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A treatise on chemistry and chemical analysis : prepared for students of The International Correspondence Schools, Scranton, Pa (Volume 3) online

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Volume III



First Edition





Qualitative Analysis : Copyright, 1898, 1899, by THE COLLIERY ENGINEER COMPANY.

Press of EATON & MAINS




Definitions and Descriptions 10 1

Apparatus 10 4

Preparation of Reagents 10 8

Deportment of Metals with Reagents . . 10 11

Analysis of Mixed Solutions 10 51

Reactions of the Common Inorganic Acids 10 77

Reactions of the Common Organic Acids . 10 89

Reactions of the Rarer Inorganic Acids . 10 93

Reactions of the Rarer Organic Acids . . 10 104
Systematic Examination of Solutions for

Acids 10 110

Special Tests for Acids 10 115

Examination of Dry Substances ... 11 1

Examination in the Closed Tube ... 11 2

Examination on the Charcoal .... 11 9

Examination in the Flame 11 16

Examination in the Bead .11 17

Examination on the Platinum Foil ... 11 19

Examination with Sulphuric Acid ... 11 20

Solution of Solid Substances ..... 11 25

Reactions of the Rare Elements ... 11 28

The Spectroscope 11 55

Analysis of Water 11 58

Examination of Urine 11 72

Common Inorganic Poisons 11 '84

Detection of Arsenic 11 84




QUALITATIVE ANALYSIS Continued. Section. Page.

Detection of Phosphorus 11 91

Detection of Hydrocyanic Acid .... 11 96

Reactions of the Volatile Alkaloids . . 11 99

Reactions of the Non-Volatile Alkaloids . 11 103


Qualitative Analysis, Parts 1 and 2 . . 10 and 11


(PART 1.)



1. Analysis. Analysis in its most general sense is tae
process of resolving more or less complex substances into
simpler ones. It is, therefore, the reverse of synthesis,
which consists in building up complex compounds from
simpler ones. Analysis consists in breaking these com-
pounds up into their component parts.

It is divided into qualitative and quantitative analysis.

Qualitative analysis is that branch of chemical science
which considers the methods of determining the elements
that compose a compound or mixture of compounds, with-
out reference to the quantities of these elements which the
substance contains.

Quantitative analysis takes up the subject where quali-
tative analysis leaves it, and determines the exact amount of
each element in a substance.

2. Methods of Qualitative Analysis. There are two
methods of qualitative analysis, known as the wet method
and the dry method. The wet method, as its name implies,
deals with solutions, while the dry method deals with solids.
In most cases, separate quantities of these solids may be put
into solution, by methods to be described later, and to these
portions the wet method may also be applied.



Each method has its advantages. The dry method is short
and simple in many instances, requires but little apparatus,
and, in case of some of the simpler substances, quickly
yields a result. Its use is almost indispensable in some cases,
but in many instances it only gives indications, which must
be confirmed by the wet method.

The wet method has the advantage that it is almost uni-
versally applicable, and its results are absolutely certain if
the work of obtaining them is properly done.

It is best to treat these two methods separately, so far as
possible, in describing them and in the early part of the
work, but after the student becomes familiar with them he
will find it a great advantage to combine the two.

3.. Abbreviations Used. In analytical work, certain
voi'Js occur so frequently that it is an advantage to use
abbreviations for them. The following is a list of the most
common ones used in this Course :

Ppt. precipitate. Cone. concentrate.

Pptd. precipitated. Dil. dilute.

Sol. soluble. O. F. oxidizing flame.

Insol. insoluble. R. F. reducing flame.

Sp. Gr. specific gravity.

4. Reaction and Reagent. A reaction is a chemical
change, and the substance that produces this change is
called a reagent.

ILLUSTRATION. If a small quantity of silver nitrate solution be placed
in a test tube and a few drops of hydrochloric acid added, a white pre-
cipitate of silver chloride is formed according to the equation

AgNO-, + HCl = AgCl + HNO*

This change is called a reaction, and the hydrochloric acid, which pro-
duced the change, is a reagent.

The attention of the student is called to the fact that when
a reagent is added to a metallic solution, the metallic com-
pound formed is similar in composition to the reagent.
Thus, if the reagent is a hydrate, a hydrate of the metal
will be produced ; a carbonate will form a carbonate of the
metal ; a sulphide produces a sulphide of the metal, etc. All


exceptions to this rule are given under * ' Deportment of the
Metals with Reagents."

