The other two processes for the detection of A. A. in organic mixtures are-1. That recommended by Marsh, in which the material is treated with dilute sulphuric acid and metallic zinc in a gas-generating apparatus, when the arsenic combining with hydrogen, forms arseniuretted hydrogen from which, in the act of escaping, the metallic arsenic, and subsequently A. A., can be obtained; and 2. That known as I3erzelius's process, in which dry arsenical compounds are mixed with the reducing flux, and heated in a constricted tube, when the metal arsenic is produced, which in its turn is converted into A. A. by heating in a wide test-tube. The processes of Marsh and Berzelius are not so generally followed as that of Reinsch; but in each and all it is absolutely neces sary, in order to avoid the possibility of mistake, (1) that metallic arsenic be obtained from the organic mixture; (2) that the metallic arsenic be converted into A. A. ; and (3) that this A. A., treated with water, should yield a solution which will give the three liquid tests mentioned previously.
A. A. forms compounds (salts) with alkalies and other bases, which are called arsenites. Some of these are employed in commerce and medicine. A. A. boiled witha solution of
potash, or carbonate of potash, forms an arsenite of potash, used in medicine, and known as Fowler's solution. The more largely used sheep-dipping mixtures are composed of A. A., soda, sulphur, and soap, whiclovhen used, are dissolved in a large quantity of water, and thus constitute essentially dilute solutions of arsenite of soda. A compound of A. A. and the oxide of copper, called the arsenite of copper, or Scheele's green, is a pigment largely used by painters as a pretty and cheap green paint. The same substance is extensively employed iu the manufacture of common green paper-hangings for the walls of rooms; and recent inquiries would lead to the belief that rooms covered with paper coated with this green arsenite of copper, arc detrimental to the health of human beings residing therein, from the readiness with which minute particles of the poisonous pigment are detached from the walls by the slightest friction, are diffused through the room, and ultimately pass into the animal system. Another green pigment is named Schweinfurth gran, and contains A. A., oxide of copper, and acetic acid, and is a double arsenite and acetate of copper.