an impure variety of corundum, of blackish or bluish-gray color, chiefly found in shapeless masses and mixed with other minerals. It contains about 82 per cent of alumina and a small portion of iron, is very hard, is infusible and is not attacked by acids. The best emery is brought from the Levant, chiefly from Cape Emeri in Naxos. It also occurs in Spain. It is employed in cutting and polishing precious stones; in smoothing the surface of the finer kinds of lenses, preparatory to their being polished; in the polishing of marble; by cutlers, locksmiths, glaziers and other artisans. For all these purposes it is pulverized in large iron mortars or in steel mills, and the powder, which is rough and sharp, is carefully washed and sifted into eight or ten different degrees of fineness. Emery paper and emery cloth are made by laying a thin coat of glue upon the fabric, and dusting the emery from a sieve of the required size. Emery wheels are made of a cement in which the ground emery is contained, and the excellence of the wheel depends upon the nature of the cement. The aim is to make a cement which will wear away with the emery and not leave the cutting material below the surface of the wheel. The cement must also be strong enough to withstand the centrifugal force so that it will not fly to pieces when the wheel revolves at a high speed. The wheel must have an even texture throughout and must have the same density, so that one side will not wear out before the other and thus throw the wheel out of balance. Various kinds of cement are made-for example, leather, treated with acids and a strong glue, hard rubber, litharge, linseed oil, sheltac, celluloid, silicate of soda, chloride of calcium, glue and oxychloride of zinc. The emery is prepared for mixing with the cement by rolling or crushing the rock. For cutting and grindstone purposes, the emery crushed under a stamp or in a rock crusher is the best, as the corners and edges of the particles are sharper; but for polishing, the emery ground between rollers is preferred. Wooden wheels with leather glued to their rims, and emery powder glued on to the leather, are used for polishing. The wooden wheel is built up from segments glued and pinned together. Buffing wheels for polishing brass, nickel-plated surfaces, copper, gold and silver are made of cotton or woolen cloth cut into disks and held together by iron flanges in the center.