Ionic Mobilities in Hydrogen, 345 



To test this, the distance d was lessened so that the voltages 

 concerned in calculating the mobility were smaller. These 

 values are distinguished in fig. 4 by squares instead of circles. 

 The same tendency to higher values was noticeable, though 

 perhaps not so marked. It is concluded that in some speci- 

 mens o£ gas at higher pressures there is a genuine tendency 

 for the normal value of the mobility of both A and JB to be 

 exceeded. At atmospheric pressure the velocity can be 

 taken as proportional to the field up to at least a velocity of 

 700 cm./sec. 



With regard to ion C * the results are not so definite or 

 complete. In order that the interpretation of a curve shall 

 be above question the ions D and B should be shown on 

 either side, and in order that the measurement shall be 

 accurate there must be a large number of the ions concerned 

 present. These conditions are rarely fulfilled together. .Also 

 with the lighter ions the various portions of the curve nre 

 more crowded together, and a single inaccurate point may 

 obscure its meaning. Three reliable values are recorded in 

 Table IV., and several others are plotted. This represents 

 the best that could be done with the present disposition of 

 the apparatus. There is not sufficient evidence to decide 

 whether or not more than one kind of ion is included in 

 this group. The required changes are being made in the 

 experimental arrangements in order that a further inves- 

 tigation may be made in this direction. 



The more mobile ions are always the first to disappear as 

 the contamination grows, and they are much more sensitive 

 to impurities at higher pressures than at lower. The relative 

 proportions of the various ions can be roughly estimated from 

 the change in slope of the curve at the point of inflexion con- 

 cerned. Thus in two cases where the gas had stood for a day 

 the ratios of B/A were : — *2 at 76 cm. and 2*0 at 24 cm., 

 showing clearly the greater stability of ion B at the lower 

 pressure in spite of the fact that the contamination of the 

 gas must be much larger in this case. Assuming that the 

 effective impurity is the oxygen content of the air which 

 leaks into the apparatus, rough measurements give : — 



Press., 9 cm., 2*0 per cent, oxygen, ratio B/A = 3*4 

 18 -6 „ -6 



37 >'2 „ -2 



* Note. — It should here be remarked that the values given in the first 

 paper as referring to ion C are spurious. The ions really present at the 

 time of measurement were A and B with a small number of a lighter ion, 

 the latter just sufficing to obscure the measurement for B. The curves 

 were not traced out in sufficient detail to make this distinction clear. 



