_--The greater part of the hydrochloric acid
manufactured in Great Britain is obtained as an intermediate product in
the Leblanc alkali process, which will presently be described, being
produced by heating common salt with vitriol. A large quantity is,
however, also produced by the so-called direct process of Hargreaves &
Robinson, which is, in principle, the same method as that employed in
the Leblanc process, except that the intermediate product, vitriol, is
not separated. It consists essentially in passing the hot gases from
pyrites kilns, as used in the manufacture of vitriol, through large
cast-iron vessels containing common salt heated to a high temperature.
Various physical conditions must be complied with in order to make the
process a success. For example, the salt is used in the form of moulded
hard porous cakes made from a damp mixture of common salt and rock salt.
The cast-iron vessels must be heated uniformly, and the hot pyrites kiln
gases must be passed downwards through the salt in order to ensure
uniform distribution.
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