 
as titanium fluoride in the absence of sulphuric acid. Hydro- 
fluoric acid is then poured in, a few drops at a time. The action 
is apt to be violent, but with care and sufficient moistening of 
the silica no loss need be incurred. The hydrofluoric acid should 
be added in sufficient quantity to dissolve the silica on warming, 
not more than one-quarter of the depth of the crucible being 
ample for this purpose. 

The crucible is then placed on the triangle of a special air- 
bath, such as is described and figured by Hillebrand.* If this is 
not available, a capacious porcelain crucible with an appropriate 
triangle made of iron or platinum wire will answer the purpose. 
The use of such an air-bath ensures uniform heating of the liquid 
at a high temperature, and hence prevents loss by boiling or 
spattering. The air-bath and the crucible within it are heated 
over a moderately low flame till the contents of the crucible are 
dry. This operation must be carried out under the hood, with 
a good draught. 

The crucible is then ignited at a bright-red heat, blasting 
for a few minutes being advisable to ensure the decomposition 
of the sulphates of iron and titanium, and the complete expul- 
sion of all traces of sulphuric acid. After cooling in the desic- 
cator the crucible is weighed, and its weight noted as Cruc. + x 

* Hillebrand, p. 23. 



ALUMINA AND TOTAL IRON OXIDES. 97 

below that of Cruc. + Si0 2 +. The difference between the two 
will be the weight of silica, to which it is necessary to add 
later the weight of the very small amount of this which is re- 
covered from the filtrate (cf. p. 110). 

The crucible containing the impurities in the silica is laid 
aside in a desiccator or other safe place, uncleaned, for use in the 
subsequent ignition of the precipitate of alumina, etc. (p. 105). 

8. ALUMINA AND TOTAL IRON OXIDES. 

In the filtrate from the silica, alumina, iron oxides, titanium, 
zirconium and phosphorus oxides are separated from man- 
ganese and nickel, lime and magnesia, by precipitation by 
ammonia alone, or by this preceded by a precipitation with 
sodium acetate. The advantages and disadvantages of the latter 
method have been discussed elsewhere (p. 63), so that it is not 
necessary again to enter into the question of their relative 
merits. Since the determination of manganese may usually 
be neglected without seriously affecting the value of the analysis, 
and since the ammonia method is the simpler and better adapted 
to the needs of the beginner, at the same time allowing of the 
determination of manganese if desired, this method will be 
described first. 

Precipitation by Ammonia. To the filtrate from the silica 
in the 400-c.c. beaker, which should amount to from 150 to 
200 c.c. in bulk, about 10 c.c. of concentrated hydrochloric 
acid are. added.* The object of this is to form ammonium 
chloride on the addition of ammonia, in sufficient quantity 
to prevent the precipitation of magnesia along with the alumina 
and iron. One should also avoid a large excess of ammonium 
chloride, so that for rocks like granites and trachytes, which 
contain but little magnesia, the addition of about 5 c.c. of 
HC1 will be sufficient. If the rock is extremely basic and 
rich in magnesium, 15 c.c. will probably not be too much. 

* Ti Idition of nitric acid is not necessary, as the ferrous iron will have 
been changed to ferric during the fusion and the two evaporations. 



98 METHODS. 

After the addition of the hydrochloric acid i\k liquid is 
heated almost to boiling, and rather diluted ammonia water * 
is added gradually and with constant stirring trfl the liquid 
smells rather strongly of ammonia.t The beaker \i then heated 
to boiling, and kept boiling for not more than i minute. As 
has been pointed out by several chemists, it ]B quite unnec- 
essary to boil off the excess of ammonia, as is /usually recom- 
mended (Fresenius), and indeed this might lead to resolution 
of some alumina through decomposition of /the ammonium 
chloride and formation of hydrochloric jacid (Fresenius, 
Classen). 

The bulky gelatinous precipitate is alloWed to settle for a 
few minutes, and then filtered through ajwbm. filter placed 
in a 3-inch (7.5 cm.) funnel, provided with a suction-tube fused 
to its lower end. The filtrate is caught in an 800-c.c. beaker. 
The clear liquid should be at first decanted as far as possible 
from the precipitate, though several washings by decantation, 
as usually recommended, are quite unnecessary and add much 
to the bulk of the filtrate. The precipitate is then brought on 
the filter, care being taken that the filter is neither filled to 
more than 2 or 3 mm. of the edge, nor that it run dry, as the 
latter will tend to consolidate the gelatinous hydroxides and 
render the filtration long and tedious. 

The beaker is rinsed out two or three times with hot water, 
each addition being passed separately through the filter, and 
any loose particles of precipitate also being washed into it, though 
complete cleaning of the beaker is not necessary. 

The tendency of such gelatinous precipitates as those of 
aluminum and iron hydroxides to run through the filter has 
often been remarked. This may be due in part to partial 
solution in hydrochloric acid formed by decomposition of 

* If this is not fresh, it should have been previously tested with CaCl 2 
(cf. p. 62) to see if ammonium carbonate is present. 

t If the ammonia water has been poured down the side of the beaker, 
. this should be rinsed down with a little water, as a strong odor of ammonia 
might otherwise be noted although the fluid was still acid. 



ALUMINA AND TOTAL IRON OXIDES. 99 

ammonium chloride if the excess of ammonia is expelled by 
boiling, as explained above; and partly to the property (noted 
by Ostwald) in such colloidal bodies of indeterminate solu- 
bility in water. This can be prevented by the presence of 
crystalline salts in the solution, which precipitate such pseudo- 
solutions.* As pointed out also by Ostwald, a high temperature 
is favorable to the precipitation of such colloidal solutions, and 
this will explain, at least in part, the tendency of the precipi- 
tate to pass through the filter as the filtration proceeds and the 
liquid becomes cool. 

To rectify this Penfield and Harper | recommend the use of a 
dilute solution of ammonium nitrate for washing, obtained by neu- 
tralizing a solution of 2 c.c. of concentrated nitric acid in 100 c.c. 
of water by ammonia. For the most exacting work, and espe- 
cially for almost purely aluminous precipitates, this may be 
used, as these two chemists made their observations on pure solu- 
tions of aluminum chloride. In the case of rocks, however, with 
their more complex ammonia precipitates, I have been seldom 
if ever troubled in this way, and, as the first precipitate is not 
washed thoroughly to complete freedom from salts, pure, hot 
water alone may be used for the washing without danger. 

After rinsing the beaker, then, the precipitate in the filter 
is washed several times with hot water, the stream from the 
wash-bottle breaking it up more or less. In this operation 
great care should be taken not to throw too hard or sudden a jet 
onto the precipitate, which might easily throw some of it out of 
the funnel. Complete washing is not necessary at this stage, 
but the precipitate should be collected in the bottom of the 
filter, and the upper edges washed clean. 

As it is invariably to be assumed that this first precipitate 
contains magnesia, its solution and reprecipitation are necessary 
in all cases. This may best be accomplished as follows : 

With the platinum spatula a side of the filter is loosened 



* Cf. Ostwald, p. 24. 

f Penfield and Harper, Am. Jour. Sci., XXXII, p. 112, 1886. 



100 METHODS. 

and a channel made between the filter and the funnel to the 
point, so that all the liquid in the suction-tube and tubular 
part of the funnel may run out into the beaker below. The 
uncleaned stirring-rod is laid across the 800-c.c. beaker, so that 
it is supported only on its clean part. The 400-c.c. beaker 
is placed conveniently near the edge of the table, to the right 
of the filter-stand, and with its lip to the left. The funnel is 
removed from the stand, and the filter gently loosened all 
around with the platinum spatula, the edges being turned 
down as little as possible, and the paper not being torn. 

The funnel is then held with its side horizontal and the 
folded part of the filter underneath, the spatula slipped beneath 
this, and the filter with its contents gently removed from the 
funnel and held on the spatula above the 400-c.c. beaker. 
With the left hand the funnel is replaced in its stand, the filter 
not being allowed to fall from the spatula. The 400-c.c. beaker 
is then tilted on one side, lip up, and the filter laid on the slop- 
ing lower side with its upper edge near the edge of the beaker. 
While the beaker is still held in a sloping position, the filter 
is unrolled, beginning at the three folds, and spread out by 
means of the spatula, the paper being torn as little as possible. 
If the operation has been properly done, the side of the beaker 
opposite the lip will be covered with the unrolled filter, the 
upper part of which is clean, and with the precipitate partly 
adherent to its lower part and partly fallen into the beaker. 

The precipitate is then pushed down with the spatula into 
the bottom of the beaker, and the paper and spatula rinsed 
free from all precipitate with jets of water, and enough more 
of this is added, if necessary, to make the volume of liquid 
100 to 150 c.c. Concentrated nitric acid is then added in 
some excess, about 10 c.c. being ample in most cases, the liquid 
being stirred constantly, and then gently heated till the pre- 
cipitate is dissolved and the liquid becomes almost perfectly 
clear. The solution is then precipitated with diluted am- 
monia water in slight excess, the filter being also moistened 
with it, and, after stirring, the whole is brought to a boil. In 



i x 

AND TOTAL IRON OXIDES. 101 

the meantime a 9-cm. filter has been fitted to the same funnel 
as before, the 8tK)-c.c. beaker being in place below it. In 
fitting the filter no more water than is needed to moisten the 
paper should be used, to avoid undue bulk of liquid. The con- 
tents of the 400-c.c. beaker are filtered through this as before, 
the first filter retaining its place against the hinder side of the 
beaker, and being washed with hot water, as well as the beaker 
and the precipitate in the filter. 

If the rock is basic and contains much magnesia, as the 
diorites, gabbros, basalts and tephrites, a second solution 
in nitric acid and reprecipitation is to be made, this being 
carried out exactly as before, and the second filter laid on 
top of the first. In this case the washing of the second pre- 
cipitate need not be thorough. It may occasionally happen 
that a third reprecipitation is called for, but this will seldom 
be necessary. 

The use of nitric acid instead of hydrochloric for the solution 
of the precipitate is recommended by Penfield and Harper. 
This should always be used, as it very greatly facilitates the 
final washing by reducing the amount of HC1 present, and so 
makes the final bulk of filtrate much less. It is essential that 
the precipitate be washed free from all traces of chlorine, as 
aluminum and ferric chlorides are volatile and the presence of 
chlorides will lead to their formation and loss on ignition. 

After the final precipitation, whether it be the second or 
third, as much as is easily possible of the precipitate is to be 
got on the filter. The beaker and adhering filters are to be 
rinsed several times with hot water, without removal of ad- 
hering precipitate, the water after each rinsing being passed 
through the filter. The contents of the filter are washed 
with many small portions of hot water, the mass being broken 
up and collected in the bottom of the filter, and the edges 
cleaned till no chlorine reaction is to be obtained from the 
last drops. For ordinary work, in the case of a third 
precipitation, only the rinsings and first washings need be 
caught in the beaker, as the amount of magnesia in the final 



102 METHODS. 

ones would be inappreciable, and they would add considerably 
to the bulk of liquid. 

The funnel containing the precipitate is then laid aside, 
well covered with a large round filter folded down all round 
the edges. If the amount of iron be great, as -may be known 
by the mineral composition of the rock, or by the depth of 
color of the precipitate, the filter (in the funnel) should be 
placed in an air-bath and heated at a temperature of 110 till 
the precipitate is thoroughly dry. 

A 7-cm. filter is then fitted to a 2J-inch (6.5 cm.) funnel 
and placed over the 800-c.c. beaker. The filters in the 400-c.c. 
beaker are then moistened, and the lower third or so torn away 
with the stirring-rod. This mass of wet paper is to be used 
as a swab to loosen and clean off the precipitate adhering to 
the beaker, the stirring-rod itself being also cleaned by rubbing 
against it. The wad of paper is transferred to the filter and 
the loose particles of precipitate are also washed into this, hot 
water being used. After a couple of washings another third 
of the filter-papers is torn off, the interior of the beaker and 
the stirring-rod cleaned with it, transferred to the filter and 
washed two or three times. This is done a third time with 
the remaining portion of paper, by which time the beaker and 
rod should be perfectly clean. Only the washings from the 
first two portions of paper need go into the 800-c.c. beaker 
with the rest of the filtrate, which is covered and laid aside. 
The filter-papers are to be washed till there is no chlorine 
reaction. 

The process * thus minutely described may seem to be com- 
plex and tedious, but it is, in reality, very simple and expe- 
ditious, and easy to carry out with a little practice. An al- 
ternative method consists in dissolving the precipitate on the 
filter with dilute nitric acid, the solution being caught in the 
400-c.c. beaker, and the filter thoroughly washed. My prefer- 

* I am indebted to Profs. Penfield and Pirsson for my knowledge of this 
method of procedure. 



ALUMINA AND TOTAL IRON OXIDES. 103 

ence is for the method described above, as it is equally accurate 
and gives rise to a smaller volume of filtrate. It is also de- 
cidedly quicker, as a rule, since the action of strong nitric acid 
on filter-paper tends to retard filtration, probably through for- 
mation of nitrocellulose and consequent swelling and filling 
of the pores. 

Precipitation by Sodium Acetate. To the cold filtrate from 
the silica, which contains a little free acid, and whose vol- 
ume is about 200 c.c., a concentrated solution of sodium car- 
bonate is added cautiously till the fluid turns a dark red and 
a slight turbidity is observed, which does not disappear on 
stirring. This addition may be made in the beaker covered 
with a watch-glass, and the solution of carbonate introduced 
through the small funnel with bent tip, so as to avoid loss 
by effervescence. The watch-glass, tip of the funnel, and the 
sides of the beaker should be rinsed down, and if these rinsings 
.are sufficiently acid to redissolve the slight precipitate, as 
may sometimes happen, a few more drops of carbonate solution 
are to be added till a slight permanent precipitate is formed 
again. 

Dilute hydrochloric acid is then to be added, drop by drop 
and very cautiously, with constant stirring, till the slight pre- 
cipitate and turbidity just disappear, but the fluid still retains 
its deep-red color. Especial caution is needed here, as any 
decided excess will set free enough extra acetic acid from the 
sodium acetate added subsequently to render the precipita- 
tion of alumina and iron incomplete. If too much has been 
.added, therefore, the solution is once more to be slightly more 
than neutralized with sodium carbonate and again treated with 
dilute hydrochloric acid more cautiously. 

Enough acetic acid of specific gravity 1.044 (33 per cent) 
is poured in to form about 3 per cent by volume of the total 
liquid, preferably rather less than more. As the final volume 
will be about 300 c.c., 8 or at most 10 c.c. of acetic acid are 
sufficient. If too little is present a slight precipitation of 
manganese is to be feared, while if too much free acid is 



104 METHODS. 

present alumina and iron will not be completely thrown down, 
but will pass in small amount into the filtrate. 

About 2 grams of sodium acetate dissolved in a little water 
are then added. This is the amount for the generality of rocks, 
but it may be varied somewhat with advantage. Thus for 
rocks low in the sesquioxides, as granites and rhyolites, 1J grams 
may serve, though 2 will not be amiss. But in such rocks as 
foyaites, phonolites, gabbros, basalts, or tephrites, which con- 
tain large amounts of these oxides, the quantity had best be 
increased to 3 grams, which may be considered the limit. 

If the liquid has not a volume of 300 c.c., it is diluted to 
this bulk, or to 350 c.c. if the larger amount of sodium acetate 
has been used. It is heated to boiling and allowed to boil for 
not more than a minute or two, as prolonged boiling renders 
the precipitate slimy and difficult to filter. After settling 
for a few minutes, the liquid is filtered through an 11-cm. filter, 
and washed only two or three times with hot water. This 
precipitate, which consists of basic acetates of aluminum and 
iron, with the titanium, zirconium, chromium arid phosphorus 
of the rock, is rather more apt to run through the filter than 
the precipitate of hydroxides produced by ammonia. The 
washing, therefore, should not be thorough, and it is as well 
to add a little sodium acetate to the hot washing-water, so as 
to have a crystalline salt present. 

After this slight washing the precipitate is dissolved in 
nitric acid by the method described on p. 99, reprecipitated 
with ammonia water, and this solution and reprecipitation re- 
peated if the rock is basic, exactly as was done in the method 
by ammonia alone. The final precipitate and the filters are 
to be ignited as described below. It must be remembered, 
however, that there will be undoubtedly another filter con- 
taining the alumina and iron which have passed through with 
the filtrate, so that the drying and ignition of the main portion 
must wait till this has been incinerated with the extra filters, 
to avoid reduction of the ferric oxide. Otherwise ignition in a 
separate crucible and consequently two fusions with potassium 



ALUMINA AND TOTAL IRON OXIDES. 105 

pyrosulphate are involved. For the treatment of the filtrate, 
see pages 113 and 115. 

Ignition of the Precipitate. The 7-cm. filter containing the 
remains of the first and second filters, with only a very small 
amount of precipitate, is placed moist in the crucible used for 
the determination of silica, and in which there still remain the 
impurities left on its evaporation with hydrofluoric acid. The 
covered crucible is heated gently till the paper is carbonized, 
and then for a short time at a stronger heat, till no more smoke 
is given off. 

The crucible is then laid on its side on the platinum triangle, 
the mouth at one of the angles, and the cover is leant against 
it, at a small angle, with its upper edge a little below the top 
of the crucible, leaving a narrow opening above and below. 
As the cover is apt to slip down, it is well to make several small 
grooves with a file at the angles of the triangle used for this 
operation, so as to hold the cover in place. The flame is directed 
against the bottom and lower third of the crucible, the flame 
not being violent enough to cause dangerous draughts, and 
the incineration of the paper is quickly accomplished, after 
which the crucible is placed on a metal or stone slab to cool. 

If the amount of iron is considerable, and the precipitate 
has been dried in an air-bath as described above, the filter is 
freed from adhering precipitate as far as possible, by reversing 
the dry filter over a small sheet of glazed, white paper, and 
gently crinkling and pressing the paper cone till the precipitate 
is loosened and falls on the paper. The filter, almost free from 
precipitate, is placed in the crucible, carbonized and incinerated 
as before, after which the precipitate is placed in the crucible 
and ignited as below. 

The object of this procedure is to avoid as far as possible 
the reducing action of the paper and carbon on the ferric oxide, 
it being almost impossible to thoroughly reoxidize the ferrous 
oxide so formed by any reasonable ignition, even after moisten- 
ing with nitric acid (Penfield, Hillebrand). 

If the amount of iron is not great, say 5 per cent or less, 



106 METHODS. 

the slight error involved by this reduction (which is only par- 
tial at most) may be disregarded. In this case the filter con- 
taining the moist precipitate is placed in the crucible with the 
platinum spatula, taking care to avoid any flying of the light 
ash or soiling the upper sides of the crucible. It is better to 
place the filter on its side with the threefold portion uppermost, 
and to leave free passage for steam from below, as was done 
with the silica. The spatula and the interior of the funnel are 
cleaned with a small piece of filter-paper, which is laid on top. 

The drying of the moist mass must be done very cautiously, 
at a considerable height (8 inches or so) above a small flame, 
the crucible being vertical and covered. Constant watching 
is necessary at first to prevent any bubbling of the pasty mass, 
which would soil the upper sides of the crucible with precipi- 
tate and render its complete solution in fused KHS0 4 difficult. 
The crucible is very gently and cautiously lowered as the mass 
dries off, until the filter is carbonized, when it is heated verti- 
cally for a short time at a bright-red heat till the cover is free 
from adhering carbon. It is then laid on its side as before, 
with the cover resting against its mouth, and heated at a bright- 
red heat for at least twenty minutes. This will ensure complete 
incineration of the filter and, to a very large extent, the re- 
oxidation of the ferrous oxide which may be formed in small 
quantity. 

It may also be advisable to allow the crucible to cool, moisten 
the contents slightly with concentrated nitric acid, heat gently 
till no more nitrous fumes are given off, and reignite. As the 
last portions of water are not always driven off by the heat of a 
Bunsen burner, it is best to blast for five or ten minutes in order 
to effect the complete dehydration of the alumina. 

After cooling in the desiccator the crucible is weighed, and 
the difference between this and the weight of the empty cru- 
cible, obtained prior to the ignition of the silica (p. 94), is that 
of the A1 2 3 , total iron as Fe 2 3 , (Cr 2 3 , V 2 3 ), Ti0 2 , Zr0 2 , 
P 2 5 and a trace of Si0 2 . This may be noted as Al 2 3 + Fe 2 3 
4-x. The amounts of these various constituents are deter- 



ALUMINA AND TOTAL IRON OXIDES. 107 

mined separately, and that of the alumina arrived at by 
difference. 

The ignited precipitate in the crucible is used for the deter- 
mination of total iron, titanium dioxide and the trace of silica, 
its solution being effected by fusion with acid potassium sul- 
phate. This process may be advantageously begun immedi- 
ately after weighing, as it takes several hours. 

Fusion with Acid Potassium Sulphate. The ignited pre- 
cipitate of alumina, ferric oxide, etc., is used for the deter- 
mination of both total iron and titanium. It may be brought 
into solution by prolonged digestion with hot concentrated 
hydrochloric acid, and subsequent repeated evaporations with 
sulphuric acid. This method is, however, very tedious, and 
the solution is apt to be incomplete, so that the method de- 
scribed below should always be adopted. It depends on 
the setting free of sulphur trioxide on fusing acid potassium 
sulphate, this forming soluble sulphates with the oxides 
present. 

Into the crucible containing the ignited precipitate about 
5 to 10 grams of coarsely powdered acid potassium sulphate 
are poured. This salt should have been previously fused (cf. 
p. 37), so as to be free from water of crystallization. The 
amount used will naturally vary with the weight of the pre- 
cipitate, but the limits mentioned will be ample in any case. In 
general, it is hardly necessary to weigh out the exact amount 
of acid sulphate, but to put in enough to fill the crucible about 
one-third, or somewhat more if the precipitate weighs over 0.30 
gram. In pouring in the coarse powder, care should be taken 
that none of the light ash is expelled and lost. 
* The crucible is placed over a low flame, that of a small glass 
alcohol lamp serving the purpose admirably, and heated gently 
till the salt is fused. It is then raised to a distance above the 
flame (about a foot or so), where the acid sulphate will remain 
in a state of fusion and the moisture which it contains and the 
water formed by its decomposition will be driven off, without 
any boiling or spattering against the crucible cover. With 



108 METHODS. 

some practice the height can be adjusted easily, and this point 
is an important one to attend to, as any drops on the cover 
or the upper sides tend to spread on further heating and run 
over the edges, leading to loss of^/iron^ The whole process must 
be carefully watched at internals, therefore, to guard against 
this. V_V 

In the course of an hour or so the water due to decom- 
position will be driven off, the acid sulphate having become 
pyrosulphate, and the crucible can be lowered gradually till 
immediately above the small flame, where it is kept for 
another hour or so. Here also the contents should be watched 
to see that there is no spattering. The precipitate has been 
gradually dissolving, and the fused salt become darker in 
color. The larger lumps stay at the bottom, while a consid- 
erable part floats on the top of the liquid. 

When the greater part of the floating portion has dissolved, 
any small particles which may be adhering to the sides above 
the level of the liquid may be washed down by a slight rotary 
motion of the crucible, and the flame is turned up, or a Bunsen 
burner substituted for the alcohol lamp. This more intense 
heating should be carried out with caution to avoid boiling, 
and, until the last stages, the bottom of the crucible should 
not be allowed to become red-hot. White vapors of sulphur 
trioxide. are given off, and the crucible is examined every now 
and then till all the floating precipitate has been dissolved. 
If any particles obstinately adhere above the liquid, the crucible 
may be held obliquely in the triangle, so as to let the fused salt 
act on these. 

