Sheep and goat skins that are particularly rich in fat are immersed in a bacterial puering liquor, containing ground castor-oil seed or castor-oil cake in suspension. The fat-decomposing ferment contained in this meal then comes into immediate action, and the liberated fatty acids form readily soluble soaps with the ammonia, originating from the degradation of the proteid substances, and with the allied bases.
Extensive practical experiments have also shown that, in the case of very fat skins, the action of the bacterial puer is increased by mixing a suitable salt of sulpho-ricinoleic acid with the puering liquor, or by washing the skins with solutions of similar soaps either before they are immersed in the puering liquor, or subsequently.
Local conditions, and the requirements laid on the finished leather, must decide which of these methods is specially advisable.
In any event, however, the combinations of the bacterial puer afford a means of obtaining an increased puering effect in many cases where puering with the separate auxiliaries mentioned does not produce a sufficient result.
Claim.—In the method of puering hides wherein bacterial cultures, their metabolic products and enzymes are employed, the combined use with these agents of digestive juices, mixtures of digestive enzymes or pure digestive enzymes (and, if desired, of fat-decomposing substances), either simultaneously with said agents or subsequently thereto.
CHAPTER IX.
DRENCHING.
In the manufacture of many kinds of light leathers, skins, after bating, are drenched. The process usually consists in placing the skins in a mixture of bran and water, half to one per cent. of bran being used (5 to 10 grm. per litre, or 1/2 to 1 lb. per 10 gall.) at a temperature of 29° to 35° C. This ferments vigorously for 18 to 24 hours, with evolution of a considerable quantity of gas, and the formation of weak organic acids.