The process of manufacture of crown leather is in principle intermediate between that of calf-kid (see p. 223), and the pure oil-tanning, if we may call it so, of which the chamois leather (see p. 210) is typical. It depends on impregnating the raw hide with a mixture of fats and albumens, to which salt or saltpetre is added to prevent putrefaction. The process as described in the original patent was as follows,--The hides were unhaired by liming or painting (with sulphides), and cleansed as usual, no plumping lime being given. After unhairing they were allowed to dry some little time in the air till no longer plump, and were then worked in a tumbler drum, without water, till uniformly soft. They were then spread on a table and brushed over on the flesh-sides with a mixture of 23 parts of ox-brain, 6-1/2 of butter, 28 of soft fat, and 4 of salt or saltpetre, with 26 of barley-flour and 12-1/2 of milk, of which the leading 4 ingredients were first to be mixed and the flour stirred in, the milk being last added. The hides were then returned to the tumbler, which was provided with tubular axes, through which a portion of exhaust steam was admitted to warm the drum. After tumbling some hours, the drum was opened, and the hides were examined. If the tanning was not complete, the hides were hung in the air for a time to dry, and the process was repeated till a cut showed that the mixture had completely penetrated the hide. From Eitner's researches it appears that the essential tanning ingredients of the mixture above described are the fat (and butter which acts simply as fat) and the albuminous matter of the milk (casein), brains (albumen, &c.), and flour (gluten); the starch serving at most to assist in the emulsification of the fats. Eitner treated crown leather with dilute potash solution to remove the albumen and fats, and after washing and drying obtained a material like an insufficiently stocked chamois leather. On again stuffing with a quantity of fat equal to that removed, but without the albumen, the leather became dark and quite greasy, so that by sharp bending oil could be pressed out. Good results may be obtained in crown leather manufactured with fats and flour only, without the use of milk or brains, so that it is obvious that the same purpose is served by either vegetable or animal albumenoids. The most important point in the purposes for which crown leather is employed is toughness, and this is given by the unaltered hide-fibres, which are merely preserved by the coating of oily matter with which, like those of chamois leather, they are surrounded. The albumen serves the purpose of filling the spaces between the fibres, and giving solidity and firmness, so that the belts may keep their shape, and not stretch inordinately. It also serves to make the leather waterproof, and fit it for water-bags for military purposes (as it gives no taste to the water) and for hose-pipes. The