The

them down, raise the middle bar, and hang them by the other end until they will easily unhair. hides should not be broken until they are taken from the vault, and ready to unhair. In a good vault, where the thermometer ranges from 44° to 56° Fahr., which it should never exceed, and where there is a free circulation of damp air, hides generally require, for unhairing, from six to twelve days. When the temperature falls below 44°, the ventilator should be partially closed; and when it rises above 56°, cold damp air must be forced in, or an increased quantity of cold spring-water may be thrown from a hose or otherwise."

The loosening of the epidermis and the roots of the hair in this process is considered not to be the result of any putrefactive decomposition of a portion of the hide, but to be produced merely by the softening action of the moisture, and this action seems to be confined to the surface or grain of the skin. But the temperature at which the operation is conducted is not low enough to prevent the occurrence of a very slight putrefaction, sufficient to disintegrate the roots of the hair, though probably not active enough to affect the gelatinous tissue. Against this idea it is urged, that no ammonia or other product of the putrefactive decomposition of animal bodies can be perceived in the vault; but the traces of these substances, which would be formed, might be completely dissolved and washed away by the constant stream of water. This question is of very little importance, however, if the gelatinous tissue remains unacted on, as is stated by those who follow the process. The loosening of the roots of the hair is

always the first effect of a putrefactive decomposition of the hide; hence purchasers estimate the soundness of hides by the force requisite to pull out the hair.

2. Preparation of kips and skins. - In this country, kips and skins are commonly cleansed and unhaired in much the same manner as hides; being first subjected, for about a fortnight, to the action of lime-water, or milk of lime of two or three different strengths, and afterwards scraped with the unhairing and fleshing knives. But particular care is required in the preparation of skins, to extract the whole of the lime which has been absorbed previous to subjecting the skins to the action of the tanning liquor. Lime, if allowed to remain in the skin in the unneutralized state, would tend to harden the leather considerably; but upper shoe-leather, and other light leathers, which are always made from kips and skins, should be quite soft and flexible : hence arises the necessity for carefully removing the lime by the process called "graining." For this purpose, the kips and skins after having been limed and scraped, are commonly immersed in an alkaline lixivium, called the "bate" or "grainer," made of the dung of hens, pigeons, and other domestic birds, in which they remain from eight to ten days, according to the temperature of the liquid. During this period they are frequently stirred about, and are occasionally scraped upon the beam, either on both sides or only on one side. Ten or twelve gallons of the dung are sufficient for a pit capable of "bating" one hundred skins.

By these operations the skins become rendered soft and pliant, the lime having been almost completely separated. Formerly the skins were withdrawn from the lixivium daily, and laid up in heaps to drain for half an hour. The process of bating then generally required nearly a fortnight.

It seems probable that, so far as the removal of the lime from the skins is concerned, the most active constituent of the bate is muriate of ammonia (sal-ammoniac), an aqueous solution of which would dissolve unneutralized lime, with the formation of chloride of calcium and free ammonia. A great inconvenience which attends the use of the common bate (the fresh dung) consists in the destruction of a portion of the gelatinous tissue of the skin by a fermentation excited through the decomposition of the animal matters of the bate. In warm weather, the grain side of the skin often becomes seriously coloured from this cause, when the process is not properly attended to. The flesh side, however, is first affected, but that is not of so much importance as the grain side. It is probable that a purer material than the bate in common use might generally be employed with advantage, particularly in summer. The use of the carbonate of ammonia as a bate, with other improvements in the process of tanning, some of which are elsewhere alluded to in the present article, was made the subject of a patent by Mr. Robert Warington, in 1841. Carbonate of ammonia does not dissolve the lime out of the skin, but destroys its causticity, by converting it into the carbonate, or chalk.

If the fresh bate is allowed to stand exposed to

the air for a few days before being used, it is much less disposed to act injuriously on the skin. Guano, which is the decomposing excrement of aquatic birds, has not the same action as the excrement of domestic birds.

Sheep-skins, before being soaked in milk of lime, for the purpose of being unhaired, should be squeezed in order to express as much as possible of the oil they contain. Bran-water is generally used as the bate in the preparation of sheep-skins. Seal-skins, which, when converted into leather, are principally used for the bindings of shoes, are well scraped, previous to being limed, for the same purpose.

Before the hides and skins are exposed to the tanning liquor, they are cut to a tolerably regular form by paring off their edges, and the clippings thus obtained are employed in the preparation of glue and size.

§ III. MODES OF APPLYING TANNIN TO PREPARED HIDES

AND SKINS.

It is generally admitted that the quality of the leather made by the old slow tanning processes is decidedly superior to that of the leather made by the quick process now commonly practised by the tanners of this country, which differs from the old methods principally in the manner in which the tannin is applied to the prepared hides and skins. In one of the old processes, the hides, instead of being digested in an infusion of oak-bark, were merely placed

in contact with the powdered bark, the latter being slightly humid. A layer of spent bark, of about six inches in thickness, was first placed at the bottom of the tan-pit, the construction of which was just the same as that of those now used; and upon this substratum was placed a layer of about one inch in thickness of finely ground fresh bark. Over this layer a hide was carefully placed, so as to lie quite flat, and upon the hide another layer of fresh bark, which was surmounted by a hide and a layer of bark alternately, until the pit was completely filled. The whole was then covered by a stratum of six inches of bark, called the "hat," and compressed by being well-trodden under the feet. At the expiration of about two or three months, by which time the tannin of the bark had become united with the animal fibre, the pit was completely emptied of its contents; and the hides, after being stretched, were again disposed in the pit, with a fresh quantity of bark, in a similar manner. This process was again repeated three or four months later; and when the bark was supposed to be spent, and the leather almost fully tanned, the pit was commonly nearly filled with a strong infusion of bark, which served to complete the process.

As tannin can penetrate the hide only in a state of solution, it is obvious that the process just described must have been extremely slow, for the only liquid present to dissolve the tannin was the water. in the hides, and the hygrometric moisture of the bark. It was usual in some places, however, to introduce to the bottom of the pit a little clean water,