The heat is then increased somewhat till the bottom of the 
crucible is a faint red, the liquid getting thicker through loss of 
sulphuric acid and the formation of the more difficultly fusible 
normal potassium sulphate. The liquid mass becomes also a 
very dark brown, almost opaque if considerable amount of iron 
is present, the depth of color increasing with the tempera- 
ture. This is due to the greater dissociation with increasing 
temperature, and the consequent larger proportion of yellow 



ALUMINA AND TOTAL IRON OXIDES. 109 

or brown iron ions. The bottom of the crucible may be 
examined, notwithstanding the opacity of the liquid, to see if 
all the precipitate has been dissolved, by removing the flame, 
and allowing the crucible to cool with the cover off. The fused 
mass will gradually become less opaque and lighter in color, 
till it is transparent enough to see through before solidification 
commences at the surface. 

When no more undissolved substance is visible, the heating 
at a low red heat is continued for ten minutes or so, to render 
complete solution certain, and the crucible is placed on a stone 
or iron slab to cool. This cake loosens from the crucible far 
more readily than that of fused alkali carbonates, and also 
usually cracks, so that it offers no difficulty in its removal. 

It may seem that this process calls for almost constant atten- 
tion and that it takes an inordinate amount of time. In reality, 
however, after one has had a little practice in adjusting the heat 
at the various stages, only an occasional glance is necessary, and 
the whole can often be accomplished in from three to four hours, 
although, as a rule, a somewhat longer time is demanded. This, 
however, is of no great importance, as the analyst can be busy 
with other parts of the analysis. 

When the sulphate is cold, water is poured in to about half 
fill the crucible, and it is gently heated till the cake loosens, 
when this is transferred by means of the platinum spatula to a 
250-c.c. beaker. The crucible is well washed with hot water into 
the same beaker, until all adhering sulphate is removed, and the 
cover is treated likewise. The final volume of liquid in the 
beaker may be about 150 c.c. About 10 c.c. of concentrated 
sulphuric acid are added, not only to facilitate the solution, but 
to prevent reversion to or precipitation of metatitanic acid, 
which would diminish the apparent amount of titanium diox- 
ide as determined later by the colorimetric method (Dunning- 
ton). The beaker is then heated over a low flame till solution 
is complete, except for traces of silica, which is practically insol- 
uble in the melted potassium pyrosulphate. 

The contents of the beaker are filtered through a 7-cm. filter 



110 METHODS. 

into a 250-c.c. flask, the beaker being well rinsed at least half a 
dozen times, and the filter also well washed. If the fusion has 
been successful but a few flakes of silica will be found in the filter- 
If not it will also contain small, dark particles of undissolved 
^ferric oxide. 

In any case, it is placed in an unweighed, small crucible, 
carbonized at a gentle heat, ignited and weighed. A drop of 
dilute sulphuric acid and two or three of hydrofluoric acid are 
added, driven off by gentle heating, the crucible again ignited 
and weighed. The Joss in weight represents the trace of silica, 
which is to be added to that of the main portion, already deter- 
mined (p. 97). It will seldom amount to more than a milli- 
gram or two. 

The residue left in the crucible, which will contain a little 
iron or titanium oxides, is dissolved by fusion with a small lump 
of acid potassium sulphate, which is quickly effected. After 
cooling, this is dissolved in the crucible in a little warm water 
containing a drop of sulphuric acid, and kept for addition to the 
main solution after reduction of the iron. 

Reduction of Ferric to Ferrous Iron. The filtered solution of 
the mixed sulphates contains all the iron in the ferric state. This 
has to be reduced to ferrous for titration with potassium per- 
manganate, to determine the total iron. As has been previously 
noted (p. 64), the use of zinc for this purpose is not to be recom- 
mended, and the best reagent is hydrogen sulphide. This com- 
mends itself on account of its certainty and rapidity of action, 
its easy and complete removability, and still more by the fact 
that it has no reducing action on the titanic sulphate present. 

A current of this gas, of course washed with water, is allowed 
to bubble through the solution in the 250-c.c. flask at the rate 
of about a bubble a second. Although Hillebrand recommends 
that the solution be hot, I have not found this necessary, and 
pass the gas through the cold solution. The current is con- 
tinued till reduction is complete, which is indicated by the 
liquid becoming turbid and masses of sulphur separating, which 
are stained brown by traces of platinum sulphide. At least 



ALUMINA AND TOTAL IRON OXIDES. Ill 

fifteen minutes should be allowed for this, as, if the reduction is 
incomplete, the amount of total iron will be too low, and that of 
alumina too high. 

The glass tube through which the gas has been introduced is 
rinsed off inside and out into the flask, and the contents are 
filtered off through a 7-cm. filter into a 400-c.c. flask. This is to 
be done as quickly as possible, and the filter kept full. The 
washing is carried out with water containing some H 2 S, six or 
eight rinsings of the smaller flask and passage through the filter 
being sufficient. Owing to the presence of finely divided sulphur, 
the filtrate is always opalescent. But this need cause no con- 
cern, as it is completely oxidized by the sulphuric acid present in 
the subsequent boiling, and the liquid becomes perfectly clear. 

The solution of the small cake of fused sulphate containing 
the residue from the trace of silica is poured in, and the crucible 
washed once or twice, the excess of H 2 S present being more than 
sufficient for the complete reduction of the ferric sulphate which 
it contains. A half dozen small pieces of platinum-foil, bent 
at right angles, are dropped in to prevent bumping, and a 
square piece of platinum-foil, through which a hole has been 
cut, is placed over the mouth of the flask and fixed in place by 
bending down the corners. 

The flask is then placed over a flame, and a carbon-dioxide 
generator set in action, the gas being freed from possible H 2 S 
(due to sulphides in the marble) by passing through a column of 
pumice soaked in copper sulphate solution, and washed by a wash- 
bottle containing water. The C0 2 is allowed to bubble at the 
rate of several bubbles a second, and is passed into the flask above 
the liquid by a short piece of glass tubing inserted through the 
hole in the platinum-foil. Complete saturation by H 2 S is shown 
by small bubbles of this gas rising in the liquid soon after the 
heating begins, and long before it has become hot enough to 
simmer or boil. 

When boiling has begun, the flow of carbon dioxide is reduced, 
but still kept up, and the boiling continued briskly until the 
liquid is reduced to one-third of its original volume of about 



112 METHODS. 

300 c.c.,* by which time the H 2 S is completely expelled. It is 
convenient to have a series of dots or lines, about half an inch 
apart, marked on the side of the flask which is used for this 
operation. This can readily be done with a little paint or black 
varnish. By this process, which will take about two hours or 
less, the H 2 S is completely expelled, with no danger of reoxidation 
of the ferrous sulphate, since at first the liquid contains hydrogen 
sulphide, and later the boiling is carried on in an atmosphere of 
steam and carbon dioxide. 

The flask is next removed from the flame, and, while the cur- 
rent of C0 2 is still passing, is filled to the beginning of the neck 
with cold water, which has been previously boiled in a large 
wash-bottle to expel all dissolved air. In doing this it is best 
to pour the cold water down the side of the flask, so as to dis- 
turb the hot liquid as little as possible. The flask is then 
placed in a basin or other receptacle and cooled quickly in a 
stream of water up to the level of the liquid contents, the cur- 
rent of C0 2 passing the while. 

Titration of Iron. When the contents of the flask are quite 
cold, it is emptied into an800-c.c. beaker, and is rinsed out several 
times with the cold, boiled water. The pieces of platinum-foil are 
allowed to drop into the beaker, and the foil cover and tube for 
the introduction of C0 2 are also washed. 

The contents of the beaker (best placed on a square of white 
porcelain or paper) are then titrated with the standard solution 
of potassium permanganate, a burette with a glass cock, of 
course, being used. The preparation and standardization of 
this solution are described on p. 37. The liquid is constantly 
stirred till it is just tinged a permanent red, and, as it is clear 
and colorless, the exact point can be struck with great accuracy. 

When the amount of standard solution needed is roughly 
known, about half of this may be added quickly in portions of 
1 or 2 c.c. at a time, with stirring to disappearance of the color 



* The boiling down must not be carried far enough to render the sul- 
phuric acid so strong as to possibly reoxidize some of the ferrous iron. 



MANGANESE AND NICKEL OXIDES. 113 

after each addition. Beyond this, the permanganate should be 
added by drops, with constant stirring, to avoid overrunning the 
mark. When the color begins to disappear slowly, single drops 
are to be added with great caution, till one of them produces a 
pink blush throughout the liquid which does not vanish on stir- 
ring for a short time. As very dilute solutions of permanganate 
are unstable, this color will vanish on standing, even when the 
reaction is complete. After waiting a few moments after the 
addition of the last drop, the burette is read off to the nearest 
tenth of a cubic centimeter. 

The number of cubic centimeters of permanganate solution 
used is then multiplied by the amount of Fe 2 3 equivalent to 
1 c.c. of the standard, the product giving the total iron in 
the rock determined as Fe 2 3 . From this is to be deducted 
the iron present as FeO, and that which may exist as FeS 2 , 
which will 'be determined later. 

After titration of the iron the solution is to be evaporated on 
the water-bath down to about 150 c.c., either in porcelain or 
platinum, the beaker being rinsed well and the rinsings added 
during the evaporation. This liquid is to be placed in a 250-c.c. 
measuring-flask, with glass stopper, but not filled to the mark, 
and reserved for the determination of Ti0 2 (see p. 146). 

9. MANGANESE AND NICKEL OXIDES. 

The combined filtrates from the precipitate of alumina, iron, 
etc., whether the basic acetate method or ammonia alone has 
been used, are evaporated down to a bulk of about 100 c.c., best 
in the platinum basin, after ammonia water has been added to 
alkaline reaction. This will in almost all cases produce a pre- 
cipitate of aluminum and ferric hydroxides, which must be fil- 
tered off on a small filter. It is at this point that there is danger 
of neglecting to collect the slight precipitate of alumina, if the 
manganese is precipitated without previous filtration, so that 
any alumina or iron present falls with it. 

The filter is ignited in the crucible which is used for the 



114 METHODS. 

ignition of the main precipitate of these oxides (see p. 104). The 
filtrate is caught in a 200-c.c. flask, and if the platinum basin is 
stained brown by deposited manganese, this is to be dissolved in 
a few drops of hydrochloric acid and a drop of sulphurous acid 
(Hillebrand) and washed into the flask. 

Enough ammonia water is added to make the contents of 
the flask strongly alkaline, and a current of H 2 S is passed 
through it for ten minutes, which precipitates the manganese, 
and also nickel, cobalt, copper and zinc, or any platinum which 
may have been derived from the basin. The flask is corked and 
allowed to stand for twenty-four hours. 

The precipitated sulphides are collected on a 7-cm. filter, and 
washed with water containing a little ammonium chloride and 
ammonium sulphide, the flask being also rinsed out with this. 
The filtrate is received in a 400-c.c. beaker, and reserved for the 
determination of lime and magnesia (p. 115). 

sulphide of manganese (and zinc) is dissolved by passing 
a few toibic centimeters of hydrogen-sulphide water acidified with 
one-fif m of its bulk of hydrochloric acid through the filter, and ' 
washingkeveral times. The liquid is received in a small porcelain 
or platinum basin and evaporated to dryness. A few drops of 
solution of sodium carbonate are added and the contents of the 
dish again evaporated to destroy ammonium salts, which would 
hinder the complete precipitation of manganese. The dry. salts 
are then dissolved in about 10 c.c. of water to which a few drops 
of hydrochloric acid are added, and are precipitated with sodium 
carbonate. The manganese carbonate is collected on a 5J-cm. 
filter, washed, ignited in a weighed crucible and weighed as 
Mn 3 0, 

The black residue on the filter may contain nickel, cobalt,, 
copper and platinum. The filter is incinerated in a porcelain 
crucible, and dissolved in a few drops of aqua regia, evaporated 
to dryness in the crucible, dissolved in a little water and hydro- 
chloric acid, and a little strong hydrogen-sulphide water added, 
which will precipitate the copper and platinum. These are 
filtered off on a small filter, and in the filtrate, to which ammonia 



LIME AND STRONTIA. 115 

is added, nickel and cobalt are precipitated by hydrogen sul- 
phide. A few drops of acetic acid are added and the liquid 
allowed to stand for some hours, when the nickel (and cobalt) 
sulphides are caught on a 5J-cm. filter, ignited and weighed as 
oxide. The amount of cobalt is so small in terrestrial rocks that 
it is not necessary to separate it from the nickel, but its pres- 
ence may be established, if desired, by testing the oxide with 
the borax bead. The above method of procedure is that of 
Hillebrand.* If it is desired to determine copper, this is best 
done in a separate portion (p. 166). 

10. LIME AND STRONTIA. 

Lime. For the determination of lime the filtrate from the 
precipitations by ammonia (p. 102), or if manganese has been 
determined, that from the precipitate of manganese sulphide, 
is used. In the last case the ammonium sulphide had best be 
destroyed by acidifying with hydrochloric acid, warming for a 
time and filtering off the precipitated sulphur. The filtrate 
from this, or from the precipitate of alumina, etc., should not 
amount to more than 500 or 600 c.c., and is held in an 800-c.c. 
beaker. If much more than this, it is advisable to evaporate 
it down to 500 c.c., but this should not be necessary if care 
has been taken to avoid unduly large quantities of washing- 
water. 

A little ammonia is added till the liquid smells slightly of it, 
and the liquid brought to a boil. In the meantime 1 gram or so 
of ammonium oxalate is dissolved in 25 to 50 c.c. of water, with 
the aid of a gentle heat, and is poured into the large beaker when 
the liquid begins to boil. The boiling is continued for a few 
minutes, and the beaker allowed to stand. 

When cool enough to be handled it is filtered through a 7- or 
9-cm. filter, according to the amount of calcium oxalate, the fil- 
trate being received in a 1000-c.c. beaker. As little as possible 

* Hillebrand, p. 60. 



116 METHODS. 

of the precipitate is allowed to pass onto the filter, and this and 
the beaker are washed only two or three times with warm water. 

About 50 c.c. of warm dilute (1:5) nitric acid are prepared in a 
small beaker, the 1000-c.c. beaker with the filtrate removed from 
beneath the funnel, and the 800-c.c. beaker in which the lime has 
been precipitated substituted for it. The filter is then filled with 
the dilute nitric acid, which, when it begins to drop through, is 
allowed to fall upon the sides of the beaker, held obliquely, at the 
upper line of adhering calcium oxalate. The beaker is turned 
round so that the acid may flow over and dissolve every part of 
the adhering precipitate, a little being also dropped on the stir- 
ring-rod. This operation is repeated two or three times, till 
the whole of the precipitate is dissolved, that which may be on 
the filter as well as that in the beaker. The filter is then well 
washed with water, for which six or eight times suffice, the wash- 
ings being caught in the 800-c.c. beaker, of course. 

After rinsing down the sides of the beaker, a few drops of 
ammonium-oxalate solution are added, and the acid liquid is 
neutralized with ammonia water till it smells rather strongly of 
this gas. The small bulk of liquid, which should not be more 
than an inch or two in depth, is then brought to a boil, allowed 
to stand for a short time, and filtered through the same filter, the 
filtrate being received in the 1000-c.c. beaker which contains the 
filtrate from the first precipitation. All the calcium oxalate 
must, of course, be transferred to the filter, and that which 
adheres to the sides be removed by rubbing with a stirring- 
rod tipped with a short piece of rubber tubing, and also 
washed into the filter. A few washings only will suffice, and 
it will be necessary to catch only the first of these in the 
beaker along with the main bulk of filtrates. 

It must be noted in the case of such fine precipitates as 
those of calcium oxalate and ammonium-magnesium phosphate, 
that they have a very strong tendency to creep up the wetted 
surfaces of their receptacles. Great care must therefore be 
taken in dealing with them to examine the whole surface of 
the beaker, so that no patches may escape the rubber-tipped 



LIME AND STRONTIA. 



117 



rod, and also to wash them into the filter with a fairly strong 
stream of water from the wash-bottle, which will overcome the 
surface tension of the liquid adhering to the sides and which 
tends to hold them back. 

This double precipitation is necessary, since the calcium 
oxalate first thrown down carries with it some sodium salts, as 
well as some magnesium. Precipitation at a boiling heat is pre- 
ferable to that in the cold, both because it is more complete, 
unless the liquid is allowed to stand for a much longer time, 
and also because the crystalline precipitate is larger grained 
and hence less liable to pass through the filter-paper. 

The filter containing the precipitate is placed moist in a 
medium-sized platinum crucible, which has been previously 
strongly ignited and weighed, and is heated gently to dryness, 
the paper carbonized and then incinerated at a higher tempera- 
ture, and finally blasted for at least ten minutes. This converts 
the calcium carbonate to oxide, as which the lime is weighed, 
with as little delay as possible after cooling in the desiccator. It 
is always a wise precaution, especially if the amount of precipi- 
tate be considerable, to blast once more after weighing, to see 
that a constant weight is obtained. 

If a blast is not available the lime may be determined as 
calcium carbonate. This is effected by the method described by 
Fresenius,* all the precautions recommended by him being ob- 
served. In brief, the method consists in drying the precipitate 
of calcium oxalate on the filter, transferring as much as possible 
of the dry precipitate to a weighed platinum crucible, burning the 
filter held in a platinum wire, the ash dropping into the crucible, 
and gently and cautiously heating at a low temperature till the 
oxalate is decomposed and the salt converted into calcium car- 
bonate, but not to calcium oxide. The method is capable of 
accurate results in experienced hands, but that of blasting and 
weighing as CaO is always to be preferred. 

Strontia. The calcium oxide as thus prepared, contains 

* Fresenius, I, p. 270. 



118 METHODS. 

the strontia of the rock, but scarcely ever more than traces of 
baryta.* If it should be desired to determine the former, it may 
be done, or at least the operation may be commenced, immedi- 
ately after the final weighing of the lime. 

While the amount of this constituent is always very small, in 
almost every case less than that of barium, yet its determination 
involves so little trouble and loss of time, that it is to be desired 
that it be done more frequently than is now the case. At the 
same time, if the amount of lime is less than 1 per cent or so; it 
will scarcely be worth while to do this, except for very exact 
analyses. The method to be employed depends on the solu- 
bility of calcium nitrate in a mixture of absolute alcohol and 
ether, and on the Insolubility of strontium nitrate in this medium. 

After the final weighing, and before it has had time to absorb 
an appreciable amount of carbon dioxide from the atmosphere, 
the lime is transferred to a 4-inch test-tube by emptying on a 
small piece of glazed paper and pouring into the tube. A few 
drops of water are added and the lime completely slaked, and 
then a few drops of concentrated nitric acid, just sufficient to 
dissolve the lime completely. 

Tne contents of the test-tube are to be evaporated to com- 
plete dryness, which is best accomplished by heating the tube in 
an air-bath at 135, the mouth of the tube projecting from one of 
the upper orifices of the oven. When completely dry and cool, 
5 or 6 c.c. of a mixture of ether and absolute alcohol in equal 
parts are added, the tube corked and laid aside for twenty-four 
hours with occasional shaking, till the calcium nitrate is entirely 
dissolved. 

The contents of the tube are then to be filtered through a 5^- 
cm. filter and well washed (six times) with the same mixture of 
absolute alcohol and ether. The filter is allowed to dry in the 
funnel, after which the strontium nitrate is dissolved in a few 
cubic centimeters of water passed through the filter and re- 
ceived in a 50-c.c. beaker, the filter being washed a few times. 

* Hillebrand, p. 63. 



MAGNESIA. 119 

A few drops of dilute sulphuric acid are added and then alcohol 
equal in amount to the volume of liquid in the beaker. After 
standing for twelve to twenty-four hours the precipitated stron- 
tium sulphate is filtered off, ignited and weighed. Its weight is 
multiplied by .56 to obtain that of SrO, and this is deducted 
from that of the lime. 

11. MAGNESIA. 

The filtrate from the calcium oxalate contains, of the original 
rock constituents, only the magnesia and alkalies, with the ba- 
rium, and part of the manganese and the nickel and other metals 
of the sulphide group, if these have not been previously deter- 
mined. There are, of course, also present the alkalies derived 
from the carbonate fusion and large amounts of ammonium salts. 
It will not be necessary to remove these last for the determi- 
nation of' the magnesia, which is the only constituent which 
interests us in this filtrate. 

Precipitation. To the liquid, which may amount to 600 or 
800 c.c., and is contained in a 1000-c.c. beaker, 3 grams of 
hydrogen-ammonium-sodium phosphate fmicrocosmic salt) dis- 
solved in a little water are added, and 100 c.c. of ammonia 
water. The mixture is well stirred with a long stirring-rod, and 
the beaker covered with a large watch-glass and set aside for 
at least twelve hours, or preferably twenty-four. 

At the end of this time the liquid is filtered through a 7-cm. 
filter, a suction-tube being connected with the funnel. The 
beaker is rinsed out and the filter washed two or three times 
with very dilute (10 per cent) ammonia water. Gooch and 
Austin * have pointed out that the strong ammoniacal water 
usually recommended (1 : 3) is entirely unnecessary. It is well, 
even with the more dilute ammonia, to connect a glass mouth- 
piece with the wash-bottle by a rubber tube about a foot long, to 
prevent any injurious effect on the delicate mucous membrane 
of the mouth. The filtrate and washings can be thrown away. 

* Gooch and Austin, Am. Jour. Sci., VII, p. 189, 1899. 



120 METHODS. 

The precipitate on the filter is dissolved in dilute nitric acid 
(1 :5), exactly as was done with the calcium oxalate, the acid 
being allowed to flow over all the sides of the beaker as far as the 
precipitate extends, and the filter well washed. The depth of 
the liquid in the 1000-c.c. beaker should not be more than 3 or 
4 cm. A drop or two of sodium-ammonium phosphate solu- 
tion are added, and then ammonia water till the liquid smells 
rather strongly of it, and the beaker allowed to stand for an hour. v 

This reprecipitation is necessary, as Neubauer* and Gooch' fc 
and Austin f have shown that if there is an excess of ammonia, 
ammonium salts and precipitating phosphate, the magnesium py- 
rophosphate will not be normal in composition, but will contain an 
excess of P 2 5 , thus increasing the apparent amount of magnesia. 
The error will not be of great magnitude in rocks poor in mag- 
nesia, as granites and trachytes, where a single precipitation may ' 
suffice if the extreme of accuracy is not required, but it may be 
considerable in more basic rocks. A reprecipitation is therefore 
always necessary in these, and advisable in those first mentioned. 

Filtration in Gooch Crucible. While the precipitate of mag- 
nesium-ammonium phosphate can be collected on a paper filter 
in the usual way, carbonized from a moist condition and ignited, 
my predilection is for the use of the Gooch filter, on account of 
involving a smaller volume of washing liquid, and not leading to 
possible loss of phosphorus through the reducing action of the 
carbon of the filter on the precipitate. 

To prepare the Gooch filter, the perforated crucible is placed 
in the rubber-covered mouth of the so-called carbon filter, and this 
is inserted in the rubber stopper of the stout Erlenmeyer flask. 
The side tubulure is connected with the suction-pump and a 
gentle aspiration applied. A few cubic centimeters of a cloudy 
mixture of asbestos and water (p. 39) are poured in, so as to 
form on complete suction a thin felt on the bottom, which must 
be completely covered. The felt must not be too thin, or there 
will be danger of its breaking, nor, on the other hand, should it 

* Neubauer, Zeits. Angew. Chem., 1896, p. 435. 
t Gooch and Austin, loc. cit., p. 190. 



MAGNESIA. 121 

be inordinately thick, as this will render the filtration un- 
necessarily slow. A little practice will enable one to prepare it 
properly. The felt is washed with a few portions of water, 
directed gently against the side of the crucible, sucked dry, and 
the aspiration stopped. 

