[Transcriber's notes: In the chemical equations, superscripts are
indicated with a ^ and subscripts are indicated with a _. The affected
item is enclosed in curly brackets {}. Examples are H^{+} for hydrogen
ion and H_{2}O for water. Since the underscore is already being used
in this project, italics are designated by an exclamation point
before and after the italicized word or phrase.]
AN INTRODUCTORY COURSE
OF
QUANTITATIVE
CHEMICAL ANALYSIS
WITH
EXPLANATORY NOTES
BY
HENRY P. TALBOT
PROFESSOR OF INORGANIC CHEMISTRY AT THE MASSACHUSETTS INSTITUTE OF
TECHNOLOGY
SIXTH EDITION, COMPLETELY REWRITTEN
PREFACE
This Introductory Course of Quantitative Analysis has been prepared
to meet the needs of students who are just entering upon the subject,
after a course of qualitative analysis. It is primarily intended to
enable the student to work successfully and intelligently without the
necessity for a larger measure of personal assistance and supervision
than can reasonably be given to each member of a large class. To this
end the directions are given in such detail that there is very little
opportunity for the student to go astray; but the manual is not, the
author believes, on this account less adapted for use with small
classes, where the instructor, by greater personal influence, can
stimulate independent thought on the part of the pupil.
The method of presentation of the subject is that suggested by
Professor A.A. Noyes' excellent manual of Qualitative Analysis. For
each analysis the procedure is given in considerable detail, and
this is accompanied by explanatory notes, which are believed to be
sufficiently expanded to enable the student to understand fully the
underlying reason for each step prescribed. The use of the book
should, nevertheless, be supplemented by classroom instruction, mainly
of the character of recitations, and the student should be taught to
consult larger works. The general directions are intended to emphasize
those matters upon which the beginner in quantitative analysis must
bestow special care, and to offer helpful suggestions. The student
can hardly be expected to appreciate the force of all the statements
contained in these directions, or, indeed, to retain them all in
the memory after a single reading; but the instructor, by frequent
reference to special paragraphs, as suitable occasion presents itself,
can soon render them familiar to the student.
The analyses selected for practice are those comprised in the first
course of quantitative analysis at the Massachusetts Institute of
Technology, and have been chosen, after an experience of years,
as affording the best preparation for more advanced work, and as
satisfactory types of gravimetric and volumetric methods. From the
latter point of view, they also seem to furnish the best insight into
quantitative analysis for those students who can devote but a limited
time to the subject, and who may never extend their study beyond the
field covered by this manual. The author has had opportunity to test
the efficiency of the course for use with such students, and has found
the results satisfactory.
In place of the usual custom of selecting simple salts as material for
preliminary practice, it has been found advantageous to substitute, in
most instances, approximately pure samples of appropriate minerals or
industrial products. The difficulties are not greatly enhanced, while
the student gains in practical experience.
The analytical procedures described in the following pages have been
selected chiefly with reference to their usefulness in teaching the
subject, and with the purpose of affording as wide a variety of
processes as is practicable within an introductory course of this
character. The scope of the manual precludes any extended attempt to
indicate alternative procedures, except through general references to
larger works on analytical chemistry. The author is indebted to the
standard works for many suggestions for which it is impracticable to
make specific acknowledgment; no considerable credit is claimed by him
for originality of procedure.
For many years, as a matter of convenience, the classes for which this
text was originally prepared were divided, one part beginning with
gravimetric processes and the other with volumetric analyses. After a
careful review of the experience thus gained the conclusion has been
reached that volumetric analysis offers the better approach to the
subject. Accordingly the arrangement of the present (the sixth)
edition of this manual has been changed to introduce volumetric
procedures first. Teachers who are familiar with earlier editions
will, however, find that the order of presentation of the material
under the various divisions is nearly the same as that previously
followed, and those who may still prefer to begin the course of
instruction with gravimetric processes will, it is believed, be able
to follow that order without difficulty.
Procedures for the determination of sulphur in insoluble sulphates,
for the determination of copper in copper ores by iodometric methods,
for the determination of iron by permanganate in hydrochloric acid
solutions, and for the standardization of potassium permanganate
solutions using sodium oxalate as a standard, and of thiosulphate
solutions using copper as a standard, have been added. The
determination of silica in silicates decomposable by acids, as a
separate procedure, has been omitted.
The explanatory notes have been rearranged to bring them into closer
association with the procedures to which they relate. The number of
problems has been considerably increased.
The author wishes to renew his expressions of appreciation of the
kindly reception accorded the earlier editions of this manual. He has
received helpful suggestions from so many of his colleagues within the
Institute, and friends elsewhere, that his sense of obligation must
be expressed to them collectively. He is under special obligations
to Professor L.F. Hamilton for assistance in the preparation of the
present edition.
