A Manual of the Chemistry of the Carbon Compounds

130 THE CHEMISTRY OF
C»H4O.CNH, which boils at 180°, with partial decomposition. On
aiding oonoentrated hydrochloric acid to this body ammonium
chloride and lactic acid are formed (compare lactic acid).
Phosphorus pentachloride acts violently upon aldehyde; the
products of the reaction being phosphorus oxychloride and dicMorethcme
C2H4Clj,
A great number of substances, such as hydrochloric acid, sulphuric
acid, carbonyl chloride, &c, even if present only in very minute
quantities, cause the condensation of the aldehyde into paraldehyde
C8HJ9Ofl, a liquid boiliug at 124°, and solidifying at a low temperature
into crystals melting at + 10-5°. On distilling paraldehyde with the
above substances, it again splits up into three molecules of acetaldehyde.
Another polymeride called 7netaldehydet the molecular weight of
which is not known, is produced when the above-mentioned substances
are brought into contact with aldehyde at a temperature
below 0". It crystallizes in colourless needles or prisms, which when
quickly heated sublime, When metaldehyde is heated in a closed
vessel to 115°, it again changes after a few hours into common
aldehyde.
On heating aldehyde with a solution of zinc chloride or some other
salts, water is eliminated, and crotan, aldehyde C4H0O is formed, a
compound whioh will be described hereafter!
ACKTIC ACID C2H4O2.
Dilute acetic acid, or vinegar, has been known from very early
times, The different modes of the formation of this acid have
already been fully described. On the large scale acetic acid is
produced by the oxjdation of alcohol, or by the destructive distillation
of wood. Pure alcohol, even when very dilute, is not
oxidized in contact with air, but in the presence of platinum black
and air it is converted into aldehyde and acetic acid. The same
change occurs when dilute alcohol ooutains certain nitrogenous
organic bodies. For this reason wine, beer, &o., in which such bodies
are contained, turn sour on exposure to the air.
In the manufacture of vinegar a mixture of wine, beer, or diluted
spirits, with some vinegar and yeast, is kept in loosely covered vafca,
at a temperature of about 24—27°, for about fourteen days, after
which time the liquid is changed into vinegar. On increasing the
surface of the liquid, the oxidation goes on much quicker. To effect
this the liquid is made to run slowly over shavings of beechwood
saturated with vinegar, contained in large vats, through which a
current of air is made to pass.
Acetic acid is found in nature in the form of acetic ethers in several
plants; it has also been found in small quantities in animal juices.