The crucible is heated over a low flame, the bottom cap being 
left off, and the flame moved about by hand. In this way the 
felt is well dried without loosening or blistering, as the steam 
generated from its lower side will escape through the perfora- 
tions. When quite dry, as is indicated by the whiteness of the 
asbestos, the bottom cap is put on, and the crucible is cov- 
ered and ignited at a bright-red heat for a short time, to drive off 
all traces of water. It is then cooled in the desiccator and 
weighed. 

The Gooch crucible, with the bottom cap and cover removed, 
is placed in position in the carbon filter, care being taken when 
inserting it in the rubber mouth, that the latter does not come in 
contact with the bottom of the crucible and rub off any small 
pieces of asbestos which may project beyond the perforations. 

The suction is then turned on, which should be gentle and at 
the same time effective, and the liquid is poured slowly into the 
crucible, the current from the stirring-rod striking the side and 
not directly on the felt. Otherwise the latter is liable to be torn 
and some of the perforations laid bare, possibly allowing some of 
the fine precipitate to pass through. The whole of the liquid is 
thus filtered, with considerable of the precipitate entering the 
crucible, so as to protect the felt. The beaker is then rinsed with 
a stream of very dilute ammonia water several times, the bulk of 
the precipitate going into the Gooch crucible. The adhering pre- 
cipitate is loosened from the sides and bottom of the beaker and 
from the stirring-rod by means of a rubber-tipped rod, and the 
last traces of it brought into the filter by gentle streams of the 
dilute ammonia from the wash-bottle. > 

The precipitate on the felt is well washed with the same fluid, 
the crucible being allowed to empty before each addition, of 
which about half a dozen will be sufficient in most cases. If 



122 METHODS. 

desired, the washing can be tested by stopping the suction, re- 
moving the stopper of the Erlenmeyer flask, and letting a few 
drops fall on a watch-glass. These are acidified with a drop or 
two of nitric acid and tested with silver nitrate. It will be well 
to do this the first few times, till one learns by experience when 
the precipitate is thoroughly washed. 

When the washing is complete the suction is continued for a 
short time in order to partially dry the precipitate, when it is cut. 
off and the side connection cautiously opened, to avoid any re- 
gurgitation of liquid up against the felt. The bottom cap is put 
on and the covered crucible is heated over a low flame till the pre- 
cipitate is dry and no more odor of ammonia is perceived. It is 
then ignited at a bright-red heat for ten minutes, blasting not 
being necessary. If the mass appears gray it can be rendered 
white by blasting, or, still better, by moistening with a few 
drops of nitric acid, drying at a gentle heat, and reigniting. 

After cooling in the desiccator the crucible and its contents 
are weighed, the gain in weight being Mg 2 P 2 7 . This is to be 
multiplied by the factor 0.3621 to reduce it to MgO. 

The correction recommended by Hillebrand for the minute 
amount of lime which he states is probably always present 
will not be called for, except in the most extremely accurate 
work. 

12. FERROUS OXIDE. 

Discussion of the Mitscherlich Method. The determination 
of ferrous oxide in rocks has long been a source of difficulty to the 
analytical chemist and of uncertainty and suspiciofcHo the petrog- 
rapher. The method which has been most commonly used up to 
within a comparatively short time, and which is still extensively 
practised abroad, is that of Mitscherlich, which consists in heat- 
ing the rock powder with dilute sulphuric acid in a sealed glass 
tube at 200 till decomposition is effected. 

The difficulties of this method are numerous. In the first place, 
a glass entirely free from iron must be obtained, since the tube 



FERROUS OXIDE. 123 

is also liable to attack, especially if a little hydrofluoric acid is 
added, as is sometimes done. The operations for ensuring an 
oxygen-free atmosphere and the proper sealing of the tube are 
troublesome, and the heating must be prolonged. Furthermore 
it is often an extremely difficult matter to ascertain when the 
decomposition is complete and also, in the case of some iron- 
bearing minerals, to ensure their complete decomposition under 
the circumstances. 

The fact was noted by Hillebrand * that the determination of 
ferrous iron by the Mitscherlich method usually gave higher re- 
sults than that in the same rock, by the alternative method of 
simple decomposition by boiling with sulphuric and hydro- 
fluoric acids in an atmosphere of carbon dioxide. The explana- 
tion was finally found in the observations of Stokes, showing the 
easy oxidizability of pyrite by ferric salts under the conditions of 
the sealed-tube method, the iron of the pyrite becoming ferrous 
sulphate and the ferric sulphate present being partially reduced 
to the ferrous condition. As, according to Hillebrand, nearly all 
rocks contain sulphides, and this is especially true of the more 
basic rocks in which iron is highest, the danger and general inac- 
curacy of the method are clear. 

For most purposes, therefore, and even for the analysis of 
rocks which are known to be free from sulphur, the Mitscherlich 
method is to be discarded, and one of the alternative ones based 
on the employment of hydrofluoric acid is to be adopted. 

Special Grinding of Powder. Whatever be the method em- 
ployed for the determination of ferrous iron, it is imperative that 
the rock powder be in an extremely fine state of division. That 
which is quite sufficiently so for most of the other methods of 
decomposition, such as the fusion with alkali carbonate, will not 
answer for the present purpose, as it is essential that the decom- 
position can be rendered certainly complete and that the time be 
reduced to its lowest limit to avoid, as far as possible, any oxida- 
tion of the ferrous iron present. 

* Hillebrand, p. 88. 



124 METHODS. 

For this determination, and, it may be added, for the deter- 
mination of the alkalies, a small amount of the main stock of rock 
powder must be ground down by hand in an agate mortar. This 
is effected in small portions at a time, of about half a gram each, 
the grinding being continued till a small pinch rubbed on a tender 
part of the skin, conveniently that between the thumb and the 
index finger, causes no gritty feeling. As each portion is ground 
to this state of fineness it is placed on a clean sheet of paper, and 
the whole, amounting to about 2 grams, is placed in a special 
small specimen tube, corked and marked. 

Simple Method. There are several modifications of the 
method of decomposition by a mixture of hydrofluoric and sul- 
phuric acids, which differ in regard to comparative simplicity 
and, to some extent also, as to accuracy. The simplest, and the 
one which I have found to be sufficiently accurate for most pur- 
poses and by far the most rapid, will be described first. 

About half a gram of the specially ground rock powder is 
weighed into a 40-c.c. platinum crucible (p. 80), the cover of 
which must fit closely. It is moistened with a little water, pre- 
cautions being* taken to avoid blowing out any of the powder. 
When thoroughly wet and pasty a few small coils of platinum 
wire are dropped in, to prevent bumping. 

In another crucible or small platinum basin a mixture is made 
of 10 c.c. of hydrofluoric acid and 10 c.c. of a mixture of sulphuric 
acid diluted with its own volume of cold, boiled water. This 
warm fluid is poured over the rock powder in the crucible, which 
is immetiiately covered and placed loosely in a triangle over a 
small flame, so that it begins to boil gently almost instantly. The 
crucible is raised till the boiling is steady, and there is no dan- 
ger of bumping or boiling over, the proper height for this being 
learned with a little practice. With a small alcohol lamp and the 
40-c.c. crucible which is regularly used for this operation, I find 
that about five inches above the flame is the right adjustment. 
But this will vary with the size of flame and other conditions, 
so that the analyst must adjust the height according to circum- 
stances. 



FERROUS OXIDE. 125 

The boiling is continued for from five to seven minutes, accord- 
ing as the rock is largely feldspathic or rich in ferromagnesian 
minerals. For the great majority of rocks I have found that six 
minutes is ample for complete decomposition, and yet not long 
enough to give rise to sensible oxidation of the ferrous iron by the 
hot sulphuric acid. There must be no interruption of the regular 
continuance of the boiling, so that the operation should be con- 
ducted in the hood. 

In the meantime an 800-c.c. beaker is half filled, or at least to 
a height above that of the crucible, with cold, boiled water, and 
placed near the crucible with its boiling contents. When the 
alloted time is up, the still covered crucible is cautiously, but 
firmly, raised from the triangle (without extinguishing the 
flame), by means of two flat pieces of wood with a projecting 
ridge at the ends a trifle wider than the overhang of the cover, and 
rounded to fit the crucible sides. These are held vertically, one 
in each hand, and the crucible grasped near the top, lifted and 
dropped into the beaker of water, and the wooden pieces im- 
mediately withdrawn.* The contents of the beaker are to be 
immediately titrated with standard permanganate solution. 

After titration the contents of the beaker should be examined 
to see if decomposition has been complete, as will be shown by the 
absence of hard, gritty particles. With rocks containing much 
lime or silica the liquid will be somewhat turbid, but this need not 
cause concern as to the decomposition being incomplete. It is 
due merely to the formation of calcium sulphate or of silica aris- 
ing from the reaction of the water on the silicon fluoride. 

It may sometimes happen, especially with rocks rich in 

* These wooden tongs may be conveniently made of two ordinary test- 
tube clamps by removing the smaller piece of each, and slightly hollowing 
the ends to fit the crucible. Some crucibles may be raised by grasping 
them firmly with the crucible tongs, one point resting on the cover, the 
other on the side, but this is rather uncertain and somewhat dangerous, 
as the tongs are apt to slip. A pair of Blair's tongs, of German silver, may 
also be used, if the curved ends are bent so as to lie at right angles with the 
handles. The operation of transferring the crucible should be first practised 
with an empty one, till there is no danger of slipping or other mishap. 



126 METHODS. 

nephelite or analcite which gelatinize with acids, that the powder 
cakes at the bottom of the crucible, preventing complete decom- 
position. This is usually due to the powder not having been 
thoroughly stirred up with enough water before the addition of 
the mixed acids. In such a case the only remedy is to repeat 
the whole operation till successful. 

The solution of permanganate is to be added till the first 
blush of red color appears, which is permanent in so far as it does- 
not disappear on stirring. This coloration, however, vanishes 
very rapidly, more quickly than that produced in the titration 
for total iron, and as Hillebrand says, the permanganate can be 
added by the cubic centimeter without obtaining a really per- 
manent color. He attributes * this to the ready oxidizability 
of manganous fluoride. The beaker should be washed out as 
soon as possible after titration, to prevent corrosion by the weak 
hydrofluoric acid. 

Pratt's Method. The simple method described above has 
been modified by Pratt,f with a decided gain in accuracy, as 
shown by the results of his experiments. If the necessary 
apparatus is at hand, his method is to be preferred to that given 
above. 

The method consists in dissolving the rock powder in a mix- 
ture of hydrofluoric and sulphuric acids over a small flame, as 
has been described above, but with the difference that a current 
of C0 2 is allowed to flow into the crucible during the operation, 
by means of a platinum tube passing through the cover. This is 
started before the heating begins, and the contents of the cruci- 
ble, after ten minutes' boiling, are cooled in the crucible while the 
current of gas still passes. The crucible with its contents is 
then placed in a platinum basin or beaker of cold, boiled water, 
and titrated with potassium permanganate as above described. 

Cooke's Method.- The third method was devised by J. P. 
Cooke,t and is the one employed by the chemists of the Geologi- 



* Hillebrand, p. 92. 

t J. H. Pratt, Am. Jour. Sci. (3), XLVIII, p. 149, 1894. 

% J. P. Cooke, ibid. (2), XLIV, p. 347, 1867. 



FERROUS OXIDE. 127 

cal Survey.* It consists in heating the rock powder with a mix- 
ture of hydrofluoric and sulphuric acids on the water-bath in an 
atmosphere of carbon dioxide. 

The medium-sized water-bath has perforations through the 
innermost rings, and preferably a groove in one of them, to fit the 
funnel with which the crucible is covered. A stream of carbon 
dioxide flows through one of the two side tubes, which should be 
near the top, and fills the space above the water. After weighing 
the powder and mixing it with 10 c.c. of dilute H 2 S0 4 (1 : 1) hi the 
crucible, it is placed on the bath, and covered with a funnel of 
appropriate size (3 inches), the tube of which has been cut off just 
at the beginning of the enlargement. Or a small beaker with a 
hole made in the center of the bottom by hydrofluoric acid may 
be used. A current of C0 2 is introduced into the space above 
the water by means of one of the side tubes, and allowed to fill 
the bath and funnel. The groove is filled with water to provide 
an air-tight joint, and is kept so by steam from the bath. 

The flame is then lighted and the water brought to a brisk 
boil. 5 or 10 c.c. of hydrofluoric acid are then added to the cru- 
cible by means of a platinum or rubber funnel to which is attached 
a platinum or small rubber tube sufficiently long to reach to the 
bottom of the crucible, through the hole above. If a platinum 
funnel with long tube be at hand this may be left in to act as a 
stirrer. If not, a long piece of platinum wire will answer the 
same purpose. Any adhering powder may be washed down into 
the crucible by a jet from the wash-bottle. 

When the boiling commences the current of C0 2 is somewhat 
diminished, but not stopped, and the boiling continued for half 
an hour or more. The flame is then extinguished and the cur- 
rent of C0 2 again turned on full. By raising the water-level ap- 
paratus the hot water in the bath is replaced by cold, the over- 
flow being caught in a large beaker, and the whole allowed to 
cool while the carbon dioxide still passes. 

When cold, the contents of the crucible are poured into the 

* Hillebrand, p. 92. 



128 METHODS 

platinum basin, and the crucible well washed with cold, boiled 
water. The fluid is then titrated with permanganate solution 
till a permanent red blush appears. 

For the influence of sulphides, vanadium and carbonaceous 
matter on the determination of ferrous iron, the reader may be 
referred to the discussion of Hillebrand.* 

The percentage of FeO is obtained by multiplying the number 
of cubic centimeters of permanganate solution used by its equiva- 
lent per cubic centimeter in terms of ferrous oxide, and dividing 
the product by the weight of substance taken. This is then to be 
calculated as Fe 2 3 by dividing by 0.9, or by multiplying the 
number of cubic centimeters by their equivalent in Fe 2 3 and 
reducing to percentage amount. The weight of this percentage 
amount of the portion of the rock powder taken for the fusion 
with alkali carbonate is calculated, and this weight subtracted 
from the weight of total iron oxides as Fe 2 3 as already obtained. 
The difference, divided by the weight of powder taken for the 
carbonate fusion, gives the percentage of Fe 2 3 . 

If an appreciable amount of sulphur as sulphides" exists in the 
rock, regard must be had to the iron in combination with it. 
If pyrrhotite is the only sulphide present, this will be decomposed 
by the mixture of acids in the determination of ferrous oxide, and 
the iron will appear as FeO. The sulphur may be either stated 
as S in the analysis, or the amount of iron necessary for the mole- 
cule Fe 7 S 8 of pyrrhotite calculated and deducted from the amount 
of FeO, and the percentage of pyrrhotite given. The former pro- 
cedure is rather the better. If the only sulphide is pyrite, this 
will not be attacked in the determination of FeO, but the iron in 
this mineral will appear as Fe 2 3 . This may be accorded treat- 
ment similar to the iron in pyrrhotite. If both sulphides are 
present, it will be impossible to estimate the real correction 
unless the relative amounts of the two minerals are known. 
Fortunately this is seldom needed, and in general the amount of 
sulphur is so small that corrections for it are not often necessary. 

* Hillebrand, p. 94 



ALKALIES. 129 



13. ALKALIES. 

Alternative Methods. For the determination of the soda and 
potash two prominent methods are available. They differ in the 
means adopted for the decomposition of the rock and for the 
elimination of all the other constituents, the object of both being 
to obtain the alkali metals alone in solution as chlorides, and the 
final separation of these by platinic chloride. 

In the older method the rock powder is decomposed by a 
mixture of sulphuric and hydrofluoric acids, or by fusion with 
BiO, PbO or B 2 3 , digestion with the acid mixture being that 
most used. The solution obtained from this is treated succes- 
sively with ammonia and with ammonium oxalate to remove 
silica, alumina, iron, titanium, phosphorus and lime. The mag- 
nesia is separated by one of several methods (preferably by the 
use of HgO), the sulphuric acid removed by lead acetate or 
barium chloride, and the alkalies determined in the filtrate as in 
the method described below. Or barium hydrate may be used 
to separate the other constituents from the alkalies (Classen). 
It is clear that any of these processes is long and complex, and 
that, not only do they suffer from the length of time needed, but 
that there is danger of loss of alkalies during the blasting neces- 
sary with some of the fluxes. Still more, the final solution is 
liable to be contaminated by alkalies derived from the many 
reagents used and taken up from the glass vessels. 

The second method is that of J. Lawrence Smith,* and con- 
sists in decomposing the rock by fusion with calcium carbonate 
and ammonium chloride, leaching with water from the insoluble 
silicate and aluminate of calcium, and carbonates of iron, cal- 
cium and magnesium, precipitation of the rest of the lime by 
ammonium carbonate, expulsion of ammonium salts by heating 
the evaporated filtrate, and final separation of the alkalies by 
platinic chloride. 

The advantages of this method are : its convenience and ex- 

* J. L. Smith, Am. Jour. Sci., I, p. 269, 1871. 



130 METHODS. 

pedition, the manipulations being few, and a day, or at most a 
day and a half, being ample for the complete determination ; the 
separation of magnesia at the start, which is a troublesome con- 
stituent to separate from the alkalies by the other methods; the 
small danger of introduction of alkalies from reagents or glass 
vessels, only three reagents being used, and half an hour being 
the length of time that the hot fluids are in contact with glass; 
and, finally, its great accuracy, which is fully equal, if not 
superior, to that of the older methods.* The only real objection 
which can be urged against this method, as compared with the 
other, is the difficulty of obtaining a calcium carbonate entirely 
free from alkalies. The amount of these, however, is easily 
rendered extremely small by prolonged washing, and it is a con- 
stant error, the correction for which can be safely applied when 
once determined for the stock of calcium carbonate. Even if 
this is not done, however, it is certain that the error involved 
will be less than those incident to the other methods if care be 
employed in the preparation of the calcium carbonate. 

This method is practically the only one which has been used 
by the chemists of the U. S. Geological Survey, of the extreme 
accuracy and almost uniquely high character of whose analyses 
there can be no question. It is likewise the method which I have 
adopted exclusively, and which is almost universally employed 
in this country. In Europe, on the other hand, it seems to be 
little known, or at least little used, and its undoubted merit and 
superiority over the other is not generally recognized. Only the 
Lawrence Smith method will be described here. 

The Lawrence Smith Method. For the determination of 
the alkalies a specially ground portion of rock powder is to be 
used, as was described under Ferrous Oxide (p. 123). Although 
Smith states that this is not absolutely necessary in all cases, 
yet it is certainly advisable, as complete decomposition can be 
secured at a lower temperature and with more certainty than if 
the powder be coarse. 

*Cf. J. L. Smith, loc. cit.; Hillebrand, p. 96; M. Dittrich, Neues Jahr- 
buch, 1903, II, p. 81. 



ALKALIES. 131 

As the powder is to be mixed with the flux before being placed 
in the crucible, it is necessary to determine its weight from the 
loss of substance taken from the tube, instead of by the method 
of weighing used previously. The small tube containing the 
specially groun^ powder is wiped perfectly dry, uncorked, 
placed on the pan on the small frame intended for this purpose 
and weighed. The handling of the tube during the operation of 
weighing is best done by means of wooden tongs, for which an 
ordinary test-tube holder will answer. 

After weighing, and noting the weight as Tube+ Subst., a half- 
gram weight is removed from the right-hand pan, and about half 
a gram of powder is carefully shaken out into the platinum basin. 
This must be done with care to avoid any loss of powder, and 
when a sufficient quantity has been poured in, the tube is to be 
gently tilted up and lightly tapped to bring the powder down 
toward the bottom, the mouth being held over the basin. Not 
more than 0.6 gram need be taken, but not less than 0.45 gram. 
Half a gram is quite sufficient to yield results fully as accurate as 
1 gram, and the consequent saving of solution of platinic chloride, 
as well as shortening of the time needed, are rather important 
considerations. The tube is then weighed again, and the differ- 
ence between this weight, recorded as Tube -Subst., and the 
former gives the weight of substance taken. 

Just as in the weighing out of the powder for the alkali car- 
bonate fusion, it may be necessary to shake out and weigh addi- 
tional small portions several times. The endeavor should be 
made to get the final weight only slightly above, and as near to 
0.5 gram as possible without undue loss of time, and a little 
practice enables one to do this very quickly. When the powder 
is in the basin this should be kept covered with a suitable watch- 
glass to prevent loss by draughts of air. 

The balance-pans are then cleared of frame and weights, the 
pair of balanced watch-glasses substituted, and an amount of 
dry ammonium chloride equal to that of the rock powder taken 
is weighed out. It is not necessary that this weight be exact, 
and it may be a decigram or so more, but should not be less. 



132 METHODS. 

This is then poured into the basin with the rock powder and the 
basin again covered. 

An amount of calcium carbonate equal to eight times the 
weight of rock powder (about 4 grams) is then weighed on the 
pair of watch-glasses. If a correction for the small amount of 
alkalies present is to be made this weighing should be carried out 
to centigrams, but if not, the weighing need be only approxi- 
mate, but should be more, rather than less, the required amount. 
With basic rocks 5 grams should be used, to prevent too great 
fluidity during the fusion. 

The weighing out of the rock powder, ammonium chloride and 
calcium carbonate being finished, the platinum basin and the 
watch-glass holding the last are placed on a clean sheet of paper 
on the work-table. A small amount of calcium carbonate is 
transferred by the platinum spatula to an unweighed 40-c.c. 
platinum crucible, just sufficient to cover the bottom, and pressed 
lightly down with the small agate pestle. 

The rock powder and the ammonium chloride are then 
thoroughly rubbed up together in the basin with the agate 
pestle, after which the greater part of the calcium carbonate is 
poured into the basin, about half a gram being left on the watch- 
glass, and thoroughly* mixed with the other powder. This is 
preferably done in small portions at a time, with a rubbing after 
each addition. The mixture must be thorough, the object being 
to have, as far as possible, some ammonium chloride and calcium 
carbonate in contact with each particle of rock, but the rubbing 
must not be violent. 

When the mixing is considered complete, it is well to con- 
tinue it for a few minutes longer. The pestle is laid down with 
its lower end in the watch-glass, and the mixture poured cau- 
tiously through the lip of the basin into the crucible. This 
transfer is aided by the platinum spatula in brushing down small 
lumps at a time, and by final gentle tapping of the spatula on the 
inside of the basin, so as to cause the whole to pass through the 
lip without loss outside the crucible. The contents of the cru- 
cible are then smoothed down with the spatula, the remaining 



ALKALIES. 133 

calcium carbonate poured into the basin, and the latter rinsed 
with it by means of the pestle, which is also cleaned at the same 
time. The spatula is cleaned by rubbing against the carbonate 
in the basin, and the final portion of this transferred as before 
into the crucible. 

The use of the platinum basin is preferred as a mixing-vessel 
to that of a large agate mortar, as recommended by Hillebrand, 
because, while the mixture may be made just as thorough, there 
is less liability to loss owing to the high sides of the basin, and 
because the mixed powders are transferred far more easily and 
safely to the crucible from the basin than from the mortar. I 
also prefer to have the powder ground specially fine before weigh- 
ing, instead of after, as recommended by Hillebrand, as the latter 
is liable to lead to loss. 

If the rock is specially ground as fine as has been described, 
the decomposition will be complete at a temperature not hfgh 
enough to vaporize the alkali chlorides. An ordinary crucible 
may therefore be employed, with a well-fitting cover, instead of 
the capped conical one recommended by Smith and by Hille- 
brand, which permits a higher temperature for the fusion. The 
latter is, of course, to be preferred, but it is a somewhat expensive, 
and otherwise unnecessary, piece of platinum, so that it is as 
well to know that perfectly satisfactory results may be obtained 
without its use, if economy be an object. 

