ALLAY

(From the French verb alloyer, to mix one metal with another, in order to coinage; derived perhaps from h la loi, the proportions of the metals being regulated by law; perhaps from allier, to unite; or allocare, to pztt together.) A term applied to compounds of the precious metals with others of le value, or to the least valuable of the metals in such compounds: thus, gold is said to be alloyed with silver, and silver with copper. Chemists generally apply the term to all combinations obtained by fusing metals with each other: thus, bra is an alloy of copper and zinc; and bronze, of copper and tin; except when mercury is one of the combining metals, in which case they call the compound an amalgam. Many of the alloys are importantly useful in the arts: thus, gold and silver, which in their pure state are too soft and flexible for the manufacture of plate, coin, trinkets, ., are hardened by the addition of a certain portion of copper; while their colour and other valuable qualities are not materitdly impaired. The standard gold in circulation in this country, is an alloy of 1 1 parts of pure gold, and one of copper. Sometimes the alloy consists partly of silver, especially in the older coins; and it is to the preponderance of one or other of these alloys that the different colour of gold coin is owing; the paler containing silver, the deeper coloured, copper. A little palladium is sometimes present, which gives the gold a disagreeable brownish hue, as seen occasionally in some sovereigns. Our standard silver, used for coin, consists in 12 parts, of ll^^ silver, and ^ copper: in these alloys it is nece ary to employ copper of the utmost purity; for a very minute portion of some of the other metals, especially of lead, renders the precious metal brittle. The silver alloy used for plate is the same as that for coin, and the purity is guaranteed by the stamp of the Goldsmiths' Company. Thg subject of alloy for coin underwent an elaborate investigation at the beginning of the present century by order of government; the inquiry was intrusted to Mr. Cavendish and Mr. Hatchett, and the latter gentleman has published a valuable account of his experiments in the " Philosophical Transactions" for 1803, to which the reader is referred. Some curious circumstances ensue in the combination of metals, as affecting their densities; the specific gravity of an alloy being sometimes greater and sometimes le than the mean of its components, — showing that in some cases expansion has taken place, and in others con traction. Alloys generally melt at a lower temperature than that required for the fusion of their component metals separately; and in some cases the most refractory metals form verv fusible alloys. There are some alloys which are crystallisable, and probably of definite composition; but the atomic doctrine applies only in a few cases to the alloys, and it is often difficult to get a ma of alloy of similar composition throughout; thus, gold made standard with copper, and then cast into bars in upright moulds, does not yield an uniform compound except under due precautions; for the upper end of the bar, containing the metal from the bottom of the crucible, will be the purest. [s. 46]