328 



Mr. S. Bidwell on the Generation of 

 Table III. 



Eate of 

 oxidation, 



Value for 



Eate of 



oxidation, 



Value for 



Eate of 

 oxidation, 



Value for 



P- 





P- 





P- 





MO 



10-5 



1-92 



8-1 



3-32 



5-8 



1-21 



10 



2-11 



7*7 



3-59 



5-6 



1-33 



96 



2*29 



7*5 



383 



5-6 



1-46 



92 



2-51 



71 



5-08 



43 



1-62 



8-3 



273 



6-8 



6-04 



37 



1-73 



9 



2-96 



66 



7-15 



3-1 



From this Table it will be seen that n, instead of having a 

 constant value, gradually diminishes as the temperature in- 

 creases, but that for a few consecutive experiments the dif- 

 ferences are such as might be referred to experimental errors, 

 and so lead to the erroneous supposition that p oc d 2 . 



So far as these experiments go, it would seem probable that, 

 for this reaction at least, the temperature function is of an 

 exponential form. Indeed, in many cases of chemical change 

 it is a common observation that the speed increases very 

 rapidly with the temperature, being, as Lemoine remarks, 

 characteristic of an exponential form. . In the course of some 

 experiments on retardation, in which ferrous chloride was the 

 material employed, instead of sulphate as in the present case, 

 it has been found that here also, in presence of agents that 

 retard the oxidation very considerably, the relation between 

 rate and temperature may be represented in the form p — act 9 . 

 A full account of these experiments, however, will, it is hoped, 

 be given at a future time. 



XXXVII. On the Generation of Electric Currents by Sulphur 

 Cells. By Shelfokd Bidwell, M.A., LL.B* 



FN a communication recently made to the Physical Society f 

 J- I ventured the suggestion that the electric conduction of 

 selenium, when prepared in such a form as to be sensitive to 

 light, was, in the literal sense of the term, electrolytic. Sele- 

 nium itself indeed could hardly be supposed to be an electrolyte; 

 but it was pointed out that when selenium was " annealed " 

 in contact with metallic electrodes, metallic selenides would, 

 at least in most cases, be formed in sufficient quantity to 

 account for the electrolytic phenomena observed ; and that 

 even if this were not the case when the electrodes consisted 

 of such a metal as platinum, yet the necessary metallic element 



* Communicated by the Physical Society: read June 27, 1885. 

 | Phil. Mag. August 1885. 



