To facilitate the evaporation, and consequently the absorption of fresh solu tions of tan, the operations are recommended to be conducted in chambers artificially warmed, and the liquor which oozes through the skin, and is received into the gutters, is directed to be conducted into vessels acting the part of refri geratories, in order that cold liquor may always be supplied to the skins ; (but how this liquor is to be preserved cold a warm chamber, the specification does not explain). When the skins are sufficiently tanned, a stitch or two of the sewing at the bottom of the bag is opened, and the liquor is received into, and carried off by, the gutter underneath.
The claim to invention in this patent consists in the mode of accelerating the penetration of the tanning liquor by exposing the outer sides of the skins to evaporation. The process seems to be well calculated to economize time, but there is one defect in the arrangement for which we would suggest a remedy. The skins being laid vertically, the pressure of the column of liquid will cause a much more rapid absorption of the tan in the lower than in the upper part of the skins ; and if no injury be sustained by the lower, by continuing the pro cess until the upper is fully saturated with tan, there is, at the least, a loss of time. It is also probable that the liquor is stronger at the bottom than at the top of the bag. From both these causes, therefore, we should not expect that the leather produced would be uniform in its quality. To obviate these defects, we recommend the patentee to suspend his frames midway upon revolving axes, and to fix at each end of his bag a charging vessel with s stop-cock, or some other simple contrivance to answer the same purpose : the bags may then be reversed at pleasure, swinging them round upon their axes into any desired position, and the lateral shifting between the bars will take place of itself. If there were only one charging vessel with a stop-cock to it, it would suffice • as by turning the frame half-way round it would serve for aperture.
Mr. Jacquemart, of Leicester Square, London, recently introduced, under a patent right, a process of tanning, which is stated to be especially applicable to the skins of small animals, such as hares, rabbits, cats, and Upon reading the specification, however, we did not find any thing essentially different from that which is well known, and in use, except that he adds a small quan tity of orpiment to the other ingredients employed in tanning; 5 or 8 ounces are mentioned as a proper quantity for a hundred of the small skins. He com
mences the process by removing the hair from the skins; fist taking off the long hair and afterward, the short; and to facilitate this operation, he steeps the skins in water slightly acidulated, (using sulphuric acid, in very snail quan tities,) or in the milk of lime; and in either of these the skins are suffered to remain till the matter which fixes the hair to the hide is decomposed. After the hair has been removed, the skins are to be again steeped in water contain ing a very small proportion of sulphuric acid, in order to raise or thicken them. The tanning is effected by the skins in an infusion of bark, with the addition of the orpiment; the manipulations being the same as is practised in ordinary.
Of the numerous substances employed in tanning, oak bark is the chief in this country, not merely on account of its suitable properties, but from its com paratively low price, and the facility with which it may be obtained almost every where. In Russia, where the best of leather is made, the bark of the black willow is preferred, and next to that, the birch bark. Chesnut bark is now much esteemed for the purpose. A tanner at Bern-castle, on the Moselle, has lately employed the myrtle with great advantage; it is reported that by the use of it as a substitute for oak bark, better leather is made by it in much less time ; a commission appointed at Treves, for the examination of leather so tanned, reported that they never before saw any article equal to it in quality. The Reeved Industrie' has recently stated, that at Narbonne, the mare of grapes, after being distilled for the separation of the alcohol, had been found a most important substitute for oak bark in tanning. After the skins had been pre pared in the usual way, they were placed in the pits containing the mare instead of bark ; the skins were completely tanned in from thirty-five to forty days. The expected advantages are, shortening the process, reducing the cost, im proved odour, and greater strength. But of all the substances of recent intro duction, the extract from the numosa, known in commerce by the terms gum catechu, and Japan earth, is the richest in tannin matter. This tree grows in vast abundance in New South Wales; • where preparations have been made for making the extract on a great scale for the tanning process. The leather made from it is of a beautiful colour, and an excellent quality.