Solutions of Nonelectrolytes

Abstract

Introduction.-The purpose of the authors in writing the following review has been to give a critical account of the more significant papers bearing upon the theory of solutions which have appeared during the year 1949. We have not hesitated to trace certain developments back into 1948, but we are not giving the earlier background as fully as might be desirable if it were not for the expected publication of the third edition of our Solubility of Nonelectrolytes (1) in which the progress in the subject has been brought down to the middle of 1948.1 It would be impossible, in the space at our disposal, to mention all the contributions pertinent to the general topic without turning this review into a mere set of abstracts such as are already available elsewhere; conse· quently, we can only apologize upon these grounds for the failure to report on a number of good pieces of work. Certain topics and types of system have been the subject of particularly active study during the year and have brought to light points of more than ordinary interest. The reviews which follow have been grouped accordingly. Iodine solutions.-The investigation of iodine solutions has for many years contributed much to the theory of solubility and has continued during the past year to yield results of considerable significance. Iodine lends itself peculiarly. well to this purpose for several reasons: its solutions can be easily and accurately analyzed; its molecular attractive field is very high, giving an enormous range to its solubilities; its molecules have nearly spherical symmetry; and chemical effects can readily be differentiated from physical effects by departures in color from the violet of iodine vapor. A general review of "The Nature of Iodine Solutions" by Kleinberg & Davidson (2) covered the subject into 1948. Late in the same year Benesi & Hildebrand (3) published a paper on the solubility of iodine in 1,2. and 1,l-dichloroethanes, cisand trans-dichloroethylenes, and perfluoro-n-hep­ tane. All these solvents give violet solutions in spite of the considerable dipole moments of all but the last two, and the temperature dependence of solu­ bility in all cases fits them into the family of regular solution curves to which all violet solutions of iodine belong, the significance of which is maximum randomness of distribution of iodine molecules; so the entropy of transfer of