680 poisons : their effects and detection. [§ 866 . 
Ointment of Subchloride of Mercury (Unguentum hydrargyri 
subchloridi). —Calomel mixed with benzoated lard ; strength, 20 per 
cent, mercurous chloride. 
White Precipitate (Hydrargyrum ammoniatum, NH 2 HgCl).—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. 
Commercial white precipitate is frequently adulterated ; Barnes has 
found carbonates of lead and lime, the latter to the extent of nearly 2 per 
cent. 1 Calomel, according to Nickles, 2 has been substituted for white 
precipitate, but this was several years ago. The methods for detection 
are obvious. 
Ointment of Ammoniated Mercury (Unguentum hydrargyri am- 
moniati). —Five parts of ammoniated mercury mixed with 95 of 
benzoated lard. 
Red Iodide of Mercury (Hydrargyrum iodidum rubrum, Hgl 2 ).— 
A crystalline powder of a scarlet colour, becoming yellow on gentle 
heating. It is sparingly soluble in water, one part requiring from 6000 
to 7000 parts ; soluble in 130 parts of cold, 150 of hot alcohol ; and 
dissolving freely in ether, or in aqueous solution of iodide of potassium. 
Ointment of Red Iodide of Mercury (Unguentum hydrargyri iodidi 
rubri). Four grms. of the substance mixed with 96 of benzoated 
lard. 
Yellow Mercuric Oxide Ointment. —Yellow mercuric oxide, 2 grms. ; 
soft yellow paraffin, 98 grms. 
Green Iodide of Mercury (Hydrargyri iodidum viride, Hgl).—A 
din gy> greenish-yellow powder, darkening on exposure to light, and 
easily transformed by heat into the red iodide. 
Red Oxide of Mercury (Hydrargyri oxidum rubrum), HgO = 216 ; 
Hg, 92*12 per cent. ; specific gravity, 11 to 11*3; small, red, shining, 
crystalline scales, slightly soluble in water, requiring about 20,000 parts ; 
entirely soluble in hydrochloric acid. By a heat below redness it may 
be volatilised, and at the same time decomposed inbo mercury and 
oxygen. Its principal impurity is nitric acid, readily detected by the 
usual tests, or by heating in a test-tube, when, if nitric acid is present, 
orange vapours will be evolved. Fixed red powders (such as brick-dust 
and minium) are detected by being left as a residue, after the application 
of heat sufficient to volatilise the mercury. An ointment (strength 
10 per cent.) is official. 
Sulphate of Mercury. A white, crystalline powder, converted by 
1 Proc. Brit. Pharm. Conf., 1867, p. 10. 
2 Journ. Pharm. et Chim., l e serie, viii. 399, 1858. 
