James Freeman Sellers.

An elementary treatise on qualitative chemical analysis online

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NaC 2 H 3 2 ).

1. Heated to redness, acetates are decomposed with
the formation of carbonates and of acetone, C 3 H 6 O, a
liquid of penetrating, pleasant, ethereal odor :

2NaC 2 H 3 2 = Na 2 C0 3 + C 3 H 6 O.

2. FeCl 3 , a few drops, added to a neutral acetate
solution, produces a deep red coloration, due to the
formation of ferric acetate, Fe(C 2 H 3 O 2 ) 3 . On boiling,
the solution is decolorized, and brown basic ferric acetate
is precipitated.

3. Heated with concentrated H 2 SO 4 and alcohol, ace-
tates yield ethyl acetate, (C 2 H 5 )C 2 H 3 O 2 , characterized
by its pungent ethereal odor :

NaC 2 H 3 2 + C 2 H 5 OH = (C 2 H 5 )C 2 H 3 O 2 + NaOH.

DETECTION OF THE ACIDS OF GKOUP III

Individual tests must be made for the three acids of
this group, in separate portions of the original solution.

If iodides or bromides are present, they must be
removed from the portion which is to be tested for
HNO 3 by adding HgCl 2 solution and filtering, rejecting
the precipitate. Otherwise, they would give a dark
coloration on the addition of H 2 SO 4 . In testing for
HNO 3 , Reactions 3 and 4 are to be used.

In testing for KC1O 3 , Reaction 3 is to be employed.
If H 3 PO 4 is present, it is to be removed before testing
for HC 2 H 3 O 2 , since it forms insoluble FePO 4 with
FeCl 3 . (See p. 111.) Use Reaction 2 in testing for
HC 2 H 3 2 .



CHAPTER XVI

THE SYSTEMATIC PROCEDURE OF ANALYSIS
PRELIMINARY TESTS

The physical properties of the substance under exami-
nation color, odor, whether solid or liquid, etc. are
first to be noted.

Solids. 1 If the substance is a solid, apply the follow-
ing tests to small portions :

(a) Blowpipe flame on charcoal (see Tables IV and

V, pp. 48, 49).

(b) Heating in a closed tube (see Table II, p. 45).

(c) Fusion with borax bead (see Table III, p. 47).

(d) Flame coloration on a platinum wire (see Table

VI, p. 51).

(e) Spectra (see Table VII, p. 58).

A larger portion of the solid is to be used for solu-
tion, in preparation for the analysis by the wet way.
First, treat it with water, determining whether the
whole or only a part dissolves. If it be insoluble, or
only partly soluble, divide the mixture into three parts,
two small and one large, which may be numbered
respectively 1, 2, and 3.

To 1, in a test-tube, add some dilute HC1 and boil.
If still insoluble or partly insoluble, add an equal volume
of concentrated HC1 and boil again. If soluble, then
treat 3, the largest portion, with concentrated HC1 and

151



152 CHEMICAL ANALYSIS

boil. If insoluble or partly insoluble, treat 2, first with
dilute, then with concentrated HNO 3 . If soluble, treat
3 in like manner.

If insoluble or partly insoluble in HNO 3 as well as in
HC1 and water, combine the strong HC1 and HNO 3
mixtures, 1 and 2, and boil. If soluble, treat 3 with
aqua regia. If insoluble or partly insoluble, recall
which of the four solvents water, HC1, HNO 3 , or
aqua regia dissolved the substance most ; and treat
the larger portion, 3, with that solvent. Filter. Fuse
the residue 1 with fusion mixture on a platinum foil
or in a platinum crucible, and boil the mass with
water. Sometimes this solution can be added directly
to the filtrate without precipitation. Generally, how-
ever, a precipitate will be formed. In order to deter-
mine this, take small portions of both liquids and mix
them. If no precipitate forms, combine the whole of
both solutions. If a precipitate forms, separate analyses
must be made of the two solutions. 2

Liquids are to be tested with litmus paper to determine
whether they are neutral, acid, or alkaline; and, also,
small portions are to be evaporated to dryness on the
water bath. No residue being left, a neutral reaction
indicates that only water is present; whereas an acid
or alkaline reaction indicates the presence of a volatile
acid or of ammonia.

If a residue is left on evaporation :

(a) A neutral reaction indicates the presence in solu-
tion of a neutral salt.