HENRY P. TALBOT
!Massachusetts Institute of Technology, September, 1921!.
CONTENTS
PART I. INTRODUCTION
SUBDIVISIONS OF ANALYTICAL CHEMISTRY
GENERAL DIRECTIONS
Accuracy and Economy of Time; Notebooks; Reagents; Wash-bottles;
Transfer of Liquids
PART II. VOLUMETRIC ANALYSIS
GENERAL DISCUSSION
Subdivisions; The Analytical Balance; Weights; Burettes;
Calibration of Measuring Devices
GENERAL DIRECTIONS
Standard and Normal Solutions
!I. Neutralization Methods!
ALKALIMETRY AND ACIDIMETRY
Preparation and Standardization of Solutions; Indicators
STANDARDIZATION OF HYDROCHLORIC ACID
DETERMINATION OF TOTAL ALKALINE STRENGTH OF SODA ASH
DETERMINATION OF ACID STRENGTH OF OXALIC ACID
!II. Oxidation Processes!
GENERAL DISCUSSION
BICHROMATE PROCESS FOR THE DETERMINATION OF IRON
DETERMINATION OF IRON IN LIMONITE BY THE BICHROMATE PROCESS
DETERMINATION OF CHROMIUM IN CHROME IRON ORE
PERMANGANATE PROCESS FOR THE DETERMINATION OF IRON
DETERMINATION OF IRON IN LIMONITE BY THE PERMANGANATE PROCESS
DETERMINATION OF IRON IN LIMONITE BY THE ZIMMERMANN-REINHARDT PROCESS
DETERMINATION OF THE OXIDIZING POWER OF PYROLUSITE
IODIMETRY
DETERMINATION OF COPPER IN ORES
DETERMINATION OF ANTIMONY IN STIBNITE
CHLORIMETRY
DETERMINATION OF AVAILABLE CHLORINE IN BLEACHING POWDER
!III. Precipitation Methods!
DETERMINATION OF SILVER BY THE THIOCYANATE PROCESS
PART III. GRAVIMETRIC ANALYSIS
GENERAL DIRECTIONS
Precipitation; Funnels and Filters; Filtration and Washing of
Precipitates; Desiccators; Crucibles and their Preparation
for Use; Ignition of Precipitates
DETERMINATION OF CHLORINE IN SODIUM CHLORIDE
DETERMINATION OF IRON AND OF SULPHUR IN FERROUS AMMONIUM SULPHATE
DETERMINATION OF SULPHUR IN BARIUM SULPHATE
DETERMINATION OF PHOSPHORIC ANHYDRIDE IN APATITE
ANALYSIS OF LIMESTONE
Determination of Moisture; Insoluble Matter and Silica; Ferric
Oxide and Alumina; Calcium; Magnesium; Carbon Dioxide
ANALYSIS OF BRASS
Electrolytic Separations; Determination of Lead, Copper, Iron
and Zinc.
DETERMINATION OF SILICA IN SILICATES
PART IV. STOICHIOMETRY
SOLUTIONS OF TYPICAL PROBLEMS
PROBLEMS
APPENDIX
ELECTROLYTIC DISSOCIATION THEORY
FOLDING OF A FILTER PAPER
SAMPLE NOTEBOOK PAGES
STRENGTH OF REAGENTS
DENSITIES AND VOLUMES OF WATER
CORRECTIONS FOR CHANGE OF TEMPERATURE OF STANDARD SOLUTIONS
ATOMIC WEIGHTS
LOGARITHM TABLES
QUANTITATIVE CHEMICAL ANALYSIS
PART I
INTRODUCTION
SUBDIVISIONS OF ANALYTICAL CHEMISTRY
A complete chemical analysis of a body of unknown composition involves
the recognition of its component parts by the methods of !qualitative
analysis!, and the determination of the proportions in which these
components are present by the processes of !quantitative analysis!.
A preliminary qualitative examination is generally indispensable, if
intelligent and proper provisions are to be made for the separation of
the various constituents under such conditions as will insure accurate
quantitative estimations.
It is assumed that the operations of qualitative analysis are familiar
to the student, who will find that the reactions made use of in
quantitative processes are frequently the same as those employed in
qualitative analyses with respect to both precipitation and systematic
separation from interfering substances; but it should be noted that
the conditions must now be regulated with greater care, and in such
a manner as to insure the most complete separation possible. For
example, in the qualitative detection of sulphates by precipitation
as barium sulphate from acid solution it is not necessary, in most
instances, to take into account the solubility of the sulphate
in hydrochloric acid, while in the quantitative determination of
sulphates by this reaction this solubility becomes an important
consideration. The operations of qualitative analysis are, therefore,
the more accurate the nearer they are made to conform to quantitative
conditions.
