SYMPOSIUM ON INTERMOLECULAR ACTION1 INTRODUCTION TO THE SYMPOSIUM* GEORGE SCATCHARD Research Laboratory of Physical Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts
Received November 1 , 1038
The Third Annual Symposium of the Division of Physical and Inorganic Chemistry of the American Chemical Society is the second in the field of physical chemistry, as the Second Annual Symposium was devoted to inorganic chemistry. The first symposium discussed molecular structure, or the character of molecules. The present symposium discusses the behavior of molecules, which is, of course, determined by their character, although in our present state of knowledge it is often impossible to predict behavior from character or even to relate a particular behavior to any specific characteristic. There is little, if any, chemistry not included under the two titles “Molecular Structure” and “Intermolecular Action”. It was therefore necessary to restrict the field of this symposium much more than the title indicates. It seemed logical to discuss first the behavior of a normal molecular society rather than molecules excited enough to undergo deep-seated chemical changes. Therefore kinetics were excluded by the committee, and it has been tacitly assumed by all the contributors that any consideration of chemical equilibrium should emphasize its change as the medium changes rather than its absolute value in any one medium. If a group of molecules in the ground state (electronic) may be likened to an agricultural society, ’This Symposium on Intermolecular Action was held, as the Third Annual Symposium of the Division of Physical and Inorganic Chemistry of the American Chemical Society, a t Brown University, Providence, Rhode Island, on December 27 to 29, 1938. The papers presented a t the symposium were classified for discussion into five groups: Part I, Gases and Pure Liquids-J. C. Slater presiding; Part 11, Non-polar Mixtures-H. Eyring presiding; Part 111, Highly Polar Mixtures-J. G . Kirkwood presiding; Part IV, Polar Mixtures-N. Bjerrum presiding; Part V, Ionic Solutions-L. P. Hammett presiding. These papers follow the introduction in order, in this issue and in the February issue. The arrangements for the symposium were made by a committee consisting of G. Scatchard, Chairman, E. J. Cohn, F. Daniels, H. Eyring, J. H. Hildebrand, L. S. Kassel, C. A. Kraus, V. K. LaMer, P. B. Leighton, a n d S . C. Lind. *Contribution No. 412 from the Research Laboratory of Physical Chemistry of the Massachusetts Institute of Technology. 1
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GEORGE SCATCHARD
we are to discuss pastoral communities. We have not excluded the nomadic molecular life as manifested in diffusion, viscosity, and conductance, but we have limited our field further by ruling out the very highly organized molecular groupings of the solid state. There is also a historical reason for this choice of subject. If physical chemistry can be said to have begun a t any specified date, that date is February, 1887, when the Zeitschrift fur physikalische Chemie was founded. The need for this journal arose from the great amount of work then being done on solutions, and such work has ever since filled a large part of this and similar journals. Even in the decade before 1887 the two subjects which seem to have thrilled the imagination of the inorganic chemist most were electrolysis and the liquefaction of gases. N o symposium can be justified either by logic or by history. The justification for this symposium must rest on the belief that the subject of “Intermolecular Action” is live enough in America today to afford a discussion which will stimulate, clarify, and point the way for future work. Substantial evidence of this life and interest is the new laboratory a t Brown University, which will be dedicated on December 27th and which is already busy with work largely in this field. The whole organization of this symposium has been planned to promote discussion. Those speakers were invited who were expected to provoke discussion, and they were asked to present new work rather than reviews. Unfortunately this procedure has eliminated some contributors from whom we should like to hear but who have no work in this field maturing in December, 1938. The number of papers has been restricted and preprints have been prepared, so that as much as possible of the time of the meetings may be devoted to discussion. The quality of the papers so obtained has exceeded our highest expectations, but we do not delude ourselves into taking credit for their quality, because we know that each of these papers would have been published somewhere if there had been no symposium. We do congratulate ourselves, however, that we have collected here the basis for a good discussion. The method of selecting papers has made it impossible to attempt to cover the field evenly or thoroughly, for the committee had no way of knowing that part of the field to which many of the speakers would contribute. Yet the papers group themselves with very little stretching into five nearly equal parts covering the six subfields in which we expected contributions. The groups have been arranged in the order of increasing complexity of the intermolecular action with one exception,-slightly polar mixtures have been placed after both non-polar mixtures and highly polar mixtures. The reason for this order is that it is simpler to study two coexistent actions by considering first the case in which one exists alone, second the case in which the other predominates, and last the case in which the two are about equally important.
INTRODUCTION TO THE STMPOSIUM
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I shall make no attempt to review the large field of “Intermolecular Action” or to show its importance, but I cannot pass over the opportunity of gaining an insight into the present state of this branch of science and its rate of development by examining the distribution of papers, comparing it with the probable distribution if such a symposium had been held a t some time in the past, and speculating a bit as to the reasons for the change. We must remember, of course, that a score of papers is not enough to eliminate the effect of requiring papers on a certain date and requesting that they be provocative of discussion, and I merely note in passing the improvement in precision both of measurements and of thinking which has taken place in the last few years. To me three developments are outstanding: The first is that the theorists are no longer confining their attention to the crystal lattice or to very dilute gases or solutions, but now offer us studies of liquids and concentrated solutions from three or four points of view. The second is that the Debye theory of interionic action appears to be no longer a question for discussion but is now taken for granted in the consideration of the more complicated effects of changing medium and of the detailed structure of the ions. The third, and perhaps the most important, is the growing recognition of the inherent unity of the subject “Intermolccular Action.”