5. The Wet Method. In wet analysis we determine
the constituents of a solution of a substance by the reactions
produced by certain common reagents. If there is but one
metal in the solution, this becomes a very simple matter.

About half an inch of the solution to be tested is placed
in a test tube and a small amount of the reagent is carefully
added, drop by drop, while the place where the two liquids
meet is closely watched. If no precipitate is formed, the
test tube is emptied, washed well with common water, and
rinsed out with distilled water. We are then ready to use a
fresh portion of the solution and test in the same way with
another reagent. A dirty test tube must never be used.
Neatness is essential in all successful analytical work.

If we obtain a precipitate, the first thing to be noted is its
color and general appearance. Its solubility may also help
to establish its identity. If we wish to test its solubility in
an excess of the reagent used to precipitate it, we pour out
all but a small portion, and to this add more of the reagent.
To test for its solubility in any other reagent, allow the
precipitate to settle to the bottom of the tube as much as
possible, pour off the supernatant liquid, retaining but a
small quantity of the precipitate in the tube ; to this add
the desired reagent, shake it up, and observe the result.

By observing the reactions of a few common reagents and
referring to the section on " Deportment of the Metals with
Reagents," we can readily tell just what metal we have.

ILLUSTRATION. If we add a few drops of hydrogen sulphide to a
small quantity of a solution in a test tube and get a black precipitate,
we know the metal is either silver, lead, mercurous, mercuric, or
copper, for these are the only metals giving black precipitates with
hydrogen sulphide. If to a fresh portion of the solution we add
sodium hydrate and get a brown precipitate, we know the metal is
silver, for that is the only one, of the five metals mentioned, that gives
a brown precipitate with sodium hydrate.

When a result is obtained in this way it should always be
confirmed by the other reactions given for the metal.


6. It will be noted that some of the metals form two
series of compounds which differ widely from each other.
Thus, mercury forms mercurous and mercuric compounds,
which, in analytical chemistry, are treated as though they
were salts of different metals.


7. The only apparatus needed for the wet reactions,
when there is but one metal in the solution, will be some
test tubes, a set of reagents in properly labeled bottles, and
a good burner. A Bunsen burner is preferable for this pur-
pose, but where gas is not available, an alcohol lamp may
be made to serve in its stead.

It is desirable that the student should become familiar
with a few dry reactions in connection with the wet ones,
and for this purpose he will need a blowpipe, a small piece
of charcoal, a piece of platinum wire, a piece of platinum
foil, a pair of forceps, a piece of blue glass, and, as the work
proceeds, closed tubes, or matrasses, will be required.

8. The Burner. A Bunsen burner, shown in Fig. 1, is
made with a perforated metal cylinder g near the base,
for regulating the air supply. In cases where the blowpipe

is not used, a full supply of air is admitted,
giving a non-luminous flame.

This consists of three parts: (1) An inner
zone of unburned gas mixed with air, as seen
at afc\ (2) the outer mantle of burning gas
mixed with an excess of air, shown at a b c .;'
and (3) the luminous cone dfe.

The different parts of this flame have two
opposite effects. In the inner flame, the
unburned gas, rich in carbon and hydrogen,
tends to reduce the substance, while the outer
FIG. i. flame, by heating the substance in the pres-
ence of the oxygen of the air, tends to oxidize it.

A substance to be reduced should be held in the luminous
cone dfe, as reduction is most rapidly accomplished here.



A substance to be oxidized should be held just within the
flame at b, as this is the point of most rapid oxidation.
These points are meant when the reducing and oxidizing
flames are mentioned.

If a substance is merely to be heated, it is held in the
flame near the top, as this is the position of greatest heat.
Some substances are volatilized and give a characteristic color
to the flame, by which they may be recognized. For this
purpose the substance is held in the lower part of the outer
mantle a b c.

9. The Blowpipe. By means of the blowpipe we obtain
an intensely heated flame, which may be directed where we
wish. There are several forms of blowpipe, the simplest
being a small curved brass tube, termina-
ting in an orifice about the size of a small
needle. With this instrument, after blow-
ing a while, the moisture which accumulates
is blown into the flame. Several forms of
blowpipe have been devised to avoid this.
A good form is shown in Fig. 2. It con-
sists of five parts. The mouthpiece A is
usually made of hard rubber, and is pressed
against the lips when in use. It fits into
the tube B, which in turn is fitted into the
moisture reservoir C. The tip holder D fits
into the side of the moisture reservoir, and
the tip E fits on to this.

