Chapter 6
Saving time in Natural Operations
47. The process of tanning will furnish us with a striking
illustration of the power of machinery in accelerating certain
processes in which natural operations have a principal effect.
The object of this art is to combine a certain principle called
tanning with every particle of the skin to be tanned. This, in
the ordinary process, is accomplished by allowing the skins to
soak in pits containing a solution of tanning matter: they remain
in the pits six, twelve, or eighteen months; and in some
instances (if the hides are very thick), they are exposed to the
operation for two years, or even during a longer period. This
length of time is apparently required in order to allow the
tanning matter to penetrate into the interior of a thick hide.
The improved process consists in placing the hides with the
solution of tan in close vessels, and then exhausting the air.
The effect is to withdraw any air which may be contained in the
pores of the hides, and to aid capillary attraction by the
pressure of the atmosphere in forcing the tan into the interior
of the skins.
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