Hides, when deprived of their hair, are converted into _leather_ by an infusion of the astringent property of bark. The old plan of tanning used to occupy a long time; but, such was the value of the process, that the old tanners used to pride themselves upon producing a substantial article--which is more than can be said in many instances under modern improved modes, which hasten the process, much to the injury of the article produced. Strong infusions of bark make leather brittle; one hundred pounds of skin, quickly tanned in a strong infusion, produce one hundred and thirty-seven pounds of leather; while a weak infusion produces only one hundred and seventeen and a half,--the additional nineteen and a half pounds serving only to deteriorate the leather, and causing it to contain much less textile animal solid. Leather thus highly charged with tanning is so spongy as to allow moisture to pass readily through its pores, to the great discomfort and injury of those who wear shoes made of it. The proper mode of tanning lasts a year, or a year and a half, according to the quality of the leather wanted and the nature of the hides. A perfect leather can be recognized by its section, which should have a glistening marbled appearance, without any white streaks in the middle. The hair which is taken off hides in tanning, is employed to mix with plaster, and is often surreptitiously put into hair-mattresses. The principal substances of which _glue_ is made are the parings of ox and other thick hides, which form the strongest article and the refuse of the leather-dresser. Both afford from forty-five to fifty-five per cent. of glue. The tendons, and many other offals of slaughter-houses, also afford materials, though of an inferior quality, for this purpose. The refuse of tanneries--such as the ears of oxen and calves--are better articles. Animal skins also, in any form, uncombined with tannin, may be worked into glue. _Ox-tallow_ is of great importance in the arts. Candles and soap are made of it, and it enters largely into the dressing of leather and the use of machinery. Large quantities are annually exported from Russia. Ox-tallow consists of seventy-six parts of stearine and twenty-four of oleine, out of one hundred parts. The _horns_ of oxen are used for many purposes. The horn consists of two parts: an outward horny case, and an inward conical-shaped substance, somewhat intermediate between indurated hair and bone, called the _fluid_ of the horn. These two parts are separated by means of a blow upon a block of wood. The horny exterior is then cut into three portions by means of a frame saw. The lowest of these, next the root of the horn, after undergoing several processes by which it is rendered flat, is made into combs.