# Dictionary of National Biography, 1927 supplement/Crookes, William

​CROOKES, Sir WILLIAM (1832-1919), man of science, was born in London 17 June 1832, the eldest son of Joseph Crookes, a tailor of north-country origin, by his second wife, Mary Scott. He received some instruction at a grammar school at Chippenham, but his scientific career began when, at the age of fifteen, he entered the Royal College of Chemistry in Hanover Square, London, under August Wilhelm von Hofmann. From 1850 to 1854 he filled the position of assistant in the college, and soon embarked upon original work, not indeed in the region of organic chemistry whither the inspiration of his distinguished teacher might have been expected to lead him, but on certain new compounds of the element selenium, the selenocyanides. These form the subject of his first published papers (1851). Leaving the Royal College, he became in 1854 superintendent of the meteorological department at the Radcliffe Observatory in Oxford, and in 1855 was appointed lecturer in chemistry at the Chester training college. In 1856 he married Ellen, daughter of William Humphrey, of Darlington, by whom he had three sons and a daughter. From this time his life was passed in London, and devoted mainly to independent work, journalistic, consulting, and academic. In 1859 he founded the Chemical News, which he edited for many years and conducted on much less formal lines than is usual with journals of scientific societies. After 1880 he lived at 7 Kensington Park Gardens, where in his private laboratory all his later work was carried out.
Crookes’s life was one of unbroken scientific activity. He was never one of those who gain influence by popular exposition; neither was he esoteric. The breadth of his interests, ranging over pure and applied science, economic and practical problems, and psychical research, made him a well-known personality, and he received many public and academic honours. He was knighted in 1897, and in 1910 received the order of merit. At various times he was president of the Chemical Society, the Institution of Electrical Engineers, the Society of Chemical Industry, the British Association, and, from 1913 to 1915, of the Royal Society. He died in London 4 April 1919, two years after his wife, to whom he had been, much devoted.
The work of Crookes extended over the regions of both chemistry and physics. Its salient characteristic was the originality of conception of his experiments, and the skill of their execution. It is probably just to say that his theoretical speculations, imaginative and stimulating as they may have been, were of less permanent importance. He was always more effective in experiment than in interpretation. His first great discovery was that of the element thallium, announced in 1861. By this work his reputation became firmly established, and he was elected a fellow of the Royal Society in 1863. The method of spectrum analysis, introduced by Bunsen and Kirchhoff, was received by Crookes with great enthusiasm, and, on applying it to the examination of the seleniferous deposit from a sulphuric acid factory, he discovered an unknown green line in the spectrum. The isolation of the new metallic element, thallium, followed, and the investigation of the properties of its compounds, which are of great chemical interest. Finally, in 1878, he determined the atomic weight of the new element in a research which is still a model of analytical precision.
Two main lines of research now occupied the attention of Crookes for many years. These were the properties of highly rarefied gases, with which he began to occupy himself immediately, and the investigation of the elements of the ‘rare earths’, upon which he embarked shortly after 1880. His attention had been attracted to the first problem in using a vacuum balance in the course of the thallium researches. He soon discovered the phenomenon upon which depends the action of the well-known little instrument, the Crookes radiometer, in which a system of vanes, each blackened on one side and polished on the other, is set in rotation when exposed to radiant energy. He did not, however, provide the true explanation of this apparent ‘attraction and repulsion resulting from radiation’. Of more fundamental importance were his researches on the passage of the electrical discharge through rarefied gases. He found that as the attenuation of the gas was made greater the dark space round the negative electrode extended, while rays, now known as cathode rays, proceed from the electrode. He investigated the properties of the rays, showing that they travel in straight lines, cause phosphorescence in objects upon which they impinge, and by their impact produce great heat. He believed that he had discovered a fourth state of matter, which he called ‘radiant matter’. But his theoretical ​views on the nature of ‘radiant matter’ proved to be mistaken. He believed the rays to consist of streams of particles of ordinary molecular magnitude. It remained for (Sir) J. J. Thomson to discover their subatomic nature, and to prove that cathode rays consist of streams of negative electrons, that is, of negatively electrified particles whose mass is only 1/1,800 that of the atom of hydrogen. Nevertheless, Crookes’s experimental work in this field was the foundation of discoveries which have changed the whole conception of chemistry and physics. Moreover, it is characteristic of him that, though already advanced in years, he readily and enthusiastically accepted the new interpretation of his work.
For many years Crookes conducted laborious experiments on the elements of the rare earths, elements so similar to one another in chemical properties that special methods for their separation had to be devised. Throughout the work he employed spectroscopic methods for following the course, and testing the completeness, of the separation of one element from another. What had been one of the most obscure regions in inorganic chemistry gradually became clear. In the course of the years during which he was thus occupied, Crookes was led to views on the existence of ‘meta-elements’, or clusters of elements resembling one another so closely that in most ways the cluster behaves as a single individual. The ‘meta-elements’ of Crookes bear a superficial resemblance to the mixtures of isotopes of which some elements are now known to consist; but the theory of meta-elements cannot justly be said to anticipate the discovery of isotopes, since it was based upon facts of a fundamentally different kind from those on which more recent views on isotopic elements are founded.
Turning his attention to the newly discovered phenomena of radio-activity, Crookes, in 1900, achieved the separation from uranium of its active transformation product, uranium-X. He observed the gradual decay of the separated transformation product, and the simultaneous reproduction of a fresh supply in the original uranium. At about the same time as this important discovery, he observed that when ‘a-particles’, ejected from radio-active substances, impinge upon zinc sulphide, each impact is accompanied by a minute scintillation, an observation which forms the basis of one of the most useful methods in the technique of radio-activity.
Crookes published numerous papers on spectroscopy, a subject which always had a great fascination for him, and he made researches on a large variety of minor subjects. In addition to various technical books, he wrote a standard treatise on Select Methods in Chemical Analysis (1871), and a small book on Diamonds (1909), a subject to which he had devoted some study during two visits to South Africa. He frequently served the government in an advisory capacity, and his work on the production of a glass which should cut off from molten glass the rays which are injurious to the eyes of the work-people, may be cited among his many public services.
Sir William Crookes was a great experimenter. His material discoveries are of lasting and fundamental value, though his theoretical speculations have not stood the test of time so well. While it is true that all scientific theories serve primarily only for the suggestion of further research, it must be admitted that Crookes’s analytical power hardly equalled his gift as an investigator of new facts. His excursions into psychical research have been strongly criticized, and they certainly led him into some very curious situations, but they show that he thought all phenomena worthy of investigation, and refused to be bound by tradition and convention. He was a man of science in the broadest sense, an influential personality, and a doyen of his profession.
There is a portrait of Crookes by E. A. Walton in the rooms of the Royal Society, and another by P. Ludovici in the National Portrait Gallery.
[Proceedings of the Royal Society, vol. xcvi, A, 1919-1920 (portrait); P. Zeemann, Scientific Worthies, Sir William Crookes, in Nature, 7 November 1907; E. E. Fournier D’Albe, Life of Sir William Crookes, 1928; Crookes’s own papers and addresses in Transactions of the Chemical Society and Proceedings of the Royal Society.]
C. N. H.