Sodium orthoarsenite

Cobalt Arsenites.—Several compounds have been prepared. Cobalt ortho arsenite, Co3(As03)2.4H20, is obtained3 as a pink precipitate when a solution of cobaltous chloride in 50 per cent, alcohol is treated with a solution of potassium orthoarsenite which has been just neutralised with acetic acid. The precipitate is soluble in dilute acids. On heating it turns black. A basic salt, of composition 7Co0.As203, is obtained when a solution of cobalt nitrate is treated with sodium orthoarsenite,6 the former being in excess the amethyst-coloured precipitate first formed contains combined water, which may be completely removed at 150° C. 

Sodium orthoarsenite is converted largely to arsenate and free arsenic when heated in an inert atmosphere 2 slow heating below 300° C. causes loss of arsenious oxide. Fusion with sodium hydroxide causes conversion to arsenate.3... 

ARSONIC ACID, SODIUM SALT (9CI) NATRIUM-ARSENIT (GERMAN) SODIUM ORTHOARSENITE... 

Sodium Orthoarsenite Sodium Arsenite Styrol Styrene... 

Ferric orthoarsenite cannot be prepared directly from ferric hydroxide and arsenious oxide.4 The brown product obtained by shaking freshly precipitated ferric hydroxide with an aqueous solution of arsenious oxide has been described 5 as a basic ferric arsenite of composition 4Fe203.As203.5H20. A similar substance is obtained by adding aqueous arsenious oxide or sodium arsenite to ferric acetate solution. If ferric chloride, sulphate or nitrate is used, the ferric salt is not completely precipitated. The product is oxidised in moist air, and decomposes when heated. It is very doubtful whether this is a chemical individual, however, for it has been shown that the removal of arsenious oxide from the solution by the ferric hydroxide is due to adsorption, the amount removed depending upon the conditions and the age of the adsorbent. This subject is discussed more fully on p. 154. 

Mercury Arsenites.—Mercurous Orthoarsenite, Hg3As03, may be obtained by treating a solution of mercurous nitrate with one of sodium orthoarsenite6 or with a solution of arsenious oxide in 50 per cent, alcohol 6 in the latter case the mercurous nitrate solution should be acidified with nitric acid and sufficient alcohol added to produce a slight turbidity. The precipitate is pale yellow, but rapidly turns brown on exposure to air. It is slightly soluble in water, being slowly decomposed with separation of mercury. It is also decomposed by hydroxides and carbonates of alkali metals and of barium, and by ammonia. It dissolves in acids, but when these are dilute, basic salts gradually separate. 

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. 

Zinc Orthoarsenite, Zn3(As03)2, is obtained7 as a white crystalline precipitate when aqueous arsenious acid is added to a solution of zinc sulphate containing ammonia and ammonium chloride precipitation occurs in the cold, an aggregate of crystalline needles being rapidly formed. A similar precipitate is thrown down by potassium orthoarsenite from a solution of zinc chloride in 50 per cent, alcohol,8 or from a solution of zinc sulphate by potassium tetrarsenite9 or sodium metarsenite.10 Zinc orthoarsenite dissolves readily in acids. It decomposes when heated. 

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