Harcourt, A. G. Vernon

(b. London, England, 24 December 1834; d. Hyde, Isle of Wight, 23 August 1919)

chemistry.

After a typical classical preparation at Cheam and Harrow, Harcourt entered the newly developing chemistry program at Oxford. Initially a student assistant to Benjamin Brodie in the basement crypts at Balliol, he progressed to the Lee Laboratory of Christ Church College and a chemistry professorship. Always active in the British Association for the Advancement of Science (his uncle William Vernon Harcourt having been the principal founder), he served as president of the chemical section in 1875 and later as general secretary for fourteen years. Elected to the Royal Society in 1863, Harcourt gave the Bakerian lecture in 1895, the same year that he was elected president of the Chemical Society.

Harcourt was no academic recluse, and his interest in the technical applications of science led to his appointment in 1872 to the board which prescribed tests and purity standards for London gas. His major contribution in the field of gas testing was to introduce the pentane lamp in place of the less reliable spermaceti candles hitherto used in brightness measurements. At the turn of the century he furthered anesthesia research by devising a method for determining the chloroform concentration in air and served as a consultant in the British Medical Association study of the anesthetic properties of chloroform.

In the realm of pure chemistry Harcourt in 1866, aided by his mathematician colleague William Esson, discovered independently of Guldberg and Waage the law of mass action in its simplest form: “The velocity of chemical change is directly proportional to the quantity of substance undergoing change.” Attracted to reaction rate studies in 1864 by Friedrich Kessler’s suggestion that manganous sulfate accelerates the reduction of potassium permanganate, Harcourt designed experiments which showed that every reactant gives a similarly shaped curve for the effect of concentration on the permanganate reduced during a fixed time period. When the two men examined the time rate of change, they obtained results which Esson identified as an exponential relation between reaction velocity and time.

In 1867 Harcourt and Esson confirmed these observations with data from the somewhat simpler reaction of hydrogen peroxide with potassium iodide but also found that the iodide gave a disproportionate increase at lower acidities. For some unknown reason, their further experimental studies of this acidity effect were not published until Harcourt’s 1895 Bakerian lecture, in which they also reported Esson’s empirical correlation between reaction rate k and absolute temperature T, that is, k/k₀ = (T/T₀)^m—which suggested that at absolute zero all chemical activity would cease. Feeling that due recognition had not been paid, they returned to this question in 1912, comparing their rate-temperature correlation with those more generally used in physical chemistry by van’t Hoff and others. Their purely empirical arguments, however, gave no theoretical support for their contentions.

BIBLIOGRAPHY

Harcourt’s Bakerian lecture is strangely omitted from Poggendorff: IV, 1560; V, 1306; VI, 2751. It may be found as “On the Laws of Connexion Between the Conditions of a Chemical Change and Its Amount,” in Philosophical Transactions of the Royal Society, 186A (1895), 817-895.

Harold Dixon, whom Harcourt led from apparent failure in classics to success in chemistry, wrote a highly appreciative obituary in Proceedings of the Royal Society, 97 (1920), vii-xi.

See also J. R. Partington, A History of Chemistry, IV (London-New York, 1964), 585-587.

Edward E. Daub