THE CHEMICAL ANALYSIS
HENRY S. WASHINGTON, Pn.D.
JOHN WILEY & SONS.
LONDON: CHAPMAN & HALL, LIMITED.
H. S. WASHINGTON.
Entered at Stationers' Hall.
ROBERT DRTJMMOND, PRINTER, NEW YORK.
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
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
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-
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.
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
APPARATUS AND REAGENTS.
1. APPARATUS. 31
2. REAGENTS 35
1. SELECTION IN THE FIELD 41
2. AMOUNT OF MATERIAL 46
3. PREPARATION OF THE SAMPLE. , 48
1. PRELIMINARY OBSERVATIONS 55
2. GENERAL COURSE OF ANALYSIS 57
3 CHIEF SOURCES OF ERROR 61
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
1. EXAMPLE OF ANALYSIS 167
2. TABLE OF MOLECULAR WEIGHTS 173
3. FACTORS FOR CALCULATION 173
INDEX.. . 175
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,
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
THE CHEMICAL ANALYSIS OF KOCKS.
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-
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.
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
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
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
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
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
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.
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
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.
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.
if the analysis is to conform to even the first requirement as to
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,
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.
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
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.
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
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.
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
* 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
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.
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
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
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
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
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.
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
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
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
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-
stituent both of the ferromagnesian minerals and of the feld-
spars. Soda precedes potash, as it is associated with lime in
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.
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-
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.
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.
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
32 APPARATUS AND REAGENTS.
Fresenius. Before commencing an analysis the balance should
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.
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
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
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
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
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).
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.
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.
Hydrofluoric acid, for which ceresine bottles should be used r
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).
Hydrogen-ammonium-sodium phosphate (microcosmic salt).
The solution is to be made as needed (p. 119).
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
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
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 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
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
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.
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
Ferrous sulphide. This is used for the generation of hydro-
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.
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
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
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
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
While the selection in the field is quite distinct from the
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
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-
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
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
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
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
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
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
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
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.
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.
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.
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
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
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
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
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.
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
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
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
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.
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-
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.
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
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
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.
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.
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
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
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
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.
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
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
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.
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
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
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
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.
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
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
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
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.
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-
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.
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).
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.
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
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-
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.
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-
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
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
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-
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
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.
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.
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
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.
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
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.
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.
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.
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
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.
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,
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.
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
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
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
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
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
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
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,
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
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
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
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
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
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
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
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
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
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-
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.
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.
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.
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
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.
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.
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.
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.
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
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
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
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 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.
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-
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.
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
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
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.
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
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
The advantages of this method are : its convenience and ex-
* J. L. Smith, Am. Jour. Sci., I, p. 269, 1871.
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.
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.
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
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
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
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. \.
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
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
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-
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
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
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.
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.
. from the alcohol wash-bottle, the depth of liquid above the felt
being so great that the drops can fall in the center without
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-
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
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
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,
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
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
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 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
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
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
Ten c.c. of diluted standard are then again run into the right-
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
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
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
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
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-
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-
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
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.
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
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
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-
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,
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.
dissolved, the former as barium carbonate and the latter as
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
yellow color disappears, a little more hydrogen peroxide is to
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
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.
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
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.
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
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.
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.
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-
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.
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-
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.
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.
H 2 0-
1310. LEUCITE-TEPHRITE, LAVA OF 1903, MT. VESUVIUS.
Cruc. + subst. = 40 . 6602
Subst. taken = 1.0040
Cruc. + SiO 3 + x= 33 . 1879
Cruc. +subst.=34. 9497
Tube + subst. = 25 . 3857
Total H,O= 0.15
H 3 O- =0.04
Cruc. + SiO 2 + z= 33 . 1879
Cruc. + x =32.7078
SiO 2 =
Extra SiO, =
Cruc. + subst. = 34 . 9497
Dried at 110= 34. 9493
Tube + H 3 O= 20. 7298
Tube -H,O= 20. 7280
EXAMPLE OF ANALYSIS.
1310. A1A, FeA
Cruc. + Al A. etc. = 33 . 0007
Cruc. + res. + SiO 2 = 33 . 8747
Cruc. + res. - SiO,= 33 . 8719
.2964 Extra SiO 2
Used 36.6 c.c. of permanganate sol.
