Glue, gelatine, animal charcoal, phosphorous, cements, pastes and mucilages - F. Dawidowsky

According to their derivation the raw materials may be divided into three groups, namely:

1. Skin-like raw materials: Skin, leather, tissues.

2. Bone raw materials.

3. Materials obtained from fishes: Air bladders, scales, etc.

1. ANIMAL SKIN.

Fig. 1.

This consists of three layers, namely: 1. The thin upper-skin—the epidermis—which consists only of cellular tissue, and is of no special importance for the manufacture of glue. 2. The actual leather-skin, or corium, which consists of fibres of connective tissue and forms the actual object of the tanner as well as of the glue boiler. Underneath the corium lies the under-skin, which consists only of cellular tissue contaminated with particles of flesh and fat, which are detrimental to the manufacture of glue. Fig. 1 represents a section of the animal skin. O, is the epidermis, L, the corium, U, the under-skin. The epidermis consists of two layers. The first, superficial one, H, is known as the cuticle or lamellar layer, and the other deeper layer, S, as the mucous or malpighian layer. The corium also consists of two layers, the upper one C, and the lower one C₁, which is the actual leather-skin. The under-skin, U, is an elastic tissue containing many deposits of fat, F, and perspiratory glands, D, which are connected with ducts, D₁, with the surface of the skin.

For the manufacturer of leather and glue, the corium is the only material of value.

The tanner trims the skins before steeping them in the ooze. From sheep and calf skins he removes the head portions, it being more advantageous to use them for glue stock. He also cuts off the skin covering the lower part of the thighs, and, to give the skin a neat finish, the ragged edges of the belly part. Of bullock hides, the ears, tails and foot pieces are utilized for glue stock, while the head parts are tanned. Such tannery waste may yield 44 to 46 per cent. of glue. Scarf skin of bullocks’ hides and waste in fleshing the hide, tendons and hinder parts of cattle yield from 30 to 35 per cent.; horse sinews from 15 to 18 per cent.