be placed upon it, and it will be found to be only slightly warm to the
touch. Such a test, however, is inconclusive, and frequently misleading,
because if more than a pound or two of carbide is present as an undivided
mass, and if water is allowed to attack one portion of it, that
particular portion may attain a high temperature while the rest is
comparatively cool: and if the bulk of the carbide is comparatively cool,
naturally the walls of the containing vessel themselves remain
practically unheated. Three causes work together to prevent this heat
being dissipated through the walls of the carbide vessel with sufficient
rapidity. In the first place, calcium carbide itself is a very bad
conductor of heat. So deficient in heat-conducting power is it that a
lump a few inches in diameter may be raised to redness in a gas flame at
one spot, and kept hot for some minutes, while the rest of the mass
remains sufficiently cool to be held comfortably in the fingers. In the
second place, commercial carbide exists in masses of highly irregular
shape, so that when they are packed into any vessel they only touch at
their angles and edges; and accordingly, even if the material were a
fairly good heat conductor of itself, the air or gas present between each
lump would act as an insulator, protecting the second piece from the heat
generated in the first. In the third place, the calcium hydroxide
produced as the by-product when calcium carbide is decomposed by water
occupies considerably more space than the original carbide--usually two
or three times as much space, the exact figures depending upon the
conditions in which it is formed--and therefore a carbide container
cannot advisedly be charged with more than one-third the quantity of
solid which it is apparently capable of holding. The remaining two-thirds
of the space is naturally full of air when the container is first put
into the generator, but the air is displaced by acetylene as soon as gas
production begins. Whether that space, however, is occupied by air, by
acetylene, or by a gradually growing loose mass of slaked lime, each