McClklland and Nolan — loim Produced hif Phosphorus. 5 



would nieet; at tlie end ol' tlie mobility tui)u. Tliis piecaulioii was not 

 considered necessary when dealing with the less mobile ions. The following 

 results were obtained : — 



Table II. 





•052 



•019 



•0073 





•051 



•017 



•006G 





•048 



■018 



•00G6 





•053 









•046? 









•053? 







Means, 



•Col 



•QIS 



■0068 



The ion of mobility 'Ool was the fastest ion that could be detected and 

 measured. The other two ions are the two smallest ions given in Table I. 

 Thus with the special arrangements we were only able to observe one more 

 group. Saturation did not occur with the ion of mobility '0068. Measure- 

 ments of this ion were taken to keep in touch with previous experiments. 



During these observations the temperature of the room was sometimes 

 between 7° C. and and 8° C. No ionisation was obtained when the tempera- 

 ture was about this point. Placing the finger on the phosphorus tube for 

 about a minute increased the temperature enough to start the ionisation. 

 The ionisation then continued without any further heating. Barus^ observed 

 that the ionisation due to phosphorus depended on the temperature, and 

 states that in a room at a temperature of about 9° C. the phosphorus is 

 nearly inert. 



A very definite case of variation from day to day in the quality of the 

 ionisation occurred during the observation of the mobility •0068 (general 

 mean value -0074). A reading of this mobility was taken in the usual way, 

 and on the next day, when a second determination was desired, the ion could 

 not be observed. The current readings for the diflerent voltages which had 

 given two straight lines now gave one straight line. On the third day, one 

 straight line was again obtained with both positive and negative electrifica- 

 tion. The phosphorus was usually scraped about once a week ; this was now 

 done to see if the change was due to the formation of oxide. The ion was 

 still absent. On the fourth day, the ion was observed ; the ion reappeared 

 without any change in tlie ai)paratus or method of working. This variation 

 imder apparently the same conditions indicates how difficult it is to obtain 



• Barus: Phil. Mag., 6tli series, vol. ii, 1901. 



