CROOKES, SIR WILLIAM English chem ist and physicist, was born in London on June 17, 1832. He studied chemistry at the Royal College of Chemistry and became an assistant under A. W. von Hofmann. In 1854 he became assistant in the meteorological department of the Radcliffe ob servatory, Oxford, and in 1855 he obtained a chemical post at Chester. From the time of his marriage in 1856 to Ellen Hum phrey he lived in London, devoting himself uninterruptedly to scientific work of various kinds. He founded and conducted the Chemical News, and had a private laboratory at his house in Kensington Park gardens. He was knighted in 1897 and received the Order of Merit in 191o. He was president at different times of many learned societies; from 1913-15 he was president of the Royal Society. He died in London on April 4, 1919.
In 1861 spectroscopic observations on the residue from the manufacture of sulphuric acid led Crookes to the discovery and isolation of thallium, a specimen of which was shown in public for the first time at the exhibition of 1862. In the course of investigations on the properties of thallium he observed the curious behaviour of the hot element while being weighed in vacuo. This led Crookes to construct the radiometer (q.v.).
His researches on the electrical discharge through a rarefied gas led to the observation of the dark space which bears his name, and Crookes developed his theory of "radiant matter" or matter in a "fourth state." (See ELECTRICITY, CONDUCTION OF : Gases.) In 1883 Crookes began an enquiry into the nature and consti tution of the rare earths, his observations on yttrium led him to the theory that all elements have been produced by evolution from one primordial stuff. He succeeded in artificially making minute diamonds ; and on the discovery of radium he took up the study of its properties. He invented the spinthariscope which shows the presence of traces of radium salt by the production of phosphorescence on a zinc sulphide screen. Crookes was constantly con sulted by the Government on chemical questions, and one of his many practical contributions to the public welfare was his production of a glass which would effectively shield the eyes of the workers from the deleterious rays emitted from molten glass.
Crookes wrote or edited various books on chemistry and chemical technology, including Select Methods of Chemical Analysis, which went through a number of editions. He was a keen student of psychic phenomena and sought to effect some correlation between them and ordinary physical laws.