Thermions emitted hy the Alkali Sulphates. 991 



is practically identical with the value found from the specimen 

 of platinum used in the experiments on lithium sulphate. 



In this set of experiments it was not possible to make 

 measurements on the ionization from sodium sulphate until 

 the heating had gone on for about two hours. Three sets of 

 observations were taken, after heating for two hours, eight 

 hours, and twenty-four hours respectively. The results are 

 shown in fig. 6. In this experiment the field strengths &c. 

 had the following values : — V=200 volts, 11 = 4650 lines 

 per cm. 2 , ^ = '497 cm. 



It will be seen that the maxima are deflected to nearly 

 the same extent in every case. However the first curves, 

 points thus : x , obtained after two hours heating, give a 

 slightly smaller deviation (2*3 turns) than the others and 

 lead to the value m = 26'6. The next, points thus : x , after 

 eight hours heating, give a deviation of 2*45, corresponding 

 to m = 23'4. After heating twenty-four hours, points thus : 

 © and [xj, the deviation is practically unaltered at 2*5 turns, 

 corresponding to m = 22'5. The effect of continued heating 

 on the sodium sulphate is clearly very different from that of 

 lithium sulphate. 



The very small size of the humps obtained after heating 

 the sodium sulphate for twenty-four hours seemed suspicious, 

 and was investigated further. It was found that these two 

 humps represented only an isolated portion of the curve, 

 which reallv extended over a much greater length in the 

 direction of x than that shown in the figure. Detailed ob- 

 servations taken after thirtv hours heating showed that a 

 measurable fraction of the ionization passed through the slit 

 all the w T ay from .£ = 10 turns to # = 11 turns. There were 

 several humps in the curve, which resembled a panoramic 

 view of a range of mountains. There was, however, no 

 evidence of any splitting up of the ions into groups charac- 

 terized by different values of e/m. The patterns were displaced 

 as a whole by the magnetic field, corresponding points being 

 displaced about equal distances, and the form of the curve 

 was the same in the absence of the magnetic field as with it. 

 It was quite different from the behaviour of lithium sulphate 

 shown in fig. 3. The peculiarities observed could be explained 

 if the sodium sulphate after continued heating tended to 

 collect in lumps at the edges of the strip where the electric 

 field is irregular. When the apparatus was taken down, the 

 salt which was left was too small in amount to be visible. 

 It was observed, however, that the strip had become contorted 

 somewhat, which would also explain the peculiar effect 

 encountered. 



Another set of observations made on sodium sulphate 



