The hydrochloric acid is condensed in stoneware
pipes connected with towers packed with coke or stoneware.
_Alkali: Leblanc Process._--The manufacture of vitriol, as I have
described it to you, is the first step in the Leblanc process. The next
stage consists in the manufacture of sodium sulphate (salt-cake) and
hydrochloric acid from the sulphuric acid and common salt; this is
called the salt-cake process. The production of salt-cake or crude
sodium sulphate is carried out in two stages. A large covered iron pan,
called the decomposing pan or salt-cake pot, is mounted in one part of
the salt-cake furnace, and alongside it is the hearth or bed on which
the second stage of the process, the drying or roasting, is effected.
The mixture of common salt and vitriol is charged into the salt-cake
pot, which is heated by a fire below. When from two-thirds to
three-quarters of the hydrochloric acid has been expelled from the
charge, the mass acquires the consistence of thick dough, and at this
stage it is raked out of the pan on to the roasting hearth alongside,
where the decomposition is completed by means of flames playing directly
on to the top of the charge.
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