DECAY OF IONS. 



93 



the colloidal nuclei of dust-free air into the aggregates much larger in 

 size representing the ions. Hence in the presence of radium under the 

 given conditions the number of efficient nuclei decreases either because 

 the ions from their size capture all the available moisture more and more 

 fully, or because the colloidal nuclei have actually been aggregated into 

 fewer but larger systems, which will in turn fall apart in the absence of 

 radium. 



Sp; 31 



140 



120 



I0O 



ZOO 



Fig. 47. Efficient nucleation observed within the fog chamber at different times after 

 exposure to radium applied outside at different exhaustions (dp). Table 37. 



It follows from what has been stated that above the fog limit of dust- 

 free air the number of efficient nuclei must increase with the removal 

 of radium at a rate which corresponds to the falling to pieces of the ions. 

 The peculiar feature of the results here in question is the manner in which 

 the efficient nucleation decays from the coarser ionized to the finer 

 non-ionized colloidal stages, when the pressure difference is decidedly 

 above the fog limit of air, so that the latter may be recognized. The 

 curves invariably pass through a minimum when the time after the 

 removal of the radium, i.e., the interval of decay, increases indefinitely. 



This minimum, moreover, is very sharp, almost cusp-like, as if one law 

 were passing abruptly into another. Thus below the minimum (/ = 1 3 

 sec, about) the curve for dp = 2> 1 nearly coincides with the curve for 

 dp = 24, which is practically independent of the colloidal nuclei of air. 

 The decay may be computed to be of the order of that of ions. After a 

 lapse of 13 seconds the effect of colloidal nuclei is marked for dp = 31; 

 and even after a lapse of 60 seconds, when the ions (lower curve) have 



