Chapman, David Leonard

(b, Wells, Norfolk, England, 6 December 1869; d. Oxford, England, 17 January 1958),

chemistry.

Chapman studied at Manchester Grammar School and Christ Church, Oxford, graduating in 1893 with first-class honors in chemistry. For ten years he was on the staff at Owens College, Manchester, where he worked out the “Chapman equation,” interpreting theoretically the gaseous explosion rates being measured there by H. B. Dixon.

In 1907 Chapman was elected fellow at Jesus College, Oxford, where he taught, conducted research, and superintended the college laboratory until his retirement in 1944. He opened a new field by being the first to carry out rate measurements on a homogeneous gas reaction, the thermal decomposition of ozone. From this he turned to a lengthy study of the photochemical reaction between hydrogen and chlorine, which had given many workers trouble because of its variable behavior. With his students Chapman showed that the mysterious “induction periods” observed were caused by minute traces of nitrogenous materials in the water used in the apparatus and was able to eliminate them.

Next Chapman examined the kinetics and the inhibiting effect of oxygen. For hydrogen-chlorine mixtures of high purity contained in large vessels, he demonstrated that the reaction chain ended in bimolecular recombination of the carriers (chlorine atoms), by showing that rates were proportional to the square root of the light intensity. With hydrogen-bromine mixtures, which also follow the squareroot law, he experimented with light interrupted by a variable-speed sector and was the first to work out the mathematical theory of the rate changes, which made it possible to estimate the lifetime of the bromine or chlorine atoms which acted as chain carriers.

Later, Chapman was interested in catalysis of gas reactions by metals; and during World War II some work for the “Tube Alloy” program (the British program to further development of an atom bomb) was carried out in his laboratory.

He was elected fellow of the Royal Society in 1913.

BIBLIOGRAPHY

A fuller account of Chapman’s work and a complete list of his publications (43 papers) is given in Biographical Memoirs of Fellows of the Royal Society, 4 (1958), 35.

E. J. Bowen