McClelland and Nolan — Ions Produced through Mercury. 31 



It will be observed that the ratios of the mobilities are not very different 

 from the ratios in the preceding sections. Further, it will be observed that 

 five groups are present, and in the preceding sections, while we have measure- 

 ments for only four groups, there was evidence of the presence of a fifth 

 group. To give an idea of the distinct character of these groups, we show on 

 fig. 4 portions of some of the curves from which the mobilities are calculated. 

 The curves are plotted on arbitrary scales, and without reference to the 

 origin. They are given to show that the curves on both sides of each bend 

 are straight lines. The upper curve shows the bend corresponding to the 

 slowest ion present. 



Undried Air. 



The mobilities were also measured about ten seconds after the production 

 of the ions, using undried air. 



In this ease also five groups were found. The positive and negative ions 

 in each group had the same mobility, and the mean values obtained were : — 



•001.3, -0045, -02, -048, -20 

 The ratios are : — 



1, 3-4, 15-4, 37 154 



The mobilities are less than for dry air with the same time interval, and 

 the amount of ionization was greater. 



The positive ions were more numerous than the negative, the excess 

 occurring chiefly in the groups with mobilities -02 and •048. Some observa- 

 tions were again made with the iron plate removed, and using a straight 

 nozzle, the other conditions being as in this section. The mobilities were 

 practically the same as when the mercury sprayed against the iron, but the 

 number of positive ions was greatly decreased. 



Summary. 

 The results in the preceding sections are collected in the following table : 



Mobilities of Groups. 



I. II. III. IV. V. 



Undried air : 



Long time interval, . -00034 -0013 "004 -014 — 



Eatios, ... 1 3-8 11^8 41 — 



Dried air : 



Long time interval, . -00056 -0021 ^0068 ^024 — 



Eatios, ... 1 -d-S 121 42^8 — 



