The hydrochloric acid evolved during the
process is condensed in much the same manner as in the process of
Hargreaves & Robinson previously described. It is a curious fact that in
the earlier years of the Leblanc process, hydrochloric acid, or "spirits
of salt," as it is frequently called, was a by-product that required all
the vigilance of the alkali-works inspectors to prevent it being allowed
to escape from the chimneys in more than a certain small regulated
amount. Now, it is the principal product; indeed, the Leblanc alkali
maker may be said to subsist on that hydrochloric acid, as his chief
instrument for producing chloride of lime or bleaching powder.
Mechanical furnaces are now used to a large extent for the salt-cake
process. They consist broadly of a large revolving furnace-hearth or
bed, on to which the mixture of salt and vitriol is charged, and on
which it is continuously agitated, and gradually moved to the place of
discharge, by rakes or the like, operated by suitable machinery.
The next stage of the Leblanc process is the manufacture of "black ash,"
or crude sodium carbonate.
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