AMALGAM, in the arts. The metals in general unite very readily with one another, and form compounds; thus pew ter is a compound of lead and tin, brass is a compound of copper and zinc, &c. These are all called alloys, except when one of the combining metals is mercury ; in that case the compound is called an amalgam : thus mercury and gold form a compound called the amalgam of gold.
The amalgam of gold is formed very readily, because there is a very strong af finity between the two metals.. If a bit of gold be dipped into mercury, its surface, by combining with mercury, becomes as white as silver. The easiest way of form ing this amalgam is, to throw small pieces of red hot gold into mercury heated till it begins to smoke. The proportions of the ingredients are not determinable, be cause they combine in any proportion. This amalgam is of a silvery whiteness. By squeezing it through leather, the ex cess of mercury may be separated, and a soft white amalgam obtained, which gra dually becomes solid, and consists of about one part of mercury to two of gold. It melts at a moderate temperature ; and in a heat below redness the mercury eva porates, and haves the gold 41 a state of purity. It is much used in gilding. The
amalgam is spread upon the metal which is to be gilt; and then, by the applica tion of a gentle and equal heat, the mer cury is driven off, and the gold left adhe ring to the metallic surface: this surface is then rubbed with a brass wire brush under water, and afterwards burnished. The amalgam of silver is made in the same manner as that of gold, and with equal-ease. It forms dentrical crystals, which contain eight parts of mercury and one of silver. It is of a white colour, and is always of a soft consistence. Its spe cific gravity is greater than the mean of the two metals. Gillert has even re marked, that when thrown into pure mer cury, it sinks to the bottom of that liquid. When heated sufficiently, the mercury is volatilized, and the silver remains behind pure. This amalgam is sometimes em ployed, like that of gold, to cover the sur faces of the inferior metals with a thin coat of silver. The amalgam of tin and mercury is much used in electricity. Sec GILDING.