The Useful Arts Volume 2; Considered in Connexion with the Applications of Science with Numerous Engravings (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1840 Excerpt: ...obtained by sublimation, or distillation. Even after these operations, the metal is seldom pure, but is combined with some other metal or metals, which have been present in the ore. If these are in small quantity, and do not injure the metal, they are in general disregarded. If it is necessary, however, to separate them, or if, from their value, the separation is an object of importance, different processes are followed, adapted to each particular metal. All the operations, subsequent to smelting, are comprehended under the general name of refining, because their effect is always to obtain a purer metal. The different metals are refined by different processes. Assaying.--The art of assaying metallic ores is that of analyzing them, in small quantities, so as to discover their component parts. It requires a knowledge of the-relations of the metals to the other chemical agents, and is varied, in its different stages, as applied to each. The general process consists, in selecting proper specimens of the ore, which is done, by taking equal portions of that which appears to be the richest, the poorest, and of medium value, and reducing these to coarse powder, which is washed, to carry off any earthy or stony matter. It is then roasted in a shallow earthen vessel, under a muffle, to expel the volatile principles. It is lastly reduced, by mixing it with fluxes, and applying a more or less intense heat, as the metal is more or less refractory. The metallic matter, existing in the ore, is thus obtained. This, it is obvious, may consist of various metals; and, if there is reason to believe this, and it be of importance to ascertain it, it is submitted to operations, adapted to the metals which may be supposed present. Sometimes, an accurate analysis is made, at once, ...