McLaughlin — Cataphoresis of Air- Bubbles in Various Liquids. 17 



of interest also to note that the two liquids which showed the phenomenon have a 

 much higher dielectric constant than those liquids in which it was absent, and, 

 accordingly, are much better ionisers. This might be expected from a law laid 

 down by Perrin as a resiilt of experiments on electric osmose — an allied 

 phenomenon: — " Electric osmose is only appreciable with ionising liquids; or, in 

 other words, ionising liquids are the only ones which give strong electrification by 

 contact." Thus, the presence of impurities would be more 1-ikely to bring about 

 cataphoresis in liquids of high dielectric constant, e.g., water and nitrobenzene. 

 The results recorded in this paper are also in keeping with Coehn and Mozer's' 

 results on contact electrification between gas-liquid surfaces investigated by 

 bubbling experiments. They found that the greater the dielectric constant of the 

 liquid, the greater was the charge recorded by bubbling a particular gas through 

 it. It is remarkable that the charge produced by bubbling hydrogen tlirough 

 various liquids was much greater in the case of water and nitrobenzene than in 

 any other tested. Benzaldehyde and aniline are recorded as giving charges in the 

 bubbling experiments, while in these experiments they gave no charge to an air- 

 bubble. 



SUMMAliV. 



Under the conditions described in the paper air-bubbles were found to show 

 no cataphoresis in the following liquids : — Methyl, ethyl and butyl alcohols, xylol, 

 benzene, toluene, bromobenzene, benzyl alcohol, benzaldehyde, aniline, cinnamic 

 aldehyde, ethyl malonate, lactic acid, oleic acid, ethyl acetate, and turpentine. 

 The results on turpentine are not in accordance with those obtained by Quincke. 



It was not found possible to trap an air-bubble in acetone and such volatile 

 liquids as carbon disulphide. In impure acetone foreign matter moved towards 

 the positive pole. 



In distilled water, air-bubbles moved towards the positive pole ; in impure 

 benzene, towards the negative pole. In "pure" nitrobenzene air-bubbles moved 

 to the negative pole. In impure nitrobenzene the motion may be to either pole. 



The solution of an air-bubble in methyl alcohol under an electric field 

 previously noted by McTaggart was confirmed. 



' Coehn u Mozer, Ann. der Pliysik, vol. xliii, p. 1048. 1914. 



CIENT. PROC. K.D.S., 70L. XVII, NO. 2. 



