A serious difficulty attending this process
arises from the destructive action of the acid upon the boiler or
chamber in which the operation is carried on, and as this vessel, which
is generally of large dimensions, is exposed to considerable pressures,
it is necessarily constructed of iron or some other sufficiently
resisting metal. An ingenious method of avoiding this difficulty has
been devised, we believe in Germany, and has been put into practice with
a certain amount of success. It consists in lining the iron boiler with
a covering of lead, caused by fusion to unite firmly to the walls of the
boiler, and thus to protect it from the action of the acid. No trouble,
it is stated, is found to arise from the difference in expansion of the
two metals, which, moreover, adhere fairly well; but, on the other hand,
we believe it does actually occur that the repairs to this lead lining
are numerous, tedious, and costly of execution, so that the system can
scarcely be regarded as meeting the requirements of the manufacturer.
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