a natural production, and the result of many chemical operations. The sulphuret thrown down from solutions of arsenic by sulphuretted-hydrogen is quite conformable in physical and chemical characters with the natural orpiment. Natural orpiment, when in mass, consists of broad scales of much brilliancy and of a rich yellow colour. It is composed of two equivalents of metal and three of sulphur. Its most striking chemical characters are the same with those of realgar, from which it is distinguished chiefly by its colour.
It has been stated by Hahnemann in his elaborate work on Arsenic, that the pure sulphurets are somewhat soluble in water,—that native orpiment is soluble in 5000 parts of water with the aid of ebullition, and that artificial orpiment by precipitation is soluble in 600 parts.[1] Hahnemann, however, was mistaken in supposing that the water dissolved these sulphurets. It does not dissolve, but decomposes them. Very lately M. Decourdemanche has found that, by slow action in cold water, and much more quickly with the aid of heat, the arsenical sulphuret is decomposed by virtue of a simultaneous decomposition of the water, hydrosulphuric acid being evolved and an oxide of arsenic remaining in solution. And he has farther remarked, that this change is promoted by the presence of animal and vegetable principles dissolved in water.[2] These facts are interesting, as they explain certain apparent anomalies to be noticed presently in the physiological properties of the sulphurets.
The common orpiment of the shops is not a pure sulphuret like the natural orpiment, but a much more active substance, a mixture of orpiment and arsenious acid. It is made by subliming in close vessels a mixture of sulphur and oxide of arsenic. It is met with in the shops in two forms, in that of a fine powder possessing a yellow colour with a faint tint of orange, and in that of concave masses composed of layers of various tints of white, yellow and orange, commonly also lined internally with tetraedral white pyramidal crystals. Till lately it was accounted a variety of sulphuret, and some ingenious conjectures were made as to the cause of its superior energy over the other sulphurets as a poison. But M. Guibourt has proved that it always contains oxide of arsenic, and is commonly impregnated with it to a very large amount, some parcels containing so much as 96 per cent.[3] The inner surface I have often seen lined with large crystals of pure oxide. In a very interesting account by Dr. Symonds of Bristol, describing the case of Mrs. Smith, for whose murder a woman Burdock was executed in that city a few years ago, it is stated that artificial orpiment was the poison given, that death took place in a very few hours, and that a sample from the druggist's shop where the poison was bought contained on an average 79 per cent. of oxide of arsenic.[4]
Another impure sulphuret, a good deal used in painting, and a favourite poison in this country for killing flies, is King's yellow. It
