Whenever a water-cooled condenser is employed after the
generator, in which the gas does not come in contact with the water, that
liquid may always be used to charge the generator. For compactness and
simplicity of parts the water of the holder seal is occasionally used as
the washing liquid, but unless the liquid of the seal is constantly
renewed it will thus become offensive, especially if the holder is under
cover, and it will also act corrosively upon the metal of the tank and
bell. The water-soluble impurities in acetylene will not be removed
completely by merely standing over the holder seal for a short time, and
it is not good practice to pass unnecessarily impure gas into a holder.
[Footnote: This is not a contradiction of what has been said in Chapter
III. about the relative position of holder and chemical purifiers,
because reference is now being made to ammonia and sulphuretted hydrogen
only.]
HARMFULNESS OF IMPURITIES.--The reasons why the carbide impurities must
be removed from acetylene before it is burned have now to be explained.
From the strictly chemical point of view there are three compounds of
phosphorus, all termed phosphoretted hydrogen or phosphine: a gas, PH_3;
a liquid, P_2H_4; and a solid, P_4H_2.
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