THE HOME MECHANIC.
865
TANNING. The process of tanning consists in the turning of the skins of animals into leather by combining, chemically, the substance of the skin with tannin, an astringent ingredient.
Tannin
is
made from Gall
certain species of oak,
Nuts, which are found upon and also occurs in a number of The galls are formed by the female
other trees and plants. insect Cynips by piercing the buds of a variety of oak called Quercus infectoria and there depositing its eggs. These, producing irritation, cause the sap of the plant to flow toward the wound, thus forming a vegetable tumor or gall. The principal species of oak which yields the Gall
Nuts of commerce is the Qiierciis infectoria. There are a large number of processes by which tannin owing to lack of space we will give but one is obtained ;
process,
nin
known as
Pelouze's Process.
—or tannic acid, as
By this
process, tan-
—
sometimes called is obtained by means of a percolator fitted into a receiver. The percolator is a cylindrical glass vessel, open at both ends, the upper opening being fitted with an air-tight stopper, and the lower end adjusted to the neck of the glass receiver. The upper vessel, or percolator, is about half filled with coarsely-powdered galls, which are prevented from falling through the lower opening by a plug of cotton; the powder is then covered with ether, which has been previously shaken up with a little water. (It is well it is
THE HOME MECHANIC.
ggg
necessary that the ether to state here that it is absolutely a fraction should be agitated with water, otherwise not in inserted now is stopper The of tannin will be obtained.) to allowed mixture the mouth of the percolator and the the stopper is withdigest for several hours, after which receiver drawn and the liquid allowed to filter into the
has passed through, the at powdered galls are washed with more ether, introduced the short time, the top as before. After standing for a
beneath.
When
all the liquid
filtered liquor will
to separate into
be found
two
distinct
The tannic acid and gallic strata of unequal density. mixture of ether and acid, being both extracted by the a solution water, now separate; the lower stratum being and the water, in color) of tannin (generally of an amber consubstances upper stratum an etherial solution of other which is Gallic tained in the galls, the most important of the aqueous separated; next acid. The two solutions are temperature solution of tannin is gently evaporated at a not exceeding 212째 Fahr.
The
result is
an amorphous, or
quite pure, uncrystallized, mass of tannin, nearly if not cent of the per the yield being frequently about 40 to 45 liquid is weight of galls used. The ether in the lighter the aid recovered by distillation, over a water bath, with ice-cold water. of a Liebig's condenser, supplied with One method of salting hides consists in spreading sprinkling the flesh the hides open upon the ground and edges and along the at side with salt, but more liberally or doubled the spinal parts. The hides are then folded down the centre the remaining folds are made
lengthwise next the over each other, commencing with the shanks upon head the peak of the belly upon the back afterwards and, lastly, the tail part, and the tail part upon the head; a square forming and fold, final doubling the whole with a three piled are they of about two feet. This being done, dissolved and or four together, and left until the salt has three penetrated their tissue, which is generally in about ;
;
;
THE HOME MECHANIC.
867
or four days. Thus preserved they are sent to market. Skms may be dried, even after having been salted, by stretching them upon poles, with the flesh side
outwards
and exposing them to dry air in a shady place. Ten pounds of salt in summer, and somewhat less in winter are requisite for each skin of ordinary
•
'
size.
Tanning of Skins with Fur On. -After softening the skm by soaking, cut off all useless parts, and, having removed all fatty substance from the inside, soak it for one hour in warm water. After this mix for each skin about
a half ounce of sulphate soda, a half ounce of borax, and a half ounce of saltpetre with enough water to make'a thin paste. Then take a brush and cover the inside of the skin with this paste, being careful to apply more to the thick parts than to the thin. Fold the skin, flesh side in, and put it in a cool place for twenty-four hours. Melt sl'owlv together,
without being allowed to boil, two ounces of hard white soap, one ounce of sal-soda, and a half ounce of borax; apply this mixture to the skin with a brush in the same way as before, after having washed the skin clean. Then double the skin together, the same as before and put It in a warm place. After allowing it to
remaiil for twenty-four hours, dissolve, in enough hot rain-water to saturate the skin, two ounces saleratus, four ounces alum, and eight ounces salt when this solution is cool enough not to burn the hands, place the skin in it and allow It to soak for twelve hours; then hang it up to dry after wringing out. Repeat this soaking and drying several times until the skin has reached a sufficient degree of softness; then even off the surface of the inside with pumice stone or sand-paper. ;
Depilation by
Sulphide of Sodium. -Dissolve four or flve pounds of the sulphide in each gallon of water Form^ this into a thin paste with lime or pipe-clay. The paste is to be spread evenly over the hair side of the hide
which
is
effected
by cue workman pouring
it
from a
pail
THE HOME MECHANIC.
