3-PHASE VAPOR TENSIOMETRY - A NEW APPARAT US AND ITS APPLICATION

A new apparatus for measuring the steady-state temperatur difference b etween two saturated solutions of the inert salt, one of them continin g a foreign substance, is discribed. The three phases are, the vapour of the solvent, a saturated solution of a supporting (inert) salts, an d the solid phase of the inert salt. The mixtures are kept on the top of temperature sensors and are first separated off from each other and the common atmosphere of the measuring cell using a specially formed lid. After balancing of the Wheatstone bridge, the lid is lifted and t he establishing of the temperature difference is recorded using the in creasing bridge potential difference Delta U, which is proportional to the total concentration of all foreign species. All dissolved ions an d molecules are to be considered as foreign species expect the ions of the inert salts. Three Phase Vapour Tensiometry (TPVT) was successful ly used to detect binuclear species formed in the titration of diaqua- Cr(III) complexes with ethyltrimethylammonium hydroxide in saturated s olution of ethyltrimethylammonium perchlorate. TPVT titrations of lant hanum nitrate with water in acetone saturated with lithium nitrate and tetraheptylammonium nitrate, respectively, gave a hydration number of 9 for La(III).