It is not possible to describe in a few words the impetus given by the discovery of these connections to physico-chemical research altogether. A school, headed by Ostwald, of most enthusiastic supporters of what has been termed (not quite properly) the physical theory of solutions, has grown up; and this school, while bringing out a mass of important researches and widening the field of chemical investigations, has naturally come to consider itself as being on the right track for elaborating a complete theory of the subject. Unhappily, this is not the case, because the chemical reactions which undoubtedly take place in solutions are not taken into account in the just-mentioned physical laws. In reality, so long as but small amounts of solids, or liquids, or gases are dissolved in a liquid, and so long as only such bodies are brought into contact as have no strong chemical affinity for each other, the above theories are quite correct. But as soon as the solution is rendered stronger, or the solvent and the dissolved body are endowed with a mutual chemical affinity, chemical reactions set in. Part of the molecules of the dissolved body dissociate, and the atoms of which they were composed, on being set free, combine with the atoms of the solvent. Chemical forces, much more energetic than the physical forces, enter into play, and most complicated chemical reactions—the intensity of which may be judged of from the changes of temperature—begin. To deny them is simply impossible, although this has been done in the excitement of polemics. The chemical reactions which take place within the solutions, and especially the formation of definite though unstable compounds of salts, acids, and bases with water, have been rendered evident by so many careful investigations of experienced chemists, that the secondary importance given to them by most adherents of the physical theory would be simply incomprehensible were it not for the hope which they cherish of ultimately explaining all chemical processes by the above-mentioned molecular movements. At any rate, in order to account for the effects of the chemical reactions, the followers of the physical theory were compelled to seek support in an additional agency—electricity. Starting from the familiar fact of solutions being decomposed by an electrical current, they admitted that in every solution part of its molecules dissociate, breaking up into their component parts, which are charged with either positive or negative electricity (the name of "ions" is usually given to those component parts). By means of this admission, they attempted to explain the discrepancies between observation and the conclusions drawn from the above-mentioned laws,
- We need only mention the names of Armstrong, Etard, Pickering, Mendeléeff, and so on.