55- 



Tables 678 and 679 



IONIC MOBILITIES AND DIFFUSIONS 



The process of ionization is the removal of an electron from a neutral molecule, the molecule thus acquiring a result- 

 ant + charge and becoming a + ion. The negative carriers in all gases at high pressures, except inert gases, consist 

 for the most part of carriers with approximately the same mobilities as the + ions. The negative electrons must, 

 therefore, change initially to ions by union with neutral molecules. 



The mobility, U , of an ion is its velocity in cm/ sec. for an electrical field of one volt per cm. The rates of diffusion, 

 D, are given in cm 3 /sec. U = DP/Ne, where P is the pressure, N , the number of molecules per unit volume of a gas 

 and e the electronic charge. 



Nature of the gas and the mobilities: (i) The mobilities are approximately proportional to the inverse sq. rts. of 

 the molecular weights of the permanent gases; better yet when the proportionality is divided by the 4th root of the 

 dielectric constant minus unity; (2) The ratio U + /U — seems to be greater than unity in all the more electro- 

 negative gases. 



Mobilities of Gaseous Mixtures: Three types: (1) Inert gases have high mobilities; small traces of electro 

 negative gases make values normal. (2) Mixed gases: lowering of mobilities is greater than would be expected from 

 simple law oi mixture. (3) Abnormal changes produced by addition of small quantities of electro-negative gases: 



e.g.: normal mobility 

 6 mm G>H;Br gave 

 6 mm C2H3I 

 10 mm CjHsOH " 

 g mm dHcO 



U+ = i.$7 U-1.S0 Wellisch, Pr. 

 1.37 1.80 Roy. Soc. 82A, 



1.37 1.80 p. 500, 1909. 



0.91 1. 10 



iiS i-37 



Temperature Coefficient of Mobility: There is no decided change with the temperature. 



Pressure Coefficient of Mobility: Mobility varies inversely with the pressure in air from 100 to 1/10 atmosphere 

 for — ion, to j/iooo, for + ion; below 1/10 atmosphere all observers agree that the negative ion in air increases 

 abnormally rapidly. 



Free Electrons: In pure He, Ar, and N, the negative carriers have a high mobility and are, in part at any rate, 

 free electrons; electrons become appreciable in air at 10 cm pressure. 



TABLE 678. — Ionic Mobilities 



Franck, Jahr. d. Rad. u. Elek. 9, p. 2, 

 from Yen, Pr. Nat. Acad. 4, ig 8. 



igi2; Wellisch, Pr. Roy. Soc. 82A, p 500, igog. The following values are 



TABLE 679. — Diffusion Coefficients 



The following table gives the observed and computed (D = jooUP/Xe = very nearly 0.0236!/) values of the 

 diffusion coefficients. The diffusion coefficients are given for some neutral molecules as actually determined for some 

 gases into gases of nearly equal molecular weight. Table taken from Loeb, " The Nature of the Gaseous Ion," J. Franklin 

 Inst. 184, p. 775, 1017. 



Gas, diffusing. 



Ar 



H2 



Air 



O2 



CO2 . . . . 

 CO2 . . . . 

 CjHsOH 



Air 



H2O . . . 

 NHs. . . . 



Gas diffused 

 into 



He 

 N 2 

 O2 

 N 2 

 N2O 

 CO 

 CO2 

 Ethyl acetate 

 Air 

 NH 3 



D 



molecules. 



o. 706 

 • 739 

 .178 



■ 31 



• o6g3 



■ og3 

 .246 



• 1 go t 



D + for ions. 



Computed. Observed 



1 . 20 

 0143 

 oo3ig 

 .0299 



■ 0193 



■ 0193 



. 00805 

 .0071 

 0319 

 .0174 



0.028 



-025 

 ■ 023' 



* CO2 into CO2. 



t Ethyl formate. t Estimated. 



Smithsonian Tables 



