CH.IIL] OF ELECTRICITY 21 



atom, was called by Dr. Johnstons Stoney an 

 " electron " or natural electrical unit. 



What we learn with great accuracy from electro- 

 lysis is the ratio of the charge to the mass of 

 substance with which it is associated. It matters 

 nothing how much substance is chosen, whether 100 

 atoms or one, whether an atom or a gramme or a ton, 

 the amount of electricity associated with it in 

 electrolysis, and liberated when the substance is 

 decomposed, increases in the same proportion ; the 

 ratio is constant for each material, and if determined 

 for one is known for all. 



This ratio is the reciprocal of what is technically 

 known as the " electrochemical equivalent " of a sub- 

 stance. In the light of Faraday's laws, if this quantity 

 is measured for one substance it is known for all, 

 because the charge is the same for every kind of 

 atom, up to a simple multiple ; and hence in specify- 

 ing electrochemical equivalents there is nothing 

 to consider but the atomic weight, or combining 

 proportion, of the substance. Thus the electro- 

 chemical equivalent of oxygen is 8 times that of 

 hydrogen, that of zinc is 32|- times, and that of silver 

 108 times that of hydrogen. The substance chosen 

 for a determination of the electrochemical equivalent 

 may be the one which can be most accurately experi- 

 mented on ; and Lord Rayleigh has shown that such a 

 substance is nitrate of silver, and has ascertained that 

 if a current of one ampere is passed from a silver anode 

 to a platinum cathode through a nitrate of silver solu- 

 tion, the cathode gains in weight by 4*025 grammes 

 every hour. Hence the electrochemical equivalent of 

 silver is 



4*025 grammes f 



1 ampere-hour ' 



