the Motion of Electrons in Argon. 595 



These results indicated that quantities of nitrogen of the 

 order of one per cent, of the argon would have large effects 

 on the velocities. 



The gas was therefore purified a second time, the process 

 being continued until the estimated quantity of nitrogen 

 remaining in the gas was very much less than one-thousandth 

 of the argon. The excess of oxygen was, in this case, 

 removed by passing the gas over hot copper several times. 



The second purification had the effect of reducing the 

 velocity in the direction of the electric force and of making a 

 further increase in the lateral divergence of the stream of ions. 

 3. The following examples of the measurements made 

 with argon show how the velocities of the electrons are 

 affected by reducing the proportion of nitrogen. 



With the gas at a pressure of 20 millimetres and an 

 electric force Z of 17 volts per centimetre the velocities W 

 in the direction of the electric force were 22 x 10 5 cms. per 

 second in impure argon, 22 X 10 r> cms. per second in argon 

 containing about one per cent, of nitrogen, and 9*3 X 10 5 cms. 

 per second in argon containing less than a tenth of one per 

 cent, of nitrogen. With the same force and pressure the 

 quantities k representing the factor by which the mean 

 energy of agitation (mu 2 /2) of an electron exceeds the 

 mean energy of agitation of a molecule of a gas at 15° C. 

 were 48*8, 73, and 155 in the three cases respectively. 



For the ratio Z/p = 17/20 the velocities Win nitrogen and 

 in hydrogen are 7*6 x 10 5 and 11*1 x 10 5 cms. per second 

 and the values of k are 19 and 7*9 in the two oases 

 respectively. 



Owing to the very large divergence of the streams of 

 electrons in argon it was impossible to make accurate 

 measurements of the values of W and k corresponding to 

 the lower pressures which were used in the experiments 

 with nitrogen and hydrogen. In the experiments with 

 the purest argou W and k were measured with pressures 

 from 20 to 120 millimetres and with electric forces from 

 12 to 34 volts per centimetre, so that the experiments are 

 over a range of comparatively small values of the ratio Z/p. 



A new apparatuses being made which is suitable for cases 

 wiiere the streams of electrons are very divergent, and we 

 hope to extend these experiments with a view to measuring 

 the velocities of electrons in argon corresponding to a wider 

 range of* the ratio Z/p. 



4. The velocities W, obtained with the argon which had 

 been purified twice, are shown in terms of the ratio (Z/p) 

 by a curve in tig. 1. The velocities W in nitrogen and 

 hydrogen are also given by curves for comparison. 



202 



