§ 713. Orpiment, or Arsenic Trisulphide.—As2S3 = 246; specific gravity, 3·48; composition in 100 parts, As 60·98, S 39·02; found native in crystals, presents itself in the laboratory usually as a brilliant yellow amorphous powder, on passing sulphuretted hydrogen through an acid solution of arsenious acid or an arsenite. It is very insoluble in water (about one in a million, Fresenius), scarcely soluble in boiling concentrated hydrochloric acid, and insoluble generally in dilute acids. Red fuming nitric acid dissolves it, converting it into arsenic and sulphuric acids; ammonia and other alkaline sulphides, the alkalies themselves, alkaline carbonates, bisulphide of potassium, and aqua regia, all dissolve it readily. In the arts it is used as King’s yellow (see [p. 532]). Tanners also formerly employed a mixture of 90 parts of orpiment and 10 of quicklime, under the name of Rusma, as a depilatory; but the alkaline sulphides from gas-works are replacing this to a great extent.
§ 714. Haloid Arsenical Compounds.—The Chloride of Arsenic, AsCl3 = 181·5; specific gravity liquid, 0° 2·205; boiling-point 134° (273·2°F.), is a heavy, colourless, oily liquid, which has been used as an escharotic in cancerous affections (principally by quacks). In one process of detecting and estimating arsenic, the properties of this substance are utilised (see [p. 575]). It is immediately decomposed by water into arsenious and hydrochloric acids.
The Iodide of Arsenic (AsI3) is used occasionally in skin diseases, but is of little interest to the analyst; it is commonly seen in the form of brick-red brilliant flakes.
§ 715. Arsenic in the Arts.—The metal is used in various alloys; for example, speculum metal is made of tin, copper, and a little arsenic; white copper is an alloy of copper and arsenic; shot is composed of 1000 parts of lead mixed with 3 of arsenic; the common Britannia metal used for tea-pots, spoons, &c., often contains arsenic; and brass is bronzed with a thin film of arsenic. It was formerly much employed in the manufacture of glass, but is being gradually superseded. It is also now used to some extent in the reduction of indigo blue, and in that of nitro-benzole in the manufacture of aniline.
In cases of suspected poisoning, therefore, and the finding of arsenic in the stomach, or elsewhere, it may be set up as a defence that the arsenic was derived from shot used in the cleansing of bottles, from the bottles themselves, or from metal vessels, such as tea-pots, &c.
The arsenic in all these alloys being extremely insoluble, any solution to a poisonous extent is in the highest degree improbable. It may, however, be necessary to treat the vessels with the fluid or fluids which have been supposed to exert this prejudicial action, and test them for arsenic. The treatment should, of course, be of a severe and exhaustive character, and the fluids should be allowed to stand cold in the vessels for twenty-four hours; then the effect of a gentle heat should be studied, and, lastly, that of boiling temperatures. The analysis of the alloy itself, or of the glass, it would seldom be of value to undertake, for the crushed and finely divided substance is in a condition very different from that of the article when entire, and inferences drawn from such analytical data would be fallacious.
Arsenious anhydride is also used for the preservation of wood, and is thrown occasionally into the holds of vessels in large quantities to prevent vegetable decomposition. In India, again, a solution of arsenic is applied to the walls as a wash, in order to prevent the attacks of insects.
§ 716. Pharmaceutical, Non-officinal, and other Preparations of Arsenic.—(1) Pharmaceutical Preparations.—The Liquor arsenicalis (Fowler’s solution), or solution of arsenic of the pharmacopœia, is composed of:—
| Carbonate of Potash, | 87 grains (5·64 grms.) |
| Arsenious Acid, | 87 gra„ns(5·64 g„ms.) |
| Compound Tincture of Lavender, | 5 drachms (17·72 c.c.) |
dissolved in 1 pint (567·9 c.c.) of water; every ounce, therefore, contains 4·3 grains of arsenious acid (or 100 c.c. = ·9As2O3); the strength is therefore nearly 1 per cent.