Prep. Usually collected in flues during the smelting of the arseniurets, and afterwards purified by introducing some of the commercial arsenious acid into a thin porcelain capsule, and covering the capsule with a glass flask filled with cold water and fitting pretty closely, then applying the heat of a lamp. The arsenious acid being volatile, rises in the form of vapour, and condenses and adheres to the bottom of the flask.

Prop. & Comp. The composition of arsenious acid is, As O3. The commercial article usually occurs in broken pieces of the cakes, into which it had been sublimed; it is transparent and glass-like at first, but becomes after a time opaque white or yellowish.

The medicinal acid, or that which has been resublimed by the above process, is in the form of a crystalline, heavy, white powder; soluble in about 100 parts of cold water - much more in boiling water, which, on cooling, deposits octahedral crystals of the acid; when sublimed slowly in a tube, the same octahedral crystals are seen. When mixed with charcoal and heated, metallic arsenic sublimes with an alliaceous odour. The solution of arsenious acid is precipitated yellow by sulphuretted hydrogen, and lemon or canary-yellow colour by ammonio-nitrate of silver, and green with sulphate of copper, after the addition of potash.

Tests for purity. It is entirely volatilized by heat. Four grains dissolved in boiling water with 8 grains of bicarbonate of soda, discharge the colour of 80.8 measures of the volumetric solution of iodine. This decolorization is effected by the conversion of the iodine into hydriodic acid. The change may be represented by the formula, As O3 + 2 HO+ 2 I=As O5 + 2 HI, two equivalents of iodine corresponding to one equivalent of arsenious acid; or one equivalent of iodine, 127, to half an equivalent of arsenious acid, 49.5. Thus 100 measures of the volumetric solution, which contain 12.7 grains (or one-tenth of an equivalent) of iodine, represent 4.95 grains (or one-tenth of half an equivalent) of arsenious acid. One hundred grains should give 124 of tersulphuret of arsenic (orpi-ment) when precipitated with sulphuretted hydrogen in an acid solution.

Off. Prep. Liquor Arsenicalis. Arsenical Solution. A mixed solution of arsenite and carbonate of potash. [Liquor Po-tassaa Arsenitis. Solution of Arsenite of Potassae. U. S.]

Synonym. Liquor Potassas Arsenitis. Lond.

Arsenious acid, broken into small pieces, carbonate of potash, each, eighty grains; compound tincture of lavender, five fluid drachms; distilled water, one pint. Boil the acid and carbonate with half a pint of water, until they are dissolved. To the cold liquor add the tincture; and lastly, as much of the water as may be requisite, that it may accurately measure a pint.) This solution was formerly known as Fowler's Solution; four grains of arsenious acid are contained in each fluid ounce. Sp. gr., 1.009. [The preparation is identical with that of the U. S. P. In the latter, however, the pint of the solution contains but 64 grains of arsenious acid, the apparent difference being caused by the use of the wine pint divided into 16 fl. ounces, instead of the imperial pint of the Br. P.] One fluid ounce boiled for five minutes with ten grains of bicarbonate of soda, and then diluted with six fluid ounces of water to which a little mucilage of starch has been added, does not give with the volumetric solution of iodine a permanent blue colour, until eighty-one measures, (representing four grains of arsenious acid) have been added. The explanation of this test is the same as that given under the head of arsenious acid itself. The addition of the starch insures the detection of free iodine more readily.

Therapeutics. In minute doses the effects of arsenic appear to be directed to the skin and nervous system, being alterative and tonic in their nature: in larger doses, irritation of the alimentary canal and of the mucous membrane of the eyes is produced; in still larger, poisonous effects ensue: externally, it acts as an escharotic, and may be absorbed to a dangerous extent. It is employed internally in chronic skin affections, more especially when of a squamous or tubercular character; also as an antiperiodic in agues and neuralgic affections; and in chorea and epilepsy it is sometimes more effectual than quinine.

Dose. Of arsenious acid 1/60 gr. to 1 gr., or 1/12 gr. Of liq. arsenicalis, 2 min. to 5 min., or occasionally to 10 min. Preparations of arsenic should be given soon after a meal, and pain in the epigastrium, nausea, and irritation of the eyelids, should be looked upon as indications for diminishing the dose.

Adulteration. Gypsum and chalk, which have been sometimes mixed with arsenious acid, can be readily detected by not subliming with heat.

Sodae Arsenias. Arseniate of Soda. [Not officinal in U. S. P.] Prep. Made by finely powdering and intimately mixing together ten ounces of arsenious acid, eight and a half ounces of nitrate of soda, and five and a half ounces of dried carbonate of soda, afterwards putting the mixture into a large clay crucible, covered with a lid, and exposing it to a full red heat, till effervescence has ceased and complete fusion has taken place.

Prop. & Comp. Occurs in colourless transparent prisms.

The formula is, 2Na O, HO, As O5 + 14 HO. Soluble in water, the solution giving a brick-red precipitate with nitrate of silver 3 Ag O, As O5), and a white precipitate with chloride of barium, chloride of calcium, and sulphate of zinc, all of which precipitates are soluble in nitric acid. The precipitate with silver is also soluble in excess of ammonia. Arseniate of soda heated to 300° loses 40.38 per cent. of its weight. A watery solution of 10 grains of the residue, treated with 5.3 measures of the volumetric solution of soda, continues to give a precipitate with the volumetric solution of nitrate of silver, until 161.3 measures of the latter have been added, equivalent to 18.5 grains of arsenic acid (As O5).

Off. Prep. Liquor Sodae Arseniatis. Solution of Arseniate of Soda. (Arseniate of Soda, rendered anhydrous by a heat not exceeding 300°, four grains; distilled water, one fluid ounce.)

Therapeutics. Arseniate of soda may be employed in the same cases as arsenious acid or the arsenical solution. Its action, measured by the amount of metallic arsenic contained in it, appears to be milder than that of the metal in the lower form of oxidation. See Therapeutics of Arsenious Acid.

Dose. Of the crystallized salt 1/12 gr. to 1/2 gr.; of the salt dried at 300°, 1/20 gr- to 1/4 gr.; of liquor sodsa arseniatis, 5 min. to 30 min. Some patients are very intolerant of arsenic, and much smaller doses must then be administered.