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Hinshelwood, Cyril Norman

Hinshelwood, Cyril Norman

(b. London, England, 19 June 1897; d. London, 9 October 1967)

Chemistry.

Hinshelwood, the only son of Norman MacMillan Hinshelwood, was educated at Westminster City School. He delayed his acceptance of a Brackenbury scholarship at Balliol College, Oxford, until 1919, in order to work for three years during World War I at Queensferry royal ordnance factory. In 1920 he was elected a fellow of Balliol College. The following year he was appointed science tutor at Trinity College, a post he held until his appointment in 1937 as Dr. Lee’s professor of chemistry at Oxford University, and fellow of Exeter College. He was knighted in 1948. In 1964 he retired from his post at Oxford and became senior research fellow of the Imperial College of Science and Technology, London.

Hinshelwood is noted for his extensive and comprehensive contributions to the development of chemical kinetics, on both the experimental and theoretical levels. These studies earned him the 1956 Nobel Prize in chemistry jointly with N. N. Semenov, particularly for the elucidation of the complex system of reactions constituting the hydrogen-oxygen explosion.

In his earliest work, no doubt influenced by his work experience at Queensferry, Hinshelwood attempted to interpret the decomposition of solid mixtures containing oxidants such as potassium permanganate and ammonium dichromate. He soon turned his attention to the study of reactions occurring in the gas phase, which occupied him for the remainder of his life. One of his most important theoretical contributions to the development of chemical kinetics came from his investigation, with H. W. Thompson, of the propionaldehyde decomposition, begun in the mid-1920’s. The rate was found to fall off at low pressures, whereas at higher pressures the rate of decomposition was higher than could be accounted for on the basis of Lindemann’s theory of collisional activation. To Lindemann’s theory Hinshelwood added the assumption that the internal energy of polyatomic molecules contributes to the activation energy. These reactions were termed “quasi-unimolecular.” To account for anomalies in the slope of the reaction rate versus pressure curves for the thermal decomposition of nitrous oxide, this theory was later extended to include spontaneous and collisionally induced transitions to different internal states (for instance, triplet) of the molecule.

In the course of a series of studies on the pyrolysis of hydrocarbons, ethers, and ketones Hinshelwood uncovered the inhibiting effect of added nitric oxide and propylene. The occurrence of a limited decomposition rate in the presence of these substances was interpreted to mean that molecular and free-radical decompositions take place simultaneously, with the free-radical process being inhibited by the added gas.

During this period (middle and late 1920’s) Hinshelwood turned to the investigation of the homogeneous reaction between hydrogen and oxygen in the presence and absence of various added gases. Briefly, he found that the reaction was surface-catalyzed at lower temperatures and surface-inhibited at higher temperatures. This discovery paved the way for the elucidation of the various critical explosion limits. The results, summarized in the Bakerian lecture to the Royal Society in 1946, led to the Nobel Prize ten years later.

Hinshelwood also investigated heterogeneous and homogeneous catalytic reactions, and undertook systematic kinetic studies of substituted aromatic molecules in nonaqueous solvents. The latter studies contributed to the development of L. P. Hammett’s theories of energy-entropy relations series of substituted aromatic molecules.

Shortly before World War II, Hinshelwood took up the study of the kinetics of bacterial cells, selecting for his work the nonpathogenic organism Aerobacter aerogenes. Two lines of inquiry developed in this series of studies: the manner of growth when the bacteria are placed in a medium containing new nutrients, to which they must adapt; and the mode of inhibition of growth in the presence of iantibacterial agents. These studies, which occupied more and more of Hinshelwood’s attention, continued until his death and led to the development of a “network” theory of interdependent enzyme balance mechanisms in the bacterial cell. He put forth this theory to supplement currently accepted theories of mutation and selection.

BIBLIOGRAPHY

The nature and scope of Hinshelwood’s contributions are well exemplified in his published books: Kinetics of Chemical Change in Gaseous Systems (Oxford, 1926; 4th ed., 1940); Thermodynamics for Students of Chemistry (London, 1926); The Reaction Between Hydrogen and Oxygen (Oxford, 1934), written with A. T. Williamson; The Chemical Kinetics of the Bacterial Cell (London, 1947); The Structure of Physical Chemistry (New York, 1951); and Growth, Function and Regulation in Bacterial Cells (Basel, 1966), written with A. C. R. Dean.

