Mercury, or quicksilver, is known from all other metals by being fluid at the ordinary temperature of the air. This is only owing to its extreme fusibility, for at 72 degrees below the freezing point of water, it also becomes solid, and may be hammered out or cut by a knife; it is very heavy, being about fifteen-and-a-half times that of water, so that most of the metals will float on its surface; it has a bright lustre and is almost as white as silver. It is found both in the fluid metallic state, and in combination with sulphur, in which last state it is called “cinnabar;” this is a heavy mass of a deep red color, and when ground to powder, of a most magnificent red, and is the vermillion so well known as a pigment; this vermillion is, however, most frequently manufactured by combining the mercury and sulphur, both first purified, in this way a more brilliant color is produced than can be got from the cinnabar. The metal is extracted by heating the cinnabar with iron-filings or lime in a retort, by which means the mercury distils over and the sulphur is left behind united with the iron or lime. Mercury is used for many purposes in the arts and sciences, for barometers, thermometers, compensating pendulums for clocks, &c., and also in the processes of water-gilding, looking glass silvering, and in the Daguerreotype process. The combinations of mercury with other metals are called “amalgams.” GOLD. Illustration: GOLD (‡ NUGGET). Gold is the heaviest of the metals with the exception of Platinum, being rather more than nineteen times heavier than water; it is of a bright yellow color, and is not tarnished by exposure to the air or moisture, hence its usefulness in ornamenting frames, cornices, &c. Gold is chiefly used, in the form of coin, as the medium of exchange; for ornamental purposes, such as jewellery; for gilding, and for staining glass, to which it gives a beautiful ruby-red color. Gold coin contains about one twelfth part, by weight, of copper, this is added to give it hardness and consequently cause it to lose less by wear in use. Gold is not dissolved by any of the pure acids, but a mixture of hydrochloric and nitric acids will dissolve it in consequence of giving out chlorine, an element which freely dissolves gold. Gold is capable of being beaten out into leaves of extreme thinness, and also of being drawn into wire of such thinness that five hundred feet of it weigh but one grain. SILVER. Illustration: SILVER.