An opaque white powder.

Solubility. - It is insoluble in cold water, alcohol, and ether.

Reactions. - Digested with caustic potash, it evolves ammonia, acquiring; a pale yellow colour, and the fluid, filtered and acidulated with nitric acid, gives a white precipitate with nitrate of silver. Boiled with a solution of chloride of tin it becomes grey, and affords globules of metallic mercury.

Preparation. - By dissolving corrosive sublimate in water, and precipitating by ammonia.

Impurities. - Chalk, sulphate of calcium, baryta, lead, carbonates, mer-curous salts.

Tests. - Entirely volatilised at a heat under redness (no chalk, etc.). It should dissolve in hydrochloric acid without residue (no mercurous salt) and without effervescence (no carbonate).

Preparation.

b. And U.S.P. Unguentum Hydrargyri Ammoniati. .1 part in 10, B. and U.S.P.

(It was about 15 per cent. B.P. 1867.) With simple ointment, B.P.; with benzoated lard, U.S.P.

Uses. - Not used internally. The ointment is used in order to destroy parasitic fungi, but more especially to kill pediculi in the hair or on the body. It is also useful in impetigo contagiosa, lichen, pityriasis, herpes, subacute eczema, and other skin-diseases.