532 Mr. J. Brown on the Difference of Potential 



experiments made gave results varying from 2*33 to 2'47 ; 

 but the alternator employed, being driven by an old type of 

 gas-engine, ran very unevenly and rendered observations 

 difficult. 



In this case it is the average value of the square of the 

 electromotive force which is required in calculating K, and 

 this was obtained directly by employing a Cardew's voltmeter 

 for determining the difference in potential of the plates. 



One of the advantages in the method described in this 

 paper is the possible avoidance (not realized, however, in the 

 form used by us) of all doubtful approximate calculations. It 

 is in this respect analogous to a method much advocated by 

 Lord Kelvin for determining the magnetic permeability of 

 iron. 



When suitably modified for the necessary diminutive size, 

 it appears also well adapted for such determinations as the 

 specific inductive capacity of crystals in different directions. 



We have much pleasure in thanking Prof. Fitz Gerald for 

 his suggestions and help on many points which arose 

 throughout our investigations. 



LXII. On the Difference of Potential at the Contact of 

 Mutually Reacting Liquids. By J. Brown*. 



1. IN 1889 I began an investigation into the difference of 

 _L potential at the contact of liquids, including aqueous 

 solutions of electrolytes ; my object being to determine the 

 connexion, if any, between this difference of potential and the 

 chemical reaction of the liquids on one another. As circum- 

 stances may for some time prevent a return to tbis work, it 

 seems well to make known what came of it, even though in a 

 somewhat unfinished state. 



The method employed was a modification of that of Exner 

 and Tuma f in their experiments on the contact potential of 

 metals and liquids, where the potential of a cylinder of filter- 

 paper saturated with the liquid is ascertained by means of a 

 funnel dropping mercury from a point in the interior of the 

 cylinder. I used a water-dropping funnel as less likely to 

 cause irregular indications by the action of gases on the 

 issuing liquid, and as obviating the need of any correction for 

 frictional electrification of the liquid at the nozzle. In the 

 first apparatus employed, two cylinders or rolls of filter-paper 

 were held in two short vertical glass tubes of about 2 centim. 

 diameter mounted on paraffin insulators. These cylinders 



* Communicated by the Author. 



f Sitzungsberichte d. Kais. Akad. Wien, xcvii. part ii. p. 1. 



