ON THE HALOGEN HYDRIDES AS CONDUCTING SOLVENTS. 165 



A possible explanation of the abnormal variation of molecular conductivity might 

 be found in the hypothesis that when acetone or ether is added to hydrogen bromide 

 the acetone or ether acts as an ionising solvent, and the hydrogen bromide is ionised. 

 When looked at from this point of view, the variation of p. which actually occurs 

 appears as a normal one. This explanation is, however, shown to be incorrect when 

 we come to consider the transport number experiments. 



Thus, during the electrolysis of ether in hydrogen bromide, the deposition of 

 1 gram-molecule of silver by the current is accompanied by a transport of - 8 gram- 

 molecule of ether to the cathode. But, if the ether did not take part in the 

 electrolysis, the same result would be obtained by the transport of a sufficient 

 quantity of bromine as anion from the cathode to the anode. 



A simple calculation, however, shows that in order to bring this about no less than 

 23 gram -molecules of bromine must be transported for every gram-molecule of silver. 



Now we have shown that FARADAY'S law is valid for solutions in hydrogen 

 bromide, and accordingly we conclude that ether takes part in the carriage of the 

 current, and that conduction is not due to ionisation of the hydrogen bromide. 



Information regarding the constitution of the electrolyte is also afforded by the 

 transport number. If we again consider the case of ether dissolved in hydrogen 

 bromide, there is in solution an electrolyte of the formula ((C 2 H 5 ) 2 0) 2 (HBr) n , which 

 can ionise either 



+ 

 (1) into H ions and a complex anion ((C 3 H 5 ) 2 0) 2 Br B 



or (2) Br cation ((C 2 H,) 2 O)oH. 



If the former, the ether will be transported to the anode as a component of a 

 complex anion ; if the latter, it will be carried to the cathode as a component of a 

 complex cation. Experiment has proved that the latter is the case not only for ether 

 but also for the other substances which have been examined. 



It has been found that the cation transport number increases considerably with 

 concentration. This increase can be easily explained if we assume, with JONES and 

 GETMAN (loc. cit.), that the number of molecules of solvent in combination with one 

 molecule of solute is greater in the more dilute solution. 



According to the theory of ABEGG and BODLANDER (' Zeit. fur Anorg. Chem.,' 

 1899, 20, p. 453), the resulting change of constitution of the electrolyte would be 

 conditioned as follows : 



Any salt in which one ion is much weaker than the other manifests a tendency to 

 form complex ions by the addition of a neutral molecule to the weaker ion. In the 

 solutions under discussion the weaker ion would undoubtedly be the complex cation, 

 which, when the active mass of the solvent (neutral molecules) was increased by 

 dilution, would tend to become still more complex by the addition of more solvent 

 molecules. 



