98 



Proceedings of the Royal Irish A cademy. 



produced by the action of tlie gases ou the ions already formed, there is a 

 reduction in the number of ions. From curve D it would appear that when 

 the alteration is produced by a substance injected into the flame there is no 

 change in the number of ions. When NH3 or SO2 are present, it would 

 appear that the stable size of the ion regarded as a compact sphere is three 

 times the normal. For if the mobility varies inversely as the square of 

 the radius, ions having masses in the ratio of 3 : 1 will have mobilities in 

 the ratio 1 : 3° = 1 : 2-08, which is roughly the ratio we have found. If, on 

 the other hand, the ion be regarded as a loose grouping, it is probable that 

 the slower ion is formed from two of the ordinary size. When the NH3 and 

 SO2 reach the ions after formation and in a region where the supply of 



Fig. 2. 



700 



water-vapour is not so great as in the immediate vicinity of the flame, it is 

 possible that the new stable size is attained largely by the formation of 

 groupings among the ions themselves and the uncharged nuclei which 

 accompany them. This would account for the reduction iu the number of 

 ions which we have noted. 



Kffectof NaCl. 

 The effect of adding NaCl to the flame is shown in fig. 2. The observa- 

 tions were taken with an air-current of half the velocity used previously. 

 This was necessary in order that saturation might be attained with the 