868
down
the middle of the hide, while another, with a mop, rubs it into every part. The hide is then folded into a cushion and set aside. In from fifteen to twenty hours it will be ready for unhairing, when it will be found that the hair is reduced to a pulp and therefore totally deIn the above concentrated condition the hair stroyed. would doubtless be destroyed in less than an hour. The hides are now thrown into cold water, to wash away the sulphide and to enable them to plump. The sulphide being highly caustic, it will, if not removed by washing, attack the nails and skin of the workmen, who should be thoroughly cautioned as to its use, otherwise they will soon suffer from alkaline sores " of a most painful characThis method of unhairing gives good weight, as also ter. tough and solid leather, but it requires to be used with very great care. If not spread evenly upon the hide, patches of hair may remain upon the pelt which will be troublesome to remove afterwards. Unless the hides, after being treated by the sulphide, are plumped by steeping in weak lime, the fleshy matters will be difficult to remove on the beam. Raising by acid is also considered necessary, since the sulphide itself has but little plumping In applying this process to dressing hides, the effect. sulphide is used in a more diluted condition, the hides being suspended in a solution of the sulphide, three-quarters of a pound being used to a hide. After suspension in this solution for about twenty -four hours the hides are in the condition for unhairing, after which they are limed to plump or swell them. Now and then sulphide of sodium fails to wholly remove the epidermis, producing ugly stains on the leather. In a case of this kind, treat the imperfectly depilated skin with milk of lime, which removes all trace of the epidermis very quickly. * *
Funcke's Tanning Process.— The unhaired skins or hides are passed through a solution of commercial soda, and then hung up until nearly dry before subjecting them
THE HOME MECHANIC. to the tanning process.
869
The skins are immersed in a soluwhich is added
tion of bark or other tanning material, to
a dilute vegetable acid. By this solution the pores of the skin are opened while being exposed to the action of the tannic acid. The skins are again subjected to the action of a stronger solution of the vegetable acid, and its action is mollified by the addition of a solution of sugar. Finally, while the skins are subjected to the usual handling, they are treated with a solution of tannic acid until the leather but since the tanning liquor used in this prois finished cess is of such strength as to impart too deep a color for most purposes, the color is reduced, when requisite, by ;
adding, in the last stage of the process, sulphuric acid and salt to the tanning liquor in which the skins are worked. The skins are partially dried after each operation before
submitting to the next. A New Tanning Process.
— In this process the hides are
subjected to two solutions, mixed as follows for the first solution, dissolve in twenty to thirty parts of wood vinegar, twenty to thirty parts of chromate of alumina, and di:
lute with water to tion, dissolve in
one thousand parts
;
for the second solu-
ammonia some ammonio-nickel
chloride
compounded with a concentrated solution of tartar. After carefully freeing the hides from lime, place them in a mixture composed of two parts of the first solution and one part of the second. For thick bullock hides eighteen twenty-one days are adequate. Page's Tanning Process.— By this process the hides and skins are limed in weak and strong solutions, unhaired, drenched in hen manure or other suitable bate, and immersed and handled in coloring liquors made from equal parts of any suitable bark and sweet fern, cutch and sweet fern, or gambler and sweet fern. A mixture is then prepared with the following ingredients: forty parts of
to
common
salt,
chloride of potassium, or
parts of alum,
and thirteen
ammonium,
parts of saltpetre.
forty
These are
: ;
870
THE HOME MECTHANIC.
thoroughly mixed and dissolved in four vats half-filled with water. The vats measure six feet by four, and are numbered 1, 2, 3, and 4. One-third more of the mixture is put into 3 and 4 tjpian into 1 and 2. After a salt solution has been thus prepared, a tin solution is prepared as follows to two gallons of the stronger salt solution are added two quarts of oil of vitriol, two gallons of muriate of tin of 140° to 150° Twaddell, twenty -eight gallons of muriatic acid of 20° to 30° Baume, and two gallons of nitric acid of 36° to 40° B. The hides are tanned by being immersed
in the four vats successively; one pint of the tin solution being first added to the solutions in vats 3 and 4, and one
pint added to each of these solutions whenever a fresh lot of hides are put in. The coloring liquor first described may, if desired, be made without sweet fern or exclu-
from sweet fern. The tanning is said to occupy a very short time, and the leather produced is stated to be exceedingly tough and close in fibre. Tanning by a Quick Process. The skins are placed in a hermetically closed fulling trough, after having been put through the usual running- water treatment. To every hundred pounds of skins, to be weighed when taken from the water, a mixture of one pound of sulphate of copper, twenty pounds of bark of oak root, thirty pounds of dividivi, thirty pounds of alum, and sixty-five pounds of acidulated barley meal is contained in the water in the fulling sively
—
In place of sulphate of copper, sulphate of ammonia or sulphate of zinc may be substituted; other materials containing tannin may be used in place of dividivi and bark of oak root and alum may be substituted by sulphate of alumina. When the skins are in the fulling trough they are turned, for twenty-four hours, repeatedly the hides are then put in a common vat together with the tanning fluid, and are taken out and put back again, daily, from fifteen to twenty days. At the end of this time they trough.
;
are transferred to
an ordinary
pit
and put in tan
;
here
THE HOME JIECHANIC. tliey are allow ed to
remain from
871
fifteen to thirty days,
when the process is completed. The feature of this process is that in the presence of sulphate of copper, tannin and alum are used at the same time.