auripigmentum, in natural history, a bituminous mineral composed of sulphur and arsenic, sometimes artificially produced, but found also native in the earth, and constituting one of the ores of arsenic. It is of two kinds, red and yellow, the former generally found in an indurated state; though Cronstedt supposes that it may also be met with in loose fealy powder, as it is sometimes met with in the shops. It is commonly found in shapeless masses, very seldom crystallised; though Baron Borne once found it in a polyhedral form on a blue clay in Hungary. The name red orpiment has been given by the more judicious to safrarach, and by the vulgar to red arsenic; but it is to be refrained only to this tincture, which is of a fine bright red, and of the regular texture of the orpiments, and answering all their characters. It is a very beautiful substance of a fine bright red, very glossy, and a little transparent, and is found in the Turkish dominions, in the islands of the Archipelago, and even in our own country, Dr Hill having received some of it from Cornwall, under the name of red mastic. The yellow kind is met with commonly of shining flexible lamellae like mica, the specific gravity about 5.515. It burns with a blue flame, and contains about one tenth of its weight of sulphur. It is found native in Hungary, and in many parts of Germany and the Turkish dominions; it is the common orpiment of the shops. Some are of opinion, that the noxious qualities of the arsenic are so much counteracted by the sulphur with which this substance is mixed, that it may be swallowed with safety; but Macquer positively affirms the contrary, and very seriously cautions against its use, even though we be certain that the orpiment is native. There is besides abroad-flaked, gold-coloured kind, well known among the ancients, as is plain from the description of it left us by Dioscorides, and much esteemed at present by our painters. This is found in several places, as in the islands of the Archipelago, in the mines of Gosselar in Saxony, in some parts of Turkey, and the East Indies, and in its utmost purity about Smyrna; this makes the finest of all yellows in painting. The small-flaked, yellow kind, which is the common orpiment of the shops, is also a fine colour, though greatly inferior to the former. The Indians use orpiment, corrected with juice of lemons, with good success against fevers.

The red arsenic, or realgar, is likewise found in an indurated state, and in irregular or stalactitical masses. It is either opaque or semitransparent; sometimes it is found quite transparent, and regularly crystallised in octoedal prisms or pyramids; in which last form it is called ruby of arsenic. Its specific gravity is about 3.225; it contains 16 per cent. of sulphur; and its red colour is easily destroyed by the nitrous acid. In order to analyse these two kinds of orpiment, they ought to be digested in marine acid, adding the nitrous by degrees to assist the solution. The sulphur is then left on the filter, while the arsenic remains in the solution, from which it may be precipitated in its metallic form by zinc, adding spirit of wine to the solution.

Orpine, in botany. See Sedum.