Thermions emitted by the Alkali Sulpluites, 981) 



It occurred to the author that the explanation of this 

 result might be as follows : It is well known that at lo v .v 

 temperatures, when the salts of the alkali metals are ionized 

 by heat, the amount of ionization produced is much greater 

 the higher the atomic weight of the metal used. This 

 tendency is well shown, for example, in experiments by 

 Smithells, Dawson, and Wilson * on the conductivity im- 

 parted to flames by alkali salt vapours. Now lithium 

 sulphate is certain to contain the sulphates of potassium and 

 sodium as impurities, and these will give rise to an amount 

 of ionization more than proportionate to the amount of them 

 which is present. In fact, it is quite conceivable that the 

 bulk of the ionization from the lithium sulphate at first may 

 be caused by the comparatively small quantities of the 

 sulphates of the metals of higher atomic weight mixed 

 with it. On this view, we should expect that the value of 

 elm would increase and that of m diminish with continued 

 heating of the lithium sulphate, and for two reasons. In the 

 first place, the decomposition and consequent removal by 

 ionization is greater the greater the atomic weight, and, in 

 addition, the volatility of the salts of the alkali metals in- 

 creases as the atomic weight of the metal increases. Oaref ul 

 observations were therefore made from time to time on 

 the deflexion, in a magnetic field, of the positive ions from 

 a specimen of lithium sulphate, which was heated continuously 

 for about 70 hours. It was found that the deviation of the 

 ions produced by the magnetic field gradually increased with 

 the lapse of time, and in fact the results were in complete 

 accordance with the view that the initial values were due to 

 the presence of salts of the metals of higher atomic weight. 



The results of the observations on the different salts will 

 now be considered in detail in the order of the atomic weights 

 of the constituent metals, commencing with lithium sulphate. 



Lithium Sulphate. 



The lithium sulphate used was supplied as pure by Messrs. 

 Eimer & Amend, New York. As was the case with all the 

 sulphates investigated, experiments were first made with the 

 initial ionization from the platinum itself. The residue of 

 this was then driven off by heating all night at a somewhat 

 higher temperature. After the emission of positi\ e ions from 

 the platinum itself had falien to a small value, the platinum 

 was taken down and a small quantity of lithium sulphate laid 



* Phil. Trans. A. vol. 19:J. p. 108 (1899). 

 Phil. Mag. S. b\ Vol. 20. No. 120. Dec. 1910. 3 T 



