Parastannic Acid

It was found by Berzelius that when β-stannic acid is heated with water at 100° C. it passes into another form of stannic acid, which when air-dried has the empirical composition 5SnO₂.8H₂O, and is probably H₂Sn₅O₁₁.7H₂O. This compound when dried in a vacuum becomes 5SnO₂.3H₂O or H₂Sn₅O₁₁.2H₂O, rather than SnO₂.H₂O or H₂Sn₅O₁₁.4H₂O, which is β-stannic acid. The potassium salt of parastannic acid is K₂Sn₅O₁₁.2 or 3H₂O, to which parastannyl chloride, shortly to be described, corresponds.