In using the blowpipe it is often neces-
sary to blow a steady stream of air through
it for several minutes, and the student
should practice until he can do this before
attempting any of the following operations.
To accomplish this, the mouthpiece is
pressed against the lips, and the cheeks
inflated. Then, by means of the muscles
of the cheeks, a steady stream of air is forced through the
blowpipe, while we breathe through the nostrils. The air



should never be forced from the lungs, as by this means we
cannot keep up a steady stream. This operation may seem
difficult at first, but by practice it will soon become easy.

In blowpipe work a rather small, luminous flame, obtained
by turning- the metal cylinder so as to reduce the supply of
air, is used, and from this we can obtain either an oxidizing
or reducing flame, according to the method of using the
blowpipe. By placing the tip of the blowpipe just outside


FIG. 3.

FIG. 4.

of the flame and blowing, we get a long, slightly luminous
flame. A substance held at a, Fig. 3, is rapidly reduced by
the unburned gas.

To get an oxidizing flame, the tip of the blowpipe should be
placed just inside of the flame. Then, by blowing through
it, a long, blue flame is obtained which will rapidly oxidize
a substance held at the point B, Fig. 4, where it is
intensely heated in the presence of an excess of air.

1C. Charcoal. In blowpiping, a small piece of
fine-grained charcoal, made from soft wood, is largely
used as a support. Common charcoal is very unsatis-
factory, but the small blocks, for sale by all chemical
dealers, are very good for this purpose. A small cavity
is made in the charcoal, to hold the substance, and,
after using, it must be well scraped out before the next

11. Platinum Wire. A short piece of fine plati-
num wire is essential in working by the dry method.
It is well to heat one end of a small glass tube in the
flame until it softens and begins to close ; then, without



withdrawing it from the flame, insert one end of the wire
and allow the glass to close over it, thus forming a handle
which does not readily transmit heat. The result is shown in
Fig. 5. The other end of the wire should be bent into a
loop about y 1 ^ inch in diameter.

This loop will serve to hold solid substances in the flame,
to hold a drop of solution in the flame in order to observe if
any color is thus imparted to it, and to hold the borax, or
microcosmic bead, to be described later.

When not in use, it is a good plan to place the wire in
dilute hydrochloric acid. Then, after burning it
off, it is nearly always clean and ready for use.
A good method of keeping the wire clean is to
insert the glass handle in the perforation of a cork
that is too large to go into a test tube, and by this
means suspend the wire in a test tube containing
hydrochloric acid, as shown in Fig. 6.

12. A small piece of platinum foil, which may
be bent into the form of a spoon, and a pair of
forceps with which to hold the foil, need
no description. It is only necessary to say
that platinum must never be heated in con-
tact with the heavy metals, such as lead,
mercury, etc., or their salts, for these will
alloy with the platinum and ruin it.

FIG. e.

13. Blue Glass. A small piece of blue glass,
which the operator may hold before his eye to look
through at the colored flames produced by some of
the metals, is indispensable when determining the

14. Matrasses. Closed tubes, or matrasses, are
much used in analyzing solids, and may as well be
described here. They are made in several forms. A
good form may be made by cutting a piece of glass
tubing, having an inside diameter of about -f^ of an inch,

FIG. ?.


into pieces about 3J inches long, and holding one end of each
piece in the flame till it softens and closes. The result is
shown in Fig. 7.

Solids may be dropped into this tube and heated at the
closed end, by holding it in the flame. To protect the fin-
gers from the heat, the tube may be held in the forceps, or
a piece of paper may be folded and wrapped around it near
the top, thus serving as a holder.


15. Preparation of Solutions. In the outfit that
we furnish to students, all reagents except nitric, hydro-
chloric, and sulphuric acids, and ammonium hydrate or
ammonia, as it is commonly called are of the proper
strength for use. Those mentioned are needed in two
strengths, concentrate and dilute. The student is furnished
with the concentrate solutions, and from these he can make
the dilute solutions by adding a small portion of each to four
times its volume of water, and mixing them well. The sul-
phuric acid must be added to the water slowly while the
solution is constantly stirred, on account of the heat gener-
ated. In this, as in every case where water is mentioned,
distilled water should be used. When a reagent is mentioned,
the dilute solution is always meant unless the concentrate
solution is specified.

