Nolan and Enhight — Experiments on Large Ions in Air. 107 



small ions per c.c. From the slope of the line the recombination coefficient 

 a was calculated. The value found was 1'610 x 10"^ the electronic charge 

 being taken as 477 x 10"'° E.S.U. This agrees well with M'Chuig's value 

 1'614 X lO"'', and Townsend's value 1'631 x 10"", and shows that the method 

 can be relied on to determine the rate of disappearance of small ions 

 accurately. 



Decay of Small Ions in presence of Large Ions. 



Two methods were adopted in making these experiments. In our first 

 set of observations, gas containing nuclei only was exposed to the X-rays; 

 in the second, the ordinary fiarae-gas was used. We have already shown 

 reason to believe that charged and uncharged nuclei should not differ much 

 in their rate of combination with small ions; but, apart from that, as later 

 experiments will show, the distribution of charges among nuclei which have 

 been exposed to X-rays will be very much the same after one or two seconds, 

 whether the nuclei were originally partially charged or not. One would expect, 

 therefore, that the two methods should give the same results. Observations 

 show that the rate of decay is faster when the small ions are mixed with the 

 natural flame-gas ; but the difference is perhaps not very great, considering 

 the difficulties and uncertainties of experiments of this class. 



In the first experiments, when the air-stream carrying the ilame-gas had 

 been running for some time, and when tests had shown that conditions were 

 steady, a potential difference of 800 volts was established in condenser A, so 

 that uncharged nuclei alone came through. The number of nuclei per c.c. of 

 gas was determined by Aitken's counter. The X-ray tube was turned on, and 

 the number of small ions driven in at each of the terminals in C was ascer- 

 tained. i*'ig. 6 A shows a decay curve obtained in this way. Now, if N is, 

 the concentration of small ions of one sign 



dN 

 dt 



= aN- -¥ r]Nn„, 



where n^ is the concentration of nuclei (including large ions of both signs), 

 and I) is the recombination constant for small ions and nuclei 



f"- 



Nn„ 



dN 



-yr can be found from the slope of the curve, the other quantities are 



known, hence the value of i; can be determined. 



In the set of experiments in which curve A was obtained the number of 



