Potassium Stannate, K₂SnO₃

Potassium Stannate, K₂SnO₃.3H₂O, is prepared similarly to the sodium salt. It cannot, however, be completely dehydrated by heating, but decomposes, forming potassium hydroxide and stannic acid. Consequently the water present is water of hydroxylation rather than of hydration, and this and other salts are derived from hexahydroxy-stannic acid, H₂Sn(OH)₆, which is analogous to hexahydroxyplatinic acid, H₂Pt(OH)₆. This conclusion is confirmed by the fact that insoluble stannates obtained by double decomposition contain the same proportion of water. Thus precipitated lead stannate is PbSnO₃.3H₂O, and may be formulated PbSn(OH)₆. This constitution relates hexahydroxystannates to the stanni-chlorides M'₂SnCl₆, which are analogous to the platini-chlorides M'₂PtCl₆. No orthostannates have hitherto been recognised, but Hedvall has prepared cobaltous orthostannate, Co₂SnO₄, by fusing cobaltous and stannic oxides with potassium chloride at 1100° C. or 1300°-1400° C., and dissolving out the excess of stannic oxide by warm, dilute hydrochloric acid. The product is dark green, and has a density of 6.30 at 18° C.