258 SPIRITS AND LIQUEURS (GENERAL METHODS)
residue being treated with 20 c.c. of water acidified with hydrochloric acid,
and then with a drop of platinum chloride and 0-2-0-3 gram of zinc dust,
so that evolution of hydrogen goes on for about 10 minutes.
When this ceases, the liquid is filtered and the filtrate, which should
be acid, cooled to about 15° and treated with 5-10 drops of a 10% aqueous
sodium nitrite solution; the acid is neutralised with sodium carbonate,
cooling meanwhile, and to the liquid, which is turbid owing to the presence
of zinc carbonate, are added 1-2 drops of alkaline a-naphthol solution (o-i
gram a-naphthol, 100 c.c. water, 5 c.c. of caustic soda solution of sp. gr.
1-35). If the spirit contains benzene or its homologues, an orange-red
coloration is produced in consequence of the formation of an azo-colouring
matter from the a-naphthol and the diazo-cornpound of the aniline or
analogous base.
6. Detection and Determination of the Methyl Alcohol
Methyl alcohol, besides occurring in spirits derived from denatured
alcohol—in which case the methods of detection and determination have
already been indicated (see p. 254)—may also be found in larger quantities,
especially in alcoholic beverages, liqueurs, etc., to which it is added fraudu-
lently in place of ethyl alcohol. In the latter case its detection and deter-
mination require the previous elimination of extraneous fixed and volatile
substances.
To eliminate the fixed substances, 100 c.c. of the sample are distilled
and exactly 100 c.c. of distillate collected. To eliminate the volatile sub-
stances from the distillate, 50 c.c. of the latter are diluted in a separating
funnel with 100-150 c.c. of water saturated with sodium chloride and shaken
for 5 minutes with 50 c.c. of ligroin or petroleum ether. After a convenient
rest, the lower layer is transferred to a distilling flask and the layer of ligroin
or petroleum ether washed with 25 c.c. of brine ; the lower layer is mixed
with the first one and the whole distilled through a small rectifying column,
the first 100 c.c. of distillate being collected in a measuring flask. The
distillate, of which the alcoholic strength by volume and in grams per 100
c.c. is determined, is used for the detection and determination of the methyl
alcohol.
1. Qualitative Test.—This is carried out by the method indicated
for the detection of denaturants (see p. 254).
2. Quantitative Determination.—i. COLORIMETRIC METHOD. This
is recommended especially with small proportions of methyl alcohol (up
to 5~6%). To 20 c.c. of the distillate (corresponding with 10 c.c. of the
original spirit), in a 100 c.c. measuring flask, is added sufficient ethyl
alcohol, free from methyl alcohol, to give 9 c.c. of total alcohols in the liquid
when diluted to 100 c.c.; the liquid is then made up to volume with water.
The colorimetric determination of the methyl alcohol is carried out on
i c.c. of this alcoholic solution according to the instructions given on p. 255.
2. GRAVIMETRIC METHOD. This is based on the fact that, by the action
of excess of potassium dichromate and sulphuric acid, methyl alcohol is
completely oxidised to water and carbon dioxide, wh§rea$ ethyl alcohol is