The methods of quantitative analysis are subdivided, according
to their nature, into those of !gravimetric analysis, volumetric
analysis!, and !colorimetric analysis!. In !gravimetric! processes the
constituent to be determined is sometimes isolated in elementary
form, but more commonly in the form of some compound possessing a
well-established and definite composition, which can be readily and
completely separated, and weighed either directly or after ignition.
From the weight of this substance and its known composition, the
amount of the constituent in question is determined.
In !volumetric! analysis, instead of the final weighing of a definite
body, a well-defined reaction is caused to take place, wherein the
reagent is added from an apparatus so designed that the volume of the
solution employed to complete the reaction can be accurately measured.
The strength of this solution (and hence its value for the reaction
in question) is accurately known, and the volume employed serves,
therefore, as a measure of the substance acted upon. An example will
make clear the distinction between these two types of analysis.
The percentage of chlorine in a sample of sodium chloride may be
determined by dissolving a weighed amount of the chloride in water
and precipitating the chloride ions as silver chloride, which is
then separated by filtration, ignited, and weighed (a !gravimetric!
process); or the sodium chloride may be dissolved in water, and a
solution of silver nitrate containing an accurately known amount of
the silver salt in each cubic centimeter may be cautiously added from
a measuring device called a burette until precipitation is complete,
when the amount of chlorine may be calculated from the number of cubic
centimeters of the silver nitrate solution involved in the reaction.
This is a !volumetric! process, and is equivalent to weighing without
the use of a balance.
Volumetric methods are generally more rapid, require less apparatus,
and are frequently capable of greater accuracy than gravimetric
methods. They are particularly useful when many determinations of the
same sort are required.
In !colorimetric! analyses the substance to be determined is converted
into some compound which imparts to its solutions a distinct color,
the intensity of which must vary in direct proportion to the amount of
the compound in the solution. Such solutions are compared with respect
to depth of color with standard solutions containing known amounts of
the colored compound, or of other similar color-producing substance
which has been found acceptable as a color standard. Colorimetric
methods are, in general, restricted to the determinations of very
small quantities, since only in dilute solutions are accurate
comparisons of color possible.
GENERAL DIRECTIONS
The following paragraphs should be read carefully and thoughtfully. A
prime essential for success as an analyst is attention to details and
the avoidance of all conditions which could destroy, or even lessen,
confidence in the analyses when completed. The suggestions here given
are the outcome of much experience, and their adoption will tend to
insure permanently work of a high grade, while neglect of them will
often lead to disappointment and loss of time.
ACCURACY AND ECONOMY OF TIME
The fundamental conception of quantitative analysis implies a
necessity for all possible care in guarding against loss of material
or the introduction of foreign matter. The laboratory desk, and all
apparatus, should be scrupulously neat and clean at all times. A
sponge should always be ready at hand, and desk and filter-stands
should be kept dry and in good order. Funnels should never be allowed
to drip upon the base of the stand. Glassware should always be
wiped with a clean, lintless towel just before use. All filters and
solutions should be covered to protect them from dust, just as far as
is practicable, and every drop of solution or particle of precipitate
must be regarded as invaluable for the success of the analysis.
An economical use of laboratory hours is best secured by acquiring
a thorough knowledge of the character of the work to be done before
undertaking it, and then by so arranging the work that no time shall
be wasted during the evaporation of liquids and like time-consuming
operations. To this end the student should read thoughtfully not only
the !entire! procedure, but the explanatory notes as well, before
any step is taken in the analysis. The explanatory notes furnish, in
general, the reasons for particular steps or precautions, but they
also occasionally contain details of manipulation not incorporated,
for various reasons, in the procedure. These notes follow the
procedures at frequent intervals, and the exact points to which they
apply are indicated by references. The student should realize that a
!failure to study the notes will inevitably lead to mistakes, loss of
time, and an inadequate understanding of the subject!.
All analyses should be made in duplicate, and in general a close
agreement of results should be expected. It should, however, be
remembered that a close concordance of results in "check analyses" is
not conclusive evidence of the accuracy of those results, although the
probability of their accuracy is, of course, considerably enhanced.
The satisfaction in obtaining "check results" in such analyses must
never be allowed to interfere with the critical examination of the
procedure employed, nor must they ever be regarded as in any measure a
substitute for absolute truth and accuracy.
