EXPERIMENTS WITH IONIZED AIR. 



45 



These data are summarized in the followinii^ table, for the tliree series of 

 results in hand. The limit of sensitiveness of the electrometer was about equiva- 

 lent to 8 c ' = .002. The largest values of c' observed were of the oi'der of .500. 



TABLE 2.— SUMMARY. DECAY OF IONIZING ACTIVITY OF PHOSPHORUS. 



The first of these series (see figure 3) shows a decrease of conductitm from 

 .39 to .33 within two hours, such as would naturally be associated with the waning 

 ionizing power of phosphorus. The succeeding series show similar fluctuations, but 

 the conduction of the condenser is retained intact after two or even three hours of 

 exposure. It is improl)able, therefore, that the number of ions (c'—n Ue(A /ca;)\oirf) 

 is supplied at a diminishing rate in the lapse of time by the phosphorus ; it is 

 much more probable that fluctuations of temperature and like incidental causes 

 account for the difference. In the first series the decrease of c' is most marked, 

 being .0007 per minute while the value .0009 occurs in instances below. Thus in 

 the 15 minutes or less (usually less than 5 minutes) which outlasts the time of a 

 single series of observations, appreciable diminution of the ionizing potency of the 

 source cannot be infened apart from the environment. 



5. J^Jfect of temperature.— The effect to be ascribed to temperature is much 

 more serious. I made the following observations (table 3) with the same condenser, 

 endeavoring to obtain the temperature discrepancy by varying the temperature of 

 the room. The observations for c'= Une (A/Cx) logs, were completed in the 

 usual way, all being satisfactory. Unfortunately the temperature of the air between 

 the plates is not identical with the superficial temperature of the phosphorus itself, 

 and it is upon the latter that the ionizing eft'ect depends. Hence the data as cou- 

 sti'ucted in the cui-ves, figure 4, show curious lag phenomena. The observations are 

 difficult, as drafts of air if but slightly too warm, ai'e liable to kindle the phosphorus. 

 Different parts of the grid often respond unecpially. In a cold room (about 9°) 

 phosphorus is nearly inert. It then rises rapidly to the large ionizing value between 

 20° and 30° ; but experiments like the present merely emphasize the need of a room 

 of constant temperature. The i-elation itself is elusive and yet to be found. 



