11. Sheep and lamb leather (goat leather) limed, thin and very light, yields but a small quantity of glue of little consistency. To this class belongs the waste in the manufacture of kid gloves. Waste of morocco and other varieties of similar leather, pressed into bales and secured with wire, comes into commerce under the name of Levant leather.
12. Waste obtained in paring kid leather and in the manufacture of gloves. It constitutes a flocculent powder and yields very thin glue liquor with slight adhesive power. Before boiling, the substances used in tanning must be completely removed by washing.
13. Surrons. These are untanned, unlimed skins of various wild animals (antelopes, gazelles) which have been used for packing leaf tobacco and various drugs. They form good glue stock.
2. BONES AND CARTILAGES.
In addition to hides, bones are a material highly valued by the glue boiler. Chemically speaking, the framework supporting the fleshy tissues of the animal order, and which we call bones, is a combination of phosphates of lime and magnesia, carbonate of lime, and alkaline salts, united with fatty and cartilaginous matter. To the latter we look for our yield of glue; to the fatty matter for the fat, and to the phosphates for the basis of fertilizers.
Bone cartilage is composed of carbon, hydrogen, oxygen and nitrogen, the percentage composition being practically constant, whether the cartilage be from an old or a young animal. The bones of the young are, however, much richer in cartilage than those of the old. This is reversed in the case of the inorganic or mineral matter, the old having the greatest yield of phosphates.
Then again, the fatty matters are more in evidence in full-grown animals than in youth or age; also in the thigh and leg bones the yield is higher than in the heads, ribs or shoulder blades, the latter averaging 12 to 13 per cent., whilst the former runs 18 to 19 per cent.[1]
[1] Bone Products and Manures. By Thomas Lambert. London, 1901.
Bones being less subject to putrefaction than skin-stock, they are not brought into commerce in a prepared state. They are mainly bought by contract from various dealers within easy access to the works. The rates are generally fixed for a certain period, and cover all classes of common bones, whether fresh butchers’ or a mixture with partly boiled bones. Bones differ considerably in their value. A fresh bone will yield the highest percentage of fat and glue. On the other hand, partly boiled bones may contain only 6 per cent. fat with 30 per cent. water. In buying bones the manufacturer should exercise great care, as the dealer sometimes finds ways and means of including hoofs, horns, iron, beefy matter, and even pieces of brick. Naturally they form weight, but, excepting the horns, have no value.
To separate the different classes of bone coming into the works, and arrange them according to the amounts they would produce of fat and glue, is no doubt a desirable object, but in practice it is seldom carried out. However, if the manufacturer wishes to undertake this tedious work, it is recommended to make the following distinctions: