Indeed, prolonged experience tends to show that a
selection between non-automatic and automatic apparatus may frequently be
made on the basis of capacity. A small plant is undoubtedly much more
convenient if automatic; a very large plant, such as that intended for a
public supply, is certainly better if non-automatic, but between these
two extremes choice may be exercised according to local conditions.
CONTROL OF THE CHEMICAL REACTION.--Coming now to study the principles
underlying the construction of an acetylene generator more closely it
will be seen that as acetylene is produced by bringing calcium carbide
into contact with water, the chemical reaction may be started either by
adding the carbide to the water, or by adding the water to the carbide.
Similarly, at least from the theoretical aspect, the reaction, may be
caused to stop by ceasing to add carbide to water, or by ceasing to add
water to carbide. Apparently if water is added by degrees to carbide,
until the carbide is exhausted, the carbide must always be in excess; and
manifestly, if carbide is added in small portions to water, the water
must always be in excess, which, as was argued in Chapter II.
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