The deleterious effects of small quantities of Arsenic when present in Copper are weI! known to all who are concerned with the working of thin latter metal, and the elimination thereof is consequently an object to which the copper smelter pays special care. Though a large number of minerals, some of which are of exceeding beauty, are found composed of Copper combined with Arsenic acid, the direct combinations, as Araenide and Sulph-Arsenide, are comparatively rare.