For the benefit of students that do not obtain our outfit,
the following directions are given for making up reagents:

Chemically pure substances should be used in every case.

Ammonium Carbonate. Dissolve 100 grams of the solid
in 300 cubic centimeters of water and 100 cubic centimeters
of concentrate ammonium hydrate, and dilute to 500 cubic
centimeters with water.

Ammonium Chloride. Dissolve 100 grams of the .dry
salt in a sufficient amount of water say 400 cubic centi-
meters and then add water to make 500 cubic centimeters
of solution.

Ammonium Oxalate. Add to 25 grams of the salt,


sufficient water to make 500 cubic centimeters of solution.
Allow it to stand until it dissolves, shaking it occasionally.

Sodium. Hydrate. Dissolve 40 grams of the solid in
water, and dilute this solution to 500 cubic centimeters with

Sodium Carbonate. Dissolve 100 grams of the dry salt,
or 270 grams of the crystals, in sufficient water to make
500 cubic centimeters of solution.

Sodium Phosphate. Dissolve 50 grams of acid sodium
phosphate NaJlPO^VkHjO in sufficient water to make
500 cubic centimeters of solution.

Potassium Chromate. Dissolve 50 grams in water and
add water to this solution to make it up to 500 cubic centi-

Potassium Ferricyanide. To 50 grams of the solid, add
water enough to make 500 cubic centimeters of solution.

Potassium Ferrocyanide and Potassium Cyanide.
These are made of the same strength and in the same man-
ner as potassium ferricyanide.

Potassium Iodide. Dissolve 20 grams of the crystal-
lized salt in 500 cubic centimeters of water.

Barium Chloride. Dissolve 25 grams of the solid in 500
cubic centimeters of water.

Silver Kitrate. Dissolve 20 grams of the crystals in 500
cubic centimeters of water.

;Lead Acetate. Dissolve 50 grams of the dry salt in
water to which 1 cubic centimeter of acetic acid has been
added, using water enough to make 500 cubic centimeters of
the solution.

Mercuric Chloride. Dissolve 25 grams of the crystals
in 500 cubic centimeters of water.

Staimous Chloride. Dissolve 25 grams of the solid
stannous chloride in 75 cubic centimeters of concentrate
hydrochloric acid, and enough water to make 500 cubic
centimeters of solution. Some metallic tin should be kept
in the solution, which should be kept in a tightly stoppered

Ferrous Sulphate. To 75 grams of the crystals, add


water enough to make 500 cubic centimeters of solution.
To this add about 1 cubic centimeter of concentrate sul-
phuric acid and a little metallic iron, and keep the solution
from the air.

Cobalt Kitrate. Dissolve 50 grams of the crystallized
salt in water, and dilute the solution to 500 cubic centimeters
with water.

Tartaric Acid. Dissolve 100 grams of the solid tartaric
acid in water sufficient to make 500 cubic centimeters of

Acetic Acid. Dilute the 33-per-cent. acid with twice its
volume of water to make the dilute acid.

Hydrogen Sulphide. Generate the gas as described in
Experiment 50, Art. 1O5, Inorganic Chemistry, PartJ, and
lead it into water until the water is saturated, when it is
ready for use. The solution should be protected from the

Ammonium Sulphide. Lead hydrogen-sulphide gas
into a bottle two-thirds full of concentrate ammonium
hydrate, until it is saturated, which is indicated by the bub-
bles coming through the liquid undiminished in size. Fill
the bottle with concentrate ammonia and mix it well.
Before using, dilute this with twice its volume of water.

Yellow Ammonium Sulphide. This is made by adding
a small quantity of flowers of sulphur to the common ammo-
nium sulphide and shaking until dissolved. Enough sulphur
should be added to give the solution an amber color.

Ammonium Sulphate. Dissolve 50 grams of the solid
ammonium sulphate in sufficient water to make 500 cubic
centimeters of solution. Its principal use is in separating
strontium and calcium.

Magnesium Sulphate. Dissolve 50 grams of the crys-
tallized salt in water enough to make 500 cubic centimeters
of the solution.

