metal. A small sample is ground together with quartz
sand, the mixture is placed on a watch-glass, moistened
with a few drops of oil of vitriol and gently warmed.

a. White vapors are evolved which redden litmus;
this indicates the presence of FLUORIDE OF CALCIUM.
Reduce a portion of the substance to a fine powder,
decompose this in a platinum crucible with sul-
phuric acid, and try the reaction on glass (§ 149),
to prove the presence of FLUORINE; boil the residue
with hydrochloric acid, filter, neutralize the filtrate.
with ammonia, and test for LIME with oxalate of
ammonia.

B. Vapors that redden litmus are not evolved. Mix a small portion of the very finely pulverized substance with 4 times the quantity of pure carbonate of soda and potassa, and fuse the mixture in a platinum crucible, or else on platinum foil. Boil the fused mass with water, filter, should a residue be left, and wash the latter. Acidulate a portion of the filtrate with hydrochloric acid, and then test with chloride of barium for SULPHURIC ACID; and in case you do not find that acid, test another portion of the filtrate for SILICIC ACID by evaporating the fluid acidified with hydrochloric acid (§ 153, 2).

If the SILICIC ACID was present in the pure state, the mass resulting from the fusion of the substance with carbonate of soda and potassa must have dissolved in water to a clear fluid; but if silicates also happened to be present, their bases are left behind undissolved. and may be further examined.

If, on the other hand, sulphuric acid has been found, the alkaline earth which was combined with it is found on the filter as a carbonate. Wash this, then dissolve it in dilute hydrochloric acid, and test the solution for BARYTA, STRONTIA, and LIME, as directed (62).

Complex Compounds.*

A. SUBSTANCES SOLUBLE IN WATER, AND ALSO SUCH AS ARE INSOLUBLE IN WATER, BUT DISSOLVE IN HYDROCHLORIC ACID, NITRIC ACID, OR NITROHYDROCHLORIC ACID.

*I use this term here, and hereafter in the present work, to designate compounds n which all the more frequently occurring bases, acids, metals, and metalloids are supposed to be present.

(Treatment with Hydrochloric Acid: Detection of Silver, Sub oxide of Mercury [Lead].)

The systematic course for the detection of the bases is 101 essentially the same for bodies soluble in water, as for those which are soluble only in acids. Where, in consequence of the different nature of the original solution, deviations are rendered necessary, the fact will be distinctly stated.

I. SOLUTION IN WATER.

MIX THE PORTION INTENDED FOR THE DETECTION OF THE
BASES WITH SOME HYDROCHLORIC ACID.

1. THE SOLUTION HAD AN ACID OR NEUTRAL REACTION PRE- 102 VIOUSLY TO THE ADDITION OF THE HYDROCHLORIC ACID.

a. No PRECIPITATE IS FORMED; this indicates the absence of silver and suboxide of mercury. Pass on to $.193.

Add more hydrochloric

b. A PRECIPITATE IS FORMED.
acid drop by drop until the precipitate ceases to in-
crease; then add about six or eight drops more of hydro-
chloric acid, shake the mixture, and filter.

The precipitate produced by hydrochloric acid may
consist of chloride of silver, subchloride of mercury,
chloride of lead, a basic salt of antimony, basic oxychlo-
ride of bismuth, possibly also of benzoic acid. The basic
salts of antimony and oxychloride of bismuth, however,
redissolve in the excess of hydrochloric acid; conse-
quently, if the instructions given have been strictly fol-
lowed, the precipitate collected upon the filter can con-
sist only of chloride of silver, subchloride of mercury,
or chloride of lead-(possibly also of benzoic acid,
which, however, is altogether disregarded here).

Wash the precipitate collected upon the filter, twice with cold water, add the washings to the filtrate, and examine the solution as directed § 193, even though the addition of the washings to the acid filtrate should pro

*The beginner should not fail to study the explanations in the Third Section horoughly before attempting the analysis of a complex substance. He will also do well to review these explanations frequently during the course of his practice. Regard is here had also to the presence of the acids of arsenic, and of those salts of the alkaline earths which dissolve in hydrochloric acid, and separate again from that solution unaltered, upon neutralization of the acid by ammonia.

Consult the remarks in the Third Section,

duce turbidity in the fluid (which indicates the presence
of compounds of antimony or bismuth).

Treat the washed precipitate on the filter as follows:

a. Pour hot water over it upon the filter, and test the fluid running off with sulphuric acid for LEAD. The non-formation of a precipitate upon the addition of the sulphuric acid simply proves that the precipitate produced by hydrochloric acid contains no lead, and does not by any means establish the total absence of this metal, as hydrochloric acid fails to precipitate lead from dilute solutions.

B. Pour over the now thrice-washed precipitate upon the filter, solution of ammonia. If this changes its color to black or gray, it is a proof of the presence of SUBOX

IDE OF MERCURY.

7. Add to the ammoniacal fluid running off in 6 nitric acid to strongly acid reaction. The formation of a white, curdy precipitate or opalescence indicates the presence of SILVER. (If the precipitate did contain lead, the ammoniacal solution generally appears turbid, owing to the separation of a basic salt of lead. This, however, does not interfere with the testing for silver, since the basic salt of lead redissolves upon the addition of nitric acid.)

