Alloys. Combinations of the metals with each other obtained by fusion. When mercury is one of the component metals, the compound is termed an amalgam. (See No. 3532.) Most of the metals unite with each other by fusion or amalgamation, and acquire new properties. Thus: copper alloyed with zinc, becomes brass, and possesses a different density, hardness, and color to either of its constituents. No general rules for the manufacture of alloys applicable to each can be given; but it may be remarked that, in uniting metals differing greatly in their melting points, the least fusible should be melted first, and the others added, one at a time, in their order of fusibility, the most fusible metal being the last to be added; also that, before the addition of each succeeding metal, the temperature of the already, fused mass should be reduced to the lowest point at which it will remain fluid, or as near as possible to the fusing point of the metal to be next introduced, so that it may not evaporate or be oxidized, and thus cause the compound to bo imperfect. This is a general rule, to be applied in most cases; but there are exceptions. For instance: gold will easily dissolve in melted tin; and platinum in many metals. If platinum were first melted, and zinc, for instance, added, the temperature necessary to obtain the fusion of platinum would be sufficient to volatilize the zinc. The mixture is usually effected under a flux, or some material that will prevent evaporation and exposure to the atmosphere. Thus: in melting lead and tin together, in forming solder, resin or tallow is thrown upon the surface; in tinning copper, the surface is rubbed with sal-ammoniac; and in combining some metals, powdered charcoal is used for the same purpose. (See No. 3470 (Flux for Copper).) As we have already said, most of the alloys are prepared by simply fusing the metals together; but if there be a considerable difference in their specific gravities, the heavier very generally subsides, and the lower part of the mass thus differs in composition from the upper. This may bo in a great measure prevented by agitating the alloy till it solidifies, but this is not always convenient. Thus, in stereotype plates, which are cast vertically, the upper side usually contains more antimony than the other. As a general rule, the substances (elements) of nature unite together in fixed and definite atomic proportions, thereby forming new compounds. Metals unite with non-metallic bodies, and obey the same general law; but metals, when united with metals, appear to form an exception, though much doubt exists on the subject. They seem to mix in any proportion, and are thereby modified, possessing thereafter properties which fit them for many purposes in commerce and art. These compounds, being considered at present non-chemical bodies, are classed together under the French term of alloys. Alloys are generally more fusible than the least fusible of the component metals; but are often harder and more brittle than the hardest and most brittle of the component metals. With some exceptions, the ductility and tenacity of an alloy is less than that of its metals.