Abstract: The interconversion between hexa- and decatungstic acids in solutions has been studied through UVabsorption spectra data.. In aq. solution at pH 1-4, H₂W₆O₁₉changes rapidly to H₄W₁₀O₃₂The rate constant k is 5.3 × 10^-3s^-1, t_1/2being 1.31s, at pH 3.57 and 25℃. Hydrogen ion retards the conversion from W₆O₁₉^2- to W₁₀O₃₂^4-.On the contrary, H₄W₁₀O₃₂in organic media slowly transforms into H₂W₆O₁₉at ordinary temparature. Its complete conversion will need about 30 days at 25℃. When temparature rises to 78℃, however, it will only require half an hour. Water inhibits the change from W₁₀O₅₂to W₆O₁₉^2-seriously.The interconversion between them can therefore be taken as.

Key words: Hexatungstic acid, Decatungstic acid, Interconversion, UV absorption spectrum