With the death of Svante Arrhenius, the world has lost a scholar whose personality and work became the embodiment of a new era in the exact sciences: the era of the fusion of two basic sciences, physics and chemistry. If the great development that took place in both sciences in the first three-quarters of the nineteenth century can be credited to their separation and the concentration of efforts within a narrower sphere that it made possible, then the blossoming experienced by both sciences in the last quarter of the century is to be attributed equally to the fact of their coming together. This unification was given visible expression in the concept of physical chemistry, the name given to the common border area. If we were to assign to Arrhenius a professional classification. we would have to call him a physical chemist.