The Mobility of Positive Ions in Flames

Mobility of positive ions of K, Rb and Cs in the Bunsen flame.---The mobility was calculated from measured values of the current density, cathode drop of potential, and the thickness of the layer at the cathode in which the potential varies rapidly. The excess of ionization over recombination in the layer was assumed to be proportional to ${(1\ensuremath{-}\frac{x}{{x}_{1}})}^{m}$, where $x$ is the distance from the cathode, ${x}_{1}$ the thickness of the layer at the cathode, and $m$ is a constant. J. J. Thomson supposed that $m=0$, and P. E. Boucher took $m=1$. The value calculated for the mobility depends on the value assumed for $m$. The results give, with $m=2$, a value of 1.8; with $m=3$, a value of 1.07 cm/sec. per volt/cm for the mobility. It is found that the mobility is the same for salts of Rb, Cs, and K, and that it does not depend on the concentration of the salt. A small increase of mobility with electric intensity is indicated by the results.