A CENTURY OF CHEMISTRY. 119 



takes place so that the metals (or metallic radicals) 

 of the salts and bases, and the hydrogen of the acids, 

 move from the positive part of the current to the 

 negative, while the acid radicals or elements, such as 

 chlorine, bromine, iodine, and also the hydroxyl of 

 bases, move in the opposite direction. These com- 

 ponents, or ions, are set free where the electrolyte 

 is in contact with metal conducting the current " 

 (Ostwald, op. cit. p. 270). In 1833, Faraday for- 

 mulated the general conclusion, fundamental to sub- 

 sequent progress, that equal quantities of electricity 

 on passing through different electrolytes require 

 equivalent quantities of the ions for their transport. 

 This may be called the foundation-stone of electro- 

 chemistry. 



It would be interesting to show how the enquiry 

 into the constitution of electrolytes, which must be 

 such that particles charged positively can move in 

 one direction while those charged negatively move in 

 the other, has led through the ideas of Williamson 

 ri851), Clausis (1857), Arrhenius (1887), Planck 

 (1887), to the theory that solutions of salts and of 

 strong acids and bases contain these substances dis- 

 sociated into ions, that a solution of potassium chlo- 

 ride contains in great part single potassium and chlo- 

 rine atoms with enormous electrical charges and with 

 their chemical properties thereby modified. It reads 

 like a romance in the invisible world — far more dar- 

 ing than the biologist has ever ventured with his 

 ids and biophors — and yet it appears to harmonise 

 a large number of observed facts. As Ostwald says, 

 " The assumption that electrolytes contain free ions 

 is not only possible but necessary." 



It would be interesting also to show how the elec- 

 tric conductivity of electrolytes was measured (Kohl- 



