Then came ingenious machines to take the place of the previous operations of the hand tools,--the fleshing machine, in one form of which the hides are placed on a curved bed, and the fleshy parts scraped off or removed by revolving glass blades, or by curved teeth of steel and wood in a roller under which a table is given a to-and-fro movement; tanning apparatus of a great variety, by which hides, after they are thoroughly washed and softened, and the pores opened by swelling, are subjected to movements in the tanning liquor vats, such as rocking or oscillating, rotary, or vertical; or treated by an air exhaust, known as the vacuum process; in all of which the object is to thoroughly impregnate in the shortest time all the interstices and pores of the skin with the tannic acid, by which the fibrous and gelatinous matter is made to combine to form leather, and by which process, also, the hide is greatly increased in weight. Reel machines are then employed to transfer the hides from one vat to another, thus subjecting them to liquors of increasing strength. Soaking in vats formerly occupied twelve or eighteen months, but under the new methods the time has been greatly reduced. And now since 1880, the chemists are pushing aside the vegetable processes, and substituting mineral processes, by which tanning is still further shortened and cheapened. The new processes depend chiefly on the use of chromium compounds. Then came scouring machines, in which a rapidly revolving stiff brush is used to scour the grain or hair side, removing the superfluous colouring matter, called the bloom, and softening and cleansing the hide; the slicking or polishing machines to clean, stretch and smooth the leather by glass, stone, or copper blades on a rapidly-moving belt carried over pulleys; whitening, buffing, skiving, fleshing and shaving machines, all for cutting off certain portions and inequalities of the leather, and reducing its thickness. In one form of this class of machines an oscillating pendulum lever is employed, carrying at its end a revolving cylinder having thirty or more spiral blades. The pendulum swings to and fro at the rate of ninety movements a minute, while the cylinder rolls over the leather at the rate of 2780 revolutions per minute. Scarfing, skiving, chamfering, bevelling, feather-edging, appear to be synonymous terms for a variety of machines for cutting the edges of leather obliquely, for the purpose chiefly of making lap seams, scarf-joints, and reducing the thickness and stiffness of leather at those and certain other points. Then there are leather-splitting machines, consisting of one or more rollers and a pressure bar, which draw and press the leather against a horizontally arranged and adjustable knife, which nicely splits the leather in two parts, and thus doubles the quantity. This thin split leather is much used in making a cheap quality of boots and shoes and other articles.