EOSACE^ 409
-strongly recommended by Schimmel & Co., but there is considerable
doubt whether it will detect minute quantities of chlorine.
(b) The sodium test is distinctly more delicate, and is carried out as
follows:—
A piece of pure metallic sodium about half the size of a pea is dropped
into 05 c.c. of the oil in a dry test tube, and heated until all chemical
action has ceased. The test tube and contents are immersed whilst still
hot in 10 c.c. of distilled water in a porcelain dish. The solution is
filtered, acidulated with nitric acid, and silver nitrate solution added.
Any turbidity or opalescence indicates the presence of chlorine com-
pounds.
A blank test should be performed to ensure the absence of chlorine
in the materials employed.
(c) The lime combustion method gives good results as a qualitative
test, although it will often fail to detect very minute traces, say below 008
per cent. It is carried out as follows :—
A mixture of 1 c.c. of benzaldehyde and 5 grams of lime are placed in
the bottom of a platinum crucible about 3 ins. in depth, a layer of lime
placed on the top and the crucible covered and gently heated; a con-
siderable escape of benzaldehyde takes place, so that it is obvious that
the results can have no quantitative value.
The temperature is then gradually increased until no further vapours
ure driven off. The mixture is then dissolved in dilute nitric acid, filtered
and tested in the usual manner with silver nitrate.
(d) The method of Carius for the determination of chlorine in organic
compounds is, of course, absolutely quantitative, but is very tedious.
Salomon
l
has recommended the following method, and appended are the
results obtained compared with those yielded by the Carius' method and
the obviously inadequate lime method.
About 1 gram of benzaldehyde is heated in a retort with 40 c.c. of
concentrated sulphuric acid, the fumes collected in a solution of silver
nitrate, and the heating continued until no further precipitate insoluble
in hot dilute nitric acid is obtained in the silver nitrate solution. This
takes about three hours.
The solution of silver nitrate is acidified with dilute nitric acid, boiled
so as to decompose any silver sulphite that might have been formed, and
the precipitate filtered, washed, etc.
A slight modification consists in using a mixture of 40 c.c. concen-
trated sulphuric acid and 5 c.c. concentrated nitric acid, the nitric acid
•being added last to the mixture of sulphuric acid and benzaldehyde.
The hydrochloric acid was evolved more rapidly, and slightly higher
results were obtained in certain cases, due probably to better oxidation.
In using this method the heating must be very gradual, and the
mixture should not be allowed to froth until the end of the operation.
The Determination of Benzaldehyde.—It is doubtful whether there is
any accurate method for the determination of benzaldehyde in essential
-oil of almonds, in the presence of hydrocyanic acid, except in so far as
the actual free aldehyde is concerned. The most modern investigation of
.this question is that of F. D. Dodge.^2
The results obtained by the use of the methods for chlorine determina-
(^1) P. and E.O.R. (1917), ±1.
(^3) Eighth International Congress of Applied Chemistry, Washington (1912), xvii. 15.