Nevertheless Wolff and Gerard have found hydrogen silicide in
crude acetylene, and Lewes looks upon it as a common impurity in small
amounts. When it occurs, it is probably derived, as Vigouroux has
suggested, from "alloys" of silicon with calcium, magnesium, and
aluminium in the carbide. The metallic constituents of these substances
would naturally be attacked by water, evolving hydrogen; and the
hydrogen, in its nascent state, would probably unite with the liberated
silicon to form hydrogen silicide. Many authorities, including Keppeler,
have virtually denied that silicon compounds exist in crude acetylene,
while the proportion 0.01 per cent. has been given by other writers as
the maximum. Caro, however, has stated that the crude gas almost
invariably contains silicon, sometimes in very small quantities, but
often up to the limit of 0.8 per cent.; the failure of previous
investigators to discover it being due to faulty analytical methods. Caro
has seen one specimen of (bad) carbide which gave a spontaneously
inflammable gas although it contained only traces of phosphine; its
inflammability being caused by 2.1 per cent. of hydrogen silicide.
Practically speaking, all the foregoing remarks made about phosphine
apply equally to hydrogen silicide: it burns to solid silicon oxide
(silica) at the burners, is insoluble in water, and is spontaneously
inflammable when alone or only slightly diluted, but never occurs in good
carbide in sufficient proportion to render the acetylene itself
inflammable.
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