Salts of Tungstic Acid-VII

Such formulation suggests a closer relation to the metatungstates than appears to be justified, and would not account for the very essential differences between the two types of compounds.

Paratungstates gradually decompose in aqueous solution with formation of the normal and metatungstates, so that while a freshly prepared solution is neutral to phenolphthalein, it gradually becomes acid on standing - more rapidly on boiling. For this reason the electrical conductivities of the solutions slowly increase at ordinary temperatures.

According to Hallopeau the free paratungstic acid is formed in dilute solution when the barium salt is treated with dilute sulphuric acid. Concentration of the solution, even in vacuo, causes decomposition, and on prolonged boiling, metatungstic acid is formed. Alkalies neutralise the solution, yielding paratungstates. There is, however, no proof that this solution contains any special modification of tungstic acid.


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