24 The Israel Chemist and Chemical Engineer Issue 4 • August 2018 • Elul 5778 Francis Simon (1893-1956): The third law of thermodynamics and the separation of uranium isotopes by gaseous diffusion Bob Weintraub Director of the Libraries, Sami Shamoon College of Engineering Beersheva and Ashdod Email: bob@sce.ac.il The third law of thermodynamics “The Third Law of Thermodynamics, stated as is now generally accepted:The entropy of all factors within a system which are in internal thermodynamic equilibriumdisappears at absolute zero.” [F. E. Simon, Yb. Phys. Soc ., 1956, 1-22]. “The fact that the Nernst heat theorem is now regarded as the 3rd law of thermodynamics, equal in fundamental importance to the 1st and 2nd laws, is largely due to Simon’s work and influence.” [N. Kurti, Bio. Mem. Fell. Roy. Soc ., 1958, 4, 225]. *** Separation of uranium isotopes by gaseous diffusion “The great achievement of Simon’s proposals was that they were framed to deal with the enormous quantities needed for U 235 separation on an industrial scale and within reasonable time. ” [M. Gowing, Britain and Atomic Energy 1939-1945 . Macmillan, London, 1964]. *** Sir Francis Simon (1956): “When the Physical Soc iet y honoured me by appointing me their 40th Guthrie Lecturer, I did not take long to choose the Third Law as my subject. One reason was that it is just about 50 years since Nernst (1906) published his origina l paper on the new “Wärme- theorem,” as he then called it. The theorem has however not been established solidly ever since but indeed has had a very chequered history. Starting from vague and rather inconclusive beginnings, it was first mainly regarded as a useful rule for calculating chemical equilibria. Next came a period when the quantum theoretical foundations of the theorem were recognized and physicists became interested in it, particularly when quantum statistics made possible a direct calculation of the entropy constants of gases. Later on, further quantum statistical considerations led to a discussion of the general validity of the law when applied to solid phases, and indicated the possibility of exceptions to the theorem, which at first seemed to find experimental confirmation. Thus, it came about that the ‘30’s were a period of utter confusion, the spirit of which I can perhaps bring home to you by quoting from a paper of Fowler and Sterne (1932): ‘We reach therefore the rather ruthless conclusion that Nernst’s heat theorem strictly applied may or may be true, but is always irrelevant and useless – applied to “ideal solid states” at the absolute zero, which are physically useful concepts, the theorem though often true, is sometimes false, and failing in generality must be rejected altogether.’ Eucken (1930) in Germany had held Bob Weintraub is the Director of the Library, The Sami Shamooon College of Engineering, Ashdod and Beersheva. He holds the Ph.D. in Physical Chemistry from the Massachusetts Institute of Technology and the Diploma in Library Science from the Hebrew University of Jerusalem. He has an interest in the history of chemistry and in scientific and technical librarianship. Figure 1. Sir Francis Simon History of Chemistry Articles

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