The Absorption Coefficient for Slow Electrons in Cadmium and Zinc Vapors

The variation with the electron velocity of the absorption coefficient, $\alpha$, or the effective collision cross-section has been measured in the vapors of cadmium and zinc and found to follow a curve of the type previously found for mercury. The cadmium curve has a maximum at about 40 volts, $\alpha =130\mathrm{}$, and a minimum at about 25 volts, $\alpha =126\mathrm{}$, followed by a steady rise with decreasing velocity to the limit of accurate measurements, 1 volt, $\alpha =300\mathrm{}$. The zinc curve has a very flat maximum at about 50 volts, $\alpha =76\mathrm{}$, a minimum at about 36 volts, $\alpha =74\mathrm{}$, followed by a steady rise to $\alpha =500\mathrm{}$ at 1 volt. The magnitudes of the maximums are in the order: Cd, $\alpha =130\mathrm{}$; Zn, $\alpha =75\mathrm{}$; and Hg, $\alpha =60\mathrm{}$. Other related properties of these atoms, such as the molar refractivity and the critical potentials, show this same irregularity in order.