GENERATOR IMPURITIES.--The generator impurities present in the crudest
acetylene consist of oxygen and nitrogen, _i.e._, the main
constituents of air, the various gaseous, liquid, and semi-solid bodies
described in Chapter II., which are produced by the polymerising and
decomposing action of heat upon the carbide, water, and acetylene in the
apparatus, and, whenever the carbide is in excess in the generator, some
lime in the form of a very fine dust. In all types of water-to-carbide
plant, and in some automatic carbide-feed apparatus, the carbide chamber
must be disconnected and opened each time a fresh charge has to be
inserted; and since only about one-third of the space in the container
can be filled with carbide, the remaining two-thirds are left full of
air. It is easy to imagine that the carbide container of a small
generator might be so large, or loaded with so small a quantity of
carbide, or that the apparatus might in other respects be so badly
designed, that the gas evolved might contain a sufficient proportion of
air to render it liable to explode in presence of a naked light, or of a
temperature superior to its inflaming-point. Were a cock, however, which
should have been shut, to be carelessly left open, an escape of gas from,
rather than an introduction of air into, the apparatus would follow,
because the pressure in the generator is above that of the atmosphere.
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