Characters. - In heavy colourless masses of prismatic crystals, possessing a highly acrid metallic taste.

Preparation. - By mixing mercuric sulphate with sodium chloride and subliming into a small chamber. To prevent the formation of any calomel some peroxide of manganese is added.

Solubility. - It is more soluble in alcohol, and still more so in ether, than in water.

Reactions. - Its aqueous solution gives the reactions of mercuric salts (p. 681) and of a chloride (p. 594).

Dose. - 1/16 to 1/8 grain. In cholera and summer diarrhoea this dose may be given every quarter of an hour, half-hour, or hour.

A solution of 1 in 500 or 1 in 1,000 (about 1/2 grain in 1 oz. or the liquor of the B.P.) may be used as an antiseptic lotion or for a spray in diphtheria.

1 Mercurous tannate has been used in doses of one grain and a half twice or thrice a day in syphilis. It is said to be efficient, and yet neither to interfere with the digestion, nor to cause any stomatitis. Zeitsch. f. Therapie, 2, 1884.

2 Jendrassik, Deutsch. Archiv f. klin. Med., vol. xxxviii. p. 499.

Officinal Preparations

B.P.

Dose.

Liquor Hydrargyri Perchloridi............

1/2-2 fl. drm.

U.S.P

None.

Lotio Hydrargyri Flava (18 grs. in 10 n. oz.).

Used in preparing. - Hydrargyri Iodidum Rubrum; Hydrargyrum Ammoniatum.

B.P. Liquor Hydrargyri Perchloridi. Solution of Perchloride of Mercury. Contains 1/2 grain of perchloride of mercury in 1 oz. of water, with 1/2 grain of ammonium chloride to keep it in solution and prevent precipitation.

Uses. - When mixed with albumen, corrosive sublimate precipitates it, forming a mercuric albuminate. It is one of the most powerful antiseptics known (p. 95). It may be applied (in the strength of 2 grains to the ounce of water) to the skin to destroy vegetable and animal parasites present upon it, such as the fungus in pityriasis versicolor, in sycosis and favus, the acarus in scabies and the pediculus pubis. It is the most powerful remedy for the removal of the pigment in chloasma, and may be applied in a lotion of bichloride of mercury 2 grains, tincture of benzoin half a drachm, and 1 ounce of almond emulsion. For the rapid removal of pigment Hebra used a solution of 5 grains to the ounce of alcohol and water, and applied it by means of compresses for 4 hours, so as to raise a blister; the relief, however, is not permanent, since pigmentation returns. The danger of absorption must be considered, so that it is unwise to apply the treatment to large surfaces. It is useful in allaying the itching of pruritis scroti and pudendi, prurigo, and urticaria. It may be employed as a wash in ophthalmia (p. 216), as a gargle in syphilitic sore-throat, as a spray in diphtheria (p. 692), and as an injection in gonorrhoea, gleet, and leucorrhcea, or for the uterus and vagina in puerperal conditions. When swallowed in strong solution it sometimes causes an irritant poisoning (p. 395 et seq.); and if this should pass off, it may be succeeded by intense salivation due to the absorption of the drug. The treatment in such cases is to give albuminous substances, such as white of egg or milk, in order to form mercuric albuminate in the stomach, and thus prevent its irritant action on the mucous membrane. If the irritation which the drug itself produces is not sufficient to cause vomiting, the stomach should be emptied by an emetic or the stomach-pump, in order to prevent digestion and absorption of the mercuric albuminate and the poisoning which might occur from its absorption. In small and frequently-repeated doses it is useful in the dysenteric diarrhoea of adults or children and in cholera, its utility probably depending, to a great extent at least, on its antiseptic power, which is not destroyed, like that of other antiseptics, by considerable admixture with organic matter, such as the faecal contents of the intestine (p. 106). After its absorption it has the same effect as the other salts of mercury, and may be used for this purpose in syphilitic cases.

B.P. Lotio Hydrargyri Plava. Yellow Wash.

Preparation. - By mixing 18 grs. of corrosive sublimate with half a pint of lime-water.

Uses. - It is used as a stimulating application to syphilitic sores in cases where the black wash is not sufficiently powerful.