The metal, arsenic, is a dark steel gray in color, when the surface is fresh, but it soon tarnishes. It is very brittle and easily powdered under the hammer, and its only use as a metal, is for an alloy with lead in making shot. Its compounds find a wider use. The white powder called “arsenic” is arsenous acid, and is used mostly in making poisons, which fortunately are easily detected in animal tissues. Copper arsenate, (_Scheele’s green_) is a pigment used in making green paint, and formerly in the green colors of wall paper. A combination of arsenous acid, copper oxide and acetic acid is the well known _Paris Green_, so much used for an insecticide. Beside these uses, arsenic serves a large number of other purposes, as in making glass and enamel, embalming fluids, and various medicines. Curiously arsenic plays a double part, acting part of the time as a metal, as in the two following minerals, and part of the time as a non-metal, as in cobaltite, niccolite, etc. Arsenopyrite FeAsS Pl. 24 Occurs in well formed crystals, grains, or masses; hardness 5.5; specific gravity 6; color silver-white; streak black; luster metallic; opaque on thin edges. When in crystals, they are usually short prisms of the orthorhombic system, either end being terminated with a low roof. Though usually described as silver-white in color, there is always a brassy cast to the color. Its appearance is much like cobaltite and smaltite, but it can be easily distinguished from both these by putting a piece in nitric acid. The arsenopyrite will not materially change the color of the fluid, but the other two turn it rose-red, and all give off the smell of sulphur. It looks sometimes like marcasite, but that is yellower, and has the fibrous structure, not found in arsenopyrite. It is found in veins or in metamorphic rocks, associated with argentite, galena, sphalerite, chalcopyrite and pyrite. It is distinctly a mineral formed by deposition from hot vapors or hot water rising from either lavas, or in the course of metamorphism. It is found in New Hampshire, Vermont, Massachusetts, Connecticut, New York, New Jersey, California, etc. Realgar AsS Pl. 24 Occurs in incrustations or scattered grains; hardness 1.5 to 2; specific gravity 3.5; color orange; streak orange; luster resinous; opaque on thin edges. Crystals are very rare, but when found are short monoclinic prisms. The color is aurora-red, changing to orange as soon as it is exposed to the air. This and the streak are entirely characteristic. It is a mineral associated with hot vapors or hot waters, and is found about volcanoes, as deposits from the hot water of the geysers in Norris Basin, Yellowstone Park, and in veins, associated with barite, stibnite, quartz, etc., as in Massachusetts, Utah, California, etc. Orpiment As₂S₃ Occurs as incrustations or powdery masses; hardness 1 to 2; specific gravity 3.5; color lemon yellow; streak yellow; luster resinous.