The crucible is covered and heated over a low flame for ten 
minutes or so, until no more vapors of ammonia or ammonium 
chloride are given off. 'The heating is then continued over the 
nearly full flame of a Bunsen burner, only the lower third of the 
crucible being heated to a not very bright red, and the crucible 
being kept well covered. This is continued for three-quarters of 
an hour, when the crucible is allowed to cool. 

When cold, the mass is soaked in the crucible with just 
enough water to cover it, and the quicklime formed allowed to 
slake, by which the disintegration is rendered almost complete. 
By the aid of the platinum spatula and a little water from the 
wash-bottle the contents of the crucible are easily transferred to 




134 METHODS. 

the platinum basin, any adhering portions being removed by the 
spatula. A little water is allowed to remain in the crucible to 
soak it out. The spatula is rinsed off into the basin, which 
should contain not more than about 50 c.c. of water. 

The partially disintegrated mass is well rubbed up with the 
agate pestle, the pestle rinsed off with a little water, and the con- 
tents of the basin brought to a boil, which should be continued 
gently for a few minutes. The liquid is then decanted through a 
9-cm. filter into a 600-c.c. beaker. The stirring-rod is rinsed off 
into the basin, and the mass once more rubbed up with the pestle 
till there are no more lumps, the pestle finally rinsed and the 
basin again heated. The liquid is decanted through the filter, 
the powder once more heated to boiling with a little water, and 
finally the contents of the basin brought on the filter. The basin 
is rinsed, and the contents of the filter washed with hot water, 
in small portions at a time, the powder being well stirred up by 
the first additions of water from the wash-bottle. 

It is impossible to ascertain when the washing is complete by 
acidifying drops of the filtrate with nitric acid and testing with 
silver nitrate, as an oxychloride of calcium is formed which dis- 
solves slowly in water, and will thus give a reaction for chlorine 
long after all alkalies are washed out. Smith states that com- 
plete washing is effected with 200 c.c. of water, but it is as well 
to be on the safe side and to use 250 to 300 c.c., which will make 
complete washing certain. This volume may be conveniently 
marked on the 600-c.c. beaker used for this operation by a small 
line of paint. 

It will be well for the beginner to test the thoroughness of the 
decomposition by dissolving a portion of the moist mass on the 
filter in hydrochloric acid. Solution should be complete if the 
fusion has been properly effected. 

To the filtrate a little ammonia water is added and the liquid 
brought to a boil.* About 1.5 to 2 grams of ammonium car- 

* Addition of ammonia is necessary to prevent the formation of soluble 
calcium bicarbonate. The iridescent scum on the surface of the liquid is, 
of course, due to the action of atmospheric CO 2 on the calcium hydroxide 
and chloride. 



ALKALIES. 135 

bonate previously dissolved in 50 c.c. of water* are then added, 
and the boiling continued for a minute or so. The lime is thus 
completely precipitated, with the exception of a trace which is 
separated later, and the alkalies left in solution as chlorides, 
along with ammonium chloride. 

The bulky precipitate of calcium carbonate is allowed to 
settle a little, and then filtered through a 9-cm. filter into a 
capacious basin (1000 c.c.). This is preferably of platinum, but 
as such a large one would be very expensive, a silver basin can be 
used with equal accuracy. In default of this a glazed porcelain 
basin will answer, with but slight danger of contamination by 
alkalies taken up from the glaze, especially as the final evapora- 
tion to dryness is carried out in platinum. A glass basin must 
not be used on any account, as the liquid will be seriously con- 
taminated with alkalies derived from it. 

The precipitate is all brought on the filter, the beaker rinsed 
and the contents of the filter washed with hot water in small por- 
tions at a time, till there is no chlorine reaction. The volume of 
liquid in the basin should be from 400 to 500 c.c. The basin is 
placed on the water-bath, or on a sand-bath Over a flame not 
high enough to produce boiling, and the liquid evaporated down 
to about 50 c.c. , when it is transferred to the platinum basin, and 
the larger basin well rinsed with hot water several times. The 
contents of the platinum basin are evaporated on the water-bath 
to dryness, which should be complete, as indicated by the white 
color of the salts. This may be done conveniently by leaving 
on the water-bath overnight. 

The basin, covered with a dry watch-glass, i^ then placed on a 
sand-bath and heated gently. This heating mVist be cautious, 
and if there is any decrepitation, due to incomplete drying, it 
should be interrupted frequently till the decrepitation subsides, 
or otherwise particles of the salts may be thrown up and stick to 
the cover-glass. If the cover is slightly dewed with moisture at 

* The solution of this should be begun when the crucible is put over the 
flame, so as to have it complete in time. It cannot be hastened by heating, 
as this decomposes the ammonium carbonate. \. 



136 METHODS. 

first, it is well to remove it frequently and wipe it off quickly, so 
as to avoid such a mishap. When decrepitation has wholly 
ceased and white vapors of ammonium chloride begin to rise, the 
heat is to be raised, with the basin still on the sand-bath. This 
is continued till the watch-glass and the sides of the basin are 
thickly coated with ammonium chloride. 

The cover is then removed, the basin placed on the ring of a 
retort-stand and the upper sides warmed with half-full flame to 
drive off the ammonium chloride. The salts at the bottom are 
next subjected to the same operation till no more white vapors 
are given off. Great care must be taken that the bottom of the 
basin is not overheated so that the salts melt and lead to the pos- 
sible vaporization of alkali chlorides. During this process the 
clear white mass becomes dark and dirty-looking, from carbon- 
ization of the traces of organic matter which even very pure 
ammonium carbonate usually contains. Prolonged gentle heat- 
ing will cause this to disappear to a large extent, but as the car- 
bon is removed by filtration its complete disappearance is not 
necessary. 

After cooling, a little water is added, just enough to dissolve 
the chlorides. If the rock contains sulphides, and especially if 
hauyne or noselite are present, a drop of barium-chloride solution 
is added to precipitate the sulphuric acid, which would otherwise 
appear later as sodium sulphate and lead to erroneous results. 
A few drops of the solution of ammonium carbonate are then 
added to precipitate the excess of barium and the lime which is 
always present in traces at this stage; or, if no sulphates are 
present, a few drops of ammonium oxalate solution are added, 
as this precipitates calcium more completely than the carbonate. 
After rinsing the interior, as high as the salts extend, by gentle 
rocking and tipping of the small bulk of liquid, so as to ensure 
their complete solution, the basin is placed on the water-bath 
and evaporated again almost to dryness. 

Two or three cubic centimeters of water are then poured in to 
dissolve the salts, and the small amount of liquid filtered through 
a 5i-cm. filter placed in a small funnel, without suction- tube, into 



ALKALIES. 137 

a previously ignited and weighed 40- or 50-c.c. platinum crucible. 
The greatest care must be taken in pouring out the first portion 
of liquid, as drops are apt to fly out of the filter if falling from too 
great a height. The loss of a single one at this stage would be 
disastrous, and would necessitate beginning the determination 
over again from the very start. The basin and filter are washed 
at least half a dozen times, preferably with warm water, and using 
only as little as possible, not over 3 or 4 c.c. at a time. When the 
washing is complete, as shown by a test for chlorine on a single 
drop toward the last, the crucible should not be more than two- 
thirds full. 

A drop of hydrochloric acid is added to the crucible, to decom- 
pose any alkali carbonates possibly present, and it is placed on 
the water-bath, and the liquid evaporated to complete dryness. 
Care must be taken to ensure this, as small amounts of water 
caught under the crust resist evaporation for a considerable 
length of time. It is not advisable, either here or in the evapora- 
tion in the basin, to use a platinum spatula or wire to break up 
the crust and hasten the operation, on account of the danger of 
loss of substance. The contents of the crucible can usually be 
rendered dry in three hours or so, if the water be kept at a brisk 
boil, or it may be left overnight. 

When dry, the crucible is placed on a platinum triangle, cov- 
ered, and very gently heated with a small flame, preferably that 
of a glass alcohol lamp, held in the hand and moved about at 
some distance beneath. When the slight decrepitation ceases 
and vapors of ammonium chloride rise, the flame is gradually 
raised (but not as far as the crucible bottom), till no more vapors 
are given off, as may be ascertained by lifting the cover from 
time to time. The cover is then freed from ammonium chloride 
by heating over the flame, and the sides of the crucible are simi- 
larly treated. The salts at the bottom are then most cautiously 
heated with the small flame till absolutely no more vapors are 
given off and they just begin to melt in places. When this hap- 
pens the flame is to be removed instantly. The bottom of the 
crucible should not be heated above a very faint red, scarcely 



138 METHODS. 

visible in daylight. It is to be remembered that one has, on the 
one hand, to ensure the dryness of the salts and the complete ex- 
pulsion of ammonium chloride, which would later be precipi- 
tated with the potassium platinichloride ; and on the other, to 
avoid any vaporization of sodium or potassium chlorides, which, 
however, only occurs considerably above their melting-points, 
and need not be feared if this temperature be not exceeded. 

If more than a drop or two of ammonium carbonate or oxa- 
late have been used to precipitate the traces of lime, the salts 
may be darkened by deposited carbon. This will usually be 
entirely burnt off, or nearly so, in the process of driving off 
the ammonium chloride and the incipient fusion of the alkali 
chlorides. The slight amount of it usually remaining is practi- 
cally unweighable, as my experience has shown, and it may 
therefore be neglected as a rule. 

The platinum crucible containing the salts is cooled in the 
desiccator, weighed quickly, and the weight recorded as Cruc. 
+ NaCl+KCl. Five or ten c.c. of water are poured hi to dis-. 
solve the salts, and if the previous operations have been properly 
conducted the solution will be clear, or at most only a few flakes 
of carbonaceous matter will be present, which may be neglected 
as explained above, unless the extreme of accuracy be required. 
If, however, there is an insoluble residue of calcium carbonate 
the contents of the crucible must be again filtered, without addi- 
tion of ammonium carbonate or oxalate, through a small filter 
into another weighed crucible, the filter washed, again evaporated 
to dryness, and the operation repeated as- before. The crucible 
and its now perfectly pure contents are weighed, and this weight 
and that of the new crucible substituted for the former ones. It 
will be found that the difference seldom amounts to more than a 
few tenths of a milligram. 

Separation of Potash. To the liquid in the crucible a solu- 
tion of platinic chloride is added to precipitate the potassium as 
platinichloride and thus separate it from the sodium. While it 
is absolutely necessary to have more than enough of this to 
change the entire amount of both sodium and potassium 



ALKALIES. 139 

chlorides into platinichlorides, yet any large excess is to be 
avoided, on account of the costliness of platinum chloride, if for 
no other reason. We therefore use a solution of platinum 
chloride made up to contain 0.1 gram of platinum to the cubic 
centimeter, as described elsewhere (p. 38). As it will take 1.68 
c.c. of this to react completely with 0.1 gram of Nad to form 
Na 2 PtCl 6 , and only 1.31 to dp the same with KC1 to foi^n 
K 2 PtCl 6 , and as nearly all rocks contain both alkalies, we are 
sure of an excess if we assume that the chlorides are wholly 
sodium chloride, and calculate the amount of platinum chloride 
solution used on this basis. We therefore multiply the weight of 
the combined chlorides by 17, and the result will be the number 
of cubic centimeters of platinum solution which is to be added. 
If the rock is extremely rich in sodic minerals, as albite or nephel- 
ite, with little or no potash, it will be well to take a few drops 
more than this. 

The crucible is then placed on the water-bath and heated, the 
water being allowed only to simmer, or attain at most a very 
gentle boiling, to avoid any dehydration of the sodiuni platini- 
chloride, although I have never observed this to happen, even 
with a fairly brisk boiling. If the precipitated potassium 
platinichloride does not wholly dissolve when the liquid has 
become warm, a few cubic centimeters of water are to be added 
to permit its solution. This will seldom if ever be necessary if 
the directions and strengths of solutions given above are followed, 
even with highly potassic, leucite rocks. 

The contents of the crucible are evaporated, with occasional 
slight shaking, to break up the crust as it forms, till the liquid 
mass solidifies on cooling. This will take place when the depth 
of the liquid is reduced to about 2 mm., but is naturally depend- 
ent on the amount of alkalies in the rock. The evaporation 
should never, under any circumstances, be carried to complete 
dryness on the water-bath, as partial dehydration of the sodium 
salt will occur, the anhydrous sodium platinichloride being solu- 
ble with some difficulty in alcohol, and thus possibly adding to- 
the apparent amount of potassium. 



140 METHODS. 

When the evaporation is finished the. crucible is removed, 
covered, and allowed to cool, so as to make sure that the liquid 
solidifies. It is then half filled with alcohol of 0.86 specific 
gravity,* contained in a small wash-bottle, and allowed to soak. 
In the mean time the. Gooch crucible is prepared with an asbestos 
felt, as already described (p. 120), ignited, cooled and weighed, 
and placed in position above the Erlenmeyer flask, f 

By this time the disintegration of the solid mass in the cruci- 
ble should be complete. If not, it may be hastened by stirring 
and rubbing cautiously with the lower end of a 5-c.c. pipette, the 
lower aperture of which should be from 1 to 2 mm. wide. When 
solution is complete, except for the precipitated, golden-yellow 
crystals of potassium platinichloride,J the suction is started 
beneath the Gooch crucible and the fluid is transferred to it by 
means of the pipette. For this purpose the crucible with the 
liquid is held in the left hand close to the Gooch, a little liquid 
sucked up into the pipette and allowed to run down the sides of 
the filter, to avoid breaking the felt. When all the liquid has 
been thus decanted, a little more alcohol is poured on the pre- 
cipitate in the crucible, and decanted as before into the Gooch 
when this is empty. After three or four decantations, by which 
time the soluble salts are nearly gone and the liquid almost 
colorless, the sides of the Gooch crucible are carefully washed 
down with a stream of alcohol, and the pipette rinsed both inside 
and out into the Gooch, which is more than half filled with alcohol 
to protect the felt. The bulk of the precipitate is then trans- 
ferred to the filter, without the use of a rod, by a gentle stream 

* If a hydrometer is not at hand an alcohol of approximately this specific 
gravity may be made by mixing five volumes of ordinary 95 per cent alcohol 
with one volume of water. 

f If this has been previously used for the determination of magnesia, it, 
as well as the carbon filter and rubber, must be thoroughly washed free 
from all traces of ammonia. 

} If the fluid is not yellow, or if small white grains (of sodium chloride) 
are present among the yellow crystals of K 2 PtCl 6 , there has not been enough 
platinum solution added. About 2^c.c. are to be added and the liquid again 
evaporated nearly to dryness. 



ALKALIES. 141 

. from the alcohol wash-bottle, the depth of liquid above the felt 
being so great that the drops can fall in the center without 
danger. 

With a slender stirring-rod capped with a bit of fine rubber 
tubing the small quantity of adhering potassium platinichloride 
is loosened and is washed into the filter, the stirring-rod being 
also rinsed off. Owing to the bright color and the high specific 
gravity of the precipitate, it is easy to be sure of its complete 
transfer. When the Gooch is again empty it is well washed, at 
least half a dozen times, the sides being also washed down, inside 
and out. Enough alcohol may be added each time to half fill the 
crucible, but it must be allowed to empty before another addition. 
After washing for the last time, aspiration is continued for a few 
minutes to partially dry the felt. 

The final drying is accomplished in an air-bath at a tempera- 
ture of 135, which is necessary to drive off all the water. The 
bottom cap of the Gooch crucible is placed in position, and the 
crucible covered while in the air-bath with a 7-cm. filter-paper 
instead of the cover. This facilitates evaporation, and at the 
same time guards against particles falling in from the top of 
the air-bath. The drying will usually be complete in half an 
hour, but it is as well after heating for this time and weighing, 
to reheat for another fifteen minutes, or to constant weight. 
After cooling in the desiccator the Gooch crucible is weighed, 
and recorded as Gooch +K 2 PtCl 6 . The weight of the potassium 
platinichloride is multiplied by 0.1939 to arrive at the weight of 
K 2 0, from which is to be subtracted the amount of K 2 present 
in 4 grams of the calcium carbonate used, if this has been deter- 
mined. 

The weight of K 2 PtCl 6 is then multiplied by 0.307 to reduce it 
to KC1, and the weight of this deducted from that of the mixed 
chlorides. The weight of the NaCl thus obtained is multiplied 
by 0.5308 to reduce it to Na 2 0, which is to be corrected for the 
amount of Na 2 present in the calcium carbonate. 

If a Gooch crucible is not available the method followed by 
Hillebrand may be adopted. This consists in filtering off the 



142 METHODS. 

excess of platinum chloride solution through a small filter (5J 
cm.) and washing with alcohol, as little of the precipitate as 
possible being brought on the filter. When the precipitate has 
been washed free from all soluble matter the small amount on 
the filter is washed into the weighed crucible by small amounts 
of hot water, the excess of liquid evaporated to dryness on the 
water-bath, and the precipitate finally dried as above at 135 Q . 
Hillebrand prefers the use of porcelain for the evaporation of 
the alcoholic platinum solution, but for most work this is 
hardly necessary. 

It is seen that the amount of Na 2 is determined by differ- 
ence. But, in view of the accuracy of the method, this is prefer- 
able to a direct determination in the filtrate. If it is desired to 
do this, the filtrate is to be freed from platinum by one of the 
methods recommended by Hillebrand (op. cit., p. 99), and the 
sodium determined as sulphate in the usual way, by evaporation 
with sulphuric acid. 

As Hillebrand says, there is scarcely ever enough lithium pres- 
ent in igneous rocks to warrant its quantitative estimation. It 
is almost invariably present in spectroscopic traces, but, so far, 
there seems to be little theoretical necessity of establishing this 
fact in every rock analysis. If it is desired to do this, the filtrate 
is to be evaporated to dryness and tested with the spectroscope. 
If it be desired to estimate it quantitatively, Hillebrand's direc- 
tions and his summary of Gooch's method are to be followed (op. 
cit., p. 99). 

14. TITANIUM DIOXIDE,, 

The Test Solution. For the determination of this constituent 
the whole bulk of solution in which the total iron has been 
titrated (p. 113) is best adapted. This contains all of the 
titanium in solution as sulphate, and with no possible traces of 
hydrofluoric acid, which exerts such a deleterious effect on the 
colorimetric method. If, for any reason, this solution is not 
available, the Ti0 2 can be determined in a separate portion of 



TITANIUM DIOXIDE. 143 

rock powder, which is brought into solution by evaporation in a .. 
platinum crucible with a mixture of dilute sulphuric acid (1 : 1) 
and hydrofluoric acid. This is continued till fumes of sulphuric 
acid are given off, but not to dryness,-when more of the dilute 
sulphuric acid is added, and the evaporation continued till there 
are no traces of hydrofluoric acid,* which may take four or five 
repetitions and additions of sulphuric acid. Or the solution in 
which ferrous oxide has been determined will answer, if it is 
evaporated down (in platinum) repeatedly with sulphuric acid, 
to expel hydrofluoric acid completely. 

There are two very distinct methods gravimetric and colori- 
metric by which titanium dioxide may be determined. The 
latter is by far the most accurate and expeditious, and is the one 
which is adopted by the chemists of the U. S. Geological Survey, 
and which I also employ. It will therefore be described first in 
some detail, the gravimetric methods being discussed later more 
cursorily, for the benefit of those who may not have the appli- 
ances necessary for the colorimetric work. 

Colorimetric Method. This method, which was first proposed 
by Weller,t depends on the yellow to brown coloration of solu- 
tions of titanic acid by hydrogen peroxide, Ti0 3 being formed, 
the depth of tint on complete oxidation being proportional to the 
amount of Ti0 2 . Vanadium, molybdenum and chromic acid 
interfere with the reaction, the first two through a similar colora- 
tion of their solutions by H 2 2 , and the last by the normal color 
of solutions of chromates. It is seldom, however, that any of 
these elements are present in rocks in sufficient amount to affect 
the method seriously. Hillebrand has shown that HF, even in 
traces, has a very marked effect in preventing the coloration 
either partially or wholly. It is absolutely necessary, therefore, 
that every trace of hydrofluoric acid be driven off from the solu- 
tions used, and that the hydrogen peroxide be free from it. This 

* Cf. T. M. Chatard, Bull. U. S. Geol. Surv., No. 78, p. 87, 1891; W. F. 
Hillebrand, p. 69. 

t Weller, Ber. Deutsch. Chem. Ges., XV, p. 2593, 1882. Cf. Hillebrand, 
p. 67. 



144 METHODS. 

is not always true of all commercial brands, so that that which is 
used should be tested for fluorine before using.* 

The essentials for the colorimetric method are a standard 
solution of titanium, containing 0.001 gram of Ti0 2 per c.c., and 
a pair of glass vessels with parallel sides which are the same dis- 
tance apart in each, although a good pair of Nessler tubes can be 
substituted for these. 

The preparation of a standard solution of titanium is some L 
what awkward, owing partly to the difficulty of obtaining pure 
titanium compounds, and the necessity for driving off all hydro- 
fluoric acid, without the use of which the solution of titanium 
compounds is difficult. If a. pure potassium titanofluoride can 
be procured, a definite weight of this is to be evaporated repeat- 
edly with sulphuric acid, but not to dryness, the final solution 
being made up with water to a volume necessary to give it the 
required strength of 0.001 gram of Ti0 2 per c.c. This is the 
method adopted in the Geological Survey laboratory. 

The solution can also be made from titanium dioxide itself, 
which can be obtained reasonably pure from some makers. This 
can be brought into solution by fusion with acid potassium sul- 
phate, acting on very small quantites at a time (about 0.10 gram), 
the fusion being prolonged and conducted with care to avoid 
loss. Or the solution can be somewhat more readily effected in 
quantity by evaporation first with sulphuric and hydrofluoric 
acids, and then repeated evaporations with sulphuric acid alone, 
which is the method I have employed. A sulphate of titanium 
of reasonable degree of purity is also sometimes obtainable, and 
this can be brought into solution in the same ways. 

Iron is the chief impurity in the titanium compounds as usu- 
ally procurable, and, although present in small amount, it is best 
to determine it in a definite volume of the titanium solution, so 
as to arrive at the correct figure for Ti0 2 . This should be done 
before the solution is diluted finally to the standard strength, 
but the volume must be known. The method used for deter- 

* Hillebrand, Jour. Am. Chem. Soc., XVII, p. 718, 1895. 



TITANIUM DIOXIDE. 145 

mining ferrous oxide may be used, 100 c.c. of the solution being 
reduced by H 2 S, the latter driven off by boiling, and the solu- 
tion titrated. After the amount of ferric oxide thus ascertained 
has been deducted from the titanium dioxide, the solution is 
diluted to the required strength. For all but the most accurate 
work, however, the amount of impurity will be so small that this 
determination of iron and correction for it may be neglected. 

As to the glass vessels used, the type recommended by Hille- 
brand is preferable to Nessler tubes. It is absolutely essential 
that two opposite sides in each be parallel, and that the distances 
apart be identical, certainly within 1 per cent of the distance. 
The other two sides need not be parallel, but should be black- 
ened on the outside to exclude light. They may be from 8 
to 12 cm. high, and from 3 to 4 cm. between the parallel sides, 
measured internally, the width in the other direction being 
immaterial. 

It seems to be a difficult matter to obtain such glasses in this 
country, or at least to find them in stock, though they can be 
ordered from abroad. They are best made of glass plates 
cemented with a material which will resist the action of dilute 
acids. One can make them by cutting plate glass (2 to 3 mm. 
thick) in the requisite shapes and cementing them with Canada 
balsam, the angles being strengthened by narrow strips of rub- 
ber tape fastened with a rubber cement. Or a suitable pair 
may be made, as Hillebrand suggests, from a couple of square 
4-oz. bottles. Two opposite sides of each are to be ground off 
until the calipers show that they are of equal dimensions and 
parallel. The upper part is sawed off just below the shoulder, 
and plates of glass cemented on with Canada balsam. 

