This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The name arsenic is applied by common usage both to the element and to its oxide, which is more correctly termed arsenious anhydride; it it also called white arsenic, or arsenious acid.
The element, formerly classed with metals, now with metalloids, occurs sometimes native, but generally in alloy with iron, copper, and other metals, as oxide and sulphide. Nearly all sulphur contains some arsenic, and from these different compounds it is liable to pass undesignedly into many pharmaceutical preparations. Mineral waters also frequently contain it; Tripier has noted its almost constant occurrence in chalybeate, and Thenard in saline springs, though in minute proportion: those of Plombieres contain but 0.0008 gr., Vichy 0.01 gr., and La Bourboule (the largest amount) 1/10 gr. in 16 oz.
The metalloid is a steel-gray solid of metallic brilliancy, readily oxidizing and tarnishing on exposure to air. It volatilizes at a dull heat, the colorless vapor having a garlic-like odor. It burns when heated in the air.