Sodium Stannovanadates or Vanadostannates. By crystallising mixed solutions of sodium stannate and sodium orthovanadate, a series of sodium stannovanadates has been prepared, the salts having the following compositions:
3Na3VO4.Na2SnO3.32H2O.
4Na3VO4.Na2SnO3.48H2O.
5Na3VO4.Na2SnO3.64H2O.
6Na3VO4.Na2SnO3.80H2O.
The constant difference between each member is Na3VO4.16H2O. The particular member obtained depends on the concentration of the constituents and on the temperature. The same compounds can be prepared by fusing together stannic oxide, SnO2, vanadium pentoxide and caustic soda, and crystallising the fused mass. They are all isomorphous, and form doubly refracting, transparent, rhombic needles. The use of sodium orthoarsenate and sodium orthophosphate instead of the vanadate gives rise to two analogous series of stannophosphates and stannoarsenates. A mixed salt having the composition of both the phosphate and arsenate has also been isolated:
4Na3(P,V)O4.Na2SnO3.48H2O.
When a solution containing sodium orthovanadate and stannous chloride is carefully neutralised with caustic soda, an amorphous yellow substance is obtained which has the composition
Na2O.4SnO2. V2O5.xH2O or Na2O.3SnO2. V2O5.xH2O.
This compound is considered to be a complex salt of a heteropoly-acid fornied from stannic oxide and vanadium pentoxide, and it is therefore comparable with the vanadoselenites and vanadotellurites. |