(b) An acid solution may be either (1) a free acid,
(2) an aqueous solution of certain normal salts like



SYSTEMATIC PROCEDURE OF ANALYSIS 153

FeCl 3 or CuSO 4 , which have acid reactions, (3) certain
acid salts like bisulphate of potassium, HKSO 4 , or (4)
an acid solution of certain salts.

(c) An alkaline solution may contain (1) a free alkali,
(2) certain normal salts like Na 2 CO 3 which have an alka-
line reaction, or (3) an alkaline solution of certain salts.
In theory an aqueous solution of a basic salt should
react alkaline ; but as the metals which form basic salts
have not a very pronounced metallic character, their
alkalinity is either too weak to be detected by litmus
or, being very weak, is neutralized by water.

SYSTEMATIC ANALYSIS FOR METALS

If the solution 1 is neutral or alkaline, 2 add dilute HC1
till acid ; if acid, boil off the excess of acid, and when
cold add dilute HC1. If a precipitate is formed, filter,
and wash the residue with cold water. Analyze the
residue for members of Group I, according to the direc-
tions on p. 80.

Acidify the filtrate strongly with more HC1, warm to
about 70, and pass a constant stream of H 2 S through it
for about fifteen minutes. Then cool and dilute the solu-
tion, and, before filtering, pass H 2 S again till saturation
is completed. If a precipitate is formed, filter, wash,
and analyze for members of Group II, as directed on
p. 94.

Boil off all traces of H 2 S from the filtrate ; test for
ferrous iron 3 with K 3 Fe(CN) 6 ; and, if it be present, add
a few drops of HNO 3 , and boil until the iron is wholly
oxidized to the ferric state. Unless the preliminary



154 CHEMICAL ANALYSIS

examination has indicated conclusively whether organic
matter or phosphates are absent or present, it will be
necessary to test for them at this point, as is directed
on p. 109. According as they are absent or present,
follow the instructions given for the precipitation and
separation of the members of Group III, on pp. 110
and 111.

Boil off all excess of NH 4 OH from the filtrate 1 which
is to be examined for Groups IV, V, and VI ; add
(NH 4 ) 2 S in moderate excess, and if a precipitate is
formed, filter and wash thoroughly. Examine it for
members of Group IV according to the directions
given on p. 118.

To the filtrate which may contain Groups V and VI
add NH 4 C1, NH 4 OH, and (NH 4 ) 2 CO 3 in quantity suffi-
cient to precipitate completely any members of Group V
which may be present. Warm the mixture gently ; and
if a precipitate has formed, filter and wash with ammo-
niated water, rejecting the washings. Examine it for
members of Group V, according to the directions given
on p. 123.

Concentrate the filtrate which is to be examined for
Group VI, and add small amounts of (NH 4 ) 2 SO 4 and
(NH 4 ) 2 C 2 O 4 , to remove any traces of Ca and Ba which
may be present. Filter and reject the precipitate, if
one be formed; and examine the filtrate for members
of Group VI, as directed on p. 127.

Concentrate some of the original solution, and test
for ammonium salts with NaOH.



SYSTEMATIC PROCEDURE OF ANALYSIS 155



SYSTEMATIC ANALYSIS FOR ACIDS

It will have been observed that the preliminary exami-
nation and the results of t'he analysis for metals throw
much light upon the nature of the acids which may be
present in the material which is being analyzed.

For example, the presence of tartaric acid may be
indicated by the result of heating in a closed tube ;
nitrates or chlorates show their presence by deflagration,
when heated on charcoal; carbonates, sulphites, sul-
phides, and cyanides are detected upon the addition of
HC1, the reagent for the metals of Group I, by efferves-
cence with or without characteristic odor.

Furthermore, the results of the analysis for metals
will show, according as Cr and As are found absent or
present, whether chromic, arsenious, and arsenic acids
are absent or possibly present.

But in addition to these indications there are others,
depending upon the nature of the metals present in a
substance and upon the character of the solution of that
substance, which may show conclusively whether certain
acids or groups of acids are absent or present. If, for
example, a metal of Group I is present in a neutral
or acid solution, it is fair to presume that no acid of
Group II can be present, since the salts of Ag, Pb, and
Hg' with such acids are almost universally insoluble,
either in water or acids. If, on the other hand, a metal
of Group V be found present in a neutral solution, it is
presumable that no acid of Group I will be present,
since the combinations between metals of Group V and
acids of Group I are all practically insoluble in water.



