A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS, 297
The stony conoretions of pears principally consist of glueodrupose
C^HjgOj,,, which by boiling with hydrochlorio acid yields dextrose
and drupom Cj-H^Og; and the latter, when boiled with weak nitric
acid, yields cellulose, whilst on fusing it with caustio potash pyrocatechin
is formed.
rcrancro.
This name has been given to a substance whioh has the greatest
resemblance to cellulose, and appears to be identical with it. It
occurs in the mantle of Ascidia (spec, of Cynthia, Phallusia, &c),
from which it is obtained by boiling the mantles first with hydrochloric
acid, and then with caustio potash. In concentrated sulphuric
acid it deliquesces to a colourless liquid, which on boiling with water
yields a glncose.
FERMENTATION.
Several kinds of sugar and other bodies undergo, under certain
conditions, a peculiar ohetnical ohange called fermentalim. Fermentation
is always caused by the presence of a ferment or a substance
in a peculiar state of decomposition. Although to start
fermentation the presence of a ferment is necessary, it does not take
part in the decomposition of the fermenting substance. The products
of fermentation vary according to the nature of the fermenting body, as
well as according to the nature of the ferment. Each peculiar kind
of fermentation requires a certain temperature, and it is nearly always
accompanied by the development of certain living bodies (infusoria
or fungi); but whether the growth of these is acause or a consequence
of the chemical ohange has not yet been decided.
In many oases fermentation sets in withont bringing a ferment in
the liquid,' thus grape-juice, when exposed to the air, soon begins to
ferment, because it contains albuminous substances which, U* contact
with the air, readily undergo decomposition or putrefaction, and are
thus converted into a ferment.
Vinous Fermentation.—-When yeaat is added to a dilute solution of
dextrose or another glucose, vinous fermentation speedily sets in ;
whilst a solution of cane-sugar undergoes fermentation only slowly,
the cause being that this sugar must first be converted into inverted
sugar before fermentation can commence. Vinous fermentation
does not take place at a temperature below 0° or above 35°, and
proceeds most rapidly at 26° to 30°, The presence of a large quantity
of acids or alkalis prevents fermentation; while if the liquid has a
faint aoid reaction, fermentation proceeds best. The ohief produote of
vinous fermentation arc ethyl aloohol ami catbon dioxide;—
C6H12O8 = 2CjH6O + 2COa