ld again be
plunged in another quantity of spent tan-water mixed with the one
thousandth part of the oil of vitriol, and thus steeped a second time;
their swelling and raising will be completed in about forty-eight
hours; after this operation the hides will acquire a yellow colour,
even to the interior part of their substance. To determine if the
swelling and raising be sufficiently completed, let one of the corners
of the hide be cut, and if it is in a proper state there will not
appear any white streak in the middle, but the hide throughout its
whole substance will have acquired a yellow colour, and
semi-transparent appearance. Mr. S---- is of opinion, that swelling and
raising hides is not necessary, and that the hides tanned without this
operation are less permeable to water. On tanning on the new principle,
as practised by Mr. S----, he places several rows of casks on stillings
sufficiently elevated above the ground to place a can or tub under
them; these casks were filled with fresh finely ground tan, then a
certain quantity of water was poured into the first of them, which
water, as it ran through the tan, exhausted and carried off the soluble
part, and as fast as it ran into the vessels below, was taken away and
poured on the second cask, and so on successively until the solution
was sufficiently saturated, and thus it may have been brought to ten or
twelve degrees of the arometer for salts. In order to exhaust the tan
of the first cask, Mr. S---- continued pouring water on the first cask
until it ran off clear; at which time the tan was deprived of its
soluble part; these liquors, as it may be easily conceived, were
carefully kept for future operations; large wooden vats are considered
the best sort of vessels for holding this solution, as well as for
making and preparing it; hogsheads, on a small scale, may be made to
answer. It is particularly in the use of this solution that Mr. S----'s
method consists; the quickness with which the solution acts is truly
astonishing, and when we see it, there is cause of surprise in thinking
why it was not found out before. As soon as the hides are taken out of
the water, impregnated with sulphuric acid, Mr. S---- puts them into a
weak solution of tan, in which he leaves them for the space of one or
two hours; he afterwards plunges them into other solutions of tan, more
or less charged with the tanning principle, in proportion to their
strength, so that in the experiments at