William Crookes, chemist and science journalist, studied at the Royal College of Chemistry, London, from the age of 16 and from 1849 to 1854 worked there as an assistant to his teacher, the chemist A.W. Hofmann. During this period he investigated new compounds of the element selenium, publishing his first paper in 1851. In 1854 he joined the meteorological department of Radcliffe Observatory, Oxford, where he developed his photographic skills. The next year he lectured in chemistry at the Chester Anglican teacher training college. From 1856 he resided in London (except for extensive travels in Europe) as an independent researcher, consultant and writer. He was a skilled experimenter and set up his own private laboratory. Initially his research related mainly to photography, but later also to various aspects of chemistry and physics. Many of his papers dealt with the rare earths and their compounds. His studies in spectroscopy led to his co-discovery of the element Thallium in 1861. To investigate its atomