Positive Thermions emitted by Alkali Sulphates. 981 



V11I. Aluminium Cell. 



To show phaseograms by more irregular currents, I have 

 made some experiments with an aluminium cell consisting 

 of an aluminium wire against sheets of lead in dilute sulphuric 

 acid (accumulator acid). 



The three phaseograms show the cell in various stages : 

 fig. 16 soon after the closing of the current ; fig. 17 when 

 the current has passed for a while; lastly fig. 18 shows an 

 inactive cell (PI. XIX.). \ I 



GX. The Positive Thermions emitted by the Alkali Sulphates. 

 By 0. W. Richardson, M.A., D.Sc, Professor of Physics, 

 Princeton University* . 



[Plate XX,] 



I EXPERIMENTS by the author f and Mr. Hulbirt t have 

 .J shown that the bulk of the positive thermions emitted by 

 the commoner conductors, which can be heated to a sufficiently 

 high temperature, possess very nearly the same value of e/m : 

 a value which corresponds to a molecular weight m for the 

 ions of abont 25, on the assumption that they carry the same 

 charge as the atom of hydrogen in electrolysis. There are a 

 number of different ways in which it might happen that the 

 various substances investigated might give rise to ions having 

 the same specific charge, and these are discussed at length in 

 the papers referred to. One of these views, and the one 

 which seemed to have the most evidence in its favour, was 

 that the ions consisted of atoms of sodium which were present 

 as a common impurity in all the substances investigated. 

 This view is supported among other things by the well-known 

 fact that sodium compounds are very widely distributed, and 

 by the fact that the value of m for the ions is very close to 

 the atomic weight of sodium (23*05). 



It was this view that suggested the present investigation. 

 For it was felt, since the alkali metals and their compounds 

 are so similar to one another in both chemical and physical 

 properties, that if sodium compounds gave rise to positive ions 

 having a certain specific charge, it ought to be possible to 

 obtain, ions having other values of e/m by substituting salts 

 of the other alkali metals for those of sodium. The author 

 therefore decided to measure the value of e/m for the positive 

 ions emitted by the sulphates of the different alkali metals 

 when heated. 



* Communicated by the Author. 



t Phil. Mag. [6] vol xvi. p. 740 (1908). 



t Phil. Mag. [(')] vol. xx. p. 545 (1910). 