156 CHEMICAL ANALYSIS

It will be seen, therefore, that a knowledge of the
solubilities which are shown in Table I, p. 34, will save
much time and labor by aiding in the interpretation of
the results of the analysis for metals in the manner
already shown, and by diminishing the number of acids
for which individual tests must be made.

In proceeding to the systematic examination for acids
it is desirable to remove any heavy metals which may
be present, since they are liable to obscure the reactions
expected from the reagents for the acids. Accordingly,
if the original substance is soluble or partly soluble,
remove the heavy metals by boiling the solution with a
small excess of Na 2 CO 3 and filtering. If the substance
is insoluble or partly insoluble, fuse the insoluble mass
with Na 2 CO 3 in a platinum foil or crucible, boil with
water, and filter. By metathesis all the heavy metals
become carbonates, and the alkali metals form soluble
salts with the acids. The filtrate from either method
of double decomposition can now be analyzed for
acids.

Fusion decomposes H 2 C 2 O 4 , H 2 C 4 H 4 O 6 , HC1O 3 , and
HC 2 H 3 O 2 ; but salts of these acids are soluble in water
or solvent acids, and must be sought for in the portion
soluble without the aid of fusion.

Of course it is necessary to test for H 2 CO 3 in the
original substance before Na 2 CO 3 is added.

Neutralize a small portion of the solution of the
alkali salts with dilute HNO 3 , and heat till all CO 2
is expelled. Add BaCl 2 . A precipitate indicates the
presence of members of Group I. Divide a larger
portion of the solution into three parts, and test for



SYSTEMATIC PROCEDURE OF ANALYSIS 157

H 2 CrO 4 , H 2 SO 3 , and H 4 SiO 4 , as directed for Sub-
group I, Group I, p. 138.

If any members of Sub-group I are present, add
dilute HC1 to another portion of the alkali salts solu-
tion, and pass H 2 S till the liquid smells of it. Boil off
excess of HC1 and H 2 S, and divide into six parts.
Examine for H 2 SO 4 , H 3 PO 4 , H 3 BO 3 ,H 2 C 2 O 4 , H 2 C 4 H 4 O 6 ,
and HF, as directed for Sub-group II, Group I, p. 139.

To a small portion of the alkali salts solution add
a solution of ZnSO 4 in NaOH. If a white precipitate
occurs, treat a larger portion of the solution in like
manner, and filter, rejecting the white residue. Divide
the filtrate, or a portion of the alkali salts solution, if
H 2 S is absent, into three parts; and analyze for HC1,
HBr, HI, HCN, H 4 Fe(CN) 6 , H 3 Fe(CN) 6 , and HCNS, as
directed for Group II, p. 145.

Divide another portion of the alkali salts solution
into three parts, and test for HNO 3 , HC1O 3 , HC 2 H 3 O 2 ,
as directed for Group III, p. 150.



158



CHEMICAL ANALYSIS





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160



CHEMICAL ANALYSIS



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ATOMIC WEIGHTS



161



TABLE IX ATOMIC WEIGHTS OF THE ELEMENTS



(F.W.
H = l
Aluminum ..... 26.9

Antimony 119.5

Argon 39.6

Arsenic 74.45

Barium 136.4

Bismuth 206.5

Boron 10.9

Bromine 79.35

Cadmium 111.55

Caesium 131.9

Calcium 39.8

Carbon 11.9

Cerium 138.0

Chlorine 35.18

Chromium 51.7

Cobalt 58.55

Colurnbium 93.0

Copper 63.1

Erbium 164.7

Fluorine 18.9

Gadolinium 155.2

Gallium 69.5

Germanium . . . . 71.9

Glucinum 9.0

Gold 195.7

Helium 3.93

Hydrogen 1.0

Indium 113.1

Iodine 125.89

Iridium 191.7

Iron 55.5

Lanthanum . . . . .137.6

Lead 205.36

Lithium 6.97

Magnesium 24. 1

Manganese 54.6

Mercury 198.50



CLARKE)

H = l

Molybdenum .... 95.3

Neodymium 142.5

Nickel 58.25

Nitrogen 13.93

Osmium 189.6

Oxygen 15.88

Palladium 106.2

Phosphorus . . . . . 30.75

Platinum 193.4

Potassium 38.82

Praseodymium . . . .139.4

Rhodium 102.2

Rubidium 84.75

Ruthenium 100.9

Samarium 149.2

Scandium 43.8

Selenium 78.6

Silicon 28.2

Silver 107.11

Sodium 22.88

Strontium 86.95

Sulphur 31.83

Tantalum 181.5

Tellurium 126.1

Terbium 158.8

Thallium ...... 202.61

Thorium 230.8

Thulium 169.4

Tin 118.1

Titanium 47.8

Tungsten 182.6

Uranium 237.8

Vanadium 51.0

Ytterbium 171.9

Yttrium 88.3

Zinc 64.9

Zirconium . . . 89.7



162



CHEMICAL ANALYSIS



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NOTES



[The heavy-face and light numbers below correspond to pages and
reference numbers in the body of the text.]

