It is a compound of arsenious acid and deutoxide of copper, is sold in powder or pulverulent cakes, and has a pale grass-green colour. Its nature may be ascertained by heating it in a glass tube. Crystals of oxide of arsenic sublime, and oxide of copper remains, which, on being dissolved in nitric acid, yields a fine violet-blue solution with ammonia.
The mineral-green of the shops, however, is seldom arsenite of copper. The substance sold in Edinburgh under that name, although believed by colourmen to be a preparation of arsenic, is not the arsenite of copper, but a mixture of hydrated oxide of copper and carbonate of lime; which will be mentioned more particularly under the head of the poisons of copper.
Process for Organic Mixtures.—The suspected mixture is to be heated with a little hydrochloric acid and well stirred. The arsenite being thus dissolved, the solution is to be allowed to cool and then filtered. A stream of hydrosulphuric-acid gas will now cause a dark-brown or yellowish-brown muddiness or precipitate, which is a mixture of sulphuret of copper and sulphuret of arsenic. The precipitate being separated after boiling, and properly cleansed by the process of subsidence and affusion, or if it is large, by washing on a filter, the two sulphurets are to be separated by ammonia, which dissolves sulphuret of arsenic but leaves the sulphuret of copper; and the sulphuret of arsenic may be recovered from the filtered fluid by expelling the ammonia with heat. The sulphuret of arsenic is next to be reduced as directed at page [211]; and the sulphuret of copper examined as recommended under the head of copper.
4. Arsenite of Potass.
This salt is an object of some importance to the medical jurist, as it forms the basis of a common medicine, Fowler’s Solution, or the Tasteless Ague Drop. This preparation contains in every ounce four grains of arsenious acid. It has a brownish-red colour, and an odour of lavender. It is strongly alkaline to litmus. When acidulated with hydrochloric acid, hydrosulphuric-acid gas causes in it a dirty brownish-yellow precipitate; and Reinsch’s process will detach arsenic from it upon copper in a state capable of being subjected to the usual tests [see p. [214]].
5. Arseniate of Potass.
This substance is so rarely met with as to be an object of little consequence to the medical jurist: nevertheless I have found in the course of reading two instances of poisoning with it. A very dangerous and tedious case has been related by Professor Bernt, which arose from too great a quantity having been given medicinally by an ignorant druggist;[[557]] and a case of accidental poisoning with it has been related in the London Medical Repository.[[558]] A singular account too has been published of the accidental poisoning of seven horses with it at Paris. They all died, most of them with the symptoms and morbid appearances of well-marked inflammation of the alimentary canal.[[559]]
When solid it forms tetraedral prismatic crystals, acuminated by four planes. It is very soluble in water, fuses at a red heat, and on cooling concretes into a crumbly, foliaceous mass, having a pearly lustre. It is easily known by the effect of the process of reduction—of the nitrate of silver, the salts of copper, and sulphuretted-hydrogen. Heated with charcoal in a tube it gives off metallic arsenic in the usual manner; but a stronger heat is required than for the reduction of the arsenious acid. Dissolved in water and treated with nitrate of silver it yields a brick-red precipitate, the arseniate of silver. With the salts of copper its solution gives a pale bluish-white precipitate, the arseniate of copper. With sulphuretted-hydrogen gas, preceded by acidulation with muriatic acid, and transmitted for a considerable length of time, it yields the yellow sulphuret of arsenic. When in solution it yields arsenic both by Reinsch’s process and the method of Marsh.
6. The Sulphurets of Arsenic.
In the arts various substances are known which contain a compound of sulphur and arsenic. In the first place, two pure sulphurets are known in chemistry and in painting, the one of a fine orange colour, and known by the name of realgar, the other of a rich sulphur-yellow, and termed orpiment. Secondly, the name of orpiment is familiarly given to a pigment in more general use than either of the former, which has a less lively colour, and consists of pure orpiment with a large admixture of arsenious acid. Lastly, orpiment also forms a great proportion of another common pigment, King’s yellow.