A1A, etc. = .2964
FeA = -0930
TiO, = .0142
Total FeA = .0930006
FeO as Fe 2 O 3 = .0680712
1. 004). 0249294(. 0248
1. 004). 1766(. 1759
Pt basin + subst. = 1 1 . 1 134 Cruc. + Mg 3 P,O 7 = 19 . 0322
Pt basin =10.0830 Cruc. =19.0165
1. 0304). 0100480(. 00975
1310. FeO, TiO 3 .
Cruc.+subst. = 35.9546
.5058=13.5 c.c. of K 2 Mn 2 O 8
.5058) .0308745(. 06104 .5058) .0343035 (.0678 =
30348 30348 FeO asFe 2 O 3 - 0680712
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
35 . 267) . 001000000( . 00002836
1. 004). 01418(. 0141
EXAMPLE OF ANALYSIS.
1310. CaO, MgO.*
1. 004). 08190(. 0816
Gooch cruc. + Mg 3 P 2 O 7 = 25 . 1389
1. 004). 4287264(. 0427
* On this page are also recorded the figures for S, Zr0 3 , and BaO, which
are omitted here.
K 3 O
Tube + subst. = 23 . 5598
Cruc. + NaCl + KC1= 35 . 5417
Gooch cruc. + K 3 Pta a = 25 . 2593
. 5335) . 04232837 ( . 07934
.0670181 ( = KC1)
.5335). 0141 1928(. 0265
* No correction was needed for the amount of alkalies in the calcium
TABLE OF MOLECULAR WEIGHTS.
2. TABLE OF MOLECULAR WEIGHTS.
ALO 3 . ,
Fe 2 O, . .
. . 56
Na 2 O
K 2 O. .
H 2 O
P.O. . .
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
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
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
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
Ash of filter-paper, neglect of 56
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
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
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
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
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
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
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
Hillebrand's method for determination of chromium 165
sulphur, zirconia and baryta 155
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
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-
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
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
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
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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* Treatise on the Military Law of United States 8vo, 7 oo
Sheep, 7 SO
De Brack's Cavalry Outpost Duties. (Carr.) 24mo morocco, 2 oo
Dietz's Soldier's First Aid Handbook i6mo^ morocco, x 25
* Dredge's Modern French Artillery 4to, half morocco, 15 oo
Durand's Resistance and Propulsion of Ships 8vo, 5 oo
* Dyer's Handbook of Light Artillery izmo, 3 oo
Eissler's Modern High Explosives 8vo, 4 oo
* Fiebeger's Text-book on Field Fortification Small 8vo, 2 oo
Hamilton's The Gunner's Catechism i8mo, x oo
* Hoff's Elementary Naval Tactics 8vo, x 50
Ingalls's Handbook of Problems in Direct Fire 8vo, 4 oo
* Ballistic Tables 8vo. x 50
* Lyons's Treatise on Electromagnetic Phenomena. Vols. I. and II. .8vo. each, 6 oo
* Mahan's Permanent Fortifications. (Mercur.) ...8vo, half morocco, 7 50
Manual for Courts-martial i6mOi morocco, x 50
* Mercur's Attack of Fortified Places i2mo, 2 oo
* Elements of the Art of War 8vo, 4 oo
Metcalf's Cost of Manufactures And the Administration of Workshops, Public
and Private 8vo, 5 oo
* Ordnance and Gunnery. 2 vols i2mo, 5 oo
Murray's Infantry Drill Regulations i8mo. paper, xo
Peabody's Naval Architecture 8ro, 7 So
* Phelps's Practical Marine Surveying ................. .............. 8vo, a 50
Powell's Army Officer's Examiner ................................. xamo, 4 oo
Sharpe's Art of Subsisting Armies in War ................... i8mo, morocco,
* Walke's Lectures on Explosives ......... ......................... 3vo
* Wheeler's Siege Operations and Military Mining ..................... 8vo,
Winthrop's Abridgment of Military Law ............................ iamo,
Woodhull's Notes on Military Hygiene ............................. i6mo,
Young's Simple Elements of Navigation ............ . ....... i6mo morocco,
Second Edition, Enlarged and Revised ............... ;i6mo, morocco, a oo
Fletcher's Practical Instructions in Quantitative Assaying with the Blowpipe.
i a mo, morocco, i 50
Furman's Manual of Practical Assaying ............................. 8vo, 3 oo
Lodge's Notes on Assaying and Metallurgical Laboratory Experiments.
