Another impure sulphuret, a good deal used in painting, and a favourite poison in this country for killing flies, is King’s yellow. It is sold in the form of a light powder or in loose conical cakes. It has an intense sulphur-yellow colour. This substance is soluble, though not entirely, in water, both cold and warm, and forms a colourless solution, from which, on cooling, or by evaporation, a yellow powder separates. In this respect it differs essentially from the pure sulphurets. The solution is not acted on by reagents in the same way as the solution of arsenious acid. Lime-water and hydrosulphuric acid have no effect on it, the ammoniacal nitrate of silver causes a copious dirty brown, and the ammoniacal sulphate of copper a scanty, dirty lemon-yellow precipitate. I have not seen any account of the mode of preparing it or an analysis of its composition. But according to my own experiments it contains a large proportion of sulphuret of arsenic, a considerable proportion of lime, and about 16 per cent. of sulphur. Its nature is best shown by the following method of analysis. Let the powder be agitated in diluted ammonia till the colour becomes white. The filtered fluid contains the sulphuret of arsenic, which, on addition of an acid, falls down, and may be separated and reduced in a tube with the black flux. The remaining white powder, well freed from adhering sulphuret by washing, is next to be agitated in diluted acetate or hydrochloric acid and again filtered. The solution on being neutralized precipitates abundantly with oxalate of ammonia and the alkaline carbonates, showing that lime was taken up by the acid: and, as the acid operates without effervescence, the lime must have been in the caustic state. The powder which remains after the action of the acid will be found to fuse with a gentle heat and to burn almost entirely away with a blue flame, emitting sulphureous vapours. These experiments make it obvious that King’s yellow contains sulphuret of arsenic, caustic lime, and free sulphur; and in all probability the lime exists in the form of a triple sulphuret of lime and arsenic. All the preparations containing the sulphuret of arsenic are interesting to the medical jurist, but particularly the two impure sulphurets last mentioned. The King’s yellow above all should be carefully studied, because on account of its frequent employment as a fly-poison it has been the source of fatal accidents. It was likewise taken intentionally a few years ago in this city, and proved fatal in thirty-six hours. Dr. Duncan also, while he was Professor of Medical Jurisprudence, met with an instance of an attempt to poison by mixing King’s yellow with tea; and at the Glasgow Spring Circuit of 1822 a woman was tried for poisoning her child with it.