The most important idea in the dissertation was his explanation of the fact that neither pure salts nor pure water is a conductor, but solutions of salts in water are.
Arrhenius' explanation was that in forming a solution, the salt dissociates into charged particles (which Michael Faraday had given the name ions many years earlier). Faraday's belief had been that ions were produced in the process of electrolysis; Arrhenius proposed that, even in the absence of an electric current, solutions of salts contained ions. He thus proposed that chemical reactions in solution were reactions between ions. For weak electrolytes this is still believed to be the case, but modifications (by Peter J. W. Debye and Erich Hückel) were found necessary to account for the behavior of strong electrolytes.
