EMERY

is an impure, amorphous, compact, and opaque variety of corundum, and consists of alumina, with a small per-centage of silica and peroxide of iron. It occurs in Spain, the isles of Greece, and other localities, and derives its name from Cape Emeri, in the island of Naxos. Its hardne is so great, that it scratches and wears down nearly all minerals except the diamond; hence the use of its powder for cutting and polishing gla and various other hard substances. For commercial purposes, the lumps of emery, as taken from the mine, are broken into pieces about the size of a hen’s egg, which are then crushed under stampers, similar to those used for pounding metallic ores. The coarse powder is then sifted through sieves covered with wire-cloth of different degrees of finene , by which it is sorted into different sizes. In this state it forms the emery of the shops, or flour emery. For delicate purposes, it is afterwards prepared by elutriation.