Domestic Encyclopædia (1802)/Supplement/Mercury

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 adulteration 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.