Studies of the process operative in solutions.-Parts II-V. - II. The displacement of chlorides from solution by alcohol and by hydrogen chloride

Abstract

Although innumerable determinations of solubility have been placed on record, little has been done to elucidate the phenomena of what may be termed competitive dissolution. A comprehensive series of determinations of the solubility of chlorides in presence of hydrogen chloride made by Engel led him to the conclusion that, up to a certain point, the hydride displaces the salt approximately equivalent by equivalent, the sum of the equivalents being practically constant; eventually, however, in every case, the chloride falls off in displacing power. Almost the only attempt to deal with the problem in a rational manner is that made by Nernst in 1888, who discussed the mutual influence which salts exercise on one another on the assumption that the gas laws are applicable to liquids and from the ionic dissociation standpoint. Having in mind the fact that, although neutral gases are without influence, a separation of ammonium chloride at once takes place if either hydrogen chloride or ammonia be introduced into a space in which these products of its dissociation are in equilibrium with the chloride, Nernst advocated the view that the degree of dissociation of a dissolved salt—and therefore its solubility—will be diminished if a compound containing either of the ions of the salt be introduced into the solution. In support of this contention, results were put forward showing that the solubility of silver acetate is diminished and to about an equal extent by equivalent amounts of the electrolytes sodium acetate and silver nitrate—which are supposed to undergo dissociation in solution to about equal ex ten ts; whilst acetic acid—which is supposed to exist in aqueous solution almost undissociated—has little if any influence. The subject was subsequently dealt with more fully from the same point of view by A. A. Noyes * The circumstance that “unionisable” (by hypothesis undissociated) neutral substances such as methylic and ethylic alcohol are powerful precipitants was ignored by Nernst and Noyes.