The processes employed for this purpose, are various ; every tanner adopting some peculiar method : we have therefore selected the following, which is practised with little difference, in the metropolis and its vicinity ; where the leather is divided into three sorts, known under the names of backs, or butts, hides, and skins.
The strongest hides are selected for the butts ; and, after being divested of the horns, they are laid in heaps for one or two days during the summer, and for the space of five or six, in the winter. Next, they are suspended on poles in a smoke-house, or room containing a fire made of wet tan, to induce a slight degree of putrefaction, so that the hair may be stripped off; an object which is effected by spreading such hides on a wooden horse, and scraping them with a curved knife. They are then immersed in water, to be cleansed from all dirt, and extended a second time on the horse, when all extraneous matters must be carefully removed. The hides are now steeped in a pit containing ooze, or a strong liquor, prepared by infusing ground oak-ark in water ; after which they are plunged into another pit, containing water powerfully impregnated with oil of vitriol, or with an acid obtained from rye or barley. They are next immersed in another pit rilled with water ; a stratum of bark being strewed between each hide. In the course of 5 or 6 weeks, the skins are taken out; and the water, together with the decayed bark, being removed, the pit is a second time filled with ooze; the hides are again macerated, with similar strata between each, for three months. The same operation is then repeated a third, and, after the lapse of three months, a fourth time : here the hides remain for three months longer, at the expiration of which they are completely tanned; being thus drawn out, they are suspended on poles; when, after being compressed by a steel pin, they are beaten by wooden hammers, or beetles, to render them smooth; and then dried for sale.
The leather known under the name of hides, is made from the skins of cows, and those of lighter oxen, in the following manner: The. horns are first taken off, the hides washed and immersed in a pit full of lime-water, where they remain for a few days; after which the hair is stripped off, as above described. They now undergo various processes, similar to those aleready detailed, excepting that the ooze is not at first of equal strength; and that the hides are shifted every second or third day, for the space of six months, into a stronger liquor; being at length put into a very rich ooze, where they are turned twice every week, for two or three months. Thus prepared, they are carried to another pit, with layers of bark arranged between each hide; the process being again repeated for a similar period, when they are taken out, and treated in the same manner as the butts. Both species of leather here described, are employed for the soles of pumps, shoes, boots, etc. ; being finer or stronger, as occasion may require.
The last division of leather is that of skins, which includes all that it manufactured from those of calves, dogs, etc. They are washed in water; then plunged in lime-water, and deprived of their hair by the same operation as hides ; after removing all uneven and superfluous matters, the skins are soaked in a pit of water impregnated with the dung of pigeons, for a week or ten days, in order to extract all the particles of lime, grease, etc. Next, they are treated in a similar manner with the hides ; and, in the course of five or six months, they will be sufficiently tanned. - The leather thus prepared, is now conveyed to the currier; and, after undergoing the process detailed, vol. ii. p. 110, it is used for the upper parts of boots, shoes, etc.
Such are the old methods commonly practised in tanning : these, however, being too tedious and expensive, various expedients have lately been devised, with a view to shorten the respective processes, and to procure substitutes for oak-bark. Thus, Dr. Macbride proposed the use of vitriolic acid, instead of that obtained from vegetables ; which, having been found very serviceable for distending the pores of the skins intended for butts, has been generally adopted by tanners; as it improves the leather in point of durability; and at the same time tends to facilitate or simplify the operations. He also recommended lime-water to be substituted for the common fluid, to promote the extraction of the astringent matter from the oak-bark ; but, the former being very powerful, and apt to injure the texture of the leather, it is seldom employed.
Oak-leaves, gall-nuts, dried and pulverized heath, the barks of the birch and willow-trees, the dried and powdered leaves of the wild laurel, and numerous other vegetable productions, have been tried, and proposed, as useful substitutes for oak-bark : numerous experiments were also made with plants, by Gleditsch, Bautsch, Boh-mEr, and other writers; but, as we state the results of these in the progress of our work, it remains only to mention the following patents, among the multitude granted at different periods; namely: 1. The privilege obtained by Mr. Samuel Ashton, in January, 1794, for his new method of tanning. - 2. Mr. John Tucker's patent, date in May, 1795, for a mode of tanning and making leather in a much shorter period, and of a superior quality, than can be effected by the common method. - 3. Air. William Desmond's, in January, 1796 ; for a process communicated to him (by M. Seguin), of tanning hides, etc. by rendering them more solid and incorruptible in water. - 4. Mr. Robert Cross's, in April, 1797, for a tan-pit on a new construction, and a method of tanning in one-half of the usual time, etc. - 5. Mr. Francis Brewin's, in June, 1799, for an improved process of tanning hides and skins. - As the specification of these patents, however interesting to the tanner, are partly too diffuse, and partly of such nature as not to admit of abridgment, the curious reader will consult the 1st, 3d, (6th, and 11th vols, of the Repertory of Arts, etc. where full specifications are inserted; and occasionally illustrated with plates. - See also Currying, Hides, Leather, Skins, etc.
Tanning. - In November, 1801, a patent was granted to Mr. Francis Brewin, for an improved method of Tanning. His process consists principally in consolidating floaters and taps, by drawing the oozes for the vats, and handlers from the floaters, etc. But, as this contrivance is by the patentee described in confused, intricate terms, and can be interesting or intelligible only to tanners, we refer the curious reader to the 16th vol. of the "Repertory of Arts, " etc. TEETH". - Various remedies have been suggested in this article, for relieving the tooth-ach. To these may be added the insect, termed Lady-bird, or Coccinella septem-punctata, L. which, on rubbing it between the fore-finger and thumb, then applying the former two or three times to the painful tooth, has generally afforded relief. Lately, also, charcoal has been found of great service, both as a preventive and cure 5 for which purposes the cavity of a carious tooth should be filled with pulverized carbon : thus, the pain will in a short time be removed.