His early work was on the conductivity of electrolytes. In 1884, based on this work, he submitted a 150-page essay on electrolytic conductivity to University of Uppsala for his doctorate. It did not impress the professors, and he received a low-class degree. Later, extensions of this work would earn him the Nobel Prize in Chemistry.
The most important idea in the thesis was his explanation 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 splits up 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' idea was that, even in the absence of an electric current, solutions of salts contained ions. He proposed that chemical reactions in solution were reactions between ions.
In an extension of his ionic scientific theory Arrhenius proposed definitions for acids and bases, in 1884. He believed that acids were substances which produce hydrogen ions in a solution and that bases were substances which produce hydroxide ions in a solution.
The Nobel Prize
About 1900, Arrhenius became involved in setting up the Nobel Institutes and the Nobel Prizes. For the rest of his life, he would be a member of the Nobel Committee on Physics and a member of the Nobel Committee on Chemistry.
He used his positions to arrange prizes for his friends (
Jacobus van't Hoff, Wilhelm Ostwald,
Theodore Richards) and to attempt to deny them to his enemies (Paul Ehrlich,
Walther Nernst). In 1903 he became the first Swedish persn to be awarded the Nobel Prize in Chemistry.