Clearly, unless the apparatus in which such mixtures as these are
intended to be prepared is designed with considerable care, the amount of
carbon dioxide in the gas will be liable to vary, and may fall to zero.
If any quantity of carbide present has been decomposed in the ordinary
way, there will be free calcium hydroxide in the generator; and if the
carbon dioxide comes into contact with this, it will be absorbed, unless
sufficient acid is employed to convert the calcium carbonate (or
hydroxide) into the corresponding normal salt of calcium. Similarly,
during purification, a material containing any free lime would tend to
remove the carbon dioxide, as would any substance which became alkaline
by retaining the ammonia of the crude gas.
It cannot altogether be granted that the value of a process for diluting
acetylene with carbon dioxide has been established, except in so far as
the mere presence of the diluent may somewhat diminish the tendency of
the acetylene to polymerise as it passes through a hot burner (_cf._
Chapter VIII.). Certainly as a fuel-gas the mixture would be less
efficient, and the extra amount of carbon dioxide produced by each flame
is not wholly to be ignored.
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