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192 PHYSICS: LOEB A ND D USA ULT PROC. N. A. S. THE MOBILI TIES OF GASEOUS IONS IN H2S-H2 MIXTURES By LEONARD B. LOZB AND L. DUSAULT PHYSICAL LABORATORY, UNIVERSITY OF CALIFORNIA Communicated December 29, 1927 Introduction.-In recent articles one of the writers (L. B. L.) cites an explanation, suggested by Dr. Edward Condon,' of the observation that the negative ion mobility is less than the positive ion mobility in vapors like HCI and H20. The latter suggests that it is due to the presence in these molecules of the proton near the surface of the molecule which causes a dipole unsymmetrically placed relative to the center of the molecule. On this basis H2S should show much the same behavior as H20, though perhaps in a less degree, since its electronegative component is relatively larger. In a preliminary notice in 1926 one of the writers and Mr. Cravath2 reported on the results of some preliminary measurements of the positive and negative mobilities in H20 and H2S. At the time the measurements were undertaken certain facts concerning the relative action of impurities on positive and negative ions were not known, and a lowering of the positive ion mobility relative to the negative ion mobility was ascribed to contact potentials. The preliminary results obtained in which, as present results show, the H2S was not especially pure, were over-corrected for this effect. In order to make certain of the effects observed the preliminary investigation was extended with a new design of ionization chamber3 and under much more carefully controlled conditions by the present writers. It is the purpose of this paper to detail the results of this investigation. A complete description of the new ionization chamber is to be published elsewhere3 inasmuch as the past experiences of one of the writers have finally led to a fairly successful form of chamber whose construction