When the gases merely
unite quietly, tetrachlorethane, or acetylene tetrachloride, is produced
thus:
C_2H_2 + 2Cl_2 = C_2H_2Cl_4;
but when the reaction is violent some hexachlorethane is formed,
presumably thus:
2C_2H_2 + 5Cl_2 = 4HCl + C_2 + C_2Cl_6.
The heat evolved by the decomposition of the acetylene by the formation
of the hydrochloric acid in the last equation is then propagated amongst
the rest of the gaseous mixture, accelerating the action, and causing the
acetylene to react with the chlorine to form more hydrochloric acid and
free carbon thus;
C_2H_2 + Cl_2 = 2HCl + C_2.
It is evident that these results do not altogether explain the mechanism
of the reactions involved. Possibly the formation of substitution
products and the consequent occurrence of an explosion is brought about
by some foreign substance which acts as a catalytic agent. Such substance
may conceivably be one of the impurities in crude acetylene, or the solid
matter of a bleaching-powder purifying material. The experiments at least
indicate the direction in which safety may be sought when bleaching-
powder is employed to purify the crude gas, viz., dilution of the powder
with an inert material, absence of air from the gas, and avoidance of
bright sunlight in the place where a spent purifier is being emptied.
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