The use of a suitable box is necessary to exclude side-lights, 
and render the comparison more delicate. An appropriate form 
is illustrated by Hillebrand (op. cit., p. 70). This may be con- 
veniently made from a box in which the ceresine bottles con- 
taining one-half pound of hydrofluoric acid are packed, if the 
glasses do not measure over 4.5 cm. in width. 

The box measures 20X9.5X9.5 cm. internally. The square 



140 METHODS. 

bottom is first removed, leaving the box open at either end. For 
the sliding cover a 3-inch plate of ground glass is substituted, 
this slipping snugly into the cover grooves, which may need a 
little widening with a penknife. About 5 cm. of the side next to 
the free edge of the glass is cut away, to allow the insertion of 
the glasses. This side now becomes the top of the box. A thin 
wooden partition (made of cigar-box board), provided with two, 
rectangular openings corresponding to the glasses, is inserted on 
the near side, and held in place by a few light brads, though I do 
not find that this partition is absolutely necessary. A narrow 
slot is cut clear across the top of the box alongside the partition, 
and the cover of the .box used to make a shutter which will slide 
stiffly up and down, so as to remain at any desired height. The 
box and partitions are blackened inside and out, and the result 
is a box which is light and compact enough to be held easily in 
the hand. 

The actual process is as follows: The solution of the rock 
powder in which the Ti0 2 is to be determined, and which we will 
call the test solution, is evaporated down, if necessary, to less 
than 200 c.c. (cf. p. 113), and placed in a 250-c.c. measuring-flask 
with glass stopper. Sufficient hydrogen peroxide is added to 
oxidize the Ti0 2 completely, 5 to 10 c.c. being ample in most 
cases, and the whole is diluted to the mark and well mixed. 

The volume of liquid depends on the amount of Ti0 2 present, 
that mentioned being suitable for the majority of rocks, in which 
the percentage of Ti0 2 runs from 0.5 to 2.0. In rocks like granite 
or rhyolite, where the amount is very small, a volume of 100 c.c. 
is preferable. In very basic rocks, containing more than 2 per 
cent of Ti0 2 , the volume should be increased proportionally. It is 
essential to have the depth of color in the test solution less than 
that of the standard solution diluted as described below. In- 
stead of using 500-c.c. or 1000-c.c. flasks, 25 c.c. of the 250-c.c. 
volume of the test solution can be diluted with 25, 50 or 75 c.c. 
of water in the test-glass. 

It must be noted that the delicacy of this method is greater 
when the color is not very deep, so that, when much Ti0 2 is'pres- 



TITANIUM DIOXIDE. 147 

ent, the dilution should be large. The most favorable tint is a 
rather deep straw-color, about that of light beer. 

An indeterminate quantity of the test solution is poured into 
one of the glasses, say the left-hand one. Or if great dilution is 
necessary, as mentioned above, 25 c.c. of the solution made up to 
250 c.c. is measured into the glass, and this diluted to the requisite 
light tint by the addition of 25, 50 or 75 c.c. of water, amounting 
respectively to a total volume of test solution of 500, 750 or 
1000 c.c. 

Ten c.c. of the standard solution, containing 0.01 gram of 
Ti0 2 , is placed in a 100-c.c. measuring-flask, provided with a 
glass stopper, 5 c.c. of hydrogen peroxide added, diluted with 
water to the mark and well mixed. Each c.c. of this diluted 
standard will then contain 0.0001 gram of Ti0 2 . This amount 
of diluted standard will suffice for the determinations in three 
rocks, and if this quantity is not required 5 c.c. of the standard 
may be taken, and diluted to 50 c.c. after addition of H 2 2 . The 
color disappears after a time, so the diluted standard must be 
made up fresh for each determination or batch of determinations. 
It is evident that the color cannot be restored by addition of 
H 2 2 to a solution already diluted to the mark, as this will 
increase the volume of liquid and so lessen the amount of Ti0 2 
per c.c. 

Two burettes are fixed in a stand, and the one filled with the 
diluted standard, the other with water, the position of the 
meniscus in each being noted. Ten c.c. of the diluted standard 
are then run into the right-hand glass, and water added from the 
other burette, in small quantities at a time, the color of the two 
being compared after each addition. The shutter should be slid 
down till only the liquid in each glass is visible, and none of the 
empty portion above. As the color of the diluted standard ap- 
proaches that of the test solution, the addition of water should 
be cautious and by a few drops at a time, till the point of agree- 
ment is reached, when the amount of water added is read off and 
noted down. 

Ten c.c. of diluted standard are then again run into the right- 



148 METHODS. 

hand glass, without emptying it if the amount of added water is 
not great, and water added as before, the water burette being re- 
filled if necessary. This operation is repeated a third time, so as 
to furnish a mean of three determinations, which should not vary 
more than 1 c.c. from each other. In adding the water the 
second and third times it is well to cover the burette with a roll 
of paper held in place by an elastic band, so as to avoid any bias 
produced by a knowledge of about the amount of water which is 
to be added to make the second and third observations like the 
first. 

When observing the color after each addition of water, the 
box is held in the hand toward a good light, as that of a window, 
if possible, without the disturbing effect of sunlit foliage out- 
side. The operation is best carried out in the daytime, as dis-' 
tinctions in the colors are then much more readily discernible 
than by artificial light. It will be found advantageous to rest 
the eyes occasionally by looking at the floor or a dark corner, as 
their sensitiveness is apt to diminish through fatigue. 

When testing the method with known amounts of Ti0 2 for 
the first few times I noticed, in my own case, a' tendency to con- 
sider that the colors matched some time before they actually 
should have done so. Any such tendency, or the reverse, which 
may be true of others, is to be guarded against. After a little 
practice one soon becomes expert in judging of exact agreement 
and in arriving at concordant results. This practice is best ob- 
tained by making up test solutions from small measured volumes 
of standard diluted with varying known volumes of water, and 
determining the Ti0 2 in these. As the amount of Ti0 2 is known, 
one has a check on the personal equation, and will soon be in a 
position to determine unknown quantities of Ti0 2 . For one who 
has never used the method, this preliminary practice should not 
be omitted. 

An example of the simple calculation necessary is given else- 
where (p. 170), the underlying principle being that, as the colors 
of the two solutions are the same, the amount of Ti0 2 per c.c. 
is equal in both. This is known from the diluted standard 



TITANIUM DIOXIDE. 149 

solution diluted with a known bulk of water, and it only remains 
to multiply this amount of Ti0 2 per c.c. by the volume of the 
test solution to arrive at the weight of Ti0 2 in the portion of 
rock powder taken, and hence its percentage. As the whole of 
the titanium dioxide is thrown down with the alumina by am- 
monia, the amount of this is to be subtracted from the weight 
of this ignited precipitate (p. 169) to arrive at the weight of the 
alumina. 

If the rock contains much iron, the test solution will be 
slightly colored by the presence of ferric sulphate, and in the 
most accurate work a correction is to be applied for this. Hille- 
brand has shown that this will amount to a deduction of 0.02 per 
cent from the apparent percentage of Ti0 2 if 10 per cent of total 
iron is present, and in proportion for larger quantities. For 
most purposes, however, this correction may be neglected. 

If the glasses described above are not available, and it is de- 
sired to use Nessler tubes, the method is modified as follows, ac- 
cording to the plan of Prof. Penfield. A light box is constructed 
of such dimensions as to snugly hold the two tubes side by side. 
These rest either on a ground-glass plate forming a false bottom, 
or on a horizontal wooden partition with holes or a broad slot 
cut so as to admit light from below. Beneath this or the ground- 
glass plate a mirror is fixed at an angle of 45 above the real 
bottom, admitting light from a side-opening and transmitting 
it vertically up through the tubes. 

The test solution is prepared as above, but the standard is 
used undiluted. One Nessler tube is filled with the colored test 
solution up to the 50-c.c. mark, and in the other is placed 5 c.c. 
of hydrogen peroxide, which is diluted with a known volume of 
water nearly up to the same mark. The standard solution is then 
added in very small quantities at a time from a burette, the 
liquid being stirred, and the colors observed after each addition, 
till there is agreement between the two. With a little practice, 
and knowledge of the approximate amount of titanium present 
in the rock, the heights of the two solutions can be made sensibly 
identical, but several determinations are always advisable. In 



150 METHODS. 

this case, the Nessler tube for the standard solution is to be emp- 
tied and washed carefully each time. 

While this modification involves the use of more easily ob- 
tainable glass vessels, as well as less standard solution, it is not 
quite as accurate as the other, although sufficiently so for most 
purposes, and far more so than the gravimetric method com- 
monly adopted. 

Gravimetric Methods. Although the colorimetric method is 
by far the simplest, most expeditious and capable of extreme 
accuracy, yet occasion may arise for the determination of Ti0 2 
in the gravimetric way. While the use of this is not advised, a 
brief description may be given. 

The best gravimetric method is that of F. A. Gooch,* which 
is fully described by Hillebrand,f to whom the reader may 
be referred. While rather complicated, it is very accurate, 
although Hillebrand has shown that it is not to be used when 
zirconia is present in the rock. 

An approximate determination of Ti0 2 may be made in the 
solution after the titration of total iron by an old and well-known 
method. This consists in diluting the solution in a 1000-c.c. 
beaker to about 500 c.c., adding ammonia or solution of sodium 
carbonate till a permanent precipitate just forms, then 4 c.c. of 
concentrated sulphuric acid and 100 c.c. of solution of sulphur 
dioxide, diluting to 750 c.c. and boiling for several hours, the 
water lost by evaporation being replaced with hot water con- 
taining S0 2 added from time to time. The titanium is precipi- 
tated as metatitanic acid, collected on a filter, ignited and 
weighed as Ti0 2 . 

As thus precipitated, the Ti0 2 is almost always contami- 
nated by notable amounts of alumina and ferric oxide, which fall 
witii it, and the operation should be repeated, after bringing the 
ignited precipitate into solution by fusion with acid potassium 
sulphate and solution in hot water containing some sulphuric 
acid. It may happen, on the other hand, that the precipitation 

* F. A. Gooch, Bull. U. S. Geol. Surv., No. 27, p. 16, 1886. 
t Hillebrand, p. 71. 



PHOSPHORIC ANHYDRIDE. 151 

of titanium is incomplete, if the liquid contains too much free 
acid. Another source of error is the tendency of the precipitated 
metatitanic acid to adhere firmly to the sides of the beaker, from 
which it is removable with great difficulty or only in part. With 
such serious defects, and in view of its tediousness, the use of 
this antiquated method should be abandoned. 

15. PHOSPHORIC ANHYDRIDE. 

As the amount of material is usually ample in rock analysis, 
it is the best plan to determine this constituent in a separate por- 
tion of rock powder, although it can also be determined in the 
solution used for the total iron and titanium dioxide, as men- 
tioned below. 

On the ground that simple digestion with nitric acid does not 
ensure complete solution of phosphoric anhydride in all cases,* 
Hillebrand t recommends the fusion of the rock powder with 
alkali carbonates and subsequent treatment to separate silica, as 
before described (p. 79), except that HN0 3 is used in place of 
HC1, and a single evaporation is sufficient. The silica is to be 
evaporated to dryness with hydrofluoric and a few drops of sul- 
phuric acids, the residue dissolved in a little boiling nitric acid 
and added to the main filtrate from the silica. This is evaporated 
to small volume, and the phosphorus precipitated with am- 
monium molybdate, after the addition of some ammonium 
nitrate. 

While this process will undoubtedly yield the whole of the 
P 2 5 , it is somewhat lengthy and complex. Simple digestion 
with a hot mixture of nitric and hydrofluoric acids decomposes 
the rock powder completely, and furnishes equally satisfactory 
results, at the same time being far more expeditious. The use 
of the following simple method is therefore advocated. 

* This would he largely because apatite occurs in the form of microscopic 
needles, which often form inclusions in minerals unattacked by nitric acid. 
Therefore if the rock powder contains grains of such minerals with unex- 
posed inclusions of apatite, these will not go into solution. 

t Hillebrand, p. 78. 



152 METHODS. 

About 1 gram of rock powder is weighed out into a small plati- 
num basin, or if that is not available, into a capacious crucible, by 
the method described on p. 80. The rock powder is then mixed 
with 10 c.c. of water, taking the precautions to prevent loss noted 
previously, and stirred up with a small platinum spatula or 
platinum wire. Ten c.c. of concentrated nitric acid are added 
and the mixture warmed slightly. If no bubbles of C0 2 rise the 
absence of that constituent may be assumed and so noted. 
About 5 c.c. of hydrofluoric acid are next poured in, and the 
mixture is heated on the water-bath or over a low flame for 
a quarter of an hour, the spatula or wire being left in for an 
occasional stirring. 

When decomposition is complete, or practically so, the con- 
tents of the small basin or crucible are filtered through a 7-cm. 
filter placed in a small platinum or rubber funnel into the large 
platinum basin. The stout platinum wire will aid in the pour- 
ing, or if a small platinum spatula is used, the face of it should 
be presented to the edge of the basin or crucible, when the 
liquid will readily flow down. 

If the platinum basin is in use otherwise, the filtrate may be 
collected in a small (S^-inch) porcelain evaporating-dish. A pre- 
vious blank test should be made to see that neither the glaze nor 
the porcelain body contains any phosphorus, which is hardly ever 
the case. Although the porcelain basin will be somewhat at- 
tacked, it may be used a number of times. The use of the plati- 
num basin is preferable when possible. 

The crucible or small basin, as well as the gelatinous mass of 
silica in the filter, is to be well washed with hot water, and the 
combined filtrates and washings are to be evaporated to dry- 
ness on the water-bath or over a low flame. This is to render 
insoluble any silica which might otherwise come down with the 
phosphorus. 

When completely dry the basin is heated till its contents be- 
come brown, and when cool the crust is moistened with 10 c.c. of 
a mixture of nitric acid diluted with twice its bulk of water, and 
gently warmed. Solution will be complete, except for the silica 



PHOSPHORIC ANHYDRIDE. 153 

present, and the liquid is filtered through a S^-cm. filter into a 
100-c.c. beaker. The beaker is to be rinsed out and the filter 
washed half a dozen times with the same warm dilute acid, less 
than 50 c.c. in all sufficing for this. Twenty-five c.c. of ammo- 
nium molybdate solution are to be added, or 50 c.c. if the 
rock contains much P 2 5 . The liquid is stirred, and laid aside 
(covered) for at least twenty-four hours. 

The liquid is then filtered through another 5^-cm. filter, the 
bright-yellow precipitate being disturbed as little as possible. 
The latter is washed with a mixture of strong solution of am- 
monium nitrate, nitric acid and ammonium molybdate solution 
in equal parts, till the addition of ammonia water in excess pro- 
duces no permanent precipitate in a few drops of the filtrate in a 
watch-glass. About 50 c.c. of the washing mixture will usually 
be ample, and it can best be prepared in a small beaker as needed. 

The phosphorus is now all in the precipitate of ammonium 
phosphomolybdate, and the beaker containing the greater part 
of this is placed beneath the funnel, which is then filled with am- 
monia water diluted with an equal amount of water. This dis- 
solves the small portion of precipitate in the filter and part or the 
whole of that in the beaker, assisted by stirring. If solution is 
not complete some more ammonia must be added. The filter is 
then well washed, half a dozen fillings with water being suf- 
ficient. 

If the fluid in the beaker is turbid, due to the formation of a 
white compound of phosphorus, as occasionally happens, this 
may be overcome by the addition of a small fragment of citric or 
tartaric acid. If this fails to remove the turbidity, the liquid is 
to be filtered through the same filter into another small beaker, 
the filter ignited in a small platinum crucible and fused with a 
pinch of sodium carbonate, the small cake dissolved in water, 
acidified with nitric acid, and the solution added to the rest 
(Hillebrand) . This will seldom be necessary. 

To the solution in the beaker, which may amount to 50 to 100 
c.c., 10 c.c. of magnesia mixture are added, which is ample for 
nearly all rocks. The beaker is allowed to stand for twelve hours, 



154 METHODS. 

then filtered through a small filter and the precipitate collected 
on the latter, that adhering to the sides of the beaker being 
rubbed off, the filter and precipitate of ammonium-magnesium 
phosphate well washed with weak ammonia water. 

The filter with its contents are then placed in a small weighed 
platinum crucible, and, after the filter has been carbonized, 
ignited at a bright-red heat. When cool it is weighed, and the 
weight of the Mg 2 P 2 7 multiplied by 0.638 to reduce it to P 2 5 . 
The appropriate weight of P 2 5 determined from this percentage 
is to be deducted from the weight of the precipitate by ammonia 
water (p. 169), to arrive at the correct weight of alumina. 

It may be borne in mind that, as the phosphomolybdate pre- 
cipitate contains only about 3.5 per cent of P 2 5 , if there is only a 
minute quantity of it, the phosphoric anhydride present will be 
so small in amount that it need not be determined, but may be 
stated as a " trace." It is best, however, in all cases to carry the 
operation through to completion, especially when one has had 
no experience as to what is a sufficiently small amount of pre- 
cipitate to justify neglect of the succeeding operations. 

Treadwell* advocates the use of either Finkener's method 
(determination as ammonium phosphomolybdate), or Woy's 
(determination as phosphomolybdic anhydride), on the grounds 
of greater expedition and accuracy. I have had no experience 
with them, but either would seem to be worthy of adoption. 

If material be scanty and it is desired to determine phos- 
phoric anhydride in the solution used for total iron and for 
titanium dioxide, the following process will serve: The acid 
solution, or an aliquot portion of it, after determination of Ti0 2 , 
is precipitated with ammonia, the precipitate washed with hot 
water a few times, dissolved on the filter with dilute nitric acid 
and the filter washed, the filtrate and washings evaporated to 
small bulk, and the phosphorus precipitated in this by ammonium 
molybdate. The subsequent operations are as described above. 

* Treadwell, II, 347. 



TOTAL SULPHUR, ZIRCONIA AAD BARYTA. 155 



16. TOTAL SULPHUR, ZIRCONIA AND BARYTA. 

These constituents may be determined in separate portions, 
but it will be found to be a great economy of time to determine 
them in the ame portion by the following plan, which was first 
published by Hillebrand,* and independently worked out by 
myself. The whole process, while apparently complicated, in 
reality takes very little extra time for its execution, as the 
volumes of liquid are small, and the various operations may 
be carried out during pauses between the main determinations, 
when solutions are being evaporated, etc. 

Decomposition. For this set of determinations 1 gram of 
rock powder is sufficient. About this amount is weighed out into 
a weighed platinum crucible, mixed with four or five times its 
weight of mixed sodium and potassium carbonates, and fused 
precisely as has been described above (p. 79). 

If pyrite is present, and it is desired to determine the sulphur, 
a small quantity, about one-quarter of a gram, of powdered po- 
tassium nitrate is mixed with the carbonates, which should have 
been tested to see if they are free from sulphur or sulphates. 
If much nitre is used the crucible is liable to be attacked. The 
reaction between the nitrate and the carbonates gives rise to 
considerable effervescence, and the fusion should therefore be 
carried on cautiously, and at as low a temperature as possible, 
till all nitrous fumes have disappeared. The temperature may 
then be raised and the operation carried on as above. 

When the cake is perfectly cold it is detached from the cruci- 
ble and thoroughly leached with water, till all soluble matter is 
dissolved, a drop or two of alcohol being added to reduce any 
sodium manganate which may be present. 

Of the constituents which immediately concern us, the sul- 
phur (that as sulphide as well as that as sulphate) passes into 
solution as sodium sulphate, while the BaO and Zr0 2 remain un- 

* Hillebrand, p. 73. 



156 METHODS. 

dissolved, the former as barium carbonate and the latter as 
sodium zirconate. 

Sulphur. The liquid is filtered through a 7-cm. filter, as 
little as possible of the undissolved residue being brought on 
this, and the residue and filter are well washed with a very dilute 
solution of sodium carbonate to prevent turbid washings (Hille- 
brand). The further treatment of the residue will be found 
below under Zirconia. 

If the filtrate shows a yellow color the presence of chromium 
is indicated, and this element is to be estimated in a separate 
portion, as described on p. 165. In general, however, it is ab- 
sent, and in any case we can proceed at once to the determination 
of the sulphur, as the free hydrochloric acid present prevents the 
precipitation of barium chromate. 

The filtrate, which should amount to from 150 to 250 c.c. in 
a 400-c.c. beaker, is slightly acidified with hydrochloric acid, the 
beaker being covered to prevent loss, about 5 c.c. being usually 
sufficient. It is heated to boiling and the acidity tested after 
expulsion of the C0 2 , and more HC1 added if necessary, though a 
large excess is to be avoided. About half, or at most, 1 gram of 
barium chloride dissolved in 25 c.c. of water is added to the boil- 
ing liquid, the cover and sides washed down, and the beaker al- 
lowed to stand till the barium sulphate has settled. There is 
little danger of silica contaminating the barium sulphate, in the 
bulk of liquid recommended above, but if this should happen it 
is removed later. It is obvious that failure of barium chloride 
to produce a precipitate indicates the absence not only of S, 
but of S0 3 . In this case this last need not be looked for, but 
both may be stated in the tabulation as absent. 

The liquid is filtered, all the barium sulphate being brought 
on a small filter (7 cm.) by means of a rubber-tipped rod and the 
wash-bottle, and the filter well washed. The filter is ignited in 
a small weighed crucible, the barium sulphate evaporated with 
a few drops of hydrofluoric and one of sulphuric acids to expel any 
silica possibly present, again ignited and weighed. Further 
purification of the barium sulphate is seldom necessary. 



TOTAL SULPHUR, ZIRCONIA AND BARYTA. 157 

If no S0 3 is present in the rock, the weight of BaS0 4 is multi- 
plied by 0.137 to reduce it to S. If S0 3 is present, the weight 
of BaS0 4 is multiplied by 0.343 to reduce it to S0 3 , which is 
changed to percentage figures by division by the weight of sub- 
stance taken. From this the percentage of S0 3 present in the 
rock as obtained in a separate portion (p. 159) is deducted, and 
the remainder multiplied by 0.401 to reduce the SO 3 to S. 

Zirconia. The whole of this is present as sodium zirconate 
in the residue insoluble in water. The small part of this which 
adheres to the filter is washed back into the beaker containing 
the bulk of the residue, by holding the funnel sidewise and direct- 
ing a strong stream of water from the wash-bottle against all 
parts of the filter, the liquid dropping into the beaker beneath. 
With care, and if done while the residue is still moist, the re- 
moval can easily be made complete. 

To the contents of the beaker, the bulk of which should be 
lees than 50 c.c.,not more than three or four drops of concentrated 
sulphuric acid are added. A larger amount is to be avoided, as 
too much free sulphuric acid prevents the entire precipitation of 
the zirconia (Hillebrand), and also retards filtration through 
action on the filter-paper. The liquid is warmed (not boiled) till 
all effervescence ceases, and another drop of sulphuric acid added 
to see if solution has been complete. The liquid should be dis- 
tinctly acid. If so, the liquid is filtered through the original 
filter into a flask of about 100 c.c., and the filter and beaker 
are washed several times with small quantities of warm water. 

The filtrate now contains all the zirconia as sulphate, while 
the baryta remains behind as insoluble barium sulphate, along 
with strontia and some lime and silica. For the treatment of 
this insoluble portion, see p. 158. 

To the filtrate in the flask is now added about 5 c.c. of hydro- 
gen peroxide, or enough to cause a permanent yellow coloration, 
and then a few drops of a solution of a soluble phosphate, as 
microcosmic salt. The flask is filled nearly to the neck, if not so 
already, and set aside in a cool place for at least twenty-four 
hours, and preferably for twice that length of time. If the 



158 METHODS. 

yellow color disappears, a little more hydrogen peroxide is to 
be added. 

