An-anhydride (not a true acid), obtained by roasting arsenical ores, and purified by sublimation.

Characters. - Occurs in sublimed masses which usually present a stratified appearance caused by the existence of separate layers differing from each other in degrees of opacity, or as a heavy white powder. When slowly sublimed in a glass tube it forms minute brilliant and transparent octahedral crystals.

Solubility. - It is sparingly soluble in water.

Reactions. - Its solution gives with ammonio-nitrate of silver a canary-yellow precipitate insoluble in water, but readily dissolved by ammonia and by nitric acid. Sprinkled on a red-hot coal it emits a garlicky odour.

Impurities. - Gypsum and chalk.

Test. - It is entirely volatilised at a temperature not exceeding 400° F. Four grains of it dissolved in boiling water with eight grains of bicarbonate of sodium discharge the colour of 808 grain-measures of the volumetric solution of iodine. As2O3 + 2H2O + 4I = As2O5 + 4HI.

Dose.- 1/60 to 1/12 of a grain, in solution. It may also be given in the so-called 'Asiatic pills,' which are used in some parts of the Continent. These consist of arsenious acid, 0.75 grm., powdered black pepper, 6 grm., gum arabic, 1.5 grm., powdered marsh-mallow root, 2 grammes, to make 100 pills, of which three are to be taken daily..

Preparations Of Arsenious Acid

Preparations of Arsenic Acid.

b. And U.S.P.

Ferri Arsenias.

Sodii Arsenias.

Liquor Sodii Arseniatis.