in Hydrogen and Nitrogen. 505 



If E be the reading of: the voltmeter at this point, a = < v /2E, 

 and 



w=const./Ej 



where the constant is 7T7id 2 /\/2, n being the frequency of the 

 alternator. The critical value E is found by plotting readings 

 of current against voltage. 



The arrangements for handling the nitrogen are shown in 

 fig. ?). It was found that the degree of purity required 

 could only be maintaine 1 by using a continuous flow of gas 

 through the apparatus. The nitrogen was contained in two 

 aspirators of capacity 15 litres each, where all traces of 

 oxygen were removed by leaving for many hours in contact 

 with phosphorus. After passing through a drying-tube the 

 gas traversed a U-tube immersed in liquid air, where the 

 phosphorus vapour and other remaining impurities were 

 removed. A capillary by-pass ensured a slow and regular 



Fijr. 3. 



Experiments/ 

 Chamber 



flow of gas, which was often maintained without interruption 

 for days. The gases to be tested as impurities were intro- 

 duced into the nitrogen stream from a graduated side tube 

 through a second capillary. Any desired proportion of ad- 

 mixture could be obtained by regulating the head of mercury. 

 A filter-pump was used to aid in washing out the tubes and 

 chamber. 



Results. 



Nitrogen. — The first experiments at once revealed the 

 presence of highly mobile negative carriers in the nitrogen, 

 ami emphasized their extreme sensitiveness to traces of 

 impurity. After the stream of pure gas had been passed 

 for some hours, the contamination from the walls of the 

 chamber was reduced to a minimum, but could never be 



