Ammonium pyroarsenite

Ammonium arsenites.—Between 70° and 80° C. ammonia reacts with a solution of arsenious oxide to form acicular crystals of ammonium meta-arsenite, NH AsOg.12 With concentrated ammonia arsenious oxide yields the crystalline ammonium pyroarsenite, (NH4)4As205, an unstable substance decomposed with evolution of ammonia on exposure to air.13... 

Calcium Pyroarsenite, Ca2As205, is a white powder obtained by slowly precipitating a solution of arsenious acid with excess of lime-water, or by adding calcium chloride or sulphate to aqueous ammonium arsenite, and heating the precipitate to 105° C.7 If the product is dried in the air at the ordinary temperature, the monohydrate is obtained. At red heat calcium arsenate is formed. The pyroarsenite is only slightly soluble in water, 100 parts dissolving 0-025 to 0-030 part of the salt. It is more soluble in the presence of alkali chlorides and some ammonium salts, such as the nitrate, sulphate, acetate and succinate.8 It also dissolves in dilute acids. 

Lead Pyroarsenite, Pb2As205, is a white powder formed by decomposing normal lead acetate with amnioniacal arsenious oxide solution,7 or with potassium tetrarsenite8 or pyroarsenite,9 According to Simon,10 it is also formed by the combination of arsenious oxide vapour with lead oxide Stavenhagen,11 however, found the product to be merely a mixture of oxides. When heated, lead pyroarsenite fuses to form a yellow glass. It liberates ammonia from ammonium salts even in the cold. 

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