In this connection it must also be emphasized that only the operator
himself can know the whole history of an analysis, and only he can
know whether his work is worthy of full confidence. No work should be
continued for a moment after such confidence is lost, but should
be resolutely discarded as soon as a cause for distrust is fully
established. The student should, however, determine to put forth his
best efforts in each analysis; it is well not to be too ready to
condone failures and to "begin again," as much time is lost in these
fruitless attempts. Nothing less than !absolute integrity! is or can
be demanded of a quantitative analyst, and any disregard of this
principle, however slight, is as fatal to success as lack of chemical
knowledge or inaptitude in manipulation can possibly be.
NOTEBOOKS
Notebooks should contain, beside the record of observations,
descriptive notes. All records of weights should be placed upon the
right-hand page, while that on the left is reserved for the notes,
calculations of factors, or the amount of reagents required.
The neat and systematic arrangement of the records of analyses is
of the first importance, and is an evidence of careful work and an
excellent credential. Of two notebooks in which the results may be,
in fact, of equal value as legal evidence, that one which is neatly
arranged will carry with it greater weight.
All records should be dated, and all observations should be recorded
at once in the notebook. The making of records upon loose paper is a
practice to be deprecated, as is also that of copying original entries
into a second notebook. The student should accustom himself to orderly
entries at the time of observation. Several sample pages of systematic
records are to be found in the Appendix. These are based upon
experience; but other arrangements, if clear and orderly, may prove
equally serviceable. The student is advised to follow the sample pages
until he is in a position to plan out a system of his own.
REAGENTS
The habit of carefully testing reagents, including distilled water,
cannot be too early acquired or too constantly practiced; for, in
spite of all reasonable precautionary measures, inferior chemicals
will occasionally find their way into the stock room, or errors will
be made in filling reagent bottles. The student should remember that
while there may be others who share the responsibility for the purity
of materials in the laboratory of an institution, the responsibility
will later be one which he must individually assume.
The stoppers of reagent bottles should never be laid upon the desk,
unless upon a clean watch-glass or paper. The neck and mouth of all
such bottles should be kept scrupulously clean, and care taken that no
confusion of stoppers occurs.
WASH-BOTTLES
Wash-bottles for distilled water should be made from flasks of about
750 cc. capacity and be provided with gracefully bent tubes, which
should not be too long. The jet should be connected with the tube
entering the wash-bottle by a short piece of rubber tubing in such
a way as to be flexible, and should deliver a stream about one
millimeter in diameter. The neck of the flask may be wound with cord,
or covered with wash-leather, for greater comfort when hot water is
used. It is well to provide several small wash-bottles for liquids
other than distilled water, which should invariably be clearly
labeled.
TRANSFER OF LIQUIDS
Liquids should never be transferred from one vessel to another, nor to
a filter, without the aid of a stirring rod held firmly against the
side or lip of the vessel. When the vessel is provided with a lip it
is not usually necessary to use other means to prevent the loss of
liquid by running down the side; whenever loss seems imminent a !very
thin! layer of vaseline, applied with the finger to the edge of the
vessel, will prevent it. The stirring rod down which the liquid runs
should never be drawn upward in such a way as to allow the solution to
collect on the under side of the rim or lip of a vessel.
The number of transfers of liquids from one vessel to another during
an analysis should be as small as possible to avoid the risk of slight
losses. Each vessel must, of course, be completely washed to insure
the transfer of all material; but it should be remembered that this
can be accomplished better by the use of successive small portions of
wash-water (perhaps 5-10 cc.), if each wash-water is allowed to drain
away for a few seconds, than by the addition of large amounts which
unnecessarily increase the volume of the solutions, causing loss of
time in subsequent filtrations or evaporations.
All stirring rods employed in quantitative analyses should be rounded
at the ends by holding them in the flame of a burner until they begin
to soften. If this is not done, the rods will scratch the inner
surface of beakers, causing them to crack on subsequent heating.
EVAPORATION OF LIQUIDS
The greatest care must be taken to prevent loss of solutions during
processes of evaporation, either from too violent ebullition, from
evaporation to dryness and spattering, or from the evolution of gas
during the heating. In general, evaporation upon the steam bath is to
be preferred to other methods on account of the impossibility of
loss by spattering. If the steam baths are well protected from dust,
solutions should be left without covers during evaporation; but
solutions which are boiled upon the hot plate, or from which gases are
escaping, should invariably be covered. In any case a watch-glass may
be supported above the vessel by means of a glass triangle, or other
similar device, and the danger of loss of material or contamination by
dust thus be avoided. It is obvious that evaporation is promoted by
the use of vessels which admit of the exposure of a broad surface to
the air.
Liquids which contain suspended matter (precipitates) should always
be cautiously heated, since the presence of the solid matter is
frequently the occasion of violent "bumping," with consequent risk to
apparatus and analysis.