The zirconia separates as a flocculent precipitate of basic zir- 
conium phosphate,* which may easily be overlooked unless the 
flask is gently agitated. It is almost or entirely 'free from ti- 
tanium, the precipitation of which is prevented by the addition 
of the hydrogen peroxide. However small the precipitate 
may appear, it is filtered off through a 5J-cm. filter, and well 
washed. For most rocks, in which the amount of Zr0 2 is very 
small, further purification is unnecessary, and the filter and pre- 
cipitate are ignited in a small weighed crucible, and weighed as 
basic zirconium phosphate. This contains 51.8 per cent of Zr0 2 , 
but for the minute quantities usually present it will suffice to 
multiply it by 0.5 to reduce it to Zr0 2 . The percentage amount 
of Zr0 2 is to be subtracted from that of tlje ignited precipitate by 
ammonia to arrive at the correct figure for alumina. 

If the precipitate is large, or if extreme accuracy is desired, 
the purification recommended by Hillebrand in every case may 
be carried out. The ignited precipitate (unweighed) is fused 
with a very little sodium carbonate, leached with water and 
filtered. The small filter and contents are ignited and then 
fused with a small lump of acid potassium sulphate, which is 
dissolved in hot water and a drop or two of dilute sulphuric acid. 
To the solution in the crucible a little hydrogen peroxide and 
a few drops of soluble phosphate are added, and the covered 
crucible is set aside as before. The precipitated zirconium 
phosphate now free from titanium, is collected, ignited and 
weighed as above. For identification of the zirconia the reader 
is referred to Hillebrand. 

Baryta. The residue left on solution of the zirconia in dilute 
sulphuric acid contains all the baryta, with traces of strontia and 
often much lime, as insoluble sulphates. To bring these into 
solution it is collected on a small filter, as described above, the 
filter and contents ignited in a small crucible and fused with 
about 1 gram of sodium carbonate, the fusion being continued 
* Cf. P. E. Browning, Introduction to the Rarer Elements, 1903, p. 55. 



SULPHURIC ANHYDRIDE. 159 

for ten to fifteen minutes to permit the conversion of the barium 
sulphate into carbonate. 

The cake is dissolved in warm water, which may be done in 
the crucible, filtered through a small filter, and well washed. 
After a fresh 250-c.c. beaker has been placed beneath the funnel, 
the carbonates are dissolved on the filter in a very little, warm, 
dilute hydrochloric acid, and the filter well washed. The liquid 
in the beaker is made up to at least 150 c.c., to prevent precipi- 
tation of the strontium and calcium sulphates, and 2 or 3 c.c. 
of concentrated sulphuric acid added. After standing for 
twenty-four hours, the precipitated barium sulphate is filtered 
off, ignited and weighed. It will seldom be necessary to purify 
it for contamination by calcium or strontium. Multiplication 
of the weight of BaS0 4 by 0.66 reduces it to BaO. 

17. SULPHURIC ANHYDRIDE. 

This constituent, which occurs only in the minerals haiiyne 
and noselite, both soluble in hydrochloric acid, is determined in 
a separate portion. About 1 gram is weighed out (p. 131) into 
a 250-c.c. beaker, and gently boiled with 50 c.c. of dilute hydro- 
chloric acid (1:5). If pyrite or pyrrhotite are present, a stream of 
carbon dioxide should be allowed to enter by the lip of the covered 
beaker, and to fill the space beneath the cover before boiling is 
begun. It is, of course, continued during the boiling. In this 
way any pyrite remains unattacked, while seven-eighths of the 
sulphur of pyrrhotite goes off as hydrogen sulphide, the remain- 
ing one-eighth being precipitated as sulphur. This need not 
be filtered off, as it is burned in the subsequent ignition. 

After boiling for about a quarter of an hour, the liquid is fil- 
tered through a 9-cm. filter, and the residue and filter washed. 
The volume of liquid should be about 200 c.c., to prevent pre- 
cipitation of silica. It is then precipitated, best while hot, with 
an excess of barium-chloride solution, allowed to stand for some 
time, the barium sulphate filtered off, well washed, ignited and 
weighed. To guard against contamination by silica it is always 
as well to evaporate the ignited precipitate with a few drops of 



160 METHODS. 

hydrofluoric and sulphuric acids, and reignite. The weight of 
BaS0 4 is multiplied by 0.343 to obtain that of S0 3 . 

It may be pointed out here that, before determining sulphur 
or sulphuric anhydride, the condition in which the sulphur exists 
in the rock should be investigated. The microscope will usually 
reveal the presence of pyrite or pyrrhotite, as well as noselite or 
haliyne. If not, the rock powder should be boiled with a little 
dilute hydrochloric acid, and if hydrogen sulphide is evolved the 
presence of pyrrhotite may be inferred, as the lazurite molecule 
is not apt to be found in rocks. A little of the filtered liquid may 
be tested with barium sulphate for S0 3 , and, whether a pyrite- 
like mineral is visible or not with the microscope, the deter- 
mination of total sulphur should be made, if the rock is at all 
basic. It takes but little time or labor, and, as Hillebrand re- 
marks, sulphur is to be found in nearly all rocks, sometimes in 
traces only, but again in quite appreciable quantities. 

18. CHLORINE. 

While Hillebrand recommends fusion with chlorine-free so- 
dium carbonate, to ensure getting all the chlorine, yet it is not 
only difficult to procure such a reagent, but the operation will be 
somewhat long and complex. For nearly all purposes simple 
solution in nitric acid, if desired with the addition of some hydro- 
fluoric acid, will be quite sufficient. 

About 1 gram of rock powder is weighed out into a 250-c.c. 
beaker and boiled with 50 c.c. of dilute nitric acid (1:5), which 
should have been previously tested as to freedom from chlorine, 
or a blank determination is to be made with the same volume of 
the acid to allow of a suitable correction if chlorine-free acid is 
unattainable. If the addition of hydrofluoric acid is desired the 
digestion should be carried out hi a capacious crucible or small 
platinum basin. 

After boiling for a quarter of an hour, the liquid is filtered,* 

* A rubber or platinum funnel and the platinum basin are to be used if 
hydrofluoric acid has been added. 



CHLORINE. 161 

the filter and residue well washed and the filtrate precipitated 
with excess of silver-nitrate solution. It is heated in a dim light, 
with constant stirring, to coagulate the silver chloride. If the 
precipitate is at all considerable, it is filtered through a small 
filter and, after washing, is dissolved on the filter with ammonia 
water, reprecipitated by acidifying with nitric acid to free it 
from possibly contaminating silica, and collected in a weighed 
Gooch crucible. After washing, it is dried, heated to incipient 
fusion and weighed. The weight of the AgCl multiplied by 
0.247, or 0.25 for small amounts, will give the weight of chlorine 
present. 

If the precipitate is very small, Hillebrand* recommends 
that it be collected on a small paper filter, which is then dried, 
wound up in a weighed platinum wire and carefully ignited. 
The increased weight of the wire is due to the metallic silver of 
the chloride which has alloyed with the platinum, and is multi- 
plied by 0.33 to arrive at the chlorine. 

If the chlorine is present only in minerals of the sodalite group, 
solution in nitric acid alone will usually be sufficient. But if 
scapolites are present, some of which are not attacked by this 
acid, the addition of hydrofluoric acid will be necessary. 

In the determination of chlorine great care should be exer- 
cised that the reagents used are free from chlorine, and a dupli- 
cate operation in blank with the same quantities will always be a 
wise precaution. Rock specimens collected near the seashore 
are sometimes contaminated with sodium chloride derived from 
sea- water. This may be estimated in a separate portion by 
thorough washing on a filter with warm water, and determina- 
tion of the chlorine dissolved out. This is, of course, to be de- 
ducted from the amount of chlorine which is found by the pre- 
vious method, and its equivalent amount of Na 2 from that of 
this constituent already found. 

* Hillebrand, p. 103. 



162 METHODS. 



19. FLUORINE. 

To determine this constituent the method of Rose * may be 
followed, with modifications proposed by Penfield and Minor.f 
This may be described as follows : 

About 2 grams of the rock powder are fused with five times 
its weight of alkali carbonates, and the cake thoroughly leached 
with hot water, filtered and washed. The filtrate contains all 
the fluorine as alkali fluorides. While still hot about 5 grams 
of ammonium carbonate are added to the filtrate, and when cold 
about the same amount is again added. The beaker is allowed 
to stand for about twelve hours, the precipitate filtered off and 
washed, and in the filtrate the ammonium carbonate is decom- 
posed by heating on the water-bath till no more carbon dioxide 
is given off. About 5 c.c. of a solution of zinc oxide in strong 
ammonia water is added and the liquid evaporated till there is 
no more odor of ammonia. After filtering off the precipitate 
and washing, nitric acid is added to the filtrate till the alkali 
carbonate is nearly, but not entirely, decomposed. If too much 
is added, a solution of sodium carbonate is poured in to a 
decided alkaline reaction. 

As chromic and phosphoric acids may be present, Hillebrand 
recommends the addition at this point of silver nitrate in excess, 
which will precipitate these substances. The liquid is heated and 
filtered, the excess of silver precipitated by sodium chloride, 
again heated to coagulation and again filtered, when a little 
sodium carbonate is added to alkaline reaction. If no chromium 
or phosphorus are present, or only small amounts, the addition 
of silver nitrate may be dispensed with. 

The heated filtrate, which contains alkali carbonate and 
fluoride, and which must not contain ammonium salts, is now 
precipitated with an excess of calcium chloride. The precipitate 
of calcium carbonate and fluoride is collected on a filter, placed in 

* Hillebrand, p. 103. 

f Penfield and Minor, Am. Jour. Sci., XLVII, p. 388, 1894. 



CARBON DIOXIDE. 163 

a weighed platinum crucible, dried and ignited gently. A little 
water and 1 or 2 c.c. of acetic acid are poured in, and the covered 
crucible heated for some time on the water-bath, and finally the 
excess of acid evaporated with the cover off. 

Hot water is poured on the dry salts, and the contents of the 
crucible are filtered through a small filter and washed. The filter 
with its contents are again ignited in the same crucible, and the 
digestion with dilute acetic acid and evaporation gone through 
with again. The ignition of the filters and the digestion with 
dilute acetic acid are repeated till all the calcium carbonate and 
oxide are dissolved as acetate, as shown by the evaporation of a 
few drops of the filtrate on platinum foil.* 

The filter and purified calcium fluoride are finally gently 
ignited in the crucible and weighed. Multiplication of the 
weight of CaF 2 by 0.49, or division by 2 in most cases, gives the 
amount of fluorine. For possible corrections see Hillebrand. 

20. CARBON DIOXIDE. 

As all the minerals which contain this constituent are soluble 
in hydrochloric or nitric acid with evolution of C0 2 (dolomite 
and siderite only on warming), its qualitative presence may be 
easily established by warming the rock powder with a little, 
somewhat dilute nitric or hydrochloric acid, and noting whether 
effervescence ensues. This may be done when the portion of 
rock powder is dissolved for the determination of phosphoric 
anhydride (p. 152). Before the addition of the acid the powder 
should be well stirred up with warm water to drive out any me- 
chanically attached air, bubbles of which might be mistaken for 
C0 2 . If the rock contains considerable pyrrhotite, the evolution 
of H 2 S may be mistaken for that of C0 2 , but the former is easily 
recognizable by its characteristic odor, as well as by the blacken- 
ing of paper soaked in lead-acetate solution to which a little 
ammonia has been added. 

* Penfield and Minor show that the addition of acetic acid in large amount 
leads to loss of calcium fluoride. 



164 METHODS. 

The determination of carbon dioxide is effected by the usual 
method, which is so well known that a brief description will suf- 
fice. Any of the well-known forms of apparatus may be used, 
and if many determinations are to be made it will be as well to 
have one permanently set up, such as that figured by Hille- 
brand.* 

At least 2 or 3 grams of rock powder are weighed out into a 
small flask. After mixing the powder with some water, th$ 
flask is connected on one side with a cylinder filled with soda- 
lime or sticks of caustic alkali, and a wash-bottle or two con- 
taining sulphuric acid, to dry the air and free it from C0 2 . On 
the other side it is connected with an upward inclined con- 
denser, or a tall cylinder filled with calcium chloride, then a U- 
tube filled with calcium chloride and one filled with pieces of 
pumice soaked in copper-sulphate solution and heated till the 
salt becomes anhydrous. This last is to retain any H 2 S or HC1 
which may escape from the flask. The weighed U-tube for the 
absorption of the C0 2 follows these, and is protected on the 
other side from the moist air of the aspirator by a U-tube con- 
taining in one arm calcium chloride and in the other soda-lime.. 

After weighing the soda-lime U-tube and connecting it in 
place, the whole apparatus is filled with dry and carbon-dioxide- 
free air by means of an aspirator attached to the last U-tube. 
About 10 c.c. of dilute hydrochloric acid are added to the flask 
containing the powder and its contents boiled gently while a 
slow current of C0 2 -free air is passing. In ten or fifteen minutes- 
decomposition is complete, when the flame is removed and the 
current of air is continued for some time longer, till all that in 
the flask and tubes has been replaced. 

The U-tube is then removed, carefully closed, and allowed to 
cool thoroughly, as the absorption of the C0 2 by the soda-lime 

* Hillebrand, p. 102. In this figure there is a slight error in drawing 
the entrance- and exit-tubes of the two wash-bottles for the air-current in the 
lower left-hand corner. The tubes which end just beneath the corks should 
extend down into the liquid, while those which do this should be cut off 
just below the corks. 



CHROMIUM AND VANADIUM. 165 

gives rise to considerable heat. It is then weighed, the increase 
being the amount of C0 2 in the portion of rock powder taken. 

21. CHROMIUM AND VANADIUM. 

These constituents are so seldom present in appreciable 
amount in silicate igneous rocks that the analyst will not often 
be called on to determine them. The determination of vanadium, 
especially, is so seldom necessary, and the method so complex, 
that it need not be given here. If it is desired to determine it, 
Hillebrand's method should be used, a full description of which 
is given by him.* 

Chromium is occasionally to be determined in such rocks as 
dunites, peridotites, pyroxenites, etc., and for this the colori- 
metric method recommended by Hillebrand t is to be used. It 
is briefly summarized here. 

At least a gram of rock powder is thoroughly fused with 
sodium carbonate, to which a little nitre is added, and the 
cake extracted with water, as in the method for total sulphur 
(p. 155). A few drops of either ethyl or methyl alcohol are 
added to destroy the color of sodium manganate, and the 
liquid is filtered. If the yellow color is very faint, or invisible, 
the liquid should be concentrated to small bulk for use as the 
test solution, and placed in a small measuring-flask of 25, 50 or 
100 c.c., according to the depth of color, which must be less 
than that of the standard solution. This last is prepared by 
dissolving 0.25525 gram of normal potassium chromate (K 2 Cr0 4 ) 
in a liter of water, the solution containing then 0.0001 gram of 
Cr 2 3 per cubic centimeter. 

The depth of color of the test solution is then compared with 
that of the standard exactly as was done in the determination of 
titanium dioxide (p. 146) by the colorimetric method, a definite 
volume of standard being diluted with water from a burette till 
the two colors are alike. The results, as shown by Hillebrand, 
are very accurate for the small quantities found in rocks. 

* Hillebrand, p. 82. t Hillebrand, p. 80. 



166 METHODS. 



22. COPPER 

If it is desired to determine copper, or other metals of the 
hydrogen-sulphide group, which may rarely be present, it is ad- 
visable to use a separate portion, rather than determine them in 
the residue left after the solution of the nickel sulphide (p. 114). 
This is partly because in this they are contaminated with plati- 
num, and partly because appreciable amounts of copper will 
probably have been introduced from the water-baths (Hille- 
brand). 

The weighed portion, preferably of 2 grams, may be decom- 
posed by sulphuric and hydrofluoric acids, and repeated evapo- 
rations with additions of the former to drive off all traces of the 
latter. Or, as seems preferable to me, the solution is effected by 
a mixture of nitric and hydrofluoric acids, filtration in a rubber 
funnel, and evaporation of the filtrate in a small porcelain basin 
(a platinum basin should not be used). Thus far the operation 
is identical with that for the determination of phosphoric an- 
hydride (p. 152). 

After heating the dried salts in the basin to drive off excess of 
acid and render the silica insoluble, they are dissolved in 25 c.c. 
of dilute hydrochloric acid, filtered, and the diluted filtrate pre- 
cipitated by a current of H 2 S. The precipitated cupric sulphide 
is filtered off rapidly and washed with water containing H 2 S. 
The filter containing it is ignited in a small weighed platinum 
crucible, moistened with a few drops of nitric acid, cautiously 
evaporated to dryness, ignited, and the residue weighed as CuO. 
Multiplication of this by 0.8 reduces it to Cu. 



APPENDIX. 

1. EXAMPLE OF ANALYSIS. 

In order to render perfectly clear the method of recording the 
results, and of carrying out the various calculations, an example 
is given of an actual analysis. That chosen is one which was 
made by me for the Carnegie Institution, and I desire to express 
my thanks to the Trustees for their permission to make use of it 
here. Some of the minor constituents which were determined 
are not given in this place. For recording an analysis the stu- 
dent should select a note-book with a sufficiently large page, 
and, in the following example, the different pages are indicated 
by the horizontal lines. 

167 



168 



APPENDIX. 



Si0 2 
48.10 



H 2 0- 
0.04 



0.11 



1310. LEUCITE-TEPHRITE, LAVA OF 1903, MT. VESUVIUS. 

Cruc. + subst. = 40 . 6602 
Cruc. =39.6562 



Subst. taken = 1.0040 



Cruc. + SiO 3 + x= 33 . 1879 
Cruc. =32.7043 



.4836 



Cruc. +subst.=34. 9497 
Cruc. =33.8717 



1.0780 
Tube + subst. = 25 . 3857 



Tube 



= 24.2037 

1.1820 

Total H,O= 0.15 
H 3 O- =0.04 

H,O+ =0.11 



Cruc. + SiO 2 + z= 33 . 1879 
Cruc. + x =32.7078 



SiO 2 = 

Extra SiO, = 



.4801 
.0028 



1.004).4829(.48098 
4016 



8130 
8032 

9800 
9036 

7640 

Cruc. + subst. = 34 . 9497 
Dried at 110= 34. 9493 



.0004 



Tube + H 3 O= 20. 7298 
Tube -H,O= 20. 7280 



1.18).00180(.0015 
118 

620 
590 

300 



EXAMPLE OF ANALYSIS. 



169 



A1A 
17.59 



FeA 
2.48 



PA 

0.98 



C0 2 
none 



1310. A1A, FeA 



Cruc. + Al A. etc. = 33 . 0007 
Cruc. =32.7043 



Cruc. + res. + SiO 2 = 33 . 8747 
Cruc. + res. - SiO,= 33 . 8719 



.2964 Extra SiO 2 
Used 36.6 c.c. of permanganate sol. 



= .0028 



A1A, etc. = .2964 
FeA = -0930 



SiO, 
PA 



.2034 
= .0028 



.2006 
.0098 



.1908 
TiO, = .0142 



.002541 
36.6 

15246 
15246 
7623 

Total FeA = .0930006 
FeO as Fe 2 O 3 = .0680712 



1. 004). 0249294(. 0248 
2008 



1. 004). 1766(. 1759 
1004 

7620 
7028 



4849 
4016 

8330 



5920 
5020 

9000 

Pt basin + subst. = 1 1 . 1 134 Cruc. + Mg 3 P,O 7 = 19 . 0322 
Pt basin =10.0830 Cruc. =19.0165 



No CO, 



1.004 
.0098 

8032 
9036 

.0098392 



1.0304 



.0157 
.64 

628 
942 

1. 0304). 0100480(. 00975 
92736 



77440 
72128 

~53120 



170 



APPENDIX. 



FeO 
6.10 



Ti0 2 
1.41 



1310. FeO, TiO 3 . 



Cruc.+subst. = 35.9546 
Cruc. =35.4488 



.5058=13.5 c.c. of K 2 Mn 2 O 8 



.002287 
13.5 

11435 
6861 
2287 



.002541 
13.5 

12705 
7623 
2511 



1.004 
.0678 

8032 
7028 
6024 



.5058) .0308745(. 06104 .5058) .0343035 (.0678 = 

30348 30348 FeO asFe 2 O 3 - 0680712 



5265 
5058 

20700 



39555 
35406 

41490 
40464 



10260 



Test solution diluted to 500 c.c. 

Dilute ( T V) standard=10c.c.+25.0 c.c. H 2 O 
(i) " =10 c.c. +25. 3 " " 
(fy " =10 c.c. +25. 5 " 

3)75. 8 c.c. H 2 O 

10-1-25.267=35.267 c.c. 



35 . 267) . 001000000( . 00002836 
70534 



294660 
282136 

125240 
105801 

194390 



.00002836 

500 

00.01418000 

1. 004). 01418(. 0141 
1004 



4140 
4016 

1240 



EXAMPLE OF ANALYSIS. 



171 



CaO 
8.16 



MgO 
4.27 



1310. CaO, MgO.* 



Cruc.+CaO=33.9533 
Cruc. =33.8714 



1. 004). 08190(. 0816 
8032 



.0819 



Gooch cruc. + Mg 3 P 2 O 7 = 25 . 1389 
Goochcruc. =25.0205 



.1184 



1580 
1004 

5760 

.1184 
.3621 

1184 
2368 
7104 
3552 

1. 004). 4287264(. 0427 
4016 

2712 
2008 



7046 



* On this page are also recorded the figures for S, Zr0 3 , and BaO, which 
are omitted here. 



172 



APPENDIX 



K 3 O 
7.93 



Na/) 
2.65 



1310. ALKALIES.* 



Tube + subst. = 23 . 5598 
Tube-subst. =23.0263 



.5335 

Cruc. + NaCl + KC1= 35 . 5417 
Cruc. =35.4481 

.0936 

Gooch cruc. + K 3 Pta a = 25 . 2593 
Goochcruc. =25.0410 



.2183 
.1939 

19647 

6549 
19647 
2183 

. 5335) . 04232837 ( . 07934 
37345 



.2183 



49833 
48015 

18187 
16005 

21820 



.2183 
.307 

15281 
65490 

.0670181 ( = KC1) 

.0936 
.0670 



.0266 
.5308 

2128 
7980 
1330 

.5335). 0141 1928(. 0265 
10670 



34492 
32010 

24828 



* No correction was needed for the amount of alkalies in the calcium 
carbonate used. 



TABLE OF MOLECULAR WEIGHTS. 



173 



2. TABLE OF MOLECULAR WEIGHTS. 



SiO, 


60 


ALO 3 . , 


102 


Fe 2 O, . . 


160 


FeO 


72 


MgO. . 


40 


CaO 


. . 56 


Na 2 O 


62 


K 2 O. . 


94 


H 2 O 


18 


CO,. . 


44 


TiO, . 


80 



ZrO 3 


123 


P.O. . . 


142 


SO,. . 


80 


Cl . 


35 5 


F 


19 


s 


32 


Cr.O, . 


152 


MnO 


71 


NiO 


75 


BaO.. 


. 153.5 



SrO 103.5 

These molecular weights are the approximate ones which are generally 
iployed in petrographical calculations. 



3. FACTORS FOR CALCULATION. 

Constituent Sought Found Factor 

Baryta BaO BaSO 4 .66 

Chlorine Cl AgCl .247 

Chlorine Cl Ag .33 

Copper Cu CuO .80 

Fluorine F CaF 2 .49 

Magnesia MgO Mg 2 P 2 O 7 .3621 

Manganous oxide MnO Mn 3 O 4 .93 

Phosphoric anhydride P 2 O 5 Mg 2 P 2 O 7 . 638 

Potash K 2 O K 2 PtCl 6 .1939 

Potash KC1 K 2 PtCl fl .3070 

Soda Na 2 O NaCl .5308 

Strontia SrO SrSO 4 .56 

Sulphur S BaSO 4 .137 

Sulphuric anhydride SO 8 BaSO 4 .343 

Zirconia ZrO a xZr0 2 .yP 2 O 6 .52 

These factors are based on the figures in Cohn's translation of Fresenius' 
Quantitative Analysis, 1904, II, pp. 1197-1211. They are only carried out 

as far as is deemed appropriate for the quantities usually found in igneous 
rocks. 



