EFFECT OF LIQUID MOTION ON ION MOBILITY IN HEXANE

The mobility of ions in liquid hexane has been determined by a variety of methods at fields between 0·4 and 7 kv cm-1 using both air-saturated and outgassed liquid. X-rays or β particles were used to produce ion injection. At room temperature and with a drift field of 1 kv cm-1 mobilities ranging between 1·2 × 10-4 and 2·4 × 10-3 cm2 v-1 s -1 were found, depending on the method of measurement and the geometry of the cell. There appeared to be little difference between the behaviour of positive and negative ions and dissolved air had no effect. The variation in apparent mobility is attributed to liquid motion which is induced by and augments the ion velocity, and depends on the hydrodynamic properties of the test cell. Experiments demonstrate clearly the importance of this effect and suggest that the true ion mobility is very small. In a low-temperature cell the mobility of positive ions was found to decrease from 1·9 × 10 -4 cm2 v-1 s-1 at 20°C to about 4·5 × 10-5 cm2 v-1 s-1 at -50°C with an activation energy of 8·7 × 10-2 ev. This value is close to the activation energy reported from viscosity studies and, contrary to earlier views, suggests that Walden's rule is obeyed provided that liquid motion is eliminated.