John Shorter University of Hull Hull, England HU6 7RX
I A. G. Vernon Harcourt
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A founder of chemical kinetics and a friend of "Lewis Carroll"
Many laboratory courses in physical chemistry feature an "iodine-clock" experiment. T h e oldest form of this involves the oxidation of iodide ion by hydrogen peroxide in acidic solution, eqn. (1).
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Hz02 + 2Hf + 21- Iz + 2H20 (1) If the reaction is carried out in the presence of starch and a small amount of thiosulfate, the latter removes the iodine instantly as it is formed and the starch-iodine hlue color does not appear until the thiosulfate has been used up. The time interval between mixing the reagents and the appearance of the hlue color is related inversely to the rate of reaction (1) under the given conditions. Through the addition of successive aliquots of thiosulfate solution, the progress of reaction (1) can he followed, ( 1 ). By suitable experiments the reaction may he shown to exhibit first order kinetics in hydrogen peroxide, in iodide, and in acid, as in eqn. (2)
This behavior supports a two-step mechanism, which may be written as in eqns. (3) and (4) H202+ H+ +I-HOI + H++ I-
HOI + H20 slow (3) Iz + Hz0 fast (4) This system was firit itwestigated by A. (;. Vernon Harcourt and W. Eison '11 Oxlind Uniwrsity during the 1W0's.' (21, and their work tugether with that uf Berthelor in France, and 01' (hldherg and M'aap in Nonvay, earal~lish~d Bertholet's l.aw of Mass kction on ;sound basis. Harcourt was Lee's Reader in Chemistry a t Christ Church and a Student (i.e., Fellow) of that College, while Esson was a Fellow of Merton College and a tutor of mathematics there.= This collaboration heean earlv in their careers and continued for half a century. iring this period they each exerted a powerful influence on the teaching and develooment of their resoective subjects a t Oxford, in an era when the classical tradition was dominant. It may uell besignificant that Harcourt found his mathematical partner in mother collegp. The mathenlatics don at Christ Churrh in thr early IdtiO's was the Reverend Charles
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The practical exercise described above is sometimes called the "Hicourt-Esson experiment." William Esson (1839-1916) is only incidental to this article, but we record that he was barn in Scotland and received his higher education at St. John's College,Oxford. He was elected a Fellow of Merton in 1860,heeame F.R.S. in 1869,and was appointed Savilian Professor of Geometry in 1897 (3). Charles Lutwidge Dodgson (1832-1898), mathematician and logician who, as "Lewis Carroll," "used his specialized knowledge to carry theart of nonsense to a peak, and whoat the same time handled a children's story with none ofthe moralizing and sententiousnessof the early 19th century," (4). He became a Student of Christ Church in 1852 and was mathematics tutor 1855-81. Harold Baily Divon (1852-1930), Professor at Manehester University 1887-1922 ( 6 ) . Frederick Daniel Chattaway (1860-1944), Fellow and Tutor of the Queen's College, Oxford, 1909-1935 (7). WNel Vincent Sidmick (1813-1952). Fellow and Tutor of Lincoln College, Oxford, 1901'-1948'(8).
Figure 1. A. G. Vernon Harcourt (1834-1'319). From ref (9).
Lutuidge Dodgiun." not yet wurld-fmnour as "1.ewii Carroll." hut already devi-ing the tales which ultimatelv hecame"Aliw:'s Adventure3 in Wonderland." Alth(~ugh1)odgson wns a fairly ahle mathemat~c~an (a geometrr, in fact like Es
