Thermions emitted by the Alkali Sulphates. Oi'3 



Potassium Sulphate. 



Several sets of: observations were made on the ionization 

 from the fresh platinum strip which was used in this experi- 

 ment. In these experiments the values of the field &c. were 

 V = 200 volts, H = 4650 lines per cm. 2 , and c=*501 cm. 

 Immediately after the heating of the strip was commenced 

 the displacement 2x of the maximum was found to be 2*42 

 turns, giving e/m = 390 and ?w = 24*8. After heating for 

 about one hour 2x had become 2*28 turns, giving e/m = 346 

 and m = 27'9. After six hours heating it was found that 

 2^=2-00 turns, e/m-266, and m=36'3. 



The gradual increase of m as the heating is continued is 

 in agreement with the author 's previous experiments on 

 platinum *. It would seem to indicate that the source of the 

 positive ionization of lower atomic weight from platinum is 

 more easily driven off by heating than that of higher atomic 

 weight. The results are in agreement with the view that 

 the ions of lower atomic weight are sodium atoms, but as the 

 substance of higher atomic weight is less easily driven off by 

 heat, it would appear th;it some impurity other than potassium 

 or its salts has to be looked for. So far the writer has not 

 been able to observe the development of humps in the curves 

 for the ionization from platinum similar to those from lithium 

 sulphate. This would seem to indicate, if the observed 

 change in the nature of the ions is real, that it takes place 

 very gradually, as there is no evidence of the simultaneous 

 emission of two groups of ions with widely separated values 

 of e/m. The experiments on the platinum ionization were 

 not continued further, as the ionization at the temperature at 

 which the experiments were being carried out became very 

 small at the end of the last experiment. 



The curves given by potassium sulphate itself were very 

 simple in character. They consisted of just a single hump, 

 and remained almost unchanged during sixty hours heating. 

 At the same time the displacement of the maximum was 

 constant within the limits of experimental error. After 

 about eighteen hours heating of the salt, however, the curves 

 broadened very considerably, but this may have been due to 

 some temporary contortion of the strip as it disappeared 

 later, and all the time aftei wards the curves were simj le 

 as at first and gave the original value of e/m. 



The results of the first few heatings of the salt are exhibited 

 in fig. 8. The left-hand curve with points thus: — x, was 

 taken as soon as the heating commenced. r lhe magnetic 



* (/. Phil. Mag. [6] vol. xvi, p.. 7^0 (1908). 



