This metal is of the first therapeutical importance, and a large number of salts and other preparations are made from it.

Hydrargyrum. - Mercury. Hg. Characters. - A fluid metal, brilliantly lustrous. Impurities. - Lead, tin, etc.; detected by being non-volatile.

Preparations.

a. Hydrargryum cum Creta, - 1, with 2 of Chalk. Dose, 3 to 8 gr.

b. Emplastrum Hydrargyri. - 1 in 3.

c. Emplastrum Ammoniaci cum Hydrargyro. - 1 in 5.

d. Pilula Hvdrargvri. - "Blue Pill." 1 in 3, with Confection of Roses and Liquorice. Lose, 3 to 8 gr.

e. Unguentum Hydrargyri. - "Blue Ointment." Nearly 1 in 2.

From Unguentum Hydrargyri are prepared: a. Linimentum Hydrargyri. - 1 of Ointment, to 1 of Liquor Aminoniae, and 1 of Linimentum Camphorae.

. Unguentum Hydrargyri Compositum. - 6, with 7 1/2 Olive Oil, Wax, and Camphor.

γ. Suppositoria Hydrargyri. - 5 gr. of ointment in each.

From Hydrargyrum are made: f. Hydrargyri Oxidum Rubrum. - Red Oxide of Mercury. HgO.

Source. - Made by triturating together and heating Mercury, and Mercuric Pernitrate obtained by dissolving Mercury in Nitric Acid. (1) 3Hg + 8HNO3=3(Hg2NO3) + 2NO + 4H1O. (2) Hg2NO3 + Hg = 2HgO + 2NO2.

Characters. - An orange-red powder, insoluble in water.

Impurities. - Red lead and brick-dust; detected by being non-volatile. Nitrate of mercury; by yielding nitrous vapours by heat.

Dose. - 1/4 to 1 gr.

Preparation. Unguentum Hydrargyri Oxidi Rubri. - "Red Precipitate Ointment." 1 in 8.

g. Hydrargyri Iodidum Viride. - Green Iodide of Mercury. HgI.

Source. - Made by rubbing together Mercury and Iodine in the presence of Rectified Spirit.

Characters. - A dull green powder, insoluble in water.

Impurity. - Biniodide of mercury, found by long keeping; detected by being soluble in ether.

Dose. - 1 to 3 gr.

h. Hydrargyri Sulphas. - Sulphate of Mercury. HgSO4.

Source. - Made by dissolving Mercury in hot Sulphuric Acid, and drying.

Characters. - A white, heavy, crystalline powder. Used only to prepare calomel and corrosive sublimate.

From Hydrargyri Sulphas are made: a. Hydrargyri Subchloridum, - Subchloride of Mercury. Calomel. HgCl.

Source. - Made by subliming a mixture of Sulphate of Mercury, Mercury, and Chloride of Sodium; and washing with boiling water. (1) HgSO4 + Hg = Hg2SO4. (2) Hg2SO4 + 2NaCl = 2HgCl + Na2SO4.

Characters. - A dull white, heavy, nearly tasteless powder, insoluble in water and spirit.

Incompatible with iodide of potassium, nitro-hydrochloric acid, hydrocyanic acid, solutions of lime, potash, and soda.

Impurities. - Perchloride of mercury; detected by being soluble in warm ether. Other chlorides; non-volatile.

Dose. - 1/2 to 5 gr.

Preparations. i. Lotio Hydrargyri Nigra. - Black Wash. Calomel, 30 gr.; Lime Water, 10 fl.oz.

ii. Pilula Hydrargyri Subchloridi Com-posita. - Hummer's Fill. Calomel, 1; Sulphurated Antimony, 1; Guaiacum Resin, 2; Castor Oil, 1. Dose, 5 to 10 gr.

iii. Unguentum Hydrargyri Subchloridi. 1 in 6 1/2 .

. Hydrargyri Perchloridum. - Ferchloride of Mercury. "Corrosive sublimate." HgCl2.

