Alloys have peculiarities demanding special and extensive study to understand them, and no laws have yet been found by which the properties of an alloy may be determined from the properties of its constituents. The properties of an alloy are not an average of like properties in its constituents, and very unexpected results may be obtained by varying the proportions of constituents of an alloy, or by introducing the slightest amount of some other ingredient.

The following items give the important peculiarities of alloys:

(1) The strength of some alloys, particularly when hammered, rolled or drawn into wire, is much greater than that of any of the composing metals. This is true of the useful brasses and bronzes.

(2) Varying the proportions of the same metals in an alloy throughout a wide range will give very different products in strength, hardness, malleability, ductility, density, fusion point, and color. These changes will not come in a line of regularity. Some of the products will differ widely from the rest.

(3) The fusing point of an alloy is usually lower than the average of the fusing points of the constituents, and sometimes lower than the fusing point of any constituent. Some alloys, composed of about 50% of bismuth, melt below the temperature of boiling water.

(4) The introduction of a slight amount of some metals, metalloids or impurities in a given alloy may bring great changes to one or more of its properties, sometimes improving the alloy, but more frequently rendering it worthless.

(5) The order of melting and mixing the several metals of an alloy influences the quality of the alloy, because some metals oxidize more readily than others in the fused state. This oxidation should be reduced to a minimum because it wastes the metal and the oxide weakens the alloy.

In making alloys, it is needless to attempt to get good results by using any but the purest of commercial metals, and scrap alloys may be used only when their composition is known and when it is suitable to the correct proportioning of the mixture to be made.

The principal requirements in melting metals for alloys are (1) melt the metal of highest fusion point, and, when melted, drop in the other metal broken up in chunks; (2) have the molten surface of metal covered with salt or other flux, or with charcoal, to prevent oxidation from atmospheric oxygen; (3) stir the metals well with an iron rod before pouring from the crucible.

If the metals in an alloy are not thoroughly mixed, they may not form a homogeneous mass upon cooling. The separating out of any masses of one of the metals is called liquation. This condition will not likely show on the surface of the alloy when cold, but will affect strength and other qualities.