Much works have been done on isopolytungstate ion formation processes by acidifying sodium tungstate solutions.
Concerning this field of research which are closely related to improving quality of the refined final tungsten products in the metallic form, there have been reports by investigators such as Kepert^1）, Jander^3-7), Souchay^8-10), Aveston¹¹⁾, and others.
However these studies were done by potentiometric, conductometric, polarographic and ultracentrifugal methods, and the results were found to be mutually inconsistent.
The cryoscopic method, however, has not been fully investigated in spite of the accuracy of this method at neutral range in contrast to the potentiometric method which have often been tried for the study of isopolytungstates.
Therefore, cryoscopic method was adopted in this work, and the following results were obtained for the condensation of isopolytungstates in various pH ranges, by mean of the pH measurement, U. V. spectrophotometric method, and cryoscopic method.
A. By cryoscopic method ;
1. Initially, HWO₄^- ions were found in dilute Na₂WO₄ solutions acidified with HClO₄.
2. The W₃O₁₁^4- ions appeared when the mole ratio of H⁺/WO₄^2- was made to 1.05, and H₂W₁₂O₄₀^6- to 1.55.
3. And, similarly, W₂O₇^2- ions appeared at the mole ratios of the following values, 1.15, 1.25, 1.30, and 1.35.
B. By pH measurement :
1. The HWO₄^- ion appeared in the solutions whose pH values were maintained from 3.7 to 6.5.
2. And W₂O₇^2- ions formed at the pH values ranging from 3.8 to 6.3, W₃O₁₁^4- ions at 6.35 and H₃W₆O₂₁^3- or H₂W₁₂O₄₀^6- ions at 3.2.
C. By U. V. spectrophotometric method :
The U. V. absorption band due to HWO₄^- ions observed to range from 335 to 430 mμ in wave length, W₂O₇^2- ions from 345 to 435 mμ, W₃O₁₁^4- ions from 350 to 440 mμ, and H₂W₁₂O₄₀^6- ions from 368 to 457 mμ.