Thermions emitted by the Alkali Sulphates. 905 



the positive ions from potassium sulphate given by this set 

 of: observations are all very near one another and quite close 

 to the value for the atom of potassium. The atomic weight 

 of this metal is 3D* 15. 



Another set of observations on potassium sulphate gave 

 for the initial ionization from platinum 2«a?=l*88 turns. 

 The corresponding quantity immediately after heating potas- 

 sium sulphate was found to be 1*80 turns. The value of z 

 for this experiment was not measured, so that the values of 

 ejm and m could not be calculated. The relative values for 

 platinum and potassium sulphate, however, confirm those 

 obtained in the more complete series of experiments just 

 described. 



Rubidium Sulphate. 



The ionization obtained from the platinum strip used in 

 this experiment gave a high value of m, probably owing to 

 the strip having been heated for some time before the 

 measurements were made. The data for this part of the 

 experiment are: — V=200 volts, H = 4700 lines per cm. 2 , 

 z = -512 cm., and 2x = 2*00 turns. These values give 

 e/jn = 240 E.M. units and m=40'3. 



The results of the observations on rubidium sulphate are 

 exhibited in fig. 10 (PL XX.). These were taken shortly after 

 commencing to heat the salt, but the exact interval of time 

 was not recorded. The left-hand curve with points thus : — x , 

 was taken first. The magnetic field was then reversed, and 

 the right-hand curve with points thus: — x , obtained. The 

 original direction of the magnetic field was now restored, 

 and the left-hand points ® were obtained. The field was 

 again reversed, giving the right-hand points, 63. The dis- 

 placement between the first two maxima is 1"24 turns, that 

 between the two second 1*30 turns. The mean is 1'27 turns. 

 The other data for this experiment are V = 3200 volts, 

 H = 4700 lines per cm. 2 , and z = '506 cm. These give 

 ejm = 101 and m = 96. The atomic weight of rubidium 

 = 85-5. 



The experiments with rubidium sulphate were not con- 

 tinued further, as it was thought at the time that this was a 

 satisfactory agreement. It may be, however, that the rubi- 

 dium sulphate contains some caesium as an impurity, and 

 that further heating would have increased the value of e/m. 

 It is worthy of note in this connexion that rubidium is the 

 only element so far for which the value of m is distinctly 

 above the atomic weight, the other cases tending to fall 



