C. and upwards,
or at a pressure of two atmospheres absolute, or higher. If that
temperature or that pressure is exceeded, dissociation (_i.e._,
decomposition into its elements), if initiated at any spot, will extend
through the whole mass of acetylene. In this sense, acetylene at or above
780 deg. C., or at two or more atmospheres pressure, is explosive in the
absence of air or oxygen, and it is thereby distinguished from the
majority of other combustible gases, such as the components of coal-gas.
But if, by dilution with another gas, the partial pressure of the
acetylene is reduced, then the mixture may be subjected to a higher
pressure than that of two atmospheres without acquiring explosiveness, as
is fully shown in Chapter XI. Thus it becomes possible safely to compress
mixtures of acetylene and oil-gas or coal-gas, whereas unadmixed
acetylene cannot be safely kept under a pressure of two atmospheres
absolute or more. In a series of experiments carried out by Dupre on
behalf of the British Home Office, and described in the Report on
Explosives for 1897, samples of moist acetylene, free from air, but
apparently not purified by any chemical process, were exposed to the
influence of a bright red-hot wire.
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