Mobility of Negative Ions in Flames by the Hall Effect Method

Abstract

Variation with potential gradient of mobility of negative flame ions.---Using a flat salted flame, previously described by Wilson, between the poles of an electromagnet giving a field of 5000 gauss, the horizontal potential gradient $X$ due to the current sent between two Pt electrodes and also the vertical potential gradient $Y$ due to the Hall effect, were measured by means of two Pt sounding wires which could be rotated about a horizontal axis and which were connected to a quadrant electrometer. For a flame containing potassium carbonate the mobility ${k}_{2}=\frac{Y}{\mathrm{HX}}$ was found to decrease from 26 m/sec for 1 volt/cm when the potential gradient was 1 volt/cm, to 16 m/sec for a gradient of 30 volts/cm. For a flame free from salt the mobility was some-what greater, decreasing from 26.5 m/sec for 5 volts/cm to 16 m/sec for 50 volts/cm. However, wide variation of concentration produced so little effect on the mobility that it could not be detected with certainty. The magneto-resistance effect which ${\mathrm{Heaps}}^{1}$ has shown enters into the mobility equation, was so small as to be negligible.Asymmetry of the Hall effect in flames.---The Hall effect was found to vary slightly with the direction of the magnetic field, the asymmetry being greater the greater the amount of salt in the flame. This asymmetry was probably due to the effect of the magnetic field on the upward velocity of the flame gases, which was evident in these experiments.