III. The treatment is of two kinds, or of a combination of both. In one
process the lumps are coated with a strong solution of glucose, with the
object of assisting in the removal of spent lime from their surface when
the carbide is immersed in water. Lime is comparatively much more soluble
in solutions of sugar (to which class of substances glucose belongs) than
in plain water; so that carbide treated with glucose is not so likely to
be covered with a closely adherent skin of spent lime when decomposed by
the addition of water to it. In the other process, the carbide is coated
with or immersed in some oil or grease to protect it from premature
decomposition. The latter idea, at least, fulfils its promises, and does
keep the carbide to a large extent unchanged if the lumps are exposed to
damp air, while solving certain troubles otherwise met with in some
generators (cf. Chapter III.); 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