PROPERTIES.--A heavy solid, occurring either as an opaque, white powder, or in irregular masses of two varieties; the one amorphous, transparent and colorless, like glass; the other crystalline, opaque, and white, resembling porcelain. Frequently the same piece has an opaque, white outer crust enclosing the glassy variety. Contact with moist air gradually changes the glassy into the white opaque variety. Both are odorless and tasteless. The glassy variety dissolves slowly in thirty parts of water; the porcelain-like in eighty parts of water. Arcenous acid is sparingly soluble in alcohol, but soluble in glycerin, hydrochloric acid and solutions of the alkali hydrates and carbonates. When heated to 424°, arcenous acid is completely volatilized without melting. INCOMPATIBLES.--Lime water, salts of iron and magnesia. DOSE.--Horses, 1 to 5 grs.; cattle, 2 to 8 grs.; sheep and pigs, 1 to 2 grs.; dogs, ¹⁄₃₀ to ¹⁄₁₀ gr. LIQUOR POTASSII ARSENITIS--SOLUTION OF POTASSIUM ARSENITE (Fowler’s Solution) DERIVATION.--Arcenous acid, potassium bicarbonate, compound tincture of lavender and distilled water. Strength one part of arcenous acid in 100. DOSE.--Horses, 2 drs. to 1 oz.; cattle, ¹⁄₂ to 1¹⁄₂ ozs.; sheep and pigs, 10 to 40 ms.; dogs, 2 to 5 ms. Average dose for horse is ¹⁄₂ oz. usually given three times daily in drinking water or bran mash. LIQUOR ACIDI ARSENOSI--SOLUTION OF ARCENOUS ACID DERIVATION.--Arcenous acid, diluted hydrochloric acid, and distilled water. Strength one part arcenous acid in 100. DOSE.--Same as liquor potassii arsenitis. LIQUOR ARSENI ET HYDRARGYRI IODIDI (Donovan’s Solution) DERIVATION.--Arcenous iodide, red mercuric iodide, and distilled water, which should contain not less then one per cent of arcenous iodide and one per cent of mercuric iodide. DOSE.--Same as liquor potassii arsenitis. ACTIONS.--Arsenic and its compounds are gastro-intestinal and pulmonary tonic, a stimulant and alterative, acting particularly on the digestive and respiratory mucous membranes and skin. It is antiperiodic and tonic; also antispasmodic in diseases of the nervous system, and is a nervine tonic. In large doses it is a corrosive-irritant poison, killing either by gastro-enteritis, or nervous paresis. Continued doses produce fatty degeneration. On account of its being a stomachic, small doses promote the appetite and digestion. Large doses inflame the stomach and derange digestion. It increases the cardiac action, respiratory power, and secretion of the intestines. It also stimulates peristalsis. When tolerance is established, large doses are taken with impunity. EXTERNALLY.--Arsenic is a very painful escharotic, exciting violent inflammation. It is a caustic, antiseptic, and parasiticide, and is frequently used as a sheep dip. It is eliminated chiefly by the kidneys, skin and saliva and milk of nursing animals.