Ferrous orthoarsenate

Ferrous orthoarsenate occurs naturally as the mineral symplesite (see p. 16), which is the octahydrate, Fe3(As04)2.8H20. This is found in pale blue or green prismatic or tabular crystals, probably isomorphous with vivianite and having axial ratios 5 a b c = 0-7806 1 0-6812, and 3 = 72° 43. The mineral is decomposed by caustic alkali with formation of ferric hydroxide.6... 

Colloidal ferrous arsenate has been obtained 7 in the form of an opalescent jelly by successively treating an aqueous solution of a ferrous salt with ammonium sulphate, acetic acid and an excess of sodium orthoarsenate. The jelly cannot be kept indefinitely, but crystallises after a few weeks. 

Ferrous Hydrogen Orthoarsenates have not been prepared in the pure state. According to Wittstein,8 the dihydrogen arsenate remains in the mother liquor when the normal orthoarsenate is precipitated (see equation above) and when iron is acted upon by arsenic acid over a long period an asbestos-like deposit is formed which probably contains a ferrous hydrogen arsenate.9... 

When heated, the salt first melts and at a higher temperature it decomposes to form silver 7 reduction to the metal occurs more readily when heated with carbon.8 Partial reduction also occurs when the orthoarsenate is treated with formaldehyde 9 or with ferrous sulphate solution 10 in the former ease silver is formed, but in the latter silver suboxide. 

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See also in sourсe #XX -- [ ]

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