On Retardation of Chemical Action. 419 



ing to any wire, 



and therefore 



E 1 =E 2 = ,..=E W . 

 Now for each wire 



where R is the resistance in the wire, Ultimately, when the 

 motion becomes steady, which it does generally in a very short 

 time, 



dt Uj 



E=R?, 



E 1 =E 2 =. . . = E, 



and therefore 



But 



therefore 



and therefore %Rq 2 , or the heat generated in the wires per unit 

 of time, is minimum, given %q. 



This is the distribution according to Ohm's law, which thus 

 appears as an analytical consequence of Thomson's theorem, 



LIII. On Retardation of Chemical Action. 

 By John J, Hood, B.Sc, Assoc. R.S.M* 



IN two former papers published in this Journal t I have 

 given the results of a series of experiments on the rate of 

 oxidation of ferrous sulphate by potassic chlorate, and showed 

 that the course of the reaction for equivalent quantities of 

 the substances is represented by the equation y(a + i)=-b; 

 the variables being the amount of unoxidized iron expressed 

 in cubic centimetres of a solution of potassic permanganate, 

 and time elapsed from a fixed point in the reaction. This 

 equation is established on the supposition that the products 

 formed have no influence on the rate at which the oxidation 

 goes on ; but when an experiment was continued for a com- 

 paratively long period, or till about 80 per cent, and upwards 

 of the oxidation had taken place, a small and ever increasing 

 difference was apparent between the calculated and observed 

 variables, indicating a retardation which was clue, without 

 doubt, to the products of the reaction. 



The present paper contains the results of a series of experi- 

 ments made to investigate this retarding effect, in a general 



* Communicated hy the Author. 



t Phil. Mag. [5] yi. p. 371 ; viii. p. 121. 



