Positive ions produced in iodine by electron impact.—With an apparatus previously described in which positive ions, formed by electrons of definite energy are accelerated and then deflected magnetically around a semicircle into a Faraday cylinder, the relative numbers of the ions ${\mathrm{I}}^{+}$, ${\mathrm{I}}_2^{+}$, and ${\mathrm{I}}_3^{+}$ were measured as a function of pressure from 2×${10}^{-5\mathrm{}}$ to 4×${10}^{-3\mathrm{}}$ mm. In the primary process of electron collision, ${\mathrm{I}}^{+}$ and ${\mathrm{I}}_2^{+}$ were both formed. ${\mathrm{I}}_2^{+}$ was also formed in secondary collision from ${\mathrm{I}}^{+}$ by the process ${\mathrm{I}}^{+}$+${\mathrm{I}}_2$=${\mathrm{I}}_2^{+}$+I and ${\mathrm{I}}_3^{+}$ was formed from ${\mathrm{I}}_2^{+}$ by the process ${\mathrm{I}}_2^{+}$+${\mathrm{I}}_2$=${\mathrm{I}}_3^{+}$+I. Evidence and argument against other possibilities are given. The disappearing potentials of ${\mathrm{I}}^{+}$ and ${\mathrm{I}}_2^{+}$ were found to be identical, 9.3 volts.

Negative ions formed from iodine gas and free electrons.—Three negative ions ${\mathrm{I}}^{-}$, ${\mathrm{I}}_2^{-}$, and ${\mathrm{I}}_3^{-}$ were found to exist in quantities comparable with those of positive ions. Pressure-intensity relationships of these ions were also determined. ${\mathrm{I}}^{-}$ is formed both near the filament and in the ionization chamber according to the equation ${\mathrm{I}}_2$+${\mathrm{E}}^{-}$=${\mathrm{I}}^{-}$+I. ${\mathrm{I}}_2^{-}$ and ${\mathrm{I}}_3^{-}$ are not formed by collision with free electrons but as a result of secondary collisions of ${\mathrm{I}}^{-}$ and ${\mathrm{I}}_2^{-}$, respectively, with ${\mathrm{I}}_2$ molecules: ${\mathrm{I}}^{-}$+${\mathrm{I}}_2$=${\mathrm{I}}_2^{-}$+I; ${\mathrm{I}}_2^{-}$+${\mathrm{I}}_2$=${\mathrm{I}}_3^{-}$+I.

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