1 deg. C.,
provided the mixture is saturated with aqueous vapour, explosion occurs
only when the percentage of hydrogen in the mixture is between 11.2 and
21.9. The range of explosibility of mixtures of acetylene and air is
similarly reduced by the addition of aqueous vapour (though the exact
figures have not been experimentally ascertained); and hence it follows
that when the temperature in an acetylene generator in which water is in
excess, or in a gasholder, rises, the risk of explosion, if air is mixed
with the gas, is automatically reduced with the rise in temperature by
reason of the higher proportion of aqueous vapour which the gas will
retain at the higher temperature. This fact is alluded to in Chapter II.
Acetone vapour also acts similarly in lowering the upper explosive limit
of acetylene (_cf._ Chapter XI.).
It may perhaps be well to indicate briefly the practical significance of
the range of explosibility of a mixture of air and a combustible gas,
such as acetylene. The lower explosive limit is the lowest percentage of
combustible gas in the mixture of it and air at which explosion will
occur in the mixture if a light or spark is applied to it.
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