A Manual of the Chemistry of the Carbon Compounds

274 THE CHEMISTRY OF
Hcxone Dibromide. ifoxoylone.
CHBr - 2HBr = C
I III
CHjBr CH
Acetylene or Etkine CgH,.—This gas is the only hydrocarbon which
lias been obtained by the direct union of its elements; it is produced
when an electric arc from a powerful galvanic battery passes between
carbon-poles in an atmosphere of hydrogen. Acetylene is always
formed when bodies containing carbon and hydrogen are burnt in a
limited supply of air, and also in the decomposition of many hydrocarbons
by the electric spark or heat, and it occurs therefore in coalgas.
Acetylene has also been obtained by the electrolysis of the
potassium salts of fumaric and maleic acids:—
Pure acetylene is prepared by heating ethene dibroinide with
alcoholic potash, and passing the vapour through a hot solution of
potash in alcohol; it may also be readily obtained by heating chloroform
with sodium:—
2CHC13 + 3 ^ = C2H4 + 6NaCl
Impure acetylene is produced in quantity by lighting the gas in a
Bunsen's burner at the small orifice in the lower end of the tube, au
incomplete combustion taking place, and acetylene is formed,
Acetylene is a colourless gaa, possessing a strong disagreeable odour;
the smell perceived when a Bunsen's burner burns down being due to
acetylene. It is readily inflammable, burning with a smoky flame,
and is tolerably soluble in water.
"When it is mixed with chlorine in the diffuse daylight, an explosion
generally takes place and carbon separates out, but sometimes tlte
two gases combine quietly, and form the compounds CgH2Cl2 and
OjHgCl^ j g ^ whioh are oily, y heavy y liquids. q It formaalso two liquid q com-
pounds d with ith bromine, b i viz. i CJIaBr2
CJIB and d CJJHJBI^, CHB the th latter ltt being bi
identical with hibromettme dibromide. By y heating g acetylene y with
iodine to 100° 100° they comhiue to acetylene acetylene diiodide di-iodide CgHjIj, CHI forming
colourless crystals melting at 70". With hydriodic acid it forms two
liquid compounds, C2HaI andCjH^; the latter being isomeric with
ethene di-iodide.
Acetylene forms a series of characteristic metallio derivatives. Wheu
it is passed over fused potassium, hydrogen is given off, and the bodies
CoHK and C2K2 are formed; both are black powders, which are
violently decomposed by water, with the re-formation of acetylene, A
similar calcium-compound has been obtained by heating an alloy of