Page:Popular Science Monthly Volume 41.djvu/836

816 especially in the case of water solutions of salts, acids, and bases, and the stronger solutions altogether. It must be recognized that many important relations between electrical conductivity and chemical action have been brought out in this way by Arrhenius and his followers, and many discrepancies between the laws of Van 't Hoff and Raoult and the observed facts have been explained. But it is also evident that, once a partial dissociation of molecules is admitted, the whole takes a chemical aspect, and reference to such an unknown cause as electricity does not simplify the matter. All kinds of chemical reactions take place in solutions. Some molecules of the dissolved body simply exchange their atoms in succession, while maintaining the same grouping of atoms, and consequently the same chemical composition. In other molecules the grouping only of the same atoms is changed, and we have reactions of replacement, or isomerism. But, at the same time, new and more or less stable combinations between the atoms of both solvent and dissolved body take place in various proportions; double decompositions most probably occur as well; while the physical phenomena of sliding of undecomposed particles continue at the same time—the physical movements of the particles being impressed by, and acting upon, the chemical movements of the atoms within the molecules.

It must be confessed that neither theory has as yet succeeded in following this multitude of movements and of catching the moment when the movements of particles are transformed into atomic movements and redistribution; and though we may name several equally important works which have been published on this subject during the last twelve months, we can mention none which have thrown new light on the subject, Let us only add that the subject itself has been immensely widened of late by the wonderful researches of Heycock and Neville on the lowering of the temperature of solidification of metals, by the addition of other metals, and of Roberts-Austen upon alloys—that is, metals dissolved in metals—which behave very much like all aqueous solutions. However, a new departure in this branch has been made, quite recently, by Messrs. Harold Picton and S. E. Linder. They studied the structure of solutions of sulphide salts which offer the advantage of giving a whole series of gradations between real solutions (that is, liquids which seem to consist of liquid particles only) and such as contain extremely small particles of solid matter in suspension. By submitting the series to various tests, it