103

2. THE ORIGINAL AQUEOUS SOLUTION HAD AN ALKALINE 104

REACTION.

a. THE ADDITION OF HYDROCHLORIC ACID TO STRONGLY
ACID REACTION FAILS TO PRODUCE EVOLUTION OF GAS OR
A PRECIPITATE, OR THE PRECIPITATE WHICH FORMS AT
FIRST REDISSOLVES UPON FURTHER ADDITION OF HYDRO-

CHLORIC ACID: pass on to § 193.

b. THE ADDITION OF HYDROCHLORIC ACID TO THE ORIGINAL SOLUTION PRODUCES A PRECIPITATE WHICH DOES NOT REDISSOLVE IN AN EXCESS OF THE PRECIPITANT, EVEN

UPON BOILING.

a. The formation of the precipitate is attended 105 neither with evolution of hydrosulphuric acid nor of hydrocyanic acid. Filter, and treat the filtrate as directed § 193.

aa. THE PRECIPITATE IS WHITE. It may, in that case, consist of a salt of lead or silver, insoluble in water and hydrochloric acid (CHLORIDE OF LEAD, SULPHATE OF LEAD, CHLORIDE OF SILVER, &c.) or may be HYDRATED SILICIC ACID. Test for the bases and acids of these compounds as directed § 206, bearing in mind that the chloride of lead or chloride of silver

which may be present may possibly have been form-
ed in the process.

bb. THE PRECIPITATE IS YELLOW OR ORANGE. In
that case it may consist of SULPHIDE OF ARSENIC (and
if the fluid from which it has separated was not boil-
ed for a long time, or only with very dilute hydro-
chloric acid, also of SULPHIDE OF ANTIMONY or
BISULPHIDE OF TIN), which substances were original-
ly dissolved in solution of ammonia, soda, potassa,
phosphate of soda, or some other alkaline fluid, with
the exception of solutions of alkaline sulphides and
cyanides. Examine the precipitate which may also
contain HYDRATED SILICA, as directed (40).

6. The formation of the precipitate is attended with 106 evolution of hydrosulphuric acid gas, but not of hydrocyanic acid.*

aa. THE PRECIPITATE IS OF A PURE WHITE COLOR, AND CONSISTS OF SEPARATED SULPHUR.

In that case

a SULPHURETTED ALKALINE SULPHIDE is present.
Boil, filter, proceed with the filtrate according to
§ 197, with the residue as directed § 206.

bb. THE PRECIPITATE IS COLORED. In that case
you may conclude that a METALLIC SULPHUR SALT is
present, i. e., a combination of an alkaline sulphur
base with a metallic sulphur acid. The precipitate
may accordingly consist of SULPHIDE OF GOLD, SUL-

PHIDE OF PLATINUM, SULPHIDE OF TIN, SULPHIde of

ARSENIC, or SULPHIDE OF ANTIMONY. It might, how-
ever, consist also of SULPHIDE OF MERCURY or of
SULPHIDE OF COPPER, or SULPHIDE OF NICKEL, or con-
tain these substances, as the first is readily soluble
in sulphide of potassium, and the last two are slightly
soluble in sulphide of ammonium. Filter, and treat
the filtrate according to § 197, the precipitate as
directed (40).

7. The formation of the precipitate is attended with 107
evolution of hydrocyanic acid, with or without simul-
taneous disengagement of hydrosulphuric acid. This
indicates the presence of an ALKALINE CYANIDE, and,
if the evolution of the hydrocyanic acid is attended
with that of hydrosulphuric acid, also of an alkaline
SULPHIDE. In that case the precipitate may, besides

Should the odor of the evolved gas leave any doubt regarding the presence of absence of hydrocyanic acid, add some chromate of potassa to a portion of the fluid previously to the addition of the hydrochloric acid.

(106),

the compounds enumerated in a (105) and
contain many other substances (e. g., cyanide of nickel,
cyanide of silver, &c.). Boil, with further addition
of hydrochloric acid, or of nitric acid, until the whole
of the hydrocyanic acid is expelled, and treat the
solution, or, if an undissolved residue has been left,
the filtrate, as directed § 193; and the residue (if any)
according to § 206.

C. THE ADDITION OF HYDROCHLORIC ACID FAILS TO PRO- 108
DUCE A PERMANENT PRECIPITATE, BUT CAUSES EVOLUTION
OF GAS.

a. The escaping gas smells of hydrosulphuric acid;
this indicates the presence of a SIMPLE ALKALINE SUL-
Proceed as in § 197.

PHIDE.

B. The escaping gas is inodorous; in that case it is
CARBONIC ACID which was combined with an alkali.
Pass on to § 193.

7. The escaping gas smells of hydrocyanic acid
(no matter whether hydrosulphuric acid or carbonic
acid is evolved at the same time or not). This indi-
cates the presence of an ALKALINE CYANIDE. Boil
until the whole of the hydrocyanic acid is expelled,
and then pass on to § 193.

II. SOLUTION IN HYDROCHLORIC ACID OR IN NITROHYDRO-
CHLORIC ACID.

Proceed as directed § 193.

III. SOLUTION IN NITRIC ACID.

Dilute a small sample of it with water; should this pro- 109 duce turbidity or a precipitate (indicative of the presence of bismuth) add nitric acid until the fluid is clear again, then hydrochloric acid.

1. No PRECIPITATE IS FORMED. Absence of silver and suboxide of mercury. Treat the principal solution as directed

193.

2. A PRECIPITATE IS FORMED. Treat a larger portion of the nitric acid solution the same way as the sample, filter, and examine the precipitate as directed (103), the filtrate as directed § 193.