378 Electrification at Liquid- Gas Surfaces. 



waterfall experiments Lenard supposes this disturbance to 

 tear apart the negative from the positive electrification in a 

 double layer at the surface. If this is so, it cannot be the 

 same double layer which surrounds a bubble of air and is 

 active in a cataphoresis experiment. If it were, there should 

 be parallel effects observed in the two cases. For example, 

 Prof. J. J. Thomson has shown in waterfall experiments that 

 the merest trace of methyl violet in the water reverses the 

 electrification produced. The author has tried solutions of 

 methyl violet in cataphoresis experiments, but found no 

 reversal. Again, Prof. Thomson in his experiments showed 

 that water falling through its own vapour gained no charge, 

 and from similar results in other cases concluded that the 

 liquid and the gas in contact must be chemically different to 

 give any electrification. The author could not try a bubble 

 of water vapour in water in a cataphoresis experiment, but 

 found that particles of ice in water moved almost as fast as 

 bubbles of air. In this case, at least, the two phases in 

 contact need not be chemically different. 



The mechanism which produces the electrification in water- 

 fall experiments is different from that in cataphoresis 

 experiments, and is most probably and most simply explained 

 on Prof. Thomson's view mentioned in the last paper. 

 Alcohol, in these cases, can unite with a molecule of oxygen 

 for example, and when the combination is violently disturbed 

 ionization may take place, while in a cataphoresis experiment 

 an adsorption of the ions in the liquid is necessary. This 

 may not be possible in alcohol. 



Summary. 



Alcohols reduce the electric charge at the liquid-air 

 surface in water, showing in this respect a parallelism with 

 their action on the surface tension of water. 



There does not appear to be any cataphoresis of air bubbles 

 in pure alcohols. 



The fatty acids reduce the charge at the gas-liquid surface 

 in aqueous solutions, but no reversal was observed with the 

 concentrations used. 



A large variation of velocity with size of air bubbles in 

 cataphoresis experiments is produced by the presence in 

 aqueous solution of substances which have a marked effect 

 on surface tension. 



Evidence is given to show that the electrification in water- 

 fall experiments is not due to the difference of potential 

 observed in the cataphoresis experiments. 



