quantity of alum and salt than that mentioned above, drying them and then rubbing them with tallow before a charcoal fire. A very strong leather may thus be prepared, a com paratively short time. The more delicate kinds of leather —especially that for making kid gloves, kid shoes, etc., are tawed by immersion in a bath containing alum, salt, yolk of eggs, wheaten flour and water. The oil contained in the egg yolks confers upon the leather a great degree of softness, the gluten of the flour seems to aid the skin in the absorption of alu minium chloride. The skins are stretched by hand and rapidly dried in the open air; they are then damped, placed between linen cloths and trodden upon until they become soft. They are finally polished by rubbing with a glass disc smeared with white of egg or a solu tion of gum, etc.
Oil So called wash leather or chamois leather is prepared from the skins of deer, sheep, calves, etc., by tawing them with oiL The skins having been washed, limed, etc., in the ordinary way, are repeatedly rubbed with animal oil, exposed to the beaters of a fulling machine, and dried. The oil employed is tur key red oil, made by treating castor oil with sulphuric acid. Other oils have been employed, but castor oil remains the only oil which has been successfully sulphonated. A small quan tity of carbolic acid is sometimes added. The skins are stretched and sprinkled with oil, which is gently rubbed in with the hand; they are then placed in bundles in the fulling ma chine and exposed to the action of the beaters for several hours. After exposure to the air the skins are again rubbed with oil and again placed under the beaters; these processes are repeated until the fleshy odor of the original skin is no longer perceptible. By exposure to a warm atmosphere a process of gentle fermen tation is originated within the skins, whereby the pores are dilated and the oil is enabled to penetrate the mass more thoroughly. The ex cess of oil is finally removed by washing with a dilute warm caustic lye; the skins are then dried and dressed. Wash-leather is much used for making military belts, gloves, socks, etc., for surgical applications, .for cleaning glass and porcelain and for polishing jewelry. A great variety of other processes are in use for tan ning, many of them being patented. These formulas call for such ingredients as witch hazel, horse chestnut, poke-root, crane's bill, blackberry roots, persimmon bark, nicotin, for mic aldehyde, sodium nitrate, chromium chlo ride, iron sulphate, zinc sulphate, etc. For spe
cific purposes these may have their uses, but the basic processes of tanning have remained unchanged for many years.
The manner in which tanning is conducted in different establishment varies much in detail, though the general principles are the same. Instead of that uniformity in the commoner processes which might be expected from accu rate knowledge, each tanner treasures his secret as to the best process for bringing about the chemical transformation which it is their com mon object to effect; and these secret methods, the value of which as the result of a limited experience is inevitably overestimated by those whose knowledge is confined to that experi ence, prevent comparison and the rejection of superfluous and perhaps injurious operations.
The trade of tanning may, however, be said to be still in its infancy, and it must be admitted that the chemical processes involved are far from being solved. It was only at the end of the 18th century that scientific methods began to be applied to leather-making, and, although not much progress has hitherto been made, con siderable activity has been shown in the pursuit of improvement. The extreme slowness of the process of leather making by any of the ordi nary processes of tanning has afforded a strong motive for inquiry as to the possibility of hastening it by additional contrivances. Much time has been saved by splitting the leather as it comes from the lime pits, and tanning the thinner splits individually. The necessity of preserving the solidity and tenacity of unsplit hides seems to militate against any rapid method of progress in the passage of the tan ning agents through and through them.
Flemming, L. A.,