ELECTROLYTIC LAWS. 21 



INFLUENCE OF THE SIZES OF THE ELECTKODES. When 

 electrolysis is carried on with electrodes of greatly different 

 sizes, the results do not appear, at first sight, to be in accord- 

 ance with the theory, but the apparent discrepancy is readily 

 explained by the intervention of secondary actions. For instance, 

 if the electric current, with a wire and a strip of platinum as 

 electrodes, passes through a bath of dilute sulphuric acid, the 

 following quantities of gases will be liberated, and these are 

 not always in the ratio to the chemical equivalents : 



Negative strip 100 cubic centimetres of hydrogen. 



Positive wire 50 oxygen. 



Negative wire 41 hydrogen. 



Positive strip 16 oxygen. 



The oxygen missing in this last experiment has simply 

 been absorbed by the platinum strip. If instead of platinum a 

 strip of spongy platinum is used, the voltameter is found to 

 contain only five volumes of oxygen against twenty of hydrogen 

 liberated by the negative wire. 



JOULE'S LAW. An electric current, passing through a 

 conductor, generates a certain quantity of heat. In the term 

 conductor we include the generator in which the current is 

 produced, as well as the apparatuses in which the work of 

 electrolysis is performed, and the metallic rods establishing a 

 continuous communication between every part of the circuit. 



Joule has made a complete study of this phenomenon, and 

 has established the following law : 



The quantity of heat developed in a conductor is pro- 

 portional to the resistance of that conductor, and to the square 

 of the intensity of the current. 



If H is the total quantity of heat developed ; 

 t the time during which the current passes ; 

 C the intensity of the current ; 

 E the resistance of the conductor ; 



424 



A the mechanical equivalent of heat (^-- - for the 



y 'oi 



electrical units in which the mass and not the weight is con- 

 cerned), we have 



IT C 2 IU . . 

 H = - calories. 



