TANNING. 
squill, the roots of bistort, of rhubarb, of 
parella, and several other plants. We have 
also found this principle in the products of 
distillation of different vegetable substances, 
where it was in some measure formed dur- 
ing the operation. 
From these different considerations, found- 
ed on experiment, the following general 
principles may be deduced : 1. Every sub- 
stance of which the infusion is capable of 
precipitating animal jelly, possesses the 
tanning property, g. Every substance 
which possesses the tanning property, like- 
wise precipitates the sulphate of iron black. 
3. Every substance which precipitates the 
sulphate of iron, but not the solution of 
glue, does not possess the tanning pro- 
perty. 
Upon M. Seguin’s principle, a patent was 
some years since taken out by Mf. W. Des- 
mond, who obtains the tanning principle by 
digesting oak-bark, or other proper mate- 
rial, in cold water, in an appa'-atus nearly 
similar to tliat used in the salt petre works. 
That is to say, tlie water which has remained 
upon the powdered baik for a certain time, 
in one vessel, is drawn off by a cock, and 
poured upon fresh tan. This is again to be 
drawn off, and poured upon other fresh tan ; 
and in this way the process is to be conti- 
nued to the fifth vessel. The liquor is then 
highly coloured, and marks, as Mr. Des- 
mond says, from six to eight degrees on the 
hydrometer for salts. He calls this the 
farming lixivium. The criterion to distin- 
guish its presence is, that it precipitates 
glue from its aqueous solution, and is also 
nsefiil to examine how far other vegetable 
substances, as well as oak-bark, may be 
suitable to the purpose of tanning, The 
strong tanning liquor is to be kept by itself. 
It is found, by trials with the glue, that the 
tanning principle of the first digester which 
receives the clear water, is, of course, first 
exhausted ; bat the same tan will still give 
a certain portion of the astriiige.nt principle, 
or gallic lixivium, to water. Tlie presence 
of tliis principle js ascertained by its strik- 
ing a black colour when added to a small 
quantity of the solution of vitriol of iron, or 
green copperas. As soon as the water from 
the digester ceases to exhibit this sign, the 
tan is exhausted, and must be replaced with 
new. The gallic lixivium is resej ved for 
the purpose of taking the hair off from 
hides. Strong hides, after washing, clean- 
ing, and fleshing, in the usual way, are to 
be immersed for two or three days in a 
mixture of gallic lixivium, and a thou- 
sandth part, by measure, of dense vitriolic 
acid. By this means the hair is detached 
from the hides, so that it may be scraped 
off with a round knife. When swelling or 
raising is required, the bides are to be im- 
mersed for ten or twelve horns in another 
vat, filled with water, and one five hun- 
dredth part of the same vitriolic acid. The 
hides being then repeatedly washed and 
dressed, are ready for tanning ; for which 
purpose they are to be immersed for some 
hours in a weak tanning lixivium, of only 
one or two degrees ; to obtain which, the 
latter portions of the infusions are set apart, 
or else some of that which has been partly 
exhausted by use in tanning. Tlie hides 
are then to be put into a stronger lixivium, 
where, in a few days, they will be brought 
to the same degree of saturation with the 
liquor in wliich they are immersed. The 
strength of the liquor will by this means be 
considerably diminished, and must therefore 
be renewed. When the hides are by this 
means completely saturated, that is to say, 
perfectly tanned, they are to be removed, 
and slowly dried in the shade. Calfskins, 
goat-skins, and the like, are to be steeped 
in lime-water, after the usual fleshing and 
washing. These are to remain in the lime- 
water, wliich contains more lime than it 
can dissolve, and requires to be stirred 
several times a-day. After two or three 
days, the skins are to be removed, and per- 
fectly cleared of their lime by washing and 
pressing in water. The tanning process is 
tlien to be accomplished in the same man- 
ner as for the strong hides ; but the lixivium 
must be considerably weaker. Mr. Des- 
mond remarks, that lime is used instead of 
tlie gallic lixivium for such hides as are re- 
quired to have a close grain ; because, the 
acid mixed with that lixivium always swells 
the skins more or less : but that it cannot, 
with the same convenience, be used with 
thick skins, on account of the considerable 
labour required to clear them of the lime ; 
any part of wliich, if left, would render 
them harsh, and liable to crack. He recom- 
mends, likewise, as the best method to 
bring the whole siirtace of tlie hides in con- 
tact with the lixivium, tiiat they should be 
suspended vertically in the fluid, by means 
of transverse rods or bars, at such a distance 
as not to touch each other. By this prac- 
tice, much of the labour of turning and 
handling may be saved. Mr. Desmond 
concludes his specification by observing, 
that in some cases it will be expedient to 
mix fresh tan witli tlie lixivium and that 