Miller's Manual of Assaying ..................... . ..... . .......... xamo, I oo
O'DriscolTs Notes on the Treatment of Gold Ores ....................... 8vo, a oo
Ricketts and Miller's Notes on Assaying .............................. 8vo, 3 OO
Hike's Modern Electrolytic Copper Refining ........................... 8vo, 3 oo
Wilson's Cyanide Processes ....................................... xarno, x 50
Chlorination Process ........................................ xarno, i 50
Comstock's Field Astronomy for Engineers ........................... 8ro, a 50
Craig's Azimuth .................................................. 4to, 3 50
Doolittle's Treatise on Practical Astronomy ........................... 8vo. 4 oo
Gore's Elements of Geodesy ................... I ........ . .......... 8vo, a 50
Hayf ord's Text-book of Geodetic Astronomy .......................... 8vo, 3 oo
Merriman's Elements of Precise Surveying and Geodesy ................ 8vo, a 50
* Michie and Harlow's Practical Astronomy .......................... 8vo, 3 oo
* White's Elements of Theoretical and Descriptive Astronomy. . ....... 12 mo, a oo
Davenport's Statistical Methods, with Special Reference to Biological Variation.
i6mo, morocco, i 35
Thome and Bennett's Structural and Physiological Botany .......... ... i6mo, a as
Westermaier's Compendium of General Botany. (Schneider.) .......... 8vo, a oo
Adriance's Laboratory Calculations and Specific Gravity Tables ........ xamo, x as
Allen's Tables for Iron Analysis ..................................... 8vo, 3 oo
Arnold's Compendium of Chemistry. (Mandel.) ................. Small 8vo, 3 50
Austen's Notes for Chemical Students .............................. iamo, x 50
* Austen and Langworthy. The Occurrence of Aluminium in Vegetable
Products, Animal Products, and Natural Waters .............. 8vo, a oo
Bernadou's Smokeless Powder. Nitro-cellulose, and Theory of the Cellulose
Molecule .............................................. laxno, a 50
Bolton's Quantitative Analysis ..................................... 8vo, x 50
* Browning's Introduction to the Rarer Elements ..................... STO, x 50
Brush and Penfield's Manual of Determinative Mineralogy .............. 8vo, 4 oo
Classen's Quantitative Chemical Analysis by Electrolysis. (Boltwood.) .... 8vo, 3 oo
Conn's Indicators and Test-papers ................................. xamo, a oo
Tests and Reagents ............................ , ............. 8vo, 3 oo
Copeland's Manual of Bacteriology. (In preparation.)
Craft's Short Course in Qualitative Chemical Analysis. (Schaeffer.). . . .xamo, x 50
Dolezalek's Theory of the Lead Accumulator (Storage Battery). (Von
Ende) ................................................. xamo, a 50
Drechsel's Chemical Reactions. (Merrill.) ......................... xamo, x as
Duhem's Thermodynamics and Chemistry. (Burgess.) ................ 8vo, 4 e
Blaster's Modern High Explosives 8vo, 4 o
Eflront's Enzymea;and .their Applications. (Prescott.) 8vo, 3 oo
Erdmann's Introduction to Chemical Preparations. (Dunlap.) i2mo, x as
Fletcher's Practical Instructions in Quantitative Assaying with the Blowpipe
i2mo, morocco, i 50
Fowler's Sewage Works Analyses lamo, 2 oo
Fresenius's Manual of Qualitative Chemical Analysis. (Wells.) 8vo, 5 oo
Manual of Qualitative Chemical Analysis. Parti. Descriptive. (Wells.)
8vo, 3 oo
System of Instruction in Quantitative Chemical Analysis. (Cohn.)
2 vols 8vo, 12 50
Fuertes's Water and Public Health i2mo, i 50
Fnrman's Manual of Practiostl Assaying 8vo, 3 oo
Getman's Exercises in Physical Chemistry i2mo.