9 1 Two other reasons are assigned for the reaction of zinc and
sulphuric acid on the dilution of the acid. Dilution increases the
ionization of the acid and correspondingly increases its solvent action.
Second, impurities in the zinc prevent polarization and enable the ions
to discharge.

10 1 The term "colloid" was used by Graham to denote substances
"incapable of taking crystalline form, and also distinguished by the
mucilaginous character of the hydrates." The class includes glue,
gums, starch, albumin, and certain arsenic and cyanogen compounds.
These compounds are, for the most part, of great molecular weight.
Crystalloids, on the other hand, consist of easily crystallizable sub-
stances, and include sugars, salts, and strong mineral acids and
bases. 2 Ann. d. Chem. u. Pharm., 121, 1. 3 A porous membrane
consists of unsized paper, unglazed porcelain, or parchment. It is
pervious to most solvents and to crystalloid solutes, but is impervious
to colloids. A semi-permeable membrane is either a colloid, or a
porous membrane whose pores are filled with a colloid. Semi-perme-
able membranes are pervious to solvents, but impervious to both
colloid and crystalloid solutes.

11 1 See Pfeffer, Osmot. Untersuch., 1887. 2 Not so much pro-
toplasm itself, but rather the covering of the protoplasm.

12 1 Zeit. f. phys. Chem., 1, 481 (1887). 2 Recent data by Morse
and Frazer from experiments with cane sugar show that this law
should be somewhat modified. Amer. Chem. Journ., July, 1905. 3
It is preferable to say that M represents the gram-molecular weight
and T the absolute temperature.

21 1 A better answer to the question is that the velocity of the
reaction is usually increased, and frequently the nature of the prod-
ucts is governed by the temperature. 2 Inasmuch as a substance
in solution is likened to a gas confined in a closed container, dilution

163



164 CHEMICAL ANALYSIS

or increase of the volume of the solvent is equivalent to increasing
the container, or decreasing the pressure.

22 1 Arrhenius., Zeit. f. Chem., 1 (1890). 2 The basic character
also of NH4OH is lowered. In a few cases, however, notably in that
of cobalt and nickel, the solvent action is increased. 3 Dr. Black
suggests a better explanation of this reaction : *' HC1 and NaC 2 H 3 2
are both highly dissociated, giving high concentrations of H+ and
C 2 H 3 O 2 - ions; but H-C 2 H 3 O 2 is highly dissociated, or H+ and
C 2 H 3 O 2 ~ ions cannot exist in great numbers in the same solution.
Hence on mixing HC1 and NaC 2 H 3 2 , the equation Ci C 2 = K C 3
for H+ and C 2 H 3 2 ~ ions must be satisfied, and as K is small, C 3 is
large and Ci C 2 small. By increasing C 2 representing C 2 H 3 2 ~, Ci
representing H+ may be still farther diminished ; or, the more
NaC 2 H 3 O 2 is added, the lower the concentration of H+ ions and the
less the acidity of the solution."

28 1 Many funnels not being exactly 60 will not fit the folded
filter described. To provide for angles slightly greater or smaller
than 60 in folding the paper the second time to form a quadrant, the
crease is made so that one half the fold shall be shorter than the
other. This can be made to fit any ordinary funnel.

45 1 As suggested on p. 73, these tables are expressions of analysis
by the dry way. They are not necessarily a guide to exact analysis,
but are merely for preliminary and confirmatory observation.

47 1 The best way to separate the bead from the wire is to dissolve
it out with hot water acidified with hydrochloric acid, and rinsed with
distilled water. The loop at the end of the wire should be permanent.
Frequent bending of the wire breaks it. When coloring the bead, if
the quantity of the metallic salt or oxide is large enough to render
it opaque, the bead can be "diluted" by taking off part of it while
hot with a glass rod, and building it up again with more borax.

54 1 Compt. rend., 55, 576.

