Lewis, William Cudmore McCullagh (1885–1956), physical chemist, was born 29 June 1885 in Belfast, the only son of the five children of Edward Lewis, linen merchant, and his wife, Frances Welsh McCullagh, daughter of Rev. William Cudmore McCullagh of Ballysillan presbyterian church, Belfast. Educated at Bangor grammar school, Co. Down, he entered QCB as a medical student but changed to a course in experimental science, graduating BA in 1905 with first-class honours in chemistry and physics. In 1906 he obtained MA with first-class honours and a university studentship in experimental science.
Lewis worked as a demonstrator in chemistry for a year, then left QCB to pursue research at the University of Liverpool under the newly appointed professor, Frederick George Donnan (qv), a fellow Ulster man and his father's first cousin. Upon completion of a very successful experimental study of Willard Gibb's theory of surface concentration he was awarded a scholarship enabling him to study for one year at Heidelberg with Georg Bredig (1866–1944), a distinguished colloid chemist. He returned to England in 1909 and was appointed demonstrator, then lecturer, at University College, London (1910). By this time his contributions to physical chemistry had attracted considerable attention, and in 1913 he succeeded Donnan in the chair of physical chemistry at Liverpool. He held this position until his retirement, on account of ill health, in 1948. During his tenure the department was one of the best schools of chemistry in the UK. He was elected a fellow of the Royal Society in 1926.
Although Lewis felt his insufficient mathematical training held him back, much of his best work was of a theoretical nature, and his early studies on the nature of chemical mechanism and catalysis pointed the way to the future use of statistical mechanics in chemistry. In 1918 he proposed a theory for chemical change which formed the basis for subsequent developments in this subject. He was widely known for his book A system of physical chemistry (1916, 1919), the first work in the English language on physical chemistry for senior students. It was the standard text for two decades and went into four editions in ten years. Written at a time when the subject was growing rapidly, it exerted a wide and lasting influence on physical chemistry in the UK. The task of preparing it was a huge undertaking and revealed Lewis's great understanding of the many developments occurring at that time.
In the years immediately following the first world war Lewis collaborated with the Liverpool Cancer Research Organisation. Formed by Professor W. Blair-Bell, this body invited professionals at the university to apply their specialist knowledge to the problems of cancer. This experience greatly influenced Lewis, and his research interests began to focus more on the area of biological and physiological problems. He studied the physico-chemical processes underlying malignancy, and he carried out a detailed study of the properties of proteins.
Lewis was a pioneering researcher who made several contributions to physical chemistry, most notably in the areas of chemical change and colloid science. Much of his work was well thought out and, though not always successful, some of the projects were undertaken before the development of techniques which would have helped considerably with the research.
Though extremely retiring, Lewis was a friendly professor, always ready to give advice or listen sympathetically to the difficulties of his students and colleagues. A man of broad outlook and considerable knowledge of many fields, he admired Samuel Johnson and was knowledgeable about early English architecture. He was sincere and kindly, with a keen sense of humour, and was devoted to university ideals, especially to research. Having been brought up in the presbyterian tradition, he remained a loyal churchman throughout his life. He married in 1914 Jeanie Waterston Darrock (Darroch); she was of Scottish extraction and her family had settled in London. Lewis died 11 February 1956 at home in Malvern. A bibliography of his ninety-four publications is included in the Royal Society memoir.