Harnwell's experiments on ionization by collisions of the second kind have been continued. Mixtures of oxygen with argon, neon and helium and incidental effects of water vapor have been studied. Evidence of the following collisions of the second kind was obtained:

(1).A⁺+O₂→O⁺₂+A

(2).A⁺+H₂O→H₂O⁺+A (very strong)

(3).H₂O⁺+O₂→O⁺₂+H₂O

(4).Ne⁺+O₂→O⁺+O+Ne

(5).He⁺+O₂→O⁺+O+He

The experiments confirm the conclusions of Hogness and Lunn as to the processes of ionization in oxygen but leave the exact value of the first ionizing potential uncertain.