Gill's Gas and Fuel Analysis for Engineers i zmo, i 25
Gro ten felt's Principles of Modern Dairy Practice. (Wo 11.) X2mo, 2 oo
Hammarsten's Text-book of Physiological Chemistry. (MandeL) 8vo, 4 oo
Helm's Principles of Mathematical Chemistry. (Morgan.) lamo, x 50
Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, a 50
Hinds's Inorganic Chemistry 8vo, 3 oo
* Laboratory Manual for Students . . . , isrno, 75
Holleman's Text-book of Inorganic Chemistry. (Cooper.) 8vo, 2 50
Text-book of Organic Chemistry. (Walker and Mott.) 8vo, 2 50
iTi . Laboratory Manual of Organic Chemistry. (Walker.) xamo, x oo
Hopkins's Oil-chemists' Handbook 8vo, 3 oo
Jackson's Directions for Laboratory Work in Physiological Chemistry . .8vo, x 25
Keep's Cast Iron ^ 8vo, 2 50
Ladd's Manual of Quantitative Chemical Analysis I2mo, i oo
Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 oo
Lassar-Cohn's Practical Urinary Analysis. (Lorenz.) i2mo, x oo
Application of Some General Reactions to Investigations in Organic
Chemistry. (Tingle.) (In press,)
Leach's The Inspection and Analysis of Food with Special Reference to State
Control. (In preparation.)
LBb's Electrolysis and Electrosyn thesis of Organic Compounds. (Lorenz.) 12 mo, i oo
Lodge's Notes on Assaying and Metallurgical Laboratory Experiments. (In
Lunge's Techno -chemical Analysis. (Cohn.) (In press.)
Mandel's Handbook for Bio-chemical Laboratory izmo, i 50
* Martin's Laboratory Guide to Qualitative Analysis with the Blowpipe . . 12 mo, 60
Mason's Water-supply. (Considered Principally from a Sanitary Standpoint.)
' 3d Edition, Rewritten 8vo, 4 oo
Examination of Water. (Chemical and Bacteriological.) X2mo, x 25
Matthews's The Textile Fibres. (In press.)
Meyer's Determination of Radicles in Carbon Compounds. (Tingle.). . xzmo,
Miller'* Manual of Assaying I2mo,
Mixter*s Elementary Text-book of Chemistry i2mo,
Morgan's Outline of Theory of Solution and its Results 12 mo,
Elements of Physical Chemistry i2mo,
Morse's Calculations used in Cane-sugar Factories x6mo, morocco,
Uulliken's General Method for the Identification of Pure Organic Compounds.
i VoL I Large 8vo, 5 oo
Nichols's Water-supply. (Considered mainly from a Chemical and Sanitary
Standpoint, 1883.) 8vo, 2 50
O'Brine's Laboratory Guide in Chemical Analysis 8vo, 2 oo
O'Driscoll's Notes on the Treatment of Gold Ores 8vo, 2 oo
Ost and Kolbeck's Text-book of Chemical Technology. (Lorenz Bozart.)
Ostwald's School of Chemistry. Part One. (Ramsey.) (In preta.)
Penfield's Notes on Determinative Mineralogy and Record of* Mineral Tests.
8vo, paper, 50
Pictet's The Alkaloids and their Chemical Constitution. (Biddle.) 8vo, 5 oo
Pinner's Introduction to Organic Chemistry. (Austen.) lamo, z 50
Poole's Calorific Power of Fuels 8vo, 3 oo
Prescott and Winslow's Elements of Water Bacteriology, with Special Refer-
ence to Sanitary Water Analysis tamo, i as
Reisig's Guide to Piece-dyeing 8vo, 25 oo
Richards and Woodman's Air, Water, and Food from a Sanitary Standpoint. 8vo, a oo
Richards's Cost of Living as Modified by Sanitary Science 12 mo, i oo
Cost of Food a Study in Dietaries lamo, i oo
Richards and Williams's The Dietary Computer 8vo, x 50
Ricketts and Russell's Skeleton Notes upon Inorganic Chemistry. (Part I.
