Alloys
A combination or mixture of two or more metals. Metals combine with metals to form alloys, and each compound may be looked upon, for many purposes, as a new metal. Alloys are always more fusible than the most infusible metal of which they are composed. A metal of low fusibility, when melted in contact with one of high fusibility, causes the latter also to melt, thus acting as a flux. This principle is employed in soldering, or the joining of two metals by means of a third. See SOLDERING.
In fact, no alloy composed of two metals, as copper and zinc, or copper and tin, either files or turns with the same facility as when a third metal is added to the alloy in suitable proportions. Lead added to copper and zinc, and zinc to copper and tin, will effect this purpose.
It should always be borne in mind that, in making alloys, the more infusible metals should be melted first; and in order that the admixture should be perfect, mechanical agitation must be effected by constant stirring with an infusible rod, or repeated pouring from one ladle or crucible to another. The surface of the metal should also be carefully protected while in a fluid state from the oxidizing influence of the atmosphere. Ordinarily, resin, pitch, or wax will answer this purpose for all alloys having a low fusing-point; but for such as have a high fusing-point, borax, pounded glass, charcoal, or salt will answer. See FLUX.
Not many of the metals may be used by the founder without some alloy, and the following represent nearly all that are employed alone, viz., iron, copper, lead, tin, zinc, gold, silver, mercury, platinum, aluminum. Some are entirely too brittle to be used alone, but may be used for imparting hardness to other metals. Among these may be mentioned bismuth, arsenic, antimony, etc. But even copper may not be employed alone for castings, as such castings are invariably unsound, and are difficult to file or machine; yet a suitable proportion of zinc alloyed with it renders it not only sound in the casting, but capable of being either machined, rolled, or hammered, and which constitutes, according to the amount of zinc used, many different kinds of the most useful alloy known, viz., brass. See BRASS.
Some of the changes produced by alloying are of great importance in the arts and manufactures, as many of the alloys produced are more valuable on account of their newly-acquired properties than any of the simple metals which enter into the composition.
Strange as it may appear, a quarter of a grain of lead will render an ounce of gold perfectly brittle, although neither of the metals composing the alloy are brittle ones.
Some metals which will not combine together immediately may be united by the intervention of a third fusible alloy. Thus, mercury will not combine directly with iron, but if tin or zinc be first added to the iron, an amalgam may be formed of it with mercury (see MERCURY; AMALGAM). When mercury is united with another metal the compound is called an amalgam.
One remarkable feature in this connection is that alloys are, as a rule, more easily oxidized than their component metals. For example, it only requires to heat an alloy of tin and lead to redness, when it will at once unite with the oxygen, or take fire and burn. (All the alloys and metals of importance will be explained under their several names.) See FLUID ALLOY; FUSIBLE ALLOY. Alum, or sulphate of alumina and potash, is a triple salt of great importance in the arts and manufactures. Sometimes it is found native, but it is chiefly manufactured artificially from alum-slate. A large quantity is prepared in this country by treating alumina or clay with sulphuric acid, and after the lapse of a few months adding potash. The whole is then leached and the alum separated from the solution by crystallization. It is of great importance in dyeing, in the manufacture of leather, and in calico-printing. Alum is soluble in 16 parts of water at 60 deg., and in three-fourths of its weight of boiling water; its composition is: sulphate of alumina 36.85, sulphate of potash 18.15, water 45.00.