A new type of investigation into surface phenomena, "tensammetry", has been developed by superimposing a small sinusoidal A.C. voltage upon the direct potential applied to a dropping mercury electrode in the presence of surface active substances and measuring the resultant A.C. currents. Wave shaped current-voltage curves are thus obtained which have their origin in adsorption processes occurring at the electrode. These waves are attributed to the movement of surface active molecules in the region of "active space" near the electrode without actual electron transfer across the electrode boundary; that is, the electrode remains polarized with respect to U.C., but is depolarized with respect to A.C. The general properties of tensammetric waves of a number of organic compounds together with their effects on one another and on D.C. and A.C. polarographic waves have been investigated. The theoretical basis and the fundamental equations governing the tensammetric, process are derived and discussed.

A method of polarographic analysis employing the superposition of a small sinusoidal alternating field of low frequency upon the direct potential applied to the dropping mercury electrode has been further developed. Equations are given for the calculation of the ionic concentration from the alternating current (maximum differential current) at the characteristic " summit potential " (analogous to E+ in conventional polarography). This current is proportional to the concentration of the ion species undergoing discharge. The advantages of the method over conventional polarography can be summarized as follows : (i) A.C. polarography can be carried out in solutions containing dissolved oxygen, i.e. in air. (ii) Tedious curve plotting is substituted by a single current reading at the summit potential which yields directly both the half-wave potential and the concentration of the electro-reducible substance. �� (iii) Small amounts of less noble ions can be estimated even in the presence of a large excess of nobler ions. (iv) Polarographic waves only 40 mV. apart are clearly separable. (v) An improved all round reproducibility is obtained. (vi) There is a simplified system of recalibration in case of capillary replacement. vii) The use of a delicate galvanometer is eliminated.

The equation of the A.C. polarographic current for processes where the frequency of the alternating field is comparable with the rate of the electrode reaction is derived. Relative values of equilibrium rate constants of some first order electrode reactions are evaluated experimentally.

The nuclear quadrupole resonance frequencies of the halogen atoms in the trihalide ions 13 and Ibr2 in some of their crystalline salts have been measured. The results have been correlated with a simple LOAD-MO bonding description and the charge distributions in the ions have been calculated. These ions can be regarded as charge-transfer complexes as described by Mulliken. The effect of the crystal field on the charge distribution in the I3 ion has been investigated.

No abstract