32) or by machine, the operation being known technically as "striking out." The machine (Fig. 34) gives quite satisfactory results and has replaced hand labour in all modern works. The hides are then "strained" (_i.e._, extended and nailed to wooden frames), or they are simply hung up to dry. In the latter case, there is a small shrinkage of the size of the hide, but the substance is maintained. With good straining, a satisfactory increase of surface measurement can be obtained. [Illustration: FIG. 32 SLEEKER] When the leather is completely dried, it may be sold at once, but if, as is generally the case, a special "nap" finish is required on the flesh side, the hides are placed in damped deal sawdust until they are in the right condition of flexibility for the next process, known as "fluffing." This is done on a rapidly revolving wheel (Fig. 33) covered with emery powder varying in the size of grain according to the effect desired on the finished leather. The abrasion of the leather on the flesh (_i.e._, the under side) raises a soft nap. Carborundum, a special abrasive made in America, by the fusion of sand, coke, and salt at a very high temperature, has to some extent supplanted the use of emery. As a final finish, the flesh side may be rubbed over with chalk or china clay to give it a clear saleable appearance. [Illustration: FIG. 33 FLUFFING MACHINE] The chrome sole leather used for ordinary boots is quite a different product, and it is only in the last two or three years that it has been used to any extent. The "Dri-ped" is the best known make of this leather. The tannage is effected by the one or two-bath methods already described. The processes preparatory to chroming are very important, as it is essential to get the maximum yield of pelt. The hides are, therefore, often treated with sulphide of sodium, which loosens the hair in twenty-four hours or less. They are then placed in fairly strong limes for two or three days to swell the fibres and saponify the grease. After being washed in cold water, the hides are treated with a weak solution of lactic, boracic, or butyric acid, or butyrate of ammonia, to remove all trace of lime, when they are ready to be chrome-tanned. After chroming them, neutralisation of the acid chrome salts is effected with borax, and the leather is ready for dressing. The principal objects of this process are to make the leather firm and waterproof, and to remedy its tendency to slip easily on wet pavements. The last-named is the greatest difficulty, and there are only about two or three firms who have really surmounted it. Each manufacturer keeps his recipe secret, but the ingredients that go to make the various dressings are drawn from the following: Stearines, mineral oil, Tragasol, resin, carnauba wax, beeswax, paraffin wax, glue. Resin, or asphalt, or both, may be used to prevent the leather slipping in contact with a wet pavement.