Potassium tetrarsenite

Ferric Orthoarsenite, FeAs03, was described by Reichard 9 as a rust-yellow powder obtained by adding potassium tetrarsenite to a dilute aqueous solution of ferric chloride. A substance of similar chemical composition has been found in a crystalline deposit formed during the Deacon process of making chlorine. The crystals of the pure salt are monoclinic, their crystallographic elements being 10... 

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... 

Magnesium Orthoarsenite, Mg3(As03)2, is obtained as a white precipitate, easily soluble in water and in dilute acids, by adding to a solution of magnesium chloride in 50 per cent, alcohol a solution of potassium orthoarsenite made just neutral with acetic acid.7 It is also formed when a solution of potassium tetrarsenite is added slow ly to an aqueous solution of a magnesium salt.8 When heated in an inert atmosphere the salt decomposes forming arsenious and magnesium oxides.9... 

Mercurous Metarsenite, HgAs02, separates as a yellowish precipitate when potassium tetrarsenite is gradually added to mercurous nitrate solution.6 The salt is dried at 125° C. It is unstable and is decomposed by excess of the alkali arsenite, by alkali hydroxides and by aqueous ammonia. 

Mercuric Pyroarsenite, Hg2As205, was described 9 as a yellowish-white mass, decomposing in light, obtained by adding a solution of potassium tetrarsenite to one of mercuric chloride. According to Dessner,10 however, the precipitate so obtained is a mixture of arsenite... 

Palladium Pyroarsenite, PdAs205, has been prepared 6 by addition of potassium tetrarsenite to a solution containing an equivalent amount of palladium tetrachloride and drying the yellow precipitate at 100° C. 

Potassium Arsenites.—At 25 C. the ternary- system K20-As203— HaO indicates the existence of two arsenites of potassium, soluble in water without decomposition 9 these are potassium tetrarsenite, K2As407, and potassium metatetrarsenite, K8As409.12H20. 

Tin Arsenites.—Stannous Orthoarsenite, Sn3(As03)2.H20, was obtained by Stavenhagen 3 by adding a solution of arsenious oxide to a solution containing potassium ehlorostannite and potassium chloride. It may also be obtained 4 by the action of sodium metarsenite or potassium tetrarsenite on a solution of stannous chloride. It is a white amorphous powder, sparingly soluble in water, but readily dissolved by dilute acids and alkalis with separation of metallic arsenic. It is also soluble in excess of arsenious acid. 

Titanyl Tetrarsenite, (TiO)5As4Ou, is obtained by the action of potassium tetrarsenite in excess on an almost neutral solution of titanyl sulphate. The gelatinous precipitate first formed gradually crystallises. The arsenite dissolves in adds without decomposition, but is insoluble in aqueous potassium hydroxide or ammonia. It decomposes when heated. 

Uranyl Metarsenite, U02(As02)2, is formed as a yellow precipitate when a solution of sodium metarsenite 2 or of potassium tetrarsenite 3 is added to one of uranyl nitrate. It is insoluble in ammonia, but dissolves readily in acids. On heating, it darkens in colour and decomposes. 

Cobalt Tetrarsenite, Co3As409, is obtained as an amethyst-coloured powder by the interaction of solutions of potassium hydrogen di-arsenite and cobaltous nitrate.8 It dissolves in dilute hydrochloric and nitric acids also in caustic potash, in which it forms a blue solution which decomposes on heating. In aqueous ammonia it gives a brown solution, and in aqueous potassium cyanide a yellow one. 

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