PHILOSOPHICAL TRANSACTIONS. 
I. The Emission of Electrons under the Influence of Chemical Action. 
By O. W. Richardson, F.R.S., Wheatstone Professor of Physics, University of 
London , King s College. 
Received October 21,—Read November 18, 1920. 
§ 1. —Several investigators have claimed that electrons are emitted from metals under 
the influence of chemical action, but the only claim* which seems well substantiated is 
that of Haber and Just,| who found that when drops of caesium or of the liquid alloy 
of sodium and potassium are attacked, at a low pressure, by a number of chemically 
active gases, the drops lose a negative but not a positive electric charge. The electric 
currents set up with the drops negatively charged are stopped by the application in a 
suitable manner of relatively small magnetic fields. This shows that the currents are 
carried by electrons emitted from the drops.J 
The object of the present investigation has been to obtain quantitative information 
about this interesting phenomenon, and, more especially, to ascertain the magnitude of 
the kinetic energy of the emitted electrons and the mode of its distribution among them. 
The importance of the subject lies in the fact that it is the only way, so far as I am 
aware, in which any information at all can be made available as to the distribution of 
energy among the individual products—molecular, atomic, ionic or electronic—of a 
chemical reaction. The majority of the experiments have been directed towards obtain¬ 
ing the curves showing the relation between the chemical electron current and the 
applied electromotive force for the case of a small spherical source concentric with a 
large spherical electrode. If the currents are small and the gas pressure is low, so that 
the motion of the liberated electrons is determined entirely by the applied electric field 
and is interfered with neither by the molecules of the gas nor by the fields of force arising 
from other electrons, we should anticipate that these electron currents would exhibit 
saturation with zero applied potential difference ; subject to the additional proviso 
* Possibly some of the cases examined by Reboul (‘ C. R.,’ vol. CXLIX., p. 110 (1909), and vol. CLII., 
p. 1660 (1911)), may turn out to be an exception to this statement. 
f ‘Ann. der Physik,’ vol. 30, p. 411 (1909)"; ibid., vol. 36, p. 308 (1911). 
J A survey of the previous work in this and allied fields, together with an account of the results of some 
of the earlier experiments of the present research, will be found on pp. 290-298 of my book ‘ The Emission 
of Eleetricity from Hot Bodies ’ (London, 1916). It will be seen that the e-arlier experiments gave results 
which differ in some important particulars from those obtained later under more satisfactory conditions. 
Cf. also ibid., pp. 49 et seq., and pp. 128 et seq. 
VOL, CCXXII.—A 594. 
B 
[Published April 30, 1921, 
