When the gas was held in the
containing vessel at the atmospheric pressure then obtaining, viz., 30.34
inches (771 mm.) of mercury, no explosion occurred. When the pressure was
raised to 45.34 inches (1150 mm.), no explosion occurred; but when the
pressure was further raised to 59.34 inches (1505 mm., or very nearly two
atmospheres absolute) the acetylene exploded, or dissociated into its
elements.
Acetylene readily polymerises when heated, as has been stated in Chapter
II., where the meaning of the term "polymerisation" has been explained.
The effects of the products of the polymerisation of acetylene on the
flame produced when the gas is burnt at the ordinary acetylene burners
have been stated in Chapter VIII., where the reasons therefor have been
indicated. The chief primary product of the polymerisation of acetylene
by heat appears to be benzene. But there are also produced, in some cases
by secondary changes, ethylene, methane, naphthalene, styrolene,
anthracene, and homologues of several of these hydrocarbons, while carbon
and hydrogen are separated. The production of these bodies by the action
of heat on acetylene is attended by a reduction of the illuminative value
of the gas, while owing to the change in the proportion of air required
for combustion (_see_ Chapter VIII.
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