Later on the more responsible
members of the trade took another view, but they attacked the problem of
purification in a perfectly empirical way, either employing some purely
mechanical scrubber filled with some moist or dry porous medium, or
perhaps with coke or the like wetted with dilute acid, or they simply
borrowed the processes adopted in the purification of coal-gas. At first
sight it might appear that the more simple methods of treating coal-gas
should be suitable for acetylene; since the former contains two of the
impurities--sulphuretted hydrogen and ammonia--characteristic of crude
acetylene. After removing the ammonia by washing with water, therefore,
it was proposed to extract the sulphur by passing the acetylene through
that variety of ferric hydroxide (hydrated oxide of iron) which is so
serviceable in the case of coal-gas. The idea, however, was quite
unsound: first, because it altogether ignores the phosphorus, which is
the most objectionable impurity in acetylene, but is not present in coal-
gas; secondly, because ferric hydroxide is used on gasworks to extract in
a marketable form the sulphur which occurs as sulphuretted hydrogen, and
true sulphuretted hydrogen need not exist in well-generated and well-
washed acetylene to any appreciable extent; thirdly, because ferric
hydroxide is not employed by gasmakers to remove sulphur compounds (this
is done with lime), being quite incapable of extracting them, or the
analogous sulphur compounds of crude acetylene.
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