Mercury and tin combined together form the substance that is used for the _silvering of looking─glasses_. The process is as follows: A quantity of tin─foil, equal in size to the glass, is evenly placed on a flat stone or table; and mercury, in which some tin has been dissolved, is poured upon it, and spread with a feather, or bunch of cloth, until its union has covered every part. A plate of glass is then cautiously slided upon it, from one end to the other, in such manner that part of the redundant mercury is driven off, or swept away before its edge. The remainder is now united to the tin. The glass is then loaded with weights all over, so as to press out still more of the mercury. By inclining the table, this remaining mercury becomes discharged; and, in a few hours, the rest of the tin─foil and mercury adhere so firmly to the glass, that the weight may be removed without any danger of its falling. About two ounces of mercury are requisite for covering, in this manner, three square feet of glass. By means of mercury a _fulminating powder_ is made, which, when struck with a hammer on an anvil or flat iron, such as is used by laundresses, explodes with a stunning and disagreeable report, and with such force as to indent both the anvil and the hammer. Four or five grains are as much of this powder as ought to be used for such experiments. Its force is much greater than that of gunpowder, but does not extend so far. Hence it is a substance which might be rendered of great use in the blasting of rocks. _Corrosive sublimate_ is an extremely poisonous preparation from mercury. Among other uses, it is employed by dyers as a mordant to fix their colours. From certain proportions of corrosive sublimate rubbed together, until they are perfectly incorporated, is formed _calomel_; a salt which, of late years, has been extensively and most usefully employed in medicine. A valuable red colour or pigment called _vermilion_, or _artificial cinnabar_, which was as well known to the ancients as it is to the moderns, is usually formed of three parts of mercury and one of sulphur, melted together, heated to redness, and then sublimated out of contact of the air. The manufacture of vermilion was long kept a secret by the Dutch; and it is stated that, before the late war, nearly 50,000 pounds weight of it were annually made, in three furnaces, by four workmen, near Amsterdam. Native cinnabar is sometimes used for the same purpose; but the artificial kind is preferred on account of the purity and brightness of its colour. 229. _SILVER is a white, brilliant, sonorous, and ductile metal, somewhat more than ten times heavier than water._