Non-metallic Elements.) 8ro, morocco, 75
Ricketts and Miller's Notes on Assaying 8vo, 3 o
Rideal's Sewage and the Bacterial Purification of Sewage 8vo, 3 5*
Disinfection and the Preservation of Food 8vo, 4 oo
Riggs's Elementary Manual for the Chemical Laboratory 8vo, I 25
Ruddiman's Incompatibilities in Prescriptions 8vo, a oo
Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 3 oo
Salkowski's Physiological and Pathological Chemistry. (Orndorff.) 8vo, 350
Schimpf's Text-book of Volumetric Analysis , xamo, a 30
Essentials of Volumetric Analysis iamo, x a
Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco, 3 OO
Handbook for Sugar Manufacturers and their Chemists. . i6mo, morocco, a oo
Stockbridge's Rocks and Soils 8vo, a 90
Tillman's Elementary Lessons in Heat SYO, x 50
Descriptive General Chemistry 8vo, 3 oo
Treadwell's Qualitative Analysis. (HalL) 8vo, 3 o
Quantitative Analysis. (Hall.) 8vo, 4 oo
Turneaure and Russell's Public Water-supplies 8ro, 5 oo
Van Deventer's Physical Chemistry for Beginners. (Boltwood.) lamo, x 50
Walke's Lectures on Explosives 8vo, 4 oo
Washington's Manual of the Chemical Analysis of Rocks. (In press.)
Wassennann's Immune Sera: Haemolysins, Cytotoxins, and Precipitins. (Bol-
duan.) xamo, x oo
Wells's Laboratory Guide in Qualitative Chemical Analysis 8vo, i 50
Short Course in Inorganic Qualitative Chemical Analysis for Engineering
Students lamo, i 50
Whipple's Microscopy of Drinking-water 8vo, 3 5*
Wiechmann's Sugar Analysis Small 8vo. a s
Wilson'* Cyanide Processes. iamo, i 5*
Chlorination Process iamo. x 50
Wulling's Elementary Course in Inorganic Pharmaceutical and Medical Chem-
istry iamo, a oo
BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF ENGINEERING
Baker's Engineers' Surveying Instruments iamo, 3 oo
Bixby's Graphical Computing Table Paper 19^X24} inches. as
** Burr's Ancient and Modern Engineering and the Isthmian Canal (Postage,
27 cents additional.) 8vo, net, 3 50
Comstock's Field Astronomy for Engineers 8vo, a 50
Davis's Elevation and Stadia Tables 8vo, x oo
Elliott's Engineering for Land Drainage xamo, x 50
Practical Farm Drainage xamo, x oo
Folwell's Sewerage. (Designing and Maintenance.) 8v, 3 oo
Freitag's Architectural Engineering, ad Edition Rewritten STO, j
French and Ives's Stereotomy 8vo, 2 50
Goodhue's Municipal Improvements lamo, x 7S
Goodrich's Economic Disposal of Towns' Refuse 8vo, 3 50
Gore's Elements of Geodesy . . .8vo, 2 so
Hayford's Text-book of Geodetic Astronomy 8vo, 3 oo
Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 2 50
Howe's Retaining Walls for Earth izmo, x 25
Johnson's Theory and Practice of Surveying Small 8vo, 4 oo
Statics by Algebraic and Graphic Methods 8vo, 2 oo
Kiersted's Sewage Disposal i2mo. 25
Laplace's Philosophical Essay on Probabilities. (Truscott and Emory.) i2mo, oo
Mahan's Treatise on Civil Engineering. (1873) (Wood.) 8vo, oo
* Descriptive Geometry 8vo, 5*
Merriman's Elements of Precise Surveying and Geodesy 8vo, 50
Elements of Sanitary Engineering 8vo, oo
Merriman and Brooks's Handbook for Surveyors i6mo, morocco, oo
Nugent's Plane Surveying . 8vo, 3 50
Ogden's Sewer Design ,. i2mo, 2 oo
Patton's Treatise on Civil Engineering 8vo half leather, 7 50
Reed's Topographical Drawing and Sketching 4to, 5 oo
Rideal's Sewage and the Bacterial Purification of Sewage 8vo, 3 50
Siebert and Biggin's Modern Stone-cutting and Masonry 8vo, x 50
Smith's Manual of Topographical Drawing. (McMillan.) 8vo, 2 50
Sondericker's Graphic Statics, wun Applications to Trusses, Beams, and
Arches 8vo, 2 oo
Taylor and Thompson's Treatise on Concrete, Plain and Reinforced. (In press.)
