Inasmuch as
both these substances possess an affinity for water (setting heat free
when they combine with it), when a further limited amount of water is
introduced into the mixture some of it will probably be attracted to the
oxide instead of to the carbide present. It is well known that at
ordinary temperatures quicklime absorbs moisture, or combines with water,
to produce slaked lime; but it is equally well known that in a furnace,
at about a red heat, slaked lime gives up water and changes into
quicklime. The reaction, in fact, between calcium oxide and water is
reversible, and whether those substances combine or dissociate is simply
a question of temperature. In other words, as the temperature rises, the
heat of hydration of calcium oxide diminishes, and calcium hydroxide
becomes constantly a less stable material. If now it should happen that
the affinity between calcium carbide and water should not diminish, or
should diminish in a lower ratio than the affinity between calcium oxide
and water as the temperature of the mass rises from one cause or other,
it is conceivable that at a certain temperature calcium carbide might be
capable of withdrawing the water of hydration from the molecule of slaked
lime, converting the latter into quicklime, and liberating one molecule
of acetylene, thus--
(3) CaC_2 + Ca_2(OH) = C_2H_2 + 2CaO.
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