Arsenicum has two oxides, the trioxide and the pentoxide.
ARSENICUM TRIOXIDE.
Synonyms.—Arsenious oxide, arsenious acid, arsenious anhydride; popularly, “arsenic,” “flour of arsenic,” or “white arsenic:” in mining districts it is sometimes called “mercury:” Latin, acidum arseniosum.
Chemical formula As2O3, or two atoms (150 parts by weight) of arsenicum, to three atoms (48 parts by weight) of oxygen.
Forms.—(1.) Crystalline. By sublimation and slow condensation on moderately heated surfaces, also by deposition from solution, we obtain regular octahedra, often so modified as to appear like equilateral triangular or hexagonal plates, or even elongated into triangular prisms, but never in the form of regular tetrahedra such as tartar emetic yields. For figures, see Guy and Ferrier’s Forens. Med., 1881, pp. 440 and 670. The crystals are transparent and highly refracting. Sp. gr. 3·69. Volatilizes without melting, except under increased pressure.
(2.) Amorphous or vitreous. Suddenly cooled, As2O3 condenses as clear transparent drops, finally cohering into a glassy mass, sp. gr. 3·74. When kept, this becomes opaque, perhaps owing to a change into the crystalline variety, constituting the “porcellanous” form found in commerce. If the lumps be broken, layers of still transparent As2O3 will be seen.
The solubility depends on the variety, temperature, length of time it is digested, fineness of powder, &c. So that exact figures cannot be given, as hardly two authorities agree. It is certain, however, that the amorphous form is less soluble than the crystalline.[131] The accepted statement is that given by Taylor (Med. Juris. 1, 250): that digested with cold water, from 1/500 to 1/1000 dissolves, equal from one half to one grain per fluid ounce; if boiled for an hour and allowed to cool, an average of twelve grains per fluid ounce remains in solution; if boiled for a shorter time, less is dissolved. See also Woodman and Tidy’s Forens. Med., 1877, pp. 133, 134. Organic matter is said to decrease its solubility; I have not found that it does so to any notable extent. Dr. Blondlot (Med. Times and Gazette, Feb. 11, 1860) states that fats, such as bacon, diminish the solubility; this must be by coating the particles and preventing contact with water. Powdered white arsenic in all cases refuses for a long time to become moistened by water, floating on the top, and collecting in little lumps as if greasy: the appearance is so peculiar as to have led sometimes to its detection. Commercial powdered white arsenic is generally the opaque form pulverized, but it may be crystalline.
As2O3 is very soluble in potash and soda and their carbonates, forming arsenites. It is less soluble in ammonia. In hydrochloric acid it dissolves easily, forming chloride of arsenic. It is less soluble (1 in 2,000) in alcohol than in water. One part dissolves in 200,000 of chloroform. It is insoluble in pure ether. It is heavy to feel, tasteless, very faintly acid to test paper, and so feeble in affinity that its soluble salts are strongly alkaline, and are decomposed by all acids with separation of As2O3. The powder and its vapour are inodorous, but when heated with charcoal or organic matter it is reduced to arsenicum, with its odour of garlic.
Uses and Occurrence.—1. As a preservative against insects and fungi, for steeping seed-wheat. Many accidents have resulted. Birds poisoned by it and afterwards eaten by man have occasioned severe symptoms. From 1830 to 1840 in France 235 accusations of arsenic poisoning occurred, of which 110 were against agricultural persons, proving that the use of the drug in farming gives dangerous facilities for crime. Sulphate of copper, or, better, a mixture of sulphate of soda and lime, are more effectual as preservatives, and the latter mixture is not poisonous. (Lancet, 1849, Jan. 20.)
2. For preserving skins and furs (arsenical soap). This use has also caused serious results in the operators. Stuffed birds, &c., kept in living rooms may prejudicially affect the inmates by giving off arsenical dust.