Evolution of gas produced in this way does not
matter in the least, because it is easy to return the gas so liberated
into the generator or into the holder; while the extent of the action,
and the consequent production of overheating, will tend to be less than
in generators such as those shown in G and H of Figs. 4 and 5, inasmuch
as the large excess of water in the carbide-feed apparatus prevents the
liquid arriving at a temperature at which it volatilises rapidly. The
main objection to the evolution of gas in the carbide vessel of a
carbide-to-water generator depends on the danger that the smooth working
of the feed-gear may be interfered with by the formation of dust or by
the aggregation of the carbide lumps.
USE OF OIL IN GENERATORS.--Calcium carbide is a material which is only
capable of attack for the purpose of evolving acetylene by a liquid that
is essentially water, or by one that contains some water mixed with it.
Oils and the like, or even such non-aqueous liquids as absolute alcohol,
have no effect upon carbide, except that the former naturally make it
greasy and somewhat more difficult to moisten. This last property has
been found of service in acetylene generation, especially on the small
scale; for if carbide is soaked in, or given a coating of, some oil, fat,
or solid hydrocarbon like petroleum, cocoanut oil, or paraffin wax, the
substance becomes comparatively indifferent towards water vapour or the
moisture present in the air, while it still remains capable of complete,
albeit slow, decomposition by liquid water when completely immersed
therein.
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