INDEX. 



PAGE 

Acid potassium carbonate, use of, in fusion 36 

Acid potassium sulphate 37 

fusion with 107 

Accuracy of analyses 4 

Agate mortar, use of 48, 53 

Alcohol 39 

Alkali carbonates 36 

fusion with 79 

Alkali chlorides, drying of 135 

ignition of 137 

Alkalies, determination of 129 

sources of error in determination of 66 

Allowable error, limits of 24 

Alteration of rocks 43 

Alumina, determination of 97 

fusion of precipitate of, with potassium pyrosulphate 107 

fusion of, with sodium hydroxide 64 

ignition of 105 

pr ecipitation of 97, 103 

sources of error in determination of 62 

Ammonia water, purity of 62 

precipitation of alumina, etc., by 97 

Ammonium carbonate, use of, in determination of alkalies 134 

Ammonium chloride, necessity for the presence of 62 

use of, in determination of alkalies 132 

vaporization of 136 

Ammonium-magnesium phosphate, precipitation of 119, 153 

Ammonium molybdate, solution of 38 

Ammonium phosphomolybdate, precipitation of 153 

Amount of material needed for analysis 46 

175 



176 INDEX. 

PAGE 

Analyses, accuracy of 4 

allowable limits of, error in 21 

amount of rock needed for 46 

character of 3 

completeness of 5 

example of 168 

general course of 57 

importance of 1 

number of constituents to be determined in 5, 8 

number of portions of powder needed for 57 

plan of 70 

preparation of sample for. 48 

selection of specimen for 41 

statement of 26 

time needed for making 68 

weight of ground sample needed for 46 

weights of portions of powder needed for 56, 57 

Analysis of leucite-tephrite from Vesuvius 168 

Analyst, qualifications of 4 

Apparatus, list of 31 

Asbestos 39 

Ash of filter-paper, neglect of 56 

Balance 31 

Barium, occurrence of 9, 19 

Barium sulphate, precipitation of 156, 159 

Baryta, determination of 17, 155 

Basic acetate method for separation of manganese 15, 63, 103 

Beryllium, occurrence of 21 

Boron, occurrence of 21 

Box for use in determination of titanium 145 

Brittleness of minerals, influence of, in pulverization 49, 54 

Cake, color of 84 

removal of, from crucible 83 

Calcium carbonate, preparation of 37 

determination of lime as 117 

use of, in determination of alkalies 132 

Calcium fluoride, precipitation of 162 

Calcium oxalate, conversion of, to calcium carbonate 117 

precipitation of 115 

Calculation of analyses, example of 168 

factors for 173 

to be carried to four decimals 29 

Carbon dioxide, apparatus for HI 

determination of . . 17 163 



INDEX. 177 

PAGE 

Carbon dioxide, examination of rock powder for 152, 163 

occurrence of 44 

Cerium, occurrence of 21 

Chlorine, determination of 17, 160 

necessity of removal of, from alumina precipitate 63, 101 

occurrence of 20 

oxygen equivalent of 23 

testing of filtrates for 93 

Chromium, determination of. 14, 165 

occurrence of 19 

Cleanliness, necessity for 55 

Cobalt, determination of 16, 115 

occurrence of 19 

Color of fused cake 84 

of permanganate solutions, evanescent character of 113, 126 

Colorimetric method for determining chromium 165 

for determining titanium 143 

Colorization of titanium solutions by hydrogen peroxide. 143 

Combined water, determination of, by loss on ignition 74 

determination of, by Penfield's method 75 

Completeness of analyses -. 5, 8 

Constituents, list of 11 

main 11 

minor 14 

number of, to be determined 5, 8 

order of, in tabulation of analyses 27 

Cooke's method for determination of ferrous oxide 126 

Cooling of melt in crucible 83 

Copper, determination of 16, 114, 166 

occurrence of 20 

Crucible, Gooch 32 

filtration with 120, 140 

platinum 32 

Crushing rock, methods for 48 

Decimals, calculations to be carried to four 29 

Digestion of rock powder in hydrochloric acid 159 

in nitric acid 151, 160 

"Dioxogen" 39 

Dittrich, comparison by, of methods for alkalies 67 

Doctoring of analyses 30 

Double evaporation to render silica insoluble 61, 89 

Double precipitation of alumina, necessity for 62, 99 

of calcium oxalate, necessity for 66, 117 

of ammonium-magnesium phosphate, necessity for 65, 120 

Drying of rock powder 73 



178 INDEX. 



Duplicate determinations 25 

Dust, loss of, in preparing sample 49 

Earths, rare, occurrence of 21 

Error, allowable limits of 24 

chief sources of 61 

Evaporation of sulphuric acid 96 

to render silica insoluble 61, 89 

Example of analyses 168 

Factors for calculation of analyses 173 

Ferric iron, reduction of, to ferrous 110 

Ferric oxide, determination of 110 

sources of error in determination of. 64 

Ferrous oxide, determination of, by Cooke's method 126 

determination of, by Pratt's method 126 

determination of, by simple method 124 

sources of error in determination of 65 

Filter, fitting of, in funnel , 90 

incineration of 95, 105 

Filter-paper 35 

neglect of ash of 56 

Filtrate, testing of, with silver nitrate 93 

Filtration 91, 98 

in Gooch crucible 120, 140 

Fluorine, determination of 17, 162 

estimation of, by the microscope 7 

influence of, in the determination of titanium 143 

occurrence of 21 

Oxygen equivalent of 23 

Freshness of rock 13, 43 

Fusion with acid potassium sulphate 107 

alkali carbonates 79 

calcium carbonate and ammonium chloride 131 

Gauze for sieve. . . . 51 

Gelatinous precipitates, washing of 98 

Glass apparatus 32 

Glasses for the determination of titanium 145 

Glucinum, occurrence of 21 

Gold, occurrence of 10 

Gooch crucible 32 

nitration in 120, 140 

Gooch's method for determining titanium 150 

for determining water 79 

Granularity, influence of, on size of specimen 46 






INDEX. 179 

PAGE 

Hillebrand's method for determination of chromium 165 

sulphur, zirconia and baryta 155 

vanadium 165 

Hydrochloric acid, digestion of rock powder in 159 

Hydrochloroplatinic acid, solution of 38 

Hydrofluoric acid, evaporation of silica with. 96 

necessity for expulsion of, in preparation of titanium solution 143 

use of, in determination of ferrous iron 124 

Hydrogen peroxide 39 

use of, in determination of titanium 143 

Hydrogen sulphide, detection of 163 

expulsion of Ill 

precipitation by 114 

use of, as a reducing agent 64, 110 

Hygroscopic water, determination of 73 

Ignition of alkali chlorides 137 

of precipitates 94, 105 

Incineration of filter 95, 105 

Iron in sulphides 128 

Iron, influence of, on determination of titanium 149 

titration of ' 112 

Iron oxides, determination of 12, 97 

ignition of 105 

precipitation of 97, 103 

sources of error in determination of 64, 65 

Lead oxide, use of, in determination of water 78 

Leucite-tephrite, analysis of 168 

Lime, determination of 115 

sources of error in determination of " 66 

use of, in determination of water 78 

Lithia, determination of 14, 142 

Lithium, occurrence of 20 

Locality, choice of, in selection of specimen 43 

Loss on ignition, determination of water by 74 



determination of 119 

sources of error in determination of 65 

Magnesia mixture 38 

Main constituents 11 

Manganese, colorization of cake by 84 

occurrence of 15, 19 

Manganous oxide, determination of 15, 113 

sources of error in determination of 15, 68 

Material, amount of, for analyses. v 46 



180 INDEX. 

PAGE 

Metatitanic acid, precipitation of 150 

Microscopical examination of thin sections 6 

Mineral composition, estimation of, by RosiwaPs method 7 

Minor constituents 8, 14 

Mitscherlich method for determination of ferrous oxide 65, 122 

Molecular ratios, statement of 29 

Molecular weights, table of 173 

Molybdenum, occurrence of 10, 21 

Mortar, steel .- 51 

Nessler tubes, use of, for determination of titanium 149 

Nickel, determination of 16, 113 

occurrence of 1 19 

Nitric acid, digestion of rock powder in 151, 160 

use of, in dissolving alumina precipitate 101 

"Not determined," use of term 29 

Notes, taking of 56 

Order of constituents in tabulation 26 

Ores, origin of 3,10 

Oxygen equivalents of chlorine, fluorine, and sulphur 25 

Penfield's method for determination of water 75 

Penfield's and Minor's method for determination of fluorine 162 

Personal equation in determination of titanium 14& 

Phosphoric anhydride, determination of 14, 151 

sources of error in determination of 67 

Phosphorus, occurrence of 20 

Physical chemistry, relation of, to petrology 2, 12 

Plan of analysis 70 

Platinum apparatus 32 

Platinum chloride, solution of 38 

Platinum, occurrence of 10, 21 

Porcelain basin, use of 152 

Porphyritic texture, influence of, on size of sample 47 

Portions for analysis, number of, needed 57 

weighing of 80, 131 

weight of 56, 57 

Potash, determination of 129 

Potassium bisulphate; see acid potassium sulphate 37 

Potassium chromate, standard solution of 165 

Potassium nitrate, use of, hi fusion 84, 155 

Potassium permanganate, standard solution of 37 

Potassium platinichloride, precipitation of 138 

Pratt' s method for determination of ferrous oxide 126 

Preparation of sample 48- 



INDEX. 181 

PAGE 

Pulverization of sample 48 

Pyrite, oxidation of, in fusion with alkali carbonates 84, 155 

influence of, in Mitscherlich's method 123 

Qualitative examination not necessary 56 

Rare earth metals, occurrence of 21 

Rare elements, occurrence of 11 

Reagents, quality of 35 

Recalculation of analyses to 100 per cent 30, 45 

Reduction of ferric to ferrous iron 110 

Representative character of specimen 3 

Rock, freshness of 43 

pulverization of 48 

Rock mass, uniformity of . . . 42 

Rock powder, special grinding of 123 

Rose's method for determination of fluorine 162 

Rosiwal's method for estimating mineral composition 7 

Sample, amount of, needed for analysis 46 

preparation of 48 

pulverization of 48, 51 

selection of 41 

Sampling of rock 54 

Sea water, sodium chloride derived from 161 

Sieve, use of 50, 51 

Silica, determination of 79 

evaporation of, with hydrofluoric acid 96 

evaporation to render, insoluble 88 

filtration of 91 

ignition of 94 

impurities in 96 

necessity for double evaporation of 89 

recovery of trace of, in alumina precipitate 109 

sources of error in determination of 61 

Silk gauze, contamination of rock powder by, discussed 50 

Silver basin, use of 32, 135 

Silver chloride, precipitation of 160 

Silver nitrate, use of, in testing filtrates 93 

Smith's method for determination of alkalies 66, 130 

Soda, determination of 129 

Sodium acetate, precipitation of alumina, etc., by 103 

Sodium carbonate 36 

fusion with 79 

Solution of ammonium molybdate 38 

of platinum chloride 38 



182 INDEX. 

PAGE! 

Solution, standard, of potassium chromate -. . . 165 

of potassium permanganate 37 

of titanium sulphate 144 

Special grinding of powder 123 

Specimen, representative character of 41 

selection of 41 

size of 46 

Specimen tubes 53 

drying of 53 

Spencer's law of evolution, application of, to igneous rocks 1 

Statement of analyses 26 

Steel, contamination of sample by 49 

Steel mortar . % 51 

Steel plate, use of, in crushing rock specimen 48 

Stokes, observations of, on oxidation of pyrite 123 

Strontia, determination of . 14, 117 

Strontium, occurrence of 19 

Suction tube, use of, in connection with funnel 34 

Sulphides, iron in 128 

occurrence of 20 

Sulphur, determination of 17, 155 

investigation of condition of 160 

occurrence of. ...... 20 

oxygen equivalent of 23 

Sulphuric anhydride, determination of '. 17, 159 

occurrence of. ........... 20 

Summation, allowable limits of 21 

causes of high and low 23 

Test solution for chromium 165 

for titanium. 142 

Texture of rocks, influence of, on weight of sample 46 

Thorium, occurrence of 21 

Time needed for analyses 68 

Tin, occurrence of . . 21 

Titanium, occurrence of 18 

standard solution of 144 

Titanium dioxide, determination of, by colorimetric method 143 

determination of, by gravimetric method 150 

importance of . . 14 

sources of error in determination of 67 

Titration of iron. 112 

Trace, definition of term. 29 

Tungsten, occurrence of 21 

Uniformity of rock mass 42 



INDEX. 183 

PAGE 

United States Geological Survey, analyses by 4,9 

Uranium, occurrence of 21 

Vanadium, determination of 14, 165 

occurrence of 10, 19 

Vesuvius, analysis of lava from 168 

Wash bottles 33 

Washing of precipitates 92, 98 

Watch glasses 33 

Water, combined, determination of, by loss on ingition 74 

determination of, by Penfield's method 75 

distilled 40 

hygroscopic, determination of 13, 73 

occurrence of 12 

Weathering of rocks 43 

Weighing of powder 80, 131 

Weight of portions for analysis 56 

Weller's method for titanium 143 

Zinc, occurrence of : 21 

precipitation of 114 

use of, as a reducing agent 64 

Zinc oxide, use of, in determination of fluorine 162 

Zirconia, determination of 14, 155 

Zirconium, occurrence of 10, 18 



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Hazen's Filtration of Public Water-supply 8vo, 3 oo 

Hazlehurst's Towers and Tanks for Water-works 8vo ; 2 50 

Herschel's 115 Experiments on the Carrying Capacity of Large, Riveted, Metal 

Conduits 8vo, 2 oo 

Mason's Water-supply. (Considered Principally from a Sanitary Stand- 
point.) 3d Edition, Rewritten 8vo, 4 oo 

Merriman's Treatise on Hydraulics, pth Edition, Rewritten 8vo, 5 oo 

* Michie's Elements of Analytical Mechanics ., 8vo, 4 oo 

Schuyler's Reservoirs for Irrigation, Water-power, and Domestic Water- 
supply Large 8vo, 5 oo 

** Thomas and Watt's Improvement of Riyers. (Post., 44 c. additional), 4to, 6 oo 

Turneaure and Russell's Public Water-supplies 8vo, 5 oo 

Wegmann's Desien and Construction of Dams 4to, 5 oo 

Water-supply of the City of New York from 1658 to 1895 4to, 10 oo 

Weisbach's Hydraulics and Hydraulic Motors. (Du Bois.) 8vo, 5 oo 

Wilson's Manual of Irrigation Engineering Small 8vo. 4 oo 

Wolff's Windmill as a Prime Mover ". 8vo, 3 oo 

Wood's Turbines 8vo, a 50 

Elements of Analytical Mechanics 8vo, 3 oo 

MATERIALS OF ENGINEERING. 

Baker's Treatise on Masonry Construction 8vo, 5 oo 

Roads and Pavements 8vo, 5 oo 

Black's United States Public Works Oblong 4to, 5 oo 

Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Burr's Elasticity and Resistance of the Materials of Engineering. 6th Edi- 
tion, Rewritten 8vo, 7 50 

Byrne's Highway Construction 8vo, 5 oo 

Inspection of the Materials and Workmanship Employed Jn Construction. 

i6mo, 3 oo 

Church's Mechanics of Engineering 8vo, 6 oo 

Du Bois's Mechanics of Engineering. Vol. I Small 4to, 7 50 

Johnson's Materials of Construction Large 8vo, 6 oo 

Keep's Cast Iron 8vo, a 50 

Lanza's Applied Mechanics 8vo, 7 50 

Martens's Handbook on Testing Materials. (Henning.) 2 vols 8vo, 7 50 

Merrill's Stones for Building and Decoration 8vo, 5 oo 

7 



Meniman's Text-book on the Mechanics of Materials 8vo, 4 oo 

Strength of Materials mo, i oo 

Metcalf's SteeL A Manual for Steel-users iamo, a oo 

Pattern's Practical Treatise on Foundations 8vo, 5 oo 

RJchey's Hanbbook for Building Superintendents of Construction. (In press.) 

Rockwell's Roads and Pavements in France i2mo, i 25 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 oo 

Smith's Materials of Machines xamo, i oo 

Snow's Principal Species of Wood 8vo, 3 50 

Spalding's Hydraulic Cement i2mo, a oo 

Text-book on Roads and Pavements i2mo, a oo 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced. (In 
press.) 

Thurtton's Materials of Engineering. 3 Parts 8vo t 8 oo 

Part L Non-metallic Materials of Engineering and Metallurgy 8vo, a oo 

Part H. Iron and Steel 8vo, 3 50 

Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents 8vo, a 50 

Thurs ton's Text-book of the Materials of Construction 8vo, 5 oo 

Tillson's Street Pavements and Paving Materials 8vo, 4 oo 

WaddeU's De Pontibus. (A Pocket-book for Bridge Engineers.) . . i6mo, mor. , 3 oo 

Specifications for Steel Bridges lamo, x as 

Wood's Treatise on the Resistance of Materials, and an Appendix on the Pres- 
ervation of Timber 8vo, a oo 

Elements of Analytical Mechanics 8vo, 3 oo 

Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. . .8vo, 4 oo 

RAILWAY ENGINEERING. 

Andrews's Handbook for Street Railway Engineers. 3X5 inches, morocco, i as 

Berg's Buildings and Structures of American Railroads 410, 5 oo 

Brooks's Handbook of Street Railroad Location i6mo, morocco, i 50 

Butts's Civil Engineer's Field-book i6mo, morocco, a 50 

Crandall's Transition Curve x6mo, morocco, i 50 

Railway and Other Earthwork Tables 8vo, x 50 

Dawson's "Engineering" and Electric Traction Pocket-book. i6mo, morocco, 5 oo 

Dredge's History of the Pennsylvania Railroad: (1879) Paper, 5 oo 

* Drinker's Tunneling, Explosive Compounds, and Rock Drills, 4to, half mor., 25 oo 

Fisher's Table of Cubic Yards Cardboard. as 

Godwin's Railroad Engineers' Field-book and Explorers' Guide i6mo, mor., a 50 

Howard's Transition Curve Field-book i6mo, morocco, x 50 

Hudson's Tables for Calculating the Cubic Contents of Excavations and Em- 
bankments 8vo, i oo 

Molitor and Beard's Manual for Resident Engineers x6mo, x oo 

Ragle's Field Manual for Railroad Engineers i6mo, morocco. 3 oo 

Philbrick's Field Manual for Engineers x6mo, morocco, 3 oo 

Searles's Field Engineering x6mo, morocco, 3 oo 

Railroad Spiral x6mo, morocco, x 50 

Taylor's Prismoidal Formula and Earthwork 8vo, x 50 

* Trautwine's Method of Calculating the Cubic Contents of Excavations and 

Embankments by the Aid of Diagrams 8vo, a oo 

The Field Practice of [Laying Out Circular Curves for Railroads. 

xamo, morocco, a 50 

Cross-section Sheet Paper, 35 

Webb's Railroad Construction, ad Edition, Rewritten x6mo. morocco, 5 oo 

Wellington's Economic Theory of the Location of Railways Small 8vo, 5 oo 

DRAWING. 

Barr's Kinematics of Machinery 8vo, a 50 

* Bartlett's Mechanical Drawing 8vo, 3 oo 

* " AbridgedEd 8ro, x s 

8 



Coolidge's Manual of Drawing 8vo, paper, x oo 

Coolidge and Freeman's Elements of General Drafting for Mechanical Engi- 
neers. (In press.) 

Durlev's Kinematics of Machines 8vo, 4 oo 

Hill's Text-book on Shades and Shadows, and Perspective 8vo, a oo 

Jamison's Elements of Mechanical Drawing. (7n press.) 
Jones's Machine Design: 

Part I. Kinematics of Machinery 8vo, i 50 

Part n. Form, Strength, and Proportions of Parts 8vo, 3 oo 

MacCord's Elements of Descriptive Geometr) . 8vo, 3 oo 

Kinematics; or. Practical Mechanism , , . 8vo, 5 oo 

Mechanical Drawing , 4to, 4 oo 

Velocity Diagrams 8vo, x 50 

Mahan's Descriptive Geometry and Stone-cutting 8vo , z SO 

Industrial Drawing. (Thompson.) 8vo, 3 50 

Moyer's Descriptive Geometry. (In press.) 

Reed's Topographical Drawing and Sketching 4to 5 oo 

Reid's Course in Mechanical Drawing STO, a oo 

Text-book of Mechanical Drawing and Elementary Machine Design. .8vo, 3 oo 

Robinson's Principles of Mechanism 8vo, 3 oo 

Smith's Manual of Topographical Drawing. (McMillan.) 8vo, a 50 

Warren's Elements of Plane and Solid Free-hand Geometrical Drawing. . xarno, z oo 

Drafting Instruments and Operations lamo, z as 

Manual of Elementary Projection Drawing zamo, z 50 

Manual of Elementary Problems hi the Linear Perspective of Form and 

Shadow zamo, z oo 

Plane Problems hi Elementary Geometry zamo, x as 

Primary Geometry zamo, 75 

Elements of Descriptive Geometry, Shadows, and Perspective 8vo, 3 so 

General Problems of Shades and Shadows 8vo, 3 oo 

Elements of Machine Construction and Drawing 8vo, 7 So 

Problems. Theorems, and Examples in Descriptive Geometry 8vo, a 50 

Weisbach's Kinematics and the Power of Transmission. (Hermann and 

Klein.) 8vo, 5 oo 

Whelpley's Practical Instruction in the Art of Letter Engraving zamo, a oo 

Wilson's Topographic Surveying 8vo, 3 50 

Free-hand Perspective 8vo, a 50 

Free-hand Lettering. 8vo, z o 

Woolf 's Elementary Course hi Descriptive Geometry Large 8vo, 3 oo 

ELECTRICITY AITD PHYSICS. 

Anthony and Brackett's Text-book of Physics. (Magie.) Small 8vo, 3 oo 

Anthony's Lecture-notes on the Theory of Electrical Measurements xamo, z oo 

Benjamin's History of Electricity 8vo, 3 oo 

Voltaic CelL 8vo, 3 oo 

Classen's Quantitative Chemical Analysis by Electrolysis. (Boltwood.). .8vo, 3 oo 

Crehore and Squier's Polarizing Photo-chronograph 8vo, 3 oo 

Dawson's "Eneineering" and Electric Traction Pocket-book. . i6mo, morocco, 5 oo 
Dolezalek's Theory of the Lead Accumulator (Storage Battery). (Von 

Ende.) zamo,~a 50 

Du hem's Thermodynamics and Chemistry. (Burgess.) 8vo, 4 oo 

Flather's Dynamometers, and the Measurement of Power zamo, oo 

Gilbert's De Magnete. (Mottelay.) 8vo, 50 

Hanchett's Alternating Currents Explained zamo, oo 

Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 50 

Holman's Precision of Measurements 8vo, oo 

Telescopic Mirror-scale Method, Adjustments, and Tests. Large Svo, 75 

9 



Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 oo 

Le Chatelier's High-temperature Measurements. (Boudouard Burgess. )i2mo, 3 oo 

LSb's Electrolysis and Electrosynthesis of Organic Compounds. (Lorenz.) i2mo, i oo 

* Lyons'? Treatise on Electromagnetic Phenomena. Vo Is. I. and II. 8vo, each, 6 oo 

* Michie. Elements of Wave Motion Relating to Sound and Light 8vo, 4 oo 

Niaudet's Elementary Treatise on Electric Batteries. (Fishoack.) 12010, a 50 

* Rosenberg's Electrical Engineering. (Haldane Gee Kinzbrunner.) Svo, I 50 

Rymn, Norris, and Hoxie's Electrical Machinery. VoL L Svo, as* 

Thurston's Stationary Steam-engines 8vo, a 50 

* TiUman's Elementary Lessons in Heat 8vo, i 50 

Tory and Pitcher's Manual of Laboratory Physics Small 8vo, a oo 

Hike's Modern Electrolytic Copper Refining Svo, 3 oo 

LAW. 

