Nolan — Ionic Mobilities in Air and Hydrogen. 81 



Summary of Results for Air. 



The final results given by the air-stream method were that the bulk of 

 the ions were divided between the following four mobilities : — 2-04, 1'79, 

 1"52, and 1"37, the negative ions tending to assume the higher values, and 

 the positive the lower vahies. In addition the following mobilities were 

 present in small numbers : — -12'2. 6'62, 4"2-'i, and 3"0. Some observations 

 of a negative ion of mobility 24 were obtained. The method just described 

 gives the four values 2-08, 1-69, 1"50, and 1'35. The other alternating- 

 field method gave for undried air the values : 2-5, 2'04, 1'73, 1'54, and 1'42. 

 In air which liad been subjected to long drying, the following values were 

 obtained for both signs : 12"3, 8-2, 5'61, 4"39, 3-04, and 2-53. in the very 

 dry air no negative ion of mobility lower than this was found, but the normal 

 positive ions were present. An ion of mobility 24'6 was found in all cases 

 among the negative, and in one case among the positive ions. As these 

 higher mobility values were deduced from fairly low voltages on the current- 

 voltage curve, it was considered unsafe to regard them as accurate. 

 Accordingly further experiments were conducted' with another apparatus of 

 such dimensions that the critical voltages were increased about 25 times. 

 The results obtained were in approximate agreement with those just quoted. 

 It has since been found, however, that an error of about 10 per cent, occurred 

 in calculating the constants for the second apparatus, so that the mobilities 

 deduced from the second apparatus should be reduced in that proportion. 

 This would yield the following values, which are doubtless more correct 

 than any of the others quoted: — 22, 11'2, 7'1, and 5' I. Tlie lower values 

 were not conveniently within the range of apparatus. 



It was suggested in a previous paper that the chance of detecting very 

 mobile ions by the alternating-field method would be much increased by 

 diminishing the time of the ions in the space above the gauze, that is, by 

 increasing the accelerating field. An attempt has since been made on 

 these lines to detect the very mobile ions in ordinary undried air. This 

 attempt was at once successful. These ions were found in quantities very 

 small, but quite accurately measurable. An apparatus which had been 

 prepared for observations on hydrogen (and which is described later) was 

 used. The ion which came out best had a mobility, positive and negative, of 

 5'23, corresponding to 5'1 above. The mobility 10'6 was also obtained, and 

 it was quite clear that a negative ion of still higher mobility was present. 

 It is hoped to deal with this work at greater length on some subsequent 

 occasion. 



' Proc Royal Irish Academy, 1922, p. 43. 



