■02 



•048 



•20 



■15-4 



■ i7 



154 



043 



■092 



•32 



32 Proceedings of the Royal Irish Academy. 



Undi'ied air : 



Short time interval, -OOl-S -0045 

 Eatios, ... 1 '6-4: 



Dried air : 



Short tirae interval, •002^2 -0064 ^043 



Eatios, ... 1 2-9 19^5 41 ■S 145 



As it happens, the shorter time inter\al employed in obtaining the 

 niimbers in this table was such that the mobility of the slowest group was 

 the same as that of the second group when stable, and other coincidences of 

 the same nature occur in the table. It should be I'emembered, however, that 

 with the short time interval the mobilities are not constant, but depend 

 on the time. We should not, therefore, specially identify a stable ion in 

 Group II with a varying ion in Group I which happens to have the same 

 mobility. 



The ratios of the mobilities in the diiferent groups are approximately the 

 same, whatever the time interval, and whether the air is dried or undried. 

 No doubt, vei-y considerable variations occur in these ratios, but, considering 

 the difficulty of deciding on the mobility in many cases, the approximate 

 constancy is striking. 



Joint Discussion of Eesults avith the Author of the rREOEDiNG Paper 



ON THE MOBIUTY OF lONS PRODUCED BY SPRAYING DISTILLED WaTER. 



The experimental results in this paper are so closely related to those in 

 the preceding paper that it is convenient to discuss them together. When 

 distilled water is sprayed, the air carries away ions of many distinct groups, 

 the five slowest of which correspond closely with the stable groups found in 

 the experiments with mercury in undried aii. The more mobile ions found in 

 the experiments with water are either entirely absent from or present only in 

 very small numbers in the mercurj- experiments. We shall first discuss the 

 probable nature of these five groups which are common to the two sets of 

 expei-iments. 



The diflerences in the behaviour in the two cases are a|)pareutly due to 

 the fact that those produced from mercury take some time to add on water- 

 vapour, and thus arrive at a stable condition, while the others produced from 

 water do not show any change of mobility with time. When the air is 

 ■' dried " in the mercury experiments, all the water-vapour is not removed, 

 but the approach to stable conditions is retarded by the diminution of the 

 vapour present. Various hypotheses might be suggested to account for the 



