The Mobility of Negative Ions in Gasoline, Hydrogen, and Hydrogen-Chlorine Flames

Abstract

The Hall effect method of measuring the mobility of the negative ions was used, the horizontal or vertical flame being placed in a field of 4000 to 5000 gauss. The Pt cathode was coated with sealing wax. The temperature was varied by control of the air or oxygen intake and was measured, relatively, by a Pt-PtRh couple. In a hydrogen flame the mobility increases with temperature somewhat for potential gradients over 25 volts/cm, but in a gasoline vapor flame the mobility decreases markedly. The addition of Cl, Br, CH${\mathrm{Cl}}_{3}$, C${\mathrm{Cl}}_{4}$, N${\mathrm{H}}_{4}$Cl or I (in alcohol) to the hydrogen and gasoline flame decreases the mobility, the effect being greatest for Cl and being progressively less for the other substances in the order given. In the hydrogen-chlorine flame values as low as 52 cm/sec. per volt/cm were obtained. Addition of NaCl, ${\mathrm{Na}}_{2}$C${\mathrm{O}}_{3}$ or KCl increases the mobility somewhat. The highest value obtained is 5600 for hydrogen flame with NaCl sprayed in, about 30 percent higher than for a similarly sprayed gasoline flame. In explanation of these variations it is suggested that when certain substances, particularly the halogens, are added to the flame, the negative ion which is normally a free electron for the greater part of its life, tends to be attached to form a cluster so that the average period during which it is a free electron is decreased and hence the mobility also. Temperature changes and potential changes probably affect the mobility by influencing the formation of these clusters.