There are two difficulties which the designer of automatic mechanism has
to contend with, and it is doubtful whether he always makes a sufficient
allowance for them. The first is that not only must calcium carbide and
liquid water be kept out of premature contact, but that moisture, or
vapour of water, must not be allowed to reach the carbide; or
alternatively, that if water vapour reaches the carbide too soon, the
undesired reaction shall not determine overheating, and the liberated gas
be not wasted or permitted to become a source of danger. The second
difficulty encountered by the designer of automata is so to construct his
apparatus that it shall behave well when attended to by completely
unskilled labour, that it shall withstand gross neglect and resist
positive ill-treatment or mismanagement. If the automatic principle is
adopted in any part of an acetylene apparatus it must be adopted
throughout, so that as far as possible--and with due knowledge and skill
it is completely possible--nothing shall be left dependent upon the
memory and common sense of the gasmaker. For instance, it must not be
necessary to shut a certain tap, or to manipulate several cocks before
opening the carbide vessel to recharge it; it must not be possible for
gas to escape backwards out of the holder; and either the carbide-feed
gear or the water-supply mechanism (as the case may be) must be
automatically locked by the mere act of taking the cover off the carbide
store, or of opening the sludge-cock at the bottom.
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