56 1 Pogg. Ann., 119, 10.

61 1 Mem. II, Phil Mag. (4), XXII, 329, 498. 2 Astronomy and
Astrophysics, 12, 321 (1893).

65 1 Dr. Montgomery gives the following instructive definition of
equivalent weight : "Valence is power to combine. If two amounts
of the substances are equivalent they have equal power to combine
or do chemical work. ' The equivalent weight of a compound is that
weight which interacts with the equivalent weight of an element '
(Smith) . As the equivalent weight of an element is that weight which



NOTES 165

will combine with 8 parts by weight of oxygen or with 1 part by
weight of hydrogen, it follows that the equivalent of an acid, base, or
salt is the molecular weight divided by the total valence of the nega-
tive, or acid, radical. If the valence of the radical is 1, the com-
pound will interact with one equivalent of an element or compound ;
if the valence is 2, with two equivalents, etc."

68 1 Parsons' Automatic Gas Generator, originally described by
Professor Charles L. Parsons in an article entitled "Distribution of
Hydrogen Sulphide to Laboratory Classes " (Journ. Amer. Chem. *Soc.,
p. 231 (1903)), has largely solved the difficult problem of delivering
hydrogen sulphide to classes, when used in connection with a distri-
bution system easily arranged in any laboratory. This generator is
sold by Eimer and Amend, New York, and is now generally used in
colleges throughout the United States. The apparatus is made of
stoneware, and a single generator will easily supply a class of fifty
students. It is perfectly automatic in its action, and the refuse is
automatically removed. The pressure on the hydrogen sulphide is
almost constant, seldom varying more than two or three millimeters.
Only fresh acid comes in contact with the solid reagent, and the full
strength of the acid is utilized. There are no stopcocks or valves, the
apparatus being controlled entirely by the exits. It is easily cleaned
and refilled without taking down. It requires absolutely no attention
for weeks at a time, and then only to refill the acid holder. It is
always ready, and generates gas only when in use. There is no escape
of gas while recharging the acid.

77 2 Throughout the remainder of the text all mention of reagents
refers to dilute ones, unless otherwise designated.

78 1 Use an exceedingly dilute solution of ammonium hydroxide
(I : 50). At first the precipitate is white AgOH, changing quickly to
Ag 2 0, then to soluble 2 AgN0 3 3NH 3 .

79 1 Hg 2 S is formed at low temperature, but is broken down on
warming. 2 The precipitate has been shown to consist of metallic
mercury and white Hg' 2 N N0 3 . J. prakt. Chem., 39, 204.

80 1 PbI 2 is soluble in excess of KI. Hence the precaution of add-
ing reagents, mentioned on p. 3 (/), should be observed.

81 1 Each group precipitate should be thoroughly washed to insure
the separation of that group from remnants of the filtrate, which might
contain members of subsequent groups. 2 Ice water with HC1. Lead
chloride is less soluble in dilute hydrochloric acid than in water.
Reject the washings. 3 Instead of washing out the lead with hot



ICO CHEMICAL ANALYSIS

water on the filter, a better method is to punch a hole in the filter
paper with a glass rod, wash the contents into a beaker, add water,
boil about five minutes, and filter through a hot-water funnel. An
ordinary funnel will usually serve the purpose. 4 In the presence of
much Hg' and a little Ag, the latter may not be found here. The
residue not soluble in aqua regia should be examined for AgCl.
Barnes, Chemical News, 51, 97 (1885).

82 1 HgI 2 is soluble either in excess of KI or in excess of HgCl 2 .
Both re-solutions produce double salts, Hg 2 Cl 2 I 2 probably being pro-
duced by excess of HgCl 2 .

84 1 This compound is probably CuS0 4 4 NH 3 .

87 1 KCNS is not a' metallo-cyanide, but is conveniently classed
here ; and besides, with ferric iron, it forms the so-called double salt
Fe(CNS) 3 9 KCNS, which is doubtless a metallo-cyanide.

89 1 This test should be made in a hood with a good draught to
insure the removal of the poisonous arsine.

90 1 " Colloidal solutions occupy a place between true solutions and
mechanical suspensions. The solute is present as particles which are
so extremely small that they can neither be removed by sedimentation
nor by ordinary filtration. By warming such solutions, and by addi-
tion of various salts, the particles may be made to increase in size


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Online LibraryJames Freeman SellersAn elementary treatise on qualitative chemical analysis → online text (page 10 of 12)