); but both operations involve additional
expense, and since ordinary carbide can be used satisfactorily in a good
fixed generator, and can be preserved without serious deterioration by
the exercise of reasonable care, treated carbide is only to be
recommended for employment in holderless generators, of which table-lamps
are the most conspicuous forms. A third variant of plain carbide is
occasionally heard of, which is termed "scented" carbide. It is difficult
to regard this material seriously. In all probability calcium carbide is
odourless, but as it begins to evolve traces of gas immediately
atmospheric moisture reaches it, a lump of carbide has always the
unpleasant smell of crude acetylene. As the material is not to be stored
in occupied rooms, and as all odour is lost to the senses directly the
carbide is put into the generator, scented carbide may be said to be
devoid of all utility.
THE REACTION BETWEEN CARBIDE AND WATER.--The reaction which occurs when
calcium carbide and water are brought into contact belongs to the class
that chemists usually term double decompositions. Calcium carbide is a
chemical compound of the metal calcium with carbon, containing one
chemical "part," or atomic weight, of the former united to two chemical
parts, or atomic weights, of the latter; its composition expressed in
symbols being CaC_2.
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