Mercury, or Quicksilver Hydrargyrus ), a mineral fluid, about fourteen or fifteen times heavier than water: it is so remarkably thin, that it requires the intense cold of 40 degrees below O, of Fahrenheit's scale, to render it solid.—When exposed to fire, it may be totally volatilized.

Quicksilver is found sometimes in a native state, as in the mines of India, South America, Hungary, etc; but more generally mixed with metals, stone, or other substances, from which it is extracted by various processes. Next to gold, and platina, mercury is the heaviest of all metals, with most of which it unites, excepting iron and antimony : hence it is employed in considerable quantities, for extracting gold and silver from the earthy matters with -which they are mixed.—The amalgam, or incorporation of quicksilver with gold,serves to gildr copper or silver, so tha these metals assume the appearance of gold: when united with tin, it is employed in the manufacture of looking-glasses or mirrors, in the manner already described, p. 125 of the present volume.

Independently of its utility in-various manufactures, mercury is extensively employed in medicine; and, though it is the most violent of poisons, when taken inadvertently in too large quantities, yet, if judiciously administered, it has frequently effected a cure, after alt other medicines had failed to procure relief. When taken into the stomach undivided, or in its native state, this fluid metal almost instantly passes through the intestines unchanged, and produces no perceptible effect, except that of promoting evacuation, if any crudities or obstructions should prevail in the alimentary canal. Hence it might be advantageously prescribed in the first stage of the Iliac Passion, before the bowels are too much weakened and corroded by the stagnant feces ; especially if it he given together with castor-oil of fat broth, but no spice. The patient, after taking this medicine, should, if possible, walk about the room; and there are instances in which several ounces, nay, half a pound, and upwards, of pure quicksilver, have been swallowed with the happiest effects. But, in the latter stages of obstinate and violent colics, when inflammation and gangrene have already taken place in the bowels, its specific gravity would infallibly rend the intestines, and accelerate the fatal crisis.—On the whole, we think, preparations of mercury are at present too often employed in medicine, under a great variety of forms, both inter-ally rid externally, for many dis-:s, the nature of which requires a very different treatment. Be-sides, the animal and vegetable kingdoms supply us with a sufficient number of the most efficacious remedies for removing all curable disorders, without the necessity of resorting to the mineral, on almost every occasion.

Mercury. - This mineral being of extensive utility, both in the arts and in medicine, various base metals are frequently combined with it, in order to increase its weight: such fraud may, however, be detected by the dull aspect of. the quicksilver ; by its tarnishing on exposure to the air; and by the black sediment deposited, when it is shaken with water, in a bottle. The substance, chiefly employed for this nefarious practice, is lead ; a very large proportion of which unites with mercury, especially if zinc or bismuth be previously added.

In order to ascertain the adul-teration with lead, quicksilver should be agitated with a little water ; after which the fluid must be strained, and the mercury digested in distilled vinegar. By this process, the oxyd of lead will be dissolved, and will deposit a blackish precipitate with sulphurated water. If mercury has been sophisticated with bismuth, the latter will appear in the form of a white sediment; on pouring a solution of nitre, prepared without heat, into a vessel containing the suspected metal and distilled water. - Tin may be discovered, in a similar manner, by a weak solution of nitro-muriate of gold, which produces a purple sediment ; but zinc may be detected by simple exposure to heat.