A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS 317
each. By the action of alcoholic potash, hydrochloric aoid is taken
out, and chlorethene C2H3Cl is formed, in which the carbon-atoms
are again licked together, as in ethene.
Hydrogen can also combine with aromatic hydrocarbons, but only
with those containing alcohol-radicals. The number of atoms of
hydrogen combining with the hydrocarbon appears to depend, not
only on the number of these radicals, but also on the relative
positions.
To obtain these additive products, the hydrocarbon is heated in
sealed tubes with phosphouiutn iodide (a compound of liydriodic aoid
with hydrogen phosphide). The hydriodic acid is the reducing agent,
being decomposed into hydrogen and iodine, which latter is immediately
acted upon by the hydrogen phosphide, and again converted
into hydriodic acid; this change going on until at last only phosphorus
iodide and red phosphorus are left behind.
By subjecting benzene to this reaction, it is not changed even at
350. Methyl-benzene combines with two atoms of hydrogen,
and forms the hydrocarbon C6H,.CH8, Dimethyl-benzene takes up
four atoms of hydrogen, yielding C9Hg| ^^, and trimethyl-benzeue
combines with six atoms of hydrogen, forming the compound
(CH
There exist also aromatic acids which will combine with hydrogen
in the nascent state.
COMPOUNDS WITH SIX ATOMS OP CARBON.
BENZENE j , ,
Benzene, or Benzol, is a colourless, strongly refractive, and mobile
liquid, boiling at 81°, aud solidifying at 0°, to colourless crystals. It
has a density of 0*899 at 0°, aud of 0-878 at 20°, and a peculiar
aromatic odour. It is very inflammable, burning with a very luminous
and very smoky flame. It is almost insoluble in water, but
dissolves freely in alcohol and ether. It dissolves iodine, sulphur,
phosphorus, fats, resins, and many other compounds, which are
insoluble or only sparingly soluble in water and alcohol; and hence
it is used for preparing or purifying many compounds.
Benzene has beeu produced artificially from its elutneute. When
acetylene, which, us we have seen (page 274), may be formed by the
direct combination of carbon with hydrogen, is heated in a long,
narrow, bent bell-jar to a temperature at which the glass begins to