Calcium Sulphate. A saturated solution is always used.
It is prepared by repeatedly shaking up some finely pow-
dered calcium sulphate in a bottle of water, taking care to
have more of the sulphate than the water will dissolve.


Allow it to stand for some time and decant the clear liquid
for use.

Barium Hydrate. To 25 grams of pure barium-hydrate
crystals, add sufficient water to make 500 cubic centimeters
of solution, and dissolve by the aid of heat. Filter into a
bottle provided with a good stopper, and close the bottle at
once to protect the solution from the air. The filtration is
performed as directed in Art. 99, Theoretical Chemistry.

Acid Sodium Tartrate. A saturated solution is used.
It is prepared by placing in a bottle, about three-fourths
filled with water, a little more of the solid salt than will be
dissolved, and shaking repeatedly. Allow it to settle, and
decant the clear solution as it is needed.

Ainmonium Molybdate. This may be made by dissolv-
ing 25 grams of powdered ammonium molybdate in 75 cubic
centimeters of concentrate ammonia, by the aid of heat.
Pour this solution slowly, and with constant stirring, into a
mixture of 300 cubic centimeters of concentrate nitric acid
and 200 cubic centimeters of water. This solution should
be allowed to stand for at least 24 hours before using.

The directions in most cases are given for making- 500 cubic
centimeters, merely because that is a convenient quantity.
More or less of any reagent may just as well be made, pro-
vided the proportions are not altered.



16. We now come to the deportment, or behavior, of the
metals with reagents. The student should not attempt to
commit all these reactions to memory, but should make him-
self so familiar with them that he can readily distinguish any
of the metals by their reactions. For this purpose only a


few reactions will generally be necessary, but the results thus
obtained should always be confirmed by all the others given.

So far as possible, it is desirable to perform cacJi of the fol-
lowing operations, using known solutions before attempting
to analyze unknown ones.

The student will soon learn to form groups of the metals
that are precipitated by the different reagents; as, for
instance, he will learn that only three metals, silver, lead,
and mercury, in the mercurous form, are precipitated by
hydrochloric acid; five by sulphuric acid, etc. In this he
will be assisted by the table at the end of this section.

Each student should keep, in a note book, a complete
record of all work done. It is especially important that any-
thing that is not understood at the time should be recorded
in this book.


17. Silver is a white metal that fuses on the charcoal
before the blowpipe, forming a bright, metallic globule. It
does not volatilize, and no incrustation* is formed. To per-
form this and similar operations, a piece of the metal, about
twice as large as the head of a pin, is placed in a small cavity
in the charcoal, made to hold it, and the blowpipe flame is
directed upon it. In all blowpipe work, only small quanti-
ties of the substance treated must be used. Silver is only
very slowly acted upon by hydrochloric acid, forming insol-
uble silver chloride AgCl. It dissolves slowly in dilute sul-
phuric acid, forming silver sulphate, and dissolves very
readily in nitric acid, forming silver nitrate AgNO. t .

This solution may be used for the silver reactions, but it
is best to make a solution for this purpose from silver-nitrate
crystals. In the case of each of the metals, directions are
given for making a solution. Of course, any other solution
would give the same reactions, but the solution given is most
easily made, and is in the form in which we are most likely
to find the metal in actual analysis.

* By an incrustation is meant a deposit on the charcoal surrounding,
or near, the substance heated.


A silver solution may be made by dissolving about 2 grams
of silver-nitrate crystals in 100 cubic centimeters of water
and adding a drop or two of nitric acid. The acid is best
added by means of a dropper, which may be made by draw-
ing out a glass tube, and cutting it as shown in Fig. 35, The-
oretical Chemistry. When the small end of this tube is
dipped into the liquid, the liquid, of course, enters it, and
may be retained in the tube by pressing the finger closely
upon the upper end. If the ringer is removed, the liquid
will be released, and by this means we can get any amount
of liquid we wish.

18. Reactions. A silver solution gives the following
reactions :

1. Ammonium hydrate, if added in very small amount to
a rather strong neutral solution of silver that does not con-
tain ammonium compounds, precipitates brown silver oxide
Agfl, which is very soluble in an excess of the reagent

1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Online LibraryInternational Correspondence SchoolsA treatise on chemistry and chemical analysis : prepared for students of The International Correspondence Schools, Scranton, Pa (Volume 3) → online text (page 1 of 21)