Ernest G. Spittler

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Sir Cyril Norman Hinshelwood

Sir Cyril Norman Hinshelwood

The English chemist Sir Cyril Norman Hinshelwood (1897-1967) was noted for his contributions to reaction kinetics.

Cyril Hinshelwood was born in London on June 19, 1897, the only child of an accountant who died in 1904. The boy was brought up by his mother. Hinshelwood won a scholarship to Oxford but was unable to accept it because of World War I. He became a chemist at an explosives factory at Queensferry, Scotland, and 2 years later he was appointed assistant chief laboratory chemist. In 1919 he entered Balliol College, Oxford, for the shortened postwar degree course. So sure was his grasp of chemical principles that his tutor, Sir Harold Hartley, recommended Hinshelwood for a fellowship at Balliol in 1920. A year later he was made a fellow of Trinity College, Oxford. He remained there until 1937, when he was named Dr. Lee's professor of chemistry at Oxford, a post he held until his retirement in 1964. He then became senior research fellow at Imperial College, London.

Hinshelwood's lifelong preoccupation with the energetics and rates of chemical reactions may be traced to his work of testing explosives at Queensferry. Early work included studies of the decomposition of solid potassium permanganate, reactions between gases on hot filaments, and reactions taking place in solution. Before long, however, he turned to the kinetics of homogeneous gas reactions. By studying the effects of pressure changes on these reactions, Hinshelwood inferred that in some circumstances molecules might gain the necessary energy to react (activation energy) by mutual collision, but in other circumstances deactivation might occur by this process.

Among the gas phase reactions studied at this time was the deceptively simple reaction between hydrogen and oxygen to form water. By studying the way in which the rate of reaction was affected by temperature and pressure changes and by examining the conditions needed for explosion, Hinshelwood was led to propose a branching chain mechanism. By observing the effect of the wall surface, and especially the ability of nitric oxide to inhibit the reaction, he concluded that free radicals played a key role, postulating as active participants H, O, OH, and HO2.

In the late 1930s Hinshelwood turned to a new field of activity. Recognizing that the growth of bacteria was essentially a complex of chemical reactions, he began to apply kinetic studies to the bacterial cell. He examined the effect of additives such as phosphorus and the alkali metals and concluded that bacteria could adapt to their new environment by a shift in the enzyme balance of their cells. He was able to systematize his results in terms of a "principle of total integration" and give them mathematical expression in his "network theorem."

Hinshelwood played an important part in the consolidation and organization of physical chemistry at Oxford for many years. He was a highly articulate scientist with deep insight into the philosophical implications of his subject, and his lectures were tinged with dry humor and delivered with great clarity. His international reputation was widened by his books. The Kinetics of Chemical Change (1926) was his masterpiece; the successive editions reveal the progressive sophistication that came to his views on his own special subject. The Structure of Physical Chemistry (1951) is a magisterial survey of the whole field from his particular viewpoint. In bacteriology, his early work, The Kinetics of the Bacterial Cell (1946), was followed by Growth, Function and Regulation in Bacterial Cells (1966).

Hinshelwood was knighted in 1948. From the Chemical Society he received the Longstaff and Faraday medals and from the Royal Society the Davy, Copley, Royal, and Leverhume medals. He became president of the Royal Society in 1955. He shared the Nobel Prize in chemistry and was admitted to the Order of Merit in 1956. He had the unique distinction of being simultaneously president of the Royal Society and of the Classical Association.

A man of many parts, Hinshelwood was a very accomplished linguist and had an expert knowledge of subjects as diverse as classical music, Chinese porcelain, and Persian carpets. He died in London on Oct. 9, 1967.

Further Reading

Biographical information on Hinshelwood is in Eduard Farber, Nobel Prize Winners in Chemistry, 1901-1961 (rev. ed. 1963), and Nobel Foundation, Chemistry: Including Presentation Speeches and Laureates' Biographies, vol. 3 (1964). For background see Aaron J. Ihde, The Development of Modern Chemistry (1964). □

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