Arsenic, Trisul′phide of. As2S3. Syn. Tersul′phide of arsenic, Yellow sul′phide of a., Sesquisul′phide of a., Or′piment; A. sesquisulphure′tum, Orpimen′tum, L.; Orpiment, Sulfure jaune d’arsenic, &c., Fr.; Auripigment, Operment, Rauschgelb, Ger. This sulphide, like the last, is found ready formed in nature; and is prepared artificially, by sublimation, from a mixture of arsenious acid and sulphur, as noticed under Orpiment and Yellow Pigments. It also falls as a precipitate when a stream of sulphuretted hydrogen gas is passed through an acid solution of arsenious acid or of an arsenite.
Prop., &c. Golden-yellow crystalline lumps, or a fine golden-yellow powder; crystals, right rhombic prisms; volatile; fusible; very soluble in pure alkalies, by which it is distinguished from sulphide of cadmium; and from trisulphide of antimony by being soluble in hydrochloric acid. The factitious sulphide (KING’S YELLOW) of the shops often contains 80 to 90% of white arsenic; and is, therefore, much more poisonous than the native trisulphide. Sp. gr. (native) 3·44 to 3·60.
Use, &c. As a dye, as a pigment, and as an ingredient in fireworks, and in some depilatories. Silk, woollen, or cotton goods soaked in a solution of pure orpiment in ammonia, and then suspended in a warm apartment or stove-room, rapidly lose their ammonia, and become permanently dyed of a superb yellow colour. The native sulphides (both red and yellow) are much less soluble, and hence less poisonous, than those prepared artificially. They also possess the richest colour; and are, therefore, preferred by artists and dyers. In former times, orpiment, like realgar, was employed in medicine. See Arsenic.
Arsenic, Pentasul′phide of. As2S5. Syn. Sulpharsen′ic acid, &c.; Arsen′ici pentasulphure′tum, &c., L. When a stream of sulphuretted hydrogen is transmitted for some time through a solution of arsenic acid, a precipitate of the PENTASULPHIDE is deposited after some hours’ repose. Its formation is accelerated by boiling the liquid.
Prop., &c. It greatly resembles the tersulphide in its appearance and general properties.
Arsenic, White‡. See Arsenious anhydride.
Arsenic, Yell′ow. Trisulphide of arsenic.
ARSENIC ACID. H3AsO4. Syn. Acidum arsen′icum, L.; Acide arsénique, Fr.; Arsenicsäure, Ger.
Prep. 1. Arsenious acid, in fine powder, 2 parts; concentrated nitric acid, 6 parts; hydrochloric acid, 1 part; mix in a flask or tubulated retort, and digest, with heat, until solution is complete; after repose, decant the clear portion and evaporate, to the consistence of a thick syrup.
2. Dissolve arsenious acid in hot hydrochloric acid, and when the solution is cold add concentrated nitric acid, in small quantities at a time, until red vapours cease to be evolved, then proceed as before.