Compound Pill of Subchloride of Mercury.—Calomel and sulphurated antimony, each 1 ounce, guiac resin 2 ounces, castor-oil 1 fluid ounce. One grain (·0648 grm.) of calomel, and the same quantity of antimony sulphide, are contained in every 5 grains (324 mgrms.) of the pill mass, i.e., calomel 20 per cent.
Ointment of Subchloride of Mercury (Unguentum hydrargyri subchloridi).—Calomel mixed with benzoated lard; strength about 1 : 61⁄2.
White Precipitate (Hydrargyrum ammoniatum, NH2HgCl).—A white, heavy powder, subliming by heat without residue, and insoluble in water, alcohol, and ether. With soda, it yields a metallic sublimate. When boiled with potash, ammonia is evolved, the yellow oxide of mercury formed, and chloride of potassium passes into solution. It should contain 79·5 per cent. of mercury.
The fusible white precipitate of the pharmacopœia of the Netherlands does not appear to be of constant composition, varying between 69·4 to 65·6 per cent. of mercury.[904] It melts on heating, and leaves as a residue chloride of sodium.
[904] Hirsch, Die Prüfung der Arzeneimittel.
Commercial white precipitate is frequently adulterated; Barnes has found carbonates of lead and lime, the latter to the extent of nearly 2 per cent.[905] Calomel, according to Nickles,[906] has been substituted for white precipitate, but this was several years ago. The methods for detection are obvious.