1911 Encyclopædia Britannica/Amalgam
AMALGAM, the name applied to alloys which contain mercury. It is said by Andreas Libavius to be a corruption of μάλαγα; in the alchemists the form algamala is also found. Many amalgams 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 negative electrode. Some amalgams are liquids, especially when containing a large proportion of mercury; others assume a crystalline form. In some cases definite compounds have been isolated from amalgams which may be regarded as mixtures of one or more of such compounds 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. Tin amalgam is used for “silvering” mirrors, gold and silver amalgam in gilding and silvering, cadmium and copper amalgam in dentistry, and an amalgam of zinc and tin for the rubbers of electrical machines; the zinc plates of electric batteries are amalgamated in order to reduce polarization.