AMALGAM Cadmium amalgam
A combination of a metal with mercury. The amalgams have the characteristic that when slightly heated, they are soft and easily workable, and they become very hard when set. They are used for filling where it is not possible to employ high temperatures. A native silver amalgam found in South America contains 26 to 95% silver. Native gold amalgams are found in California and Colombia, and they contain about 40% gold. Although native amalgams are chemical combinations of the metals, some of the artificial amalgams are alloys and others are compounds. Dental amalgams are prepared by mixing mercury with finely divided alloys composed of varying proportions of silver, tin, and copper. A silver-tin alloy, developed at the National Institute of Standards and Technology, is mercury-free and less brittle than standard amalgams. Also promising is NIST’s development of fine silver powder that can be compacted and consolidated with conventional dental tools.
Cadmium amalgam was formerly employed for filling holes in metals and was called Evans’ metallic cement. It is a silvery-white compound of composition Cd5Hg8, with about 74% mercury, the excess mercury separating out on standing. It softens at about 100°F (38°C) and can be kneaded like wax, remaining soft for a considerable time and then becoming hard and crystalline. Tin or bismuth may be added. Amalgams with an excess of cadmium are ductile and can be hammered into sheet. Bismuth amalgams are lustrous, very fluid combinations of mercury and bismuth, used for silvering mirrors. They are also added to white bearing metals to make them more plastic and to fusible alloys to lower the melting point. Crilley metal was a self-lubricating bearing alloy containing bismuth amalgam. The binary amalgams of mercury and bismuth are usually too fluid for ordinary use.
The usual quaternary alloy has equal parts of bismuth, mercury tin, and lead, with the proportion of mercury increased to give greater fluidity. A bismuth amalgam containing bismuth, lead, and mercury was used for lead pencils. A thallium amalgam, with 8.5% thallium, which freezes at — 76°F (—60°C), is used for thermometers for low readings. Mackenzie’s amalgam is a two-part amalgam in which each part is a solid but becomes fluid when the parts are ground together in a mortar at ordinary temperatures. One part contains bismuth and mercury, and the other part contains lead and mercury. Sodium amalgam contains from 2 to 10% sodium. It is a silvery-white mass which decomposes water and can be used for producing hydrogen. Potassium amalgam, made by mixing sodium amalgam with potash, is a true chemical compound, used for amalgamating with other metals.

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