158 Prof. J. Traube : 
down to 2 mm. the rate of leak was found to be nearly pro- 
portional to the pressure, in accordance with the results of 
previous observers. But, when the pressure was lowered 
beyond that, a different state of things began to be apparent. 
The rate of leak diminished more and more slowly, apparently 
reaching a limit. Exhaustion was continued until the vacuum 
was so high that a discharge could not be forced through 
the Réntgen tube attached. Even then a_ considerable 
leakage was observed from the charged system. ‘This leakage 
was of about the magnitude which would correspond to 
+ mm. pressure if the law of proportionality, which held 
good at higher pressures, were applicable to low ones. This 
leak was the same whether the charge was positive or negative. 
It is certain, therefore, that the current carried by the @ rays 
must be small in comparison with it. The leak which occurs 
in high vacua must be quite distinct from the ordinary leak 
due to ionization of the gas ; for the latter, at a pressure as 
low as that used in these experiments, would be at least a 
hundred times smaller, The nature of this conduction at 
high vacua is a difficult problem. It is very repugnant to 
modern ideas to believe that the current is carried independ- 
ently of moving ions; as these cannot be derived from the 
gas, the only alternative seems to be that they are derived 
from the material of the radioactive substance, being torn 
away from it by the issuing a2 particle. 
XVII. A Theory of Solutions. By Professor J. TRAuBE*. 
YW it is true that the theory of electrolytic disso- 
ciation has at all times had many admirers, it cannot 
be denied that the same theory has also always had a great 
many adversariest who, in spite of all its success, have felt 
themselves unable to accept it. 
There are many objections to this theory. Firstly, we 
are to believe that the ions attract each other by electric but 
not by chemical forces ; there we create a distinction which 
does not exist, for if we follow Faraday, Helmholtz, and 
others {, the chemical forces are entirely, or in a great part, of 
electric nature. 
Further, Arrhenius tried to support his theory by remark- 
ing on the additive qualities of the dissolved electrolytes. But 
* Communicated by the Author. , 
+ Compare, among others, J. Traube, Chemiker Zeitung, xxvi. No. 96 
(1902), and Wied. Ann. Phys. lxii. p. 504 (1897); Kahlenberg, Journ. 
Phys. Chem. v. p. 339 (1901). 
t Ebert, Wied. Ann. Phys. 1. p. 265 (1893). 
