Arsenites, derived from the acid H₃AsO₃, such as hydrogen cupric arsenite or " Scheele's green," HCuAsO₃, produced by adding to a solution of copper sulphate potassium arsenite, arsenious oxide, and a little ammonia; pyro-arsenites, such as K₄As₂O₅, and metarsenites, K AsO₂; also ortho- and meta-thioarsenites, K₃AsS₃ and KAsS₂, are known. They show no signs of isomerism like that of the phosphites and nitrites, and they are doubtless salts of As(OH)₃ and 0=As-OH, and the corresponding sulphur acids, although the acids corresponding to the sulphur salts are unknown. Metantimonite of sodium, NaSbO₂, and meta-thioantimonite, NaSbS₂, are formed by dissolving antimonious oxide, Sb₄O₆, or the sulphide, Sb₂S₃, in caustic soda, and precipitating with alcohol.