A Contribution to the Theory of Electrocapillarity , 475 



•appears in the spectrum of the capillary, in the capillary dis- 

 charge, only very faintly if at all, but in the discharge in 

 dilute sulphuric acid it is the most important part of the 

 spectrum of the bubble which forms at each end of the 

 capillary. 



The lines of the metal of the dissolved salt appear in the 

 brush. In the case of lithium their relative intensity varies 

 with the salt used and also with the current. In weak solu- 

 tions the metal lines are destroyed by the heavier condensed 

 discharges. The metal lines appear very feebly in a capil- 

 lary, and they are produced strongly only in the immediate 

 neighbourhood of a metal electrode. 



The spark-lines of platinum appear with the condensed 

 discharges when a spark-gap is used. 



In conclusion I wish to thank Professor H. Stroud, of 

 Armstrong College, for the kind interest shown in this in- 

 vestigation. My thanks also are due to Mr. H. Morris-Airey, 

 w T ho suggested to me this problem for research and who was 

 at all times willing to offer criticism and advice. 



LI. A Contribution to the Theory of Electrocapillarity, 

 By David Leonakd Chapman *. 



FOR any substance which satisfies the laws of a perfect 

 gas we obtain by equating to zero the variation of the 

 sum of the potential and free energy the equation 



F 1 -T 2 + ntlog e p 1 — Utlog e p 2 =0, 



T 1 and P 2 being the potential energies at the points 1 and 2 

 of a gram molecule of the substance, and p 1 and p 2 the 

 respective hydrostatic pressures. 



If the potential energy is electrical the above equation 

 becomes 



(Vi-Vg^ + Rdog^i-Knog^-O, 



in which V is the line integral of electromotive intensity, and 

 q the charge on a gram molecule of the substance. 



The potential f of a monovalent metal in contact with a 

 solution of one of its salts is therefore, according to Nernst's 



* Communicated by the Author. 



t Although it sometimes leads to confusion, we shall for brevity adopt 

 the usual convention of calling the line integral of electromotive intensity 

 potential. Throughout the electrostatic system of units will be used. 



