Using an apparatus previously described, in which ions formed by impact of electrons of definite energy are analyzed by Dempster's positive ray method, the relative numbers of the ions N${\mathrm{O}}^{+}$, ${\mathrm{N}}^{+}$ and ${\mathrm{O}}^{+}$ were measured over a large range of pressures and electron energies. The percentages of ${\mathrm{N}}^{+}$ and ${\mathrm{O}}^{+}$ increased gradually with increase in pressure from approximately 4 and 1.5 percent at zero (extrapolated) pressure to 9 and 3 percent, respectively, at 0.01 mm. Evidence is thus given that impact electrons of sufficient energy can ionize the molecules forming N${\mathrm{O}}^{+}$ ions some of which spontaneously dissociate forming ${\mathrm{N}}^{+}$ and ${\mathrm{O}}^{+}$, and others of which are disrupted on collision with gas molecules into the atomic ions. The ionization potentials for the formation of N${\mathrm{O}}^{+}$, ${\mathrm{N}}^{+}$ and ${\mathrm{O}}^{+}$ were found to be 9, 21 and 22 volts, respectively. The second, together with the ionization potential of the oxygen atom, gives 7.5 volts (175,000 cal. per mol) for the heat of dissociation of nitric oxide.

In mixtures of NO and A and of NO and He, increase in the relative intensities of N${\mathrm{O}}^{+}$ with increase in pressure gave definite evidence of collisions of the second kind: NO+${\mathrm{A}}^{+}$ = N${\mathrm{O}}^{+}$+A and NO+${\mathrm{He}}^{+}$=N${\mathrm{O}}^{+}$+He.

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