[en] The dissocation state of very low concentrations of the following solutes: a - V₂O₅, NH₄VO₃, NaVO₃, KVO₃, NaV₃O₈, Na₄V₂O₇, K₄V₂O₇ in molten K₂Cr₂O₇ and b - NaVO₃, KVO₃, Na₄V₂O₇, K₄V₂O₇, Na₃VO₄ in molten KNO₃ was studied cryoscopically. The depression in freezing point was obtained by measuring the corresponding cooling curves. The results with the solvent K₂Cr₂O₇ showed that a reaction occured between it and the solutes, which was not a simple one. Generally, heteropolyions such as (CrVO₇)^3-, (Cr₂VO₁₀)^3-, (CrV₂O₁₀)^4- and (Cr₂V₃O₁₆)^5- were probably formed. In case of the solvent KNO₃, the results showed that the investigated types of vanadates were dissociated giving the orthovanadate (VO₄)^3- ions. (author)