242 Dr. C. It. A. Wright on the Determination of 



Law I. may be thus expressed : — Let n be the number of 

 grammes of compound decomposed, and q the quantity of elec- 

 tricity passing ; then 



no: q. 



Law II. states that, if a be the "equivalent" of a given 

 compound, 



n oc a. 

 Hence 



n <x aq ; 

 and consequently 



n = aqxx, 

 where % is a multiplier independent of the quantity of electri- 

 city passing, and of the value of the " equivalent " of the 

 compound. 



When n=a, %=- ; that is, % is the reciprocal of the quan- 

 tity of electricity requisite to decompose a gramme-equivalent 

 of the electrolyte employed. For convenience of reference, 

 % may be termed the electrochemical constant. 



8. The term " electrochemical equivalent of a substance " 



is employed to mean the quantity of substance decomposed by 



n 

 a unit quantity of electricity, i. e. the value of - (which = a)() ; 



and the term " electrochemical equivalent of an element," in 

 reference to such a compound, is used to indicate the quantity 

 of that element evolved during electrolysis of that compound 

 during the passage of a unit of electricity. If b be the equi- 

 valent of the element in reference to the compound employed, 

 the equivalent of the compound being a, the electrochemical 

 equivalent of the element in reference to the compound is 



n b 

 - • -> 

 q a 



which =5%. 



n is of necessity a constant for any given compound : and 

 so is b in many cases : that is, in such cases, no matter what 

 compound of a particular element be electrolyzed, the same 

 quantity of that element is set free by the passage of a unit of 

 electricity. In other cases, however, b varies with the cha- 

 racter of the compound employed ; that is, the same quantity 

 of element is not necessarily always evolved by the passage of 

 a unit of electricity. For example, the value of b for hydro- 

 gen, chlorine, and silver appears to be constantly 1, 35*5, and 

 108 respectively ; whilst for copper the value is 31*75 for 

 compounds of the class known as cupric salts, and 63*5 for 

 compounds of the class known as cuprous salts. When b is 



