For some purposes the leather is required to be very thin, and of exactly one thickness. This is obtained by the process of splitting, for which a machine is used whose exactness is such, that one slice is taken from the inner part of the whole skin, reducing it in thickness without cutting a hole in any part. The skin is stretched tightly round a roller, which slowly revolves against a straight knife-edge, fixed at a certain distance from it, according to the thickness of the skin, and which is passed by the machine backwards and forwards, cutting the skin a little further each time. GLUE AND SIZE. Glue is made from the clippings of hides or any other refuse of skins, horn shavings, bones, &c. All these substances are piled up in a boiler having a second bottom within, perforated with holes, and kept from the true bottom by short feet; this arrangement is to prevent the substances boiled from burning at the bottom of the boiler. After many hours’ boiling the liquid is tested, and if it “sets” into a sort of jelly readily, the liquor is drawn off into another boiler, where it is kept warm, that it may not set till used. From this boiler it is strained through flannel into square wooden boxes, having ridges at the bottom dividing them into squares (to direct the workmen where to cut the glue when cold); these boxes are set apart, and when the contents have become cold and set into a firm jelly, a knife is passed between the sides of the box and its contents, and the glue turned out in a large solid square. This is now cut by means of a wire with a handle at each end into squares of about eight inches each way and an inch thick; these are now placed on nets made of cord fixed in frames one above another in a “drying-room,” which is open to the air at the sides, and able to be closed up in case of wet weather. In this room the glue dries up, shrinks, and hardens, until it is quite brittle; the marks of the net can be seen on every square of glue. Size is the same as glue, but instead of being dried it is put into small barrels. Two qualities of size are made, single and double size. It is much used by whitewashers, paper-hangers, and others, but for any purpose requiring good size, it may be made by soaking isinglass or gelatine in cold water till it is softened, and then standing the vessel in boiling water till it is dissolved; this produces a jelly nearly pure. A cheaper kind of size, almost as pure, may be made by boiling clippings of clean parchment till they are dissolved, and straining off the solution. Gelatine is the same as glue, but made of materials that are clean and fresh. Isinglass is the “sound” or swimming-bladder of the sturgeon, cleaned, dried, and cut up into fine shreds. PARCHMENT.