But when
the generating vessels and the holder of a non-automatic apparatus are
properly designed and constructed, the gas in the latter is acetylene
practically free from air, and therefore while being, as acetylene
inevitably is, inflammable, is devoid of explosive properties, always
assuming, as must be the case in a water-sealed holder, that the
temperature of the gas is below 780 deg. C.; and also assuming, as must
always be the case in good plant, that the pressure under which the gas
is stored remains less than two atmospheres absolute. It is perfectly
true that calcium carbide is non-inflammable and non-explosive, that it
is absolutely inert and incapable of change; but so comprehensive an
assertion only applies to carbide in its original drum, or in some
impervious vessel to which moisture and water have no access. Until it is
exhausted, an automatic acetylene generator contains carbide in one place
and water in another, dependence being put upon some mechanical
arrangement to prevent the two substances coming into contact
prematurely. Many of the devices adopted by builders of acetylene
apparatus for keeping the carbide and water separate, and for mixing them
in the requisite quantities when the proper time arrives, are as
trustworthy, perhaps, as it is possible for any automatic gear to be; but
some are objectionably complicated, and a few are positively inefficient.
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