CHAPTER III. 



CRITICAL CONDITIONS IN THE FORMATION OF IONS AND 



OF NUCLEI. 



The present chapter is a close continuation of the last, and is sepa- 

 rated from it for convenience in treatment. Dust-free air, energized 

 or not by radiation, is always in question. The subject considered in 

 the earlier paragraphs is a comparison of fleeting and of continuous 

 nuclei and the passage of one form into the other either by increasing 

 the strength or quality of the radiation, or by solution. The effect 

 of both methods in changing the fleeting into the persistent form 

 is possibly the same. Afterwards the inquiry is reversed and the 

 radiation itself examined in terms of the nucleation produced. It is 

 noteworthy that penetrating radiation is a powerful nucleator. 



41. Apparatus X-ray bulbs. A number of medium-sized bulbs of 

 German pattern, about 10 cm. in diameter with an anticathode 2 cm. 

 in diameter, were used. The differences between these were no greater 

 than the differences between the same bulb after varying periods of 

 action. The table summarizes a few data. There seems to be a 

 voltage at which the nucleation (N) produced is a maximum. 



TABLE 28. Comparison of different bulbs. Pressure difference 3^ = 25 cm. X-ray 

 bulb 200 cm. from fog chamber. Exposure, 3 sec. Exhaustion during exposure. 

 Bulbs 10 cm. diameter. Anticathode 2 cm. diameter, except No. 2, which was 

 smaller. 



The radium referred to was a weak sample (io,oooX), o.oi gram of 

 which inclosed in a hermetically sealed tube of thin aluminum (walls 

 o.i mm. thick) sufficed for the experiments. 



47 



