Arsenic suboxide

Arsenic Suboxide ( ), As20, was considered by Berzelius 1 to constitute the superficial dark brown film which forms on arsenic owing to oxidation. Retgers 2 stated that the brown deposit which accompanies the mirror formed by sublimation of commercial arsenic was the suboxide. It was looked upon 3 as an intermediate product in the oxidation of arsenic, but the material so described was undoubtedly a mixture of arsenic and arsenious oxide 4 or, in some cases, merely the amorphous variety of arsenic. 

Arsenic Suboxide—Arsenious Oxide Polymorphism and Physical Properties of Arsenious Oxide, Chemical Properties, Uses—The Arsenites—Arsenic Tetroxide. 

Two well-defined oxides are known arsenious oxide, As2Oa, and arsenic pentoxide, As2Os. The former is the most important compound of arsenic, being the form in which the element is most used. A suboxide, As20, and a tetroxide, As204, have been described, but the existence of neither as a pure compound has been established. 

Lead Orthoarsenite, Pb3(As03)2, is obtained as a white precipitate on adding a solution of basic lead acetate to a boiling aqueous solution of arsenious oxide,9 or of potassium tetrarsenite,10 or by the action of an alkali plumbite on an alkali arsenite.11 When dried in a dark air oven the arsenite remains white, but when exposed to light some specimens turn brown, a change which has been attributed to reduction of the lead to suboxide,12 but some arsenate and free arsenic are formed. All specimens... 

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