The Ionization of Caesium Vapor and the Mobility of Electrons in the Bunsen Flame

Abstract

Ionization of caesium vapor in a flame.—A flame with a cross section about 2 by 4 cm was formed above rows of quartz tubes fed with air and gas into which dilute Cs salt solution was automatically sprayed. The conductivity $c$ as a function of concentration $k$ of the solution was determined from the potential gradient measured by means of platinum test wires and from the current to the central disk of a guarded anode. The concentration of vapor $m$ in the flame as a function of $k$ was computed from the velocity of the flame, measured stroboscopically, and from the amount of solution sprayed. The black body temperature was measured by introducing NaCl vapor and matching the emission against that of a tungsten filament for the same wave-length, assuming the emission to be merely a temperature effect. These results enabled the equilibrium constant of Saha $K$ to be computed for comparison with that given by Saha's equation, for it is shown that $\frac{\mathrm{mc}}{(c^2-1)}=A+Bc$, where $A$ and $B$ are constants, and that $K=\left(\frac{B^2}{A}\right)RT$, when $R$ is the gas constant. Actually the value of $K$ was inserted in Saha's equation and it was solved for $T$. The two best values obtained agree within 25° with the observed temperatures; this result tends to confirm the Saha theory.