* Trantwine's Civil Engineer's Pocket-book i6mo, morocco, 5 oo
Wait's Engineering and Architectural Jurisprudence 8vo, 6 oo
Sheep, 6 50
Law of Operations Preliminary to Construction in Engineering and Archi-
tecture 8vo, 5 oo
Sheep, 5 50
Law of Contracts 8vo, 3 oo
Warren's Stereotomy Problems in Stone-cutting . 8vo, 2 50
Webb's Problems in the U?e and Adjustment of Engineering Instruments.
i6mo, morocco, x 25
* Wheeler's Elementary Course of Civil Engineering 8vo, 4 oo
Wilson's Topographic Surveying 8vo, 3 50
BRIDGES AND ROOFS.
Boiler's Practical Treatise on the Construction of Iron Highway Bridges. .8vo, 2 oo
* Thames River Bridge 4to, paper, 5 oo
Burr's Course on the Stresses in Bridges and Roof Trusses, Arched Ribs, and
Suspension Bridges 8vo, 3 50
Du Bois's Mechanics of Engineering. Vol. II Small 4to, 10 oo
Foster's Treatise on Wooden Trestle Bridges 4to, 5 oo
Fowler's Coffer-dam Process for Piers 8vo, 2 50
6wne's Roof Trusses. 8vo, x 25
Bridge Trusses 8vo, 2 50
Arches in Wood, Iron, and Stone 8vo, 2 50
Howe's Treatise on Arches 8vo, 4 oo
Design of Simple Roof -trusses in Wood and Steel 8vo, 2 oo
Johnson. Bryan, and Turneaure's Theory and Practice in the Designing of
Modern Framed Structures Small 4to, xo oo
Merriman and Jacoby's Text-book on Roofs and Bridges:
Parti. Stresses in Simple Trusses 8vo, 2 50
Part II. Graphic Statics 8vo, 2 50
Part III. Bridge Design. 4 th Edition, Rewritten.' ....[..... '. '. '. '. .8vo, 2 50
Part IV. Higher Structures 8vo, 2 50
Morison's Memphis Bridge , . . 4 to, 10 oo
Waddell's De Pontibus, a Pocket-book for Bridge Engineers. . . i6mo, morocco, 3 o
Specifications for Steel Bridges i2mo, i 25
Wood's Treatise on the Theory of the Construction of Bridges and Roofs.Svo, 2 oo
Wright's Designing of Draw-spans:
Part L Plate-girder Draws 8vo, a 50
Part II. Riveted-truss and Pin-connected Long-span Draws 8vo, 2 50
Two parts in one volume 8vo, 3 50
Bazin's Experiments upon the Contraction of the Liquid Vein Issuing from an
Orifice. (Trautwine.) 8vo, 2 oo
Bovey's Treatise on Hydraulics 8vo, 5 oo
Church's Mechanics of Engineering 8vo, 6 oo
Diagrams of Mean Velocity of Water in Open Channels paper, i 50
Coffin's Graphical Solution of Hydraulic Problems i6mo, morocco, a 50
Flather's Dynamometers, and the Measurement of Power iamo, 3 oo
Folwell's Water-supply Engineering 8vo, 4 oo
Prizell's Water-power 8vo, 5 oo
Puertes's Water and Public Health izmo, i 50
Water-filtration Works iamo, 2 50
Ganguillet and Kutter's General Formula for the Uniform Flow of Water in
Rivers and Other Channels. (Hering and Trautwine.) 8vo, 4 oo
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
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
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
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
Barr's Kinematics of Machinery 8vo, a 50
* Bartlett's Mechanical Drawing 8vo, 3 oo
* " AbridgedEd 8ro, x s
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
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
* 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
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
Thurston's Manual of Steam-boilers, their Designs, Construction and Opera-
tion Svo, 5 oo
* 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
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
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-
Clerk's Gas and Oil Engine Small 8vo, 4 oo
Coolidge's Manual of Drawing 8vo, paper, x oo
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
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.
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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
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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
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
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
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
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,
Hydraulic and Placer Mining xamo, a oo
Treatise on Practical and Theoretical Mine Ventilation xamo I as
>* 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,
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
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.
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Letteris's Hebrew Bible 8vo , a 3
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