The liquid is spontaneously
inflammable in presence of air; that is to say, it catches fire of itself
without the assistance of spark or flame immediately it comes in contact
with atmospheric oxygen; being very volatile, it is easily carried as
vapour by any permanent gas. The gaseous phosphine is not actually
spontaneously inflammable at temperatures below 100 deg. C.; but it oxidises
so rapidly in air, even when somewhat diluted, that the temperature may
quickly rise to the point of inflammation. In the earliest days of the
acetylene industry, directly it was recognised that phosphine always
accompanies crude acetylene from the generator, it was believed that
unless the proportion were strictly limited by decomposing only a carbide
practically free from phosphides, the crude acetylene might exhibit
spontaneously inflammable properties. Lewes, indeed, has found that a
sample of carbide containing 1 per cent of calcium phosphide gave
(probably by local decomposition--the bulk of the phosphide suffering
attack first) a spontaneously inflammable gas; but when examining
specimens of commercial carbide the highest amount of phosphine he
discovered in the acetylene was 2.
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