ARSENIC, steel-gray metal having a high lustre when freshly broken but soon tarnishing. It is very brittle and has a specific gravity of 5.7. Compounds of this element have been known for many centuries, chiefly on account of their poisonous character. The yellow sulphide of arsenic, otherwise called
fresh clay and two parts of pulverized bricks or old retorts, and are coated with a mixture of blood, loam, forge scales and alum, which produces a glaze through which the poisonous vapors of the arsenic cannot penetrate. They are then fired. Practically all the arsenic mar keted in the United States is a by-product of the smelting of arsenical lead and copper. In 1916 there were made in this way 5,986 short tons valued at $555,186. It would have been as easy to have made 20,000 tons had there been a demand for it. Owing to the fact that the smelters which work on arsenical pyrites (chiefly copper) are located in the Far West, a price of four cents a pound in the New York market is the minimum at which the production of arsenic as a by-product becomes commer cially advantageous. It is interesting to note that besides the domestic production there was imported into the United States, in 1916, 1,071 tons of white arsenic, and 1,092 tons of orpi ment (arsenic sulphide). The total value of these imports was $232,694.
Arsenic is crystalline, and its hardness, on the mineralogical scale, is about 3.5. It has several allotropic forms, one of which is crys talline, and the other black and amorphous. The specific heat of the crystalline variety is 0.083, and that of the amorphous variety is 0.076. Arsenic conducts electricity better than mercury does; for if the specific resistance of mercury at 32° F. be taken as unity, the specific resistance of arsenic is 0.373 at 32° F., and 0.534 at 212° F. The chemical symbol of arsenic is As, and its atomic weight is about 74.44 (Clarke). Its coefficient of expansion is .000.. 00311 per degree F. Arsenic oxidizes slowly when exposed to the air, forming a gray pow der which is sometimes sold under the name of •fly-powder.* It is not affected by pure water. When heated in the air it burns with a blue flame, giving off a characteristic, highly dis agreeable, garlic-like odor. When protected from the air, metallic arsenic volatilizes at a red heat without melting; its vapor being a light citron yellow, and phosphorescent. When heated under heavy pressure arsenic melts at about 900° F.