ORPIMENT(auripigmentum), the trisulphide of arsenic, As. 2 S 3 , or yellow realgar, occurs in small quantities as a native mineral of a brilliant golden-yellow colour in Bohemia, Peru, &c. For industrial purposes an artificial orpiment is manufactured by subliming one part of sulphur with two of arsenious acid. The sublimate varies in colour from yellow to red, according to the intimacy of the combination of the ingredients; and by varying the relative quantities used many intermediate tones may be obtained. These artificial preparations all contain free ∙arsenious acid, and are therefore highly poisonous. Formerly, under the name of king’s yellow, a preparation of orpiment was in considerable use as a pigment, but now it has been largely superseded by chrome-yellow. It was also at one time used in dyeing and calico-printing, and for the unhairing of skins, &c.; but safer and equally efficient substitutes have been found.