4: Mr. J. Swinburne on some 



intermediate vessel, and their Peltier effect, or difference of 

 potential due to heat-formation, may be found as in the case 

 of the plates. 



Several workers, for instance M. Bouty and H. Gockel, 

 have been investigating and measuring the temperature- 

 coefficient or the Peltier effect directly. 



Prof. J. Willard Gibbs has, of course, discussed the subject. 

 In a letter to Dr. Lodge * he took a theoretical case in which 

 this cell could be heated to the temperature of dissociation. 

 He has written a second letter going more fully into the 

 subject f. 



This leads at once among the various conflicting views of 

 electrolysis. One view, which seems tenable, is that electro- 

 lysis is always a case of double decomposition : that there is 

 really a change. According to orthodox chemistry, if 2HC1 

 is electrolysed H 2 and Cl 2 are obtained, and not 2H and 2C1. 

 The hydrogen and chlorine form combinations with themselves. 

 Dissociation does not always split a compound in the same 

 way as electrolysis, and the results of it are often " free 

 atoms." It might be urged that in such a case as the electro- 

 lysis of NH4CI free atoms of NH 4 cannot exist, so NH 3 and 

 HC1 are produced by a sort of secondary action. 



The cells discussed have been assumed to be reversible ; 

 and some question may arise as to what the chemical work 

 means. For instance, in a Daniell cell are we to take such 

 data as Zn,0 = 85,430 and Cu,0 = 37,160 £ from a convenient 

 treatise on Thermochemistry, and to consider that the conver- 

 sion into sulphate and other actions in the cell are secondary? 

 It is to be regretted that writers on Thermochemistry seldom 

 give their data so that their meaning is clear. Zn,0, for 

 instance, often means that metallic zinc is burned in gaseous 

 oxygen. Allowance must then be made for the physical states 

 of the components before, and of the products after the 

 combination. 



Returning to the reversible cell, however, before discharging 

 a coulomb there are certain quantities of certain substances in 

 certain physical and chemical conditions. After the discharge 

 certain chemical and physical changes have taken place. 

 Suppose any one of these is a secondary, or non-adjuvant 

 action. For instance, suppose in discharging a Daniell cell 

 that the conversion of zinc into oxide is a primary action, and 

 the conversion of zinc oxide into zinc sulphate secondary or 



* B, A. Report, 1886, p. 388. 

 t B. A. Report, 1888, p. 343. 



% J. Thomsen, Thermochemische Untersuchungen, iii. pp. 275 and 

 320. 



