AMALGAM, the name applied to an alloy containing mercury, and said by Andreas Libavius to be a corruption of µaXayua ; in the alchemists the form algamala is also found. Many amal gams are formed by the direct contact of a metal with mercury, sometimes with absorption, sometimes with evolution, of heat. Other methods are to place the metal and mercury together in dilute acid, to add mercury to the solution of a metallic salt, to place a metal in a solution of mercuric nitrate, or to electrolyse a metallic salt using mercury as the cathode or negative electrode. Some amalgams are liquids, especially when they contain a large proportion of mercury; others are crystalline. In some cases definite compounds have been isolated from amalgams, which may be regarded as mixtures of one or more of such com pounds with mercury in excess. In general these compounds are decomposable by heat, but some of them, such as those of gold, silver, copper and the alkali metals, even when heated above the boiling point of mercury retain mercury and leave residues of definite composition. The use of tin amalgam in "silvering" mir rors, and of gold and silver amalgams in gilding and silvering has been almost completely superseded by chemical deposition of sil ver and by electroplating respectively. Cadmium and copper amalgam are employed in dentistry, and an amalgam of zinc and tin for the rubbers of electrical machines. The zinc plates of elec tric batteries are amalgamated in order to reduce polarization. Native amalgams of gold and silver have been found in various parts of the world, and the "amalgamation process" has been a standard method for the extraction of these two metals from their ores. Although it is still used to a reduced extent on gold ores, its use for silver ores is now practically obsolete.