16 THE THEOKY OF IONIZATION OF GASES 



the ions in liquids are quite different from the ions ii 

 gases, although they have the same charges. Thus, ii 

 a solution of hydrochloric acid, the chlorine atom (whicl 

 is the constituent of the molecule with the larger mass 

 has a negative charge and the hydrogen atom a positive 

 charge. In the gaseous state, on the other hand, hydro- 

 chloric acid conducts at low pressures just as other 

 gases, and the negative ion is associated with a mass 

 which is small compared with that of the positive ion. 



At first sight the conclusions to which the experiments 

 on the effects of collisions lead as to the masses of the 

 ions appear to be inconsistent with experiments on the 

 velocities of the ions and the rates of diffusion, which 

 show that at high pressures there is no great difference 

 between the apparent masses of positive and negative 

 ions. In these cases the ions move in the gas as if 

 comparatively large masses were connected with the 

 atomic charges, a fact deduced from determinations of 

 the rates of diffusion, which show, for example, that the 

 rate of diffusion of ions in hydrogen is small as compared 

 with the rate of diffusion of carbonic acid into hydrogen. 

 The result thus obtained may be explained on the sup- 

 position that each ion is accompanied by a group of 

 molecules which are attracted by the strong electric field 

 in the neighbourhood of the ion. The number of mole- 

 cules of the gas which are so affected would be determined 

 principally by the charge on the ion, so that there would 

 not be any great difference between the positive and 

 negative ions as they have the same charges. The 

 groups of molecules would remain attached to the ions 

 when they are not moving with large velocities, but when 

 large forces are acting and the ions move with large 

 velocities in the gas at low pressure, the effect of the 



