-------------+--------+-----------+---------- | | Per cent. |Weight of Draught. |Gallons.|Gelatine in|Gelatine. | | Solution. | Lbs. -------------+--------+-----------+---------- 1 | 126·48 | 6·775 | 85·64 2 | 128·96 | 6·052 | 78·04 3 and 4 mixed| 135·20 | 9·446 | 127·63 +--------+ +---------- Total | 390·64 | | 291·31 -------------+--------+-----------+---------- Percentage of gelatine on weight of wet skins = 13·69. A similar trial on the same class of wet hide pieces gave a yield of 13·23 per cent. Two trials, of a somewhat different class of wet hide pieces, gave respectively 13·11 and 12·8 per cent. The temperature of the draught water should be approximately as follows:-- --------+-------------+---------- Draught.|At Beginning.| At End. --------+-------------+---------- 1 | 120° F. | 150° F. 2 | 130° F. | 160° F. 3 and 4 | 140° F. | 180° F. --------+-------------+---------- In the final draught it is often necessary to use live steam at the finish, but this should be avoided if possible. The water contained in wet hide pieces varies from 77 to 90 per cent. in the different pieces, but in the bulk the average may be taken at 85 per cent. _Casein._--Casein is the nitrogenous principle of milk, and belongs to the class of proteids which are definite compounds of oxygen, hydrogen, carbon, and nitrogen, forming the basis of the most important constituents of all animal fibres, albumen, casein, and gluten. A very pure form of casein is cheese made from skimmed milk. Casein belongs to that class of albumens which are soluble in water, _e.g._, egg albumen, blood albumen or serum, and lactalbumen, or milk albumen; these are mostly precipitated from solution by saturation with sodium chloride (common salt) or magnesium sulphate; but they are all coagulated by heat. By the action of rennet on milk the proteid or albumen principle is converted into a curd (casein). This curd, when freed from fats, is insoluble in water, but is soluble in dilute acids, or alkalies, or alkaline carbonates, from which substances, however, it is reprecipitated by acidulation. Instead of the above method, casein may be precipitated from milk by saturation with sulphate of magnesia, and washing the precipitate with a solution of that salt until the washings contain no albumen, and then redissolving the prepared casein by adding water. The salt still adhering to the precipitate enables it to dissolve. On a large scale the casein is usually prepared by treating the milk with acid. Casein is readily dissolved by alkalies and alkaline carbonates, borax, boracic acid solution, caustic soda, and bicarbonate of soda.