Source. - Made by subliming a mixture of Sulphate of Mercury, Chloride of Sodium, and Black Oxide of Manganese. HgSO4 + 2NaCl = HgCl2 + Na2SO4. The manganese simply prevents the for-imation of calomel.

Characters. - Heavy colourless masses of prismatic crystals. Solubility, 1 in 20 of water.

Incompatible with alkalies and their carbonates, lime-water, tartar emetic, nitrate of silver, acetate of lead, albumen, iodide of potassium, soaps, decoction of bark.

Impurities. - Fixed salts; detected by not volatilising.

Dose. - 1/16 to 1/8 gr.

Preparations.

i. Liquor Hydrargyri Ferchloridi.-1/2 gr. in 1 fl.oz. (1/16 gr. in 1 fl.dr.). Dose, 30 to 120 min.

ii. Lotio Hydrargyri Flava. - "Yellow Wash." Corrosive Sublimate, 18 gr.; Lime Water, 10 fl.oz.

From Hydrargyri Perchloridum are made: iii. Hydrargyri Iodidum Rubrum. - Red Iodide of Mercury. HgI2.

Source. - Made by mixing hot solutions of Perchloride of Mercury, and Iodide of Fotas-sium, and purifying the precipitate. HgCl2 + 2KI = HgI2 + 2Cl.

Characters. - A vermilion crystalline powder. Soluble feebly in water, freely in ether.

Impurities. - As in the perchloride.

Dose. - 1/16 to 1/4 gr.

Preparation.

Unguentum Hydrargyri Iodidi Rubri. - 1 in 28.

iv. Hydrargyrum Ammoniatum. - Am-moniated Mercury. "White Precipita NH1HgCl Source. - Made by precipitating a solution of Perchloride of Mercury with Solution of Ammonia. HgCl2 + 2NH4HO = NH1HgCl +

NH4C1 + 2H1O.

Characters. - An opaque white powder, insoluble in water, spirit, and ether.

Impurities. - As in the perchloride.

Preparation.

Unguentum Hydrargyri Ammoniati. - 1 in 8 v. Hydrargyri Oxidum Flavum. - Yellow Oxide of Mercury. HgO.

Source. - Made by precipitating a solution of Perchloride of Mercury with a Solution of Soda.

Characters. - A yellow powder.

Impurities. - As in the perchloride.

i. Liquor Hydrargyri Nitratis Acidus. - Nitrate of Mercury, Hg2NO3, in solution in nitric acid.

Source. - Made by dissolving Mercury in Nitric Acid and "Water.

Characters. - A colourless, strongly-acid liquid.

Impurity. - Subnitrate of mercury; detected by giving precipitate when dropped into diluted hydrochloric acid.

j. Unguentum Hydrargyri Nitratis.- Citrine Ointment. Made by adding Lard melted in Olive Oil to a solution of Mercury in Nitric Acid.

Non-officinal Preparations of Mercury.

Oleate of Mercury. - Made by dissolving 6 to 20 per cent. of Yellow Oxide of Mercury in Oleic Acid.

Donovan's Solution. - Solution of Hydriodate of Mercury and Arsenic. Dose, 10 to 30 min.

Action And Uses. 1. Immediate Local Action And Uses

Externally. - Mercury in the form of the acid solution of the nitrate is a powerful caustic, employed to destroy growths on the skin, such as lupus, but must he used with caution. The perchloride applied in weak solutions is not absorbed, but acts destructively on organisms on or in the skin, such as those of ringworm. Stronger solutions cause inflammation of the skin, and concentrated solutions are caustic; but neither effect is surgically employed. A weak solution (gr.1/4 to the oz.) is used as a disinfectant and stimulant to ulcers, acting like other metallic salts (see pages 60 and 64), at the same time being absorbed, and producing the specific effects of the metal. Mercury itself, and most of the other preparations, cause little or no irritation of the skin, unless rubbed into it for some time.