Article pubs.acs.org/jchemeduc
Periodic Reactions: The Early Works of William C. Bray and Alfred J. Lotka Rinaldo Cervellati* and Emanuela Greco Department of Chemistry, University of Bologna, Emilia-Romagna, Bologna 40126, Italy ABSTRACT: Oscillating chemical reactions in the homogeneous phase have been studied intensively only since the mid-1960s, but they were known since 1920, having as forerunners the chemist William C. Bray and an “atypical” chemist Alfred J. Lotka. This contribution is the result of a careful reading of their literature and patient research into their work.
KEYWORDS: History/Philosophy, Physical Chemistry, Graduate Education/Research, General Public, Communication/Writing
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INTRODUCTION The topic of chemical oscillations1 is included in many higher education chemistry curricula. 2,3 The most impressive Belousov−Zhabotinsky or Briggs−Rauscher reactions are often used in chemical demonstrations for secondary school students or to interest young students in chemistry.4−7 Even if the discovery of the first oscillating chemical reaction is generally attributed to the Russian Soviet chemist Boris Pavlovich Belousov in the 1950s, the evidence of periodic behavior in a chemical reaction was reported by the naturalized American chemist William C. Bray in 1921. A scheme of a hypothetical reaction leading to oscillations of the concentration of intermediates was proposed a year earlier by the Polish−American scientist Alfred J. Lotka. What exactly was the contribution of these two researchers? The goal of this paper is to highlight the importance of their work. It is easy to collect biographical information about the greatest scientists; on the contrary, it is difficult to retrace the events of lesser-known researchers who were pioneers of considerable discoveries or theories. This is the case for periodic or oscillating chemical reactions, which had as forerunners the chemist W.C. Bray and an “atypical” chemist A.J. Lotka.
one of the founders of modern physical chemistry. There he got his Ph.D. in 1905 discussing a thesis on reaction kinetics and mechanisms of halogen halides and oxo-compounds (published in Z. Physik. Chem. and Z. Anorg. Chem., 1906). Bray was then invited to join Arthur A. Noyes’s remarkable group at the Massachusetts Institute of Technology, where Bray continued to perform research in inorganic and physical chemistry, particularly of halogen compounds. J.H. Hildebrand follows Bray’s next steps:8 In 1912, he joined the group of enthusiastic young chemists gathered by Gilbert N. Lewis at the University of California at Berkeley. Here, in addition to continuing his research activity, he played a prominent part in developing the methods in both undergraduate and graduate instruction which have had wide influence throughout the United States. Lewis and his co-workers were convinced that research and teaching should be regarded as inseparable activities, and that students should begin doing research in their first year in order to have, down the road, graduate students who are eager and skilled in research.8 In this context, particular mention must to be made of Bray’s book Laboratory Manual of General Chemistry,9 which greatly influenced chemistry teaching (and not only in the United States). Bray was named associated professor in 1916 and then full professor of chemistry at Berkeley, where he worked until his death in 1946.8 Around 1916, Bray was studying the dual role of hydrogen peroxide as an oxidizing and reducing agent together with his student, Asa L. Caulkins. The reactions they studied were the
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THE CONTRIBUTION OF WILLIAM CROWELL BRAY W.C. Bray was born 1879 in Wingham, Ontario, Canada. After a childhood marred by the death first of his father and then of his mother, young William was entrusted to his great-aunt and great-uncle. He attended the Collegiate Institute of London, Ontario. In 1898, Bray enrolled at the University of Toronto, graduating in chemistry with honors in 1902. Having won a traveling fellowship, Bray went to Leipzig, where he attended the University of Leipzig and studied with Wilhelm Ostwald, © XXXX American Chemical Society and Division of Chemical Education, Inc.
Received: June 9, 2016 Revised: November 22, 2016
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DOI: 10.1021/acs.jchemed.6b00342 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Article
oxidation of iodine to iodate ions and the reduction of iodate ions to iodine, that is 5H 2O2 + I 2 → 2IO3− + 2H+ + 4H 2O
(1)
5H 2O2 + 2IO3− + 2H+ → I 2 + 5O2 + 6H 2O
(2)
both of which are involved in the IO3−, H+/I2 redox couple. This couple was selected by the two researchers because, based on thermodynamic calculations, they expected that it would catalyze the decomposition reaction of hydrogen peroxide: H 2O2 → H 2O + 1/2O2
(3)
Note that eq 3 = (1/10)(eq 1 + eq 2). In his 1921 paper, Bray said10 “Its purpose [of the paper] is merely to describe an interesting phenomenon which was first observed in the summer of 1917 just before the close of Caulkins’ work.” In fact, in 1916, Caulkins presented his thesis, “A Study of the Reactions Involving Hydrogen Peroxide, Iodine and Iodate Ion” (supervised by Bray), for the degree of Master of Arts in Chemistry.11 At that point it had been established that • The reaction in eq 1 was markedly autocatalytic and proceeded rapidly in solutions containing iodate and moderately high concentration of acid (sulfuric). • The reaction in eq 2 proceeded relatively slowly even under the most favorable conditions, namely at very low concentrations of H+. • In all cases, hydrogen peroxide disappeared to a greater degree than would be expected on the basis of eqs 1 and 2, proof that such reactions must be accompanied by the catalytic decomposition of hydrogen peroxide, via the reaction in eq 3. The interesting phenomenon observed by Bray was that, at given concentrations of hydrogen peroxide and iodate in the concentration range of H2SO4 between >0.055 N and
