96 



Proceedings of the Royal Irish A eademy. 



ions. When SO2 is t'ed in at a later stage, it is inefiective. Similar experi- 

 ments with ammonia showed no effect. It would appear that this substance 

 has not the property of starting the growth of the nucleus. 



Effect on Molility. 

 The effects of these substances on the development of the ions can be 

 tested by measurements of mobility. If sufficient time is allowed between 

 the production and observation of the ions so that they may attain their 

 final stable states, a considerable loss by recombination is incurred, it is 

 necessary then that the ionisation should be very dense at the beginning in 

 order that readable observations may be obtained. For measurements of 

 this sort small flames are unsuitable. 





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We therefore used a large Bimsen flame burning inside a chimney. 

 Through this the ordinary room air was drawn, carrying with it the ions 

 produced by the flame. The substances to be tested could be fed in at the 

 flame or mixed with the gas subsequently. The ionised air was drawn through 

 a number of vessels in series, so that a considerable time elapsed before it 



