524 MEDICAL JURISPRUDENCE kept long and exposed to light, a portion of the mercury is converted into mercuric oxide which produces a poisonous action on the system. 2. Pilula hydrargyri (Blue pill).—It contains 33 per cent of mercury. The dose is 4 to 8 grains. 3. Unguentum hydrargyri (Blue ointment).—It contains 30 per cent of mercury. 4. Unguentum hydrargyri dilutum,—It contains 10 per cent of mercury. 5. Unguentum hydrargyri composition.—It contains 12 per cent of mercury. 6. Unguentum hydrargyri nitratis forte.—It contains 6.7 per cent of mercury. 7. Unguentum hydrargyri nitratis dilutum.—It contains not less than the equivalent of 1.34 per cent of mercury. COMPOUNDS OF MERCURY 1. Mercuric Oxide, HgO.—This is known in the vernacular as Sipichand. It is a brick-red crystalline powder but it forms an amorphous yellow powder when a mercuric salt is acted upon by caustic soda or potash. Both the red and yellow varieties ,are insoluble in water. The red variety is a B.P.C. pre- paration, and is known as Hydrargyri oxidum rubrura (red precipitate), the dose being 1/16 to i grain. It is used for preparing a B.P.C. ointment, Unguentum Hydrargyri oxidi rubri (red ointment). The yellow variety is a pharmacopoeial preparation, and is known as Hydrargyri oxidum flavum. It is contained in the official preparations of Oculentum hydrargyri oxidi and Oculentum atropinos cum hydrargyri oxido and enters into the com- position of Hydrargyri oleatum (mercuric oleate) and Unguentum hydrar- gyri oleati. 2. Mercuric Chloride (Perchloride of Mercury, Corrosive Sublimate), HgCL.—It exists in the form of heavy, colourless masses of prismatic crystals or as a white, crystalline powder. It has a styptic, nauseous, metallic taste. It is soluble in eighteen parts of cold water and three parts of boiling water. It is readily soluble in alcohol (90 per cent), ether and glycerin and is very soluble in solutions of the alkaline chlorides. On account of its antiseptic properties it is largely used in medicine as well as in taxidermy. It is a violent poison, and is obtained in the bazaar, often mixed with impure subchloride. The official dose of mercuric chloride (Hydrargyri per- chloridum) is 1/32 to 1/16 grain. The pharmacopoeial solution, Liquor hydrargyri perchloridi, contains 0.1 per cent of mercuric chloride, the dose being 30 to 60 minims. When ammonia is added to a watery solution of mercuric chloride, ammonio-chloride of mercury is formed. It is also known as ammoniated mercury or white precipitate (Hydrargyrum ammoniatum, B.P.). It is a white, heavy, tasteless powder, insoluble in water, alcohol (90 per cent) and ether, but readily soluble in warm hydrochloric acid and in warm acetic acid. It is used in preparing an official ointment, Unguentum hydrargyri ammoniati (whi£e precipitate ointment) t, 3. Mercuric Iodide, HgI2.—This is also called red iodide of mercury or biniodide of mercury. It is a scarlet red powder, obtained by the action of a watery solution of mercuric chloride on one of potassium iodide. It is almost ^ insoluble in water, but soluble in about 130 parts of alcohol, and freely in ether, in nitric acid and in a solution of potassium iodide or mer- curic chloride. It forms one of the constituents of a non-official preparation, Liquor arseni et hydrargyri iodidi (Donovan's solution), the dose of which is 5 to 15 minims.