Gunpowder-paper is prepared by spreading an explosive substance on paper, which is then dried and rolled up in the form of a cartridge. ♦Sand and emery♦ Sand and emery papers are produced by coating a stout paper with glue, and then sprinkling sand or emery-dust upon the surface. Man’s skill has devised for this purpose an ingenious machine. This first coats the paper with glue from a revolving brush, which plays over the surface of melted glue in a steam gluing-pot below. Having accomplished this result, it softens the glue with a spray of steam, and sifts the sand upon the surface, all surplus sand dropping into a box below as the sanded or emery-surfaced paper passes over a roller. Other loose particles are blown off by a fan, while the remaining ones are still more firmly fixed by a second jet of steam. ♦Cork♦ Cork-paper, an American invention, is made by coating one side of a thick, soft and flexible paper with a preparation of glue, gelatine, and molasses, and covering it with finely ground cork lightly rolled in. This paper is used for packing bottles, glassware, etc. ♦Slate♦ Slate-paper, which takes its name from the fact that it can be cleansed like a slate, is prepared from the regular product, of the required thickness and consistency, by the use of benzine, followed by a preparation made of lead, zinc oxide, turpentine, seed-oil, copal, and sandarach. Soft plate-paper is a thick unsized paper, especially adapted to receive impressions for fine engravings printed from steel and other plates. ♦Filter♦ Filtering-paper, much used by chemists and druggists, is simply unsized open or porous paper. With such paper, of course, the process of manufacture ceases at the first drying or crushing rollers, all the finishing or hardening operations being omitted. [Illustration: CUTTING FROM THE ROLL--PAGE 82] ♦Waterproof♦ Waterproof papers comprise a large and most useful class. It is practically only within the past twenty-five years that a process has been known and employed for rendering a paper waterproof by destroying its absorptive properties. At the present time there are many and various methods used in waterproofing, such as soaking the stock in dissolved shellac and borax. This method is found especially satisfactory in waterproofing heavy paper and boards. Another process is by brushing the surface of the paper with boiled oil, and paper thus prepared was formerly used largely in lieu of bladders and gut-skins for wrapping butter, covering fruit-jars, etc., but it has been almost entirely superseded by the introduction of parchment-paper, of which mention will be made later. ♦Paraffin♦