SAND-BLAST. The erosive influence of driven sand is turned to useful account for several industrial purposes by means of an apparatus devised, about 1870, by Mr B. C. Tilghman of Philadelphia. Tilgliman’s sand-blast consists of a contrivance for impelling, with graduated degrees of velocity, a jet or column of sand, by means of compressed air or steam, against the object or surface to be acted on. The apparatus is principally adapted for obscuring, engraving, and ornamenting glass, but according to the velocity with which the sand is impelled it may be used to carve deep patterns in granite, marble, and other hard stones, to bite into steel, &c., and even to cut and perforate holes through these and other most refractory materials. Sheets of glass 4 feet wide are obscured at the rate of 3 feet per minute, with a blast of air having a pressure of 1 lb) per inch. With the aid of tough elastic stencils, patterns and letters are engraved on flashed glass, globes for lamps and gaslights are ornamented, druggists’ bottles are lettered, &c. Driven with moderate velocity against a metal surface, the sand produces by its impact a fine uniform pitted appearance without removing the metal; and in this way it is used for “frosting” plated goods. A strong blast is largely used for sharpening files, which, as they leave the cutter, have always a slight backward curve or “burr” on their cutting edges which blunts their biting effect. By directing a blast of very fine sand, mixed with water into a thin mud, with steam pressure of 70 ft), at an angle against the back of the teeth, this burr is ground off, the shape of the teeth is improved, and the file is rendered very keen. While the use of steam for impelling the sand-blast is most simple and economical, many practical ...