* Davis's Element! of Law Svo, a 50 

* Treatise on the Military Law of United States Svo, 7 oo 

* Sheep, 7 50 

Manual for Courts-martial ,. i6mo, morocco, i 50 

Wait's Engineering and Architectural Jurisprudence Svo, 6 oo 

Sheep, 6 50 

Law of Operations Preliminary to Construction in Engineering and Archi- 
tecture , Svo, s oo 

Sheep, 5 50 

Law of Contracts Svo, 3 oo 

Winthrop's Abridgment of Military Law xamo, a 50 

MANUFACTURES. 

Bernadou's Smokeless Powder Nitro-cellulose and Theory of the Cellulose 

Molecule zarno, a 50 

Holland's Iron Founder . izmo, a 50 

" The Iron Founder," Supplement xamo, a 50 

Encyclopedia of Founding and Dictionary of Foundry Terms Used in the 

Practice of Moulding iamo, 3 oo 

Bissler's Modern High Explosives Svo, 4 oo 

Eff rent's Enzymes and their Applications. (Prescott. ) Svo, 3 oo 

Fitzgerald's Boston Machinist iSmo, i oo 

Ford's Boiler Making for Boiler Makers xSmo, i oo 

Hopkins's Oil-chemists' Handbook Svo, 3 oo 

Keep's Cast Iron Svo, a 50 

Leach's The Inspection and Analysis of Food with Special Reference to State 

Control. (In preparation.) 
Matthews's The Textile Fibres. (In press.) 

Metcalf's SteeL A Manual for Steel-users lamo. a oo 

Metcalfe's Cost of Manufactures And the Administration of Workshops, 

Public and Private Svo, 5 oo 

Meyer's Modern Locomotive Construction 4to, 10 oo 

Morse's Calculations used in Cane-sugar Factories i6mo, morocco, x 50 

Reisig's Guide to Piece-dyeing Svo, as oo 

Sabin's Industrial and Artistic Technology of Paints and Varnish Svo, 3 oo 

Smith's Press-working of Metals Svo, 3 oo 

Spalding's Hydraulic Cement xamo, a oo 

Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco, 3 oo 

Handbook tor sugar Manufacturers ana their Chemists.. . i6mo, morocco, a oo 
Taylor and Thompson's Treatise on Concrete, Plain and Reinforced. (In 

pre*8.) 

Thurston's Manual of Steam-boilers, their Designs, Construction and Opera- 
tion Svo, 5 oo 

10 



* Walke's Lectures on Explosives 8vo, 4 oo 

West's American Foundry Practice xamo, a 50 

Moulder's Text-book i2mo, a 50 

Wiechmann's Sugar Analysis Small 8vo, a 50 

Wolff's Windmill as a Prime Mover 8vo, 3 oo 

Woodbury's Fire Protection of MiUs .8vo, a 50 

Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. . .8vo, 4 oo 

MATHEMATICS. 

Baker's Elliptic Functions 8vo, I so 

* Bass's Elements of Differential Calculus zarno, 4 oo 

Briggs's Elements of Plane Analytic Geometry xamo, I oo 

Compton's Manual of Logarithmic Computations iamo, x 50 

Davis's Introduction to the Logic of Algebra 8vo, z 50 

* Dickson's College Algebra Large 1 2mo, x 50 

* Answers to Dickson's College Algebra 8vo, paper, as 

* Introduction to the Theory of Algebraic Equations Large lamo, x as 

Halsted's Elements of Geometry 8vo. i 75 

Elementary Synthetic Geometry 8vo, i 50 

Rational Geometry ; xamo, 

Johnson's Three-place Logarithmic Tables: Vest-pocket size paper, 15 

100 copies for 5 oo 

* Mounted on heavy cardboard, 8 X 10 inches, as 

10 copies for a oo 

Elementary Treatise on the Integral Calculus Small 8vo, x 50 

Curve Tracing in Cartesian Co-ordinates i2ino, x oo 

Treatise on Ordinary and Partial Differential Equations Small 8vo, 3 50 

Theory of Errors and the Method of Least Squares 12 mo, i 50 

* Theoretical Mechanics iamo, 3 oo 

Laplace's Philosophical Essay on Probabilities. (Truscott and Emory.) xamo, a oo 

* Ludlow and Bass. Elements of Trigonometry and Logarithmic and Other 

Tables 8vo, 3 oo 

Trigonometry and Tables published separately Each, a oo 

* Lud low's Logarithmic and Trigonometric Tables 8vo, x oo 

Maurer's Technical Mechanics 8vo, 4 oo 

Merriman and Woodward's Higher Mathematics 8vo, 5 oo 

Merriman's Method of Least Squares 8vo, a oo 

Rice and Johnson's Elementary Treatise on the Differential Calculus . Sm., 8vo, 3 oo 

Differential and Integral Calculus, a vols. in one Small 8vo, a 50 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 oo 

Wood's Elements of Co-ordinate Geometry 8vo, a oo 

Trigonometry: Analytical, Plane, and Spherical. 12 mo, x oo 

MECHANICAL ENGINEERING. 

MATERIALS OF ENGINEERING, STEAM-ENGINES AND BOILERS. 

Bacon's Forge Practice xamo, x 50 

Baldwin's Steam Heating for Buildings xamo, a 50 

Barr's Kinematics of Machinery 8vo, a 50 

* Bartlett's Mechanical Drawing 8vo, 3 oo 

Abridged Ed .8vo, x s 

Benjamin's Wrinkles and Recipes 1 2 mo, a oo 

Carpenter's Experimental Engineering 8vo, 6 oo 

& .Heating and Ventilating Buildings 8vo, 4 oo 

Cory's Smoke Suppression in Plants using Bituminous Coal. (In prep- 
aration.) 

Clerk's Gas and Oil Engine Small 8vo, 4 oo 

Coolidge's Manual of Drawing 8vo, paper, x oo 

11 



Coolidge and Freeman's Elements of General Drafting for Mechanical En- 
gineers, (fn press.) 

Cromwell's Treatise on Toothed Gearing tamo, x 50 

Treatise on Belts and Pulleys lamo, x SO 

Durley's Kinematics of Machines 8vo, 4 00 

Jlather's Dynamometers and the Measurement of Power lamo, 3 oo 

Rope Driving I2mo, 2 oo 

Gill's Gas and Fuel Analysis for Engineers - 12 mo, x 25 

Hall's Car Lubrication i2mo, i oo 

Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50 

Button's The Gas Engine .. 8vo. 5 00 

Jones's Machine Design: 

Part I. Kinematics of Machinery Svo, x 50 

Part II. Form, Strength, and Proportions of Parts 8vo, 3 oo 

Kent's Mechanical Engineer's Pocket-book x6mo, morocco, 5 oo 

Kerr's Power and Power Transmission Svo, a oo 

Leonard's Machine Shops. Tools, and Methods. (In prena.) 

MacCord's Kinematics; or, Practical Mechanism 8vo, 5 oo 

Mechanical Drawing '. 4to, 4 oo 

Velocity Diagrams. 8vo, I SO 

Mahan's Industrial Drawing. (Thompson.) 8vo, 3 SO 

Poole's Calorific Power of Fuels. 8vo, 3 oo 

Reid's Course in Mechanical Drawing 8vo. 2 oo 

Text-book of Mechanical Drawing and Elementary Machine Design. .8vo, 3 oo 

Richards's Compressed Air 12010, x 50 

Robinson's Principles of Mechanism 8vo, 3 oo 

Schwamb and Merrill's Elements of Mechanism. (In press.) 

Smith's Press-working of Metals 8vo, 3 oo 

Thurston's Treatise on Friction and Lost Work in Machinery and Mill 

Work 8vo, 3 oo 

Animal as a Machine and Prime Motor, and the Laws of Energetics . i2mo, i oo 

Warren's Elements of Machine Construction and Drawing 8ro, 7 50 

Weisbach's Kinematics and the Power of Transmission. Herrmann 

Klein.) 8vo, 5 oo 

Machinery of Transmission and Governors. (Herrmann Klein.). .8vo, 5 oo 

Hydraul-cs and Hydraulic Motors. (Du Bois.) 8vo, 5 oo 

Wolff's Windmill as a Prime Mover 8vo, 3 oo 

Wood's Turbines 8vo, a 50 

MATERIALS OF ENGINEERING. 

Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Burr's Elasticity and Resistance of the Materials of Engineering. 6th Edition, 

Reset 8vo, 7 50 

Church's Mechanics of Engineering 8vo, 6 oo 

Johnson'" Materials of Construction Large 8vo, 6 oo 

Keep's Cast Iron Svo, 2 50 

Lanza's Applied Mechanics. 8vo, 7 50 

Martens's Handbook on Testing Materials. (Henning.) 8vo, 7 50 

Merriman's Text-book on the Mechanics of Materials 8vo, 4 oo 

Strength of Materials i2mo, i oo 

Metcalf's SteeL A Manual for Steel-users i2mo a oo 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 oo 

Smith's Materials of Machines I2mo, x oo 

Thurston's Materials of Engineering 3 vote , Svo, 8 oo 

Part n. Iron and Steel Svo, 3 50 

Part HI. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents. Svo 2 50 

Text-book of the Materials of Construction Svo, 5 oo 

12 



Wood's Treatise on the Resistance of Materials and an Appendix on the 

Presentation of Timber 8vo, a oo 

Elements of Analytical Mechanics 8vo, 3 oo 

Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel. . ,8vo, 4 oo 



STEAM-ENGINES AND BOILERS. 

Carnot's Reflections on the Motive Power of Heat. (Thurston. ) i amo , z 50 

Dawson's "Engineering" and Electric Traction Pocket-book. .i6mo, mor., 5 oo 

Ford's Boiler Making for Boiler Makers iSmo, i oo 

Goss's Locomotive Sparks 8vo, a oo 

Hemtnway's Indicator Practice and Steam-engine Economy 12 mo, a oo 

Button'* Mechanical Engineering of Power Plants 8vo, 5 oo 

Heat and Heat-engines 8vo, 5 oo 

Kent's Steam-bo'ler Economy 8vo, 4 oo 

Kneass's Practice and Theory of the Injector 8vo i 50 

KacCord's Slide-valves 8vo, a oo 

Meyer's Modern Locomotive Construction 4to, xo oo 

Peabody's Manual of the Steam-engine Indicator xamo, x 50 

Tables of the Properties of Saturated Steam and Other Vapors 8vo, x oo 

Thermodynamics of the Steam-engine and Other Heat-engines 8vo, 5 oo 

Valve-gears for Steam-engines .' 8vo, a 50 

Peabody and Miller's Steam-boilers 8vo, 4 oo 

Pray's Twenty Yean with the Indicator Large 8vo, a 50 

Pupln's Thermodynamics of Reversible Cycles in Gases and Saturated Vapors. 

(Osterberg.) xamo, x as 

Reagan's Locomotives : Simple, Compound, and Electric xamo, a 5* 

Rontgen's Principles of Thermodynamics. (Du Bois.) 8vo, 5 oo 

Sinclair's Locomotive Engine Running and Management xamo, a oo 

Smart's Handbook of Engineering Laboratory Practice xamo, a 50 

Snow's Steam-boiler Practice 8vo, 3 oo 

Spangler's Valve-gears 8vo, a 50 

Notes on Thermodynamics xamo, x oo 

Spangler, Greene, and Marshall's Elements of Steam-engineering 8vo, 3 oo 

Thurston's Handy Tables 8vo, x 50 

Manual of the Steam-engine a vote. 8vo, 10 oo 

Part I. History. Structuce, and Theory 8vo, 6 oo 

Part n. Design, Construction, and Operation 8vo, 6 oo 

Handbook of Engine and Boiler Trials, and the Use of the Indicator and 

the Prony Brake 8vo 5 oo 

Stationary Steam-engines 8vo, a 50 

Steam-boiler Explosions in Theory and in Practice xamo x 50 

Manual of Steam-boilerp , Their Designs, Construction, and Operation . 8vo , 5 oo 

Weisbach's Heat, Steam, and Steam-engines. (Du Bois.) 8vo, 5 oo 

Whitham's Steam-engine Design 8vo, 5 oo 

Wilson's Treatise on Steam-boilers. (Plainer. ) x6mo, a 50 

Wood's Thermodynamics Heat Motors, and Refrigerating Machines 8vo, 4 oo 



MECHANICS AND MACHINERY. 

Barr's Kinematics of Machinery 8vo, a 50 

Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Chase's The Art of Pattern-making xamo, a 50 

ChordaL Extracts from Letters xamo, a oo 

Church's Mechanics of Engineering 8vo, 6 oo 

Notes and Examples in Mechanics 8vo, a oo 

13 



Compton's First Lessons in Metal-working iamo, 50 

Compton and De Groodt's The Speed Lathe ramo, 50 

Cromwell's Treatise on Toothed Gearing 1 2010 , 50 

Treatise on Belts and Pulleys iamo, 50 

Dana's Text-book of Elementary Mechanics for the Use of Colleges and 

Schools i zmo, 50 

Dingey's Machinery Pattern Making xamo, oo 

Dredge's Record of the Transportation Exhibits Building of the World's 

Columbian Exposition of 1893 4to, half morocco, 5 oo 

Du Bois's Elementary Principles of Mechanics : 

VoL I. Kinematics. 8vo, 3 50 

Vol. H. Statics i 8vo, 4 oo 

Vol. HI. Kinetics 8vo, 3 So 

Mechanics of Engineering. VoL I. Small 4to, 7 50 

VoL H. Small 4to, 10 oo 

Durley's Kinematics of Machines 8vo, 4 oo 

Fitzgerald's Boston Machinist i6mo, i oo 

Flather's Dynamometers, and the Measurement of Power lamo, 3 oo 

Rope Driving , iamo, a oo 

Gose's Locomotive Sparks * 8vo a oo 

Hall's Car Lubrication xamo, i oo 

Holly's Art of Saw Filing i8mo. 75 

* Johnson's Theoretical Mechanics. I iamo, 3 oo 

Statics by Graphic and Algebraic Methods 8vo, a oo 

Jones's Machine Design: 

Part I. Kinematics of Machinery 8vo, i 50 

Part n. Form, Strength, and Proportions of Parts 8vo, 3 oo 

Kerr's Power and Power Transmission 8vo, a oo 

Lanza's Applied Mechanics 8vo, 7 50 

Leonard s Machine Shops, Tools, and Methods. (In press.) 

MacCord's Kinematics; or, Practical Mechanism 8vo, 5 oo 

Velocity Diagrams 8ro, i 50 

Maurer's Technical Mechanics .8vo, 4 oo 

Merriman's Text-book on the Mechanics of Material* 8vo, 4 oo 

* Michie'8 Elements of Analytical Mechanics 8ro, 4 oo 

Reagan's Locomotives: Simple, Compound, and Electric xamo, a 50 

Reid's Course in Mechanical Drawing 8vo, a oo 

Text-book of Mechanical Drawing and Elementary Machine Design . . 8vo, 3 oo 

Richards's Compressed Air iamo, i 50 

Robinson's Principles of Mechanism 8vo, 3 oo 

Ryan, Norris, and Hoxie's Electrical Machinery. Vol.1 8vo, a 5* 

Schwamb and Merrill's Elements of Mechanism. (In press.) 

Sinclair's Locomotive-engine Running and Management 12 mo, a oo 

Smith's Press-working of Metals 8vo, 3 oo 

Materials of Machines iamo, i oo 

Spangler, Greene, and Marshall's Elements of Steam-engineering 8vo, 3 oo 

Thurston's Treatise on Friction and Lost Work in Machinery and Mill 

Work 8vo, 3 oo 

Animal as a Machine and Prime Motor, and the Laws of Energetics . iamo, i oo 

Warren's Elements of Machine Construction and Drawing 8vo, 7 50 

Weisbach's Kinematics and the Power of Transmission. (Herrmann 

Klein.) 8vo, 5 oo 

Machinery of Transmission and Governors. (Herrmann Klein.). 8 vo, 5 oo 

Wood's Elements of Analytical Mechanics 8vo, 3 oo 

Principles of Elementary Mechanics iamo, i 25 

Turbines 8vo, a 50 

The World's Columbian Exposition of 1893 , 4 to, i oo 

14 



METALLURGY. 

Egleston's Metallurgy of Silver, Gold, and Mercury: 

VoL I. SUver 8vo, 7 So 

VoL II. Gold and Mercury 8vo, 7 So 

** Iles's Lead-smelting. (Postage 9 cents additional.) lamo, 50 

Keep's Cast Iron 8vo, 50 

Kunhardt's Practice of Ore Dressing in Europe 8vo, 50 

Le Chatelier's High-temperature Measurements. (Boudouard Burgess.). lamo, oo 

Metcalf's Steel. A Manual for Steel-users lamo, oo 

Smith's Materials of Machines lamo, oo 

Thurston's Materials of Engineering. In Three Parts 8vo, 8 oo 

Part H. Iron and Steel 8vo, 3 So 

Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents 8vo, a 50 

Hike's Modern Electrolytic Copper Refining 8vo, 3 oo 

MINERALOGY. 

Barringer's Description of Minerals of Commercial Value. Oblong, morocco, a 50 

Boyd's Resources of Southwest Virginia 8vo, 3 oo 

Map of Southwest Virginia , Pocket-book form, a oo 

Brush's Manual of Determinative Mineralogy. (Penfield.) 8vo, 4 oo 

Chester's Catalogue of Minerals 8vo, paper, x oo 

Cloth, x as 

Dictionary of the Names of Minerals 8vo, 3 50 

Dana's System of Mineralogy Large 8vo, half leather, xa 50 

First Appendix to Dana's New "System of Mineralogy." Large 8 vo, x oo 

Text-book of Mineralogy 8vo, 4 oo 

Minerals and How to Study Them. xamo, x 50 

Catalogue of American Localities of Minerals Large 8vo, i oo 

Manual of Mineralogy and Petrography xamo, a oo 

Eakle's Mineral Tables. '. 8vo, x as 

Egleston's Catalogue of Minerals and Synonyms 8vo, a 50 

Hussak's The Determination of Rock-forming Minerals. (Smith.) Small 8vo, 2 oo 

Merrill's Non-metallic Minerals: Their Occurrence and Uses. 8vo, 4 oo 

* Penfield's Notes on Determinative Mineralogy and Record of Mineral Tests. 

8vo, paper, o 50 
Rosenbusch's Microscopical Physiography of the Rock-making Minerals. 

(Iddings.) 8vo, 5 oo 

* Tillman's Text-book of Important Minerals and Docks 8vo, a oo 

Williams's Manual of Lithology 8vo, 3 oo 

MINING. 

Beard's Ventilation of Mines xamo, a 50 

Boyd's Resources of Southwest Virginia 8vo, 3 oo 

Map of Southwest Virginia Pocket-book form, a oo 

* Drinker's Tunneling, Explosive Compounds, and Rock Drills. 

4to, half morocco, as oo 

Eissler's Modern High Explosives ,. 8vo, 4 oo 

Fowler's Sewage Works Analyses xamo, 

Goodyear 's Coal-mines of the Western Coast of the United States xamo, 

Ihlseng's Manual of Mining. .8vo, 



oo 
So 

00 

So 
So 

00 
00 

50 
So 

Hydraulic and Placer Mining xamo, a oo 

Treatise on Practical and Theoretical Mine Ventilation xamo I as 

15 



>* Iles's Lead-smelting. (Postage gc. additional.) xamo, 

Kunhardt's Practice of Ore Dressing in Europe 8vo, 

O'Driscoll's Notes on the Treatment of Gold Ores 8vo, 

* Walke's Lectures on Explosives 8vo, 

Wilson's Cyanide Processes xamo, 

Chlorination Process ... . . xamo, 



SANITARY SCIENCE. 

Copeland's Manual of Bacteriology. (In preparation.) 

FolwelTs Sewerage. (Designing, Construction and Maintenance.) 8vo, 3 oo 

Water-supply Engineering .8vo, 4 oo 

Fuertes's Water and Public HeaKh .xarno. i 50 

Water-filtration Works iamo, 2 50 

Gerhard's Guide to Sanitary House-inspection i6mo, i oo 

Goodrich's Economical Disposal of Town's Refuse Demy 8ro, 3 5 

Hazen's Filtration of Public Water-supplies 8vo, 3 oo 

Kiersted's Sewage Disposal larno. x 25 

Leach's The Inspection and Analysis of Food with Special Reference to State 

Control. (In preparation.) 

Mason's Water-supply. (Considered Principally from a Sanitary Stand- 
point.) 3d Edition, Rewritten 8vo, 4 o 

Examination of Water. (Chemical and Bacteriological) lamo, t 25 

Merriman's Elements of Sanitary Engineering 8vo, * o 

Nichols's Water-supply. (Considered Mainly from a Chemical and Sanitary 

Standpoint) (1883.) 8vo, 2 50 

Ogden's Sewer Design I2mo, a oo 

Prescott and Winslow's Elements of Water Bacteriology, with Special Reference 

to Sanitary Water Analysis I2mo, i 25 

* Price's Handbook on Sanitation X2mo, x 50 

Richards's Cost of Food. A Study in Dietaries izmo, x oo 

Cost of Living as Modified by Sanitary Science xamo, x oo 

Richards and Woodman's Air* Water, and Food from a Sanitary Stand- 
point 8ro, a oo 

Richards and Williams's The Dietary Computer 8vo, x 50 

Rideal's Sewage and Bacterial Purification of Sewage 8vo, 3 so 

Turneaure and Russell's Public Water-supplies. 8vo, 5 oo 

Whipple's Microscopy of Drinking-water 8vo, 3 50 

Woodhull's Notes and Military Hygiene i6mo, x 50 

MISCELLANEOUS. 

Barker's Deep-sea Soundings 8vo, 2 oo 

Bmmons's Geological Guide-book of the Rocky Mountain Excursion of the 

International Congress of Geologists Large 8ro $ 

Ferret's Popular Treatise on the Winds 8vo *o 

Haines's American Railway Management xamo* 50 

Mott's Composition, Digestibility, and Nutritive Value of Food. Mounted chart. 5 

Fallacy of the Present Theory of Sound x6ino oo 

Ricketts's History of Rensselaer Polytechnic Institute, 1824-1894. Small 8vo, oo 

Rotherham's Emphasized New Testament Large 8vo, oo 

Steel's Treatise on the Diseases of the Dog 8vo, 50 

Totten's Important Question in Metrology 8vo 50 

The World's Columbian Exposition ot 1803 4to, oo 

Von Bearing's Suppression of Tuberculosis. (Bolduan.) (In preu.) 
Worcester and Atkinson. Small Hospitals, Establishment and Maintenance, 
and Suggestions for Hospital Architecture, with Plans for a Small 

Hospital tamo, I as 

HEBREW AND CHALDEE TEXT-BOOKS. 

Green's Grammar of the Hebrew Language 8vo, 3 oo 

Elementary Hebrew Grammar X 2mo, x 25 

Hebrew Chrestomathy 8vo, a oo 

Gesenius's Hebrew and Chaldee Lexicon to the Old Testament Scriptures. 

(Tregelles.) Small 4 to, half morocco. 5 oo 

Letteris's Hebrew Bible 8vo , a 3 

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