the Cation in Voltaic Combinations. 463 



In 12, heat was evolved on adding iodine chloride to 

 benzol. This, no doubt, reduces the available energy of the 

 electrolyte. 



26. Regarding the three-fluid cells in Table II., the solu- 

 tions noted in the fourth column for 18 and 2 ( J were used 

 with the idea that they might protect the negative plate from 

 contact with the chlorine compound, and substitute a bromine 

 combination ; in the latter case, for instance, by dissolving the 

 bromide, which is insoluble in water. Nos. 19 and 20 are 

 for comparison with 17 and 18, when the bromine chloride is 

 omitted. 



Some other three-fluid combinations were tried, but the 

 reaction in these cells seems very complicated and needs 

 further investigation. In calculating the theoretical values 

 for 18 and 20, however, the combining heat Cu, Br 2 has been 

 subtracted instead of Cu, Cl 2 , which gives a result nearer the 

 observed value. 



27. Thallium (22, 23, 26) as a negative plate was chosen as 

 the only metal whose heat of combination with bromine is 

 greater than with chlorine ; that is, comparing the heat of the 

 insoluble bromide 82,590 with that of the chloride in aqueous 

 solution 76,960, the object being to form a cell where one 

 metal attracted the anion and the other the cation, and note 

 the effect on the observed force. In this particular case it 

 seemed possible that thallium might by attracting the bro- 

 mine increase the force of the cell in the same way as the 

 oxygen of hypochlorous acid in 10 may be supposed to do by 

 its combination with the iodine. The assumption that this 

 might occur is doubtless at variance with the theory that 

 metals are " electropositive /'■ and therefore could not combine 

 with the bromine, which has here the role of an " electro- 

 positive " body. Still it was thought worth while to try the 

 experiment, which after all, however, is scarcely decisive, 

 since thallium chloride is not very soluble, and has also a 

 negative heat of solution, and therefore perhaps the heat of 

 the anhydrous chloride should be taken. This being 97,160, 

 is greater than that of the bromide 82,590, and would place 

 thallium in the same category as the other metals. 



The forces observed with thallium as negative plate are 

 rather variable, owing probably to the difficulty of cleaning- 

 its surface from oxide. Probably the higher values are 

 nearest the truth, in which case 22 and 23 would agree with 

 the hypothesis involved in § 22. 



1 have to acknowledge my indebtedness to Professor 

 Everett for his kind permission and encouragement to work 

 at the Physical Laboratory, Queen's College, Belfast. 



