It must be
avoided, because whenever the temperature in the immediate neighbourhood
of a mass of calcium carbide which is evolving acetylene under the attack
of water rises materially above the boiling-point of water, one or more
of three several objectionable effects is produced--(_a_) upon the
gas generated, (_b_) upon the carbide decomposed, and (_c_)
upon the general chemical reaction taking place.
It has been stated above that in moat generators when the action between
the carbide and the water is proceeding smoothly, it occurs according to
equation (2)--
(2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2
rather than in accordance with equation (1)--
(1) CaC_2 + H_2O = C_2H_2 + CaO.
This is because calcium oxide, or quicklime, the by-product in (1), has
considerable affinity for water, evolving a noteworthy quantity of heat
when it combines with one molecule of water to form one molecule of
calcium hydroxide, or slaked lime, the by-product in (2). If, then, a
small amount of water is added to a large amount of calcium carbide, the
corresponding quantity of acetylene may be liberated on the lines of
equation (1), and there will remain behind a mixture of unaltered calcium
carbide, together with a certain amount of calcium oxide.
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