AMALGAM (Lat. Gk. pRayaa, malagnm, on emollient. plaster, from paXcuMc, malakos, soft). An alloy of mercury with one or lucre other metals. An amalgam of silver crystal lizing in the isometric system has been found native; a gold amalgam, ton, has been reported from several h 'ea i ties, including California. Artificially, amalgams are made (1) by bringing metallic mercury into contact with another metal, as antimony, arsenic, bismuth, etc.; (2) by bringing mercury into contact with a satu rated solution of a salt of the other metal, when part of the mercury goes into solution and the remainder combines with the liberated metal, which is the ease with calcium, iron, and certain other metals: (3) by placing the metal to he amalgamated in a solution of a salt of mercury. which is the usual method for amalgamating copper and aluminum; finally (4) by placing the metal to he amalgamated in contact with mercury and dilute acids.
Amalgams may be either solid or liquid. Those which are liquid are regarded as solutions in which there is an excess of mercury. The more important amalgams are as follows: Cop per amalgam, which is made by triturating finely divided metallic copper with mercurous sulphate under hot water. This amalgam has the property of softening when kneaded, and be coming quite hard after standing some hours, which hasled to its use for filling teeth. Gold amalgam is formed by heating mercury with powdered gold or gold foil. The readiness with which mercury combines with gold has been made the basis of an important process for the extraction of the latter from ores. After
the ore or the gold quartz has been stamped to fine powder, the powder is brought in con tact with mercury. The gold readily unites with the mercury, forming an amalgam. which is then placed in a retort, from which the mercury is expelled by heating, and be collected for further use, while the gold remains in the retort. Silver amalgam is formed by the union of mercury with finely divided silver, and this fact is taken advantage of fur the extraction of silver from its ores by a process analogous to that described in connec tion with gold amalgam. An amalgam consist ing of S parts of mercury to 1 part of silver is used for silvering metals. Mercury readily combines with sodium when the two elements are brought in contact with each other, yield ing an amalgam which is largely used by chem ists as a reducing agent. Tin amalgam is formed when mercury is brought in contact with tin in the proportions of 3 parts of the former to 1 part of the latter. This amalgam is the one commonly used for silvering mirrors. Zinc amalgam results when zinc filings are mixed with mercury at a heat below the boiling point of the latter. It is used for coating the rubbers of electric machines. Amal gams of bismuth, cadmium. magnesium. potas sium, and other metals are known, hut have no important commercial uses. Consult Dudley. "An Index to the Literature of Amalgams," in Pro ceedings of the A hi erica n _.Lssociat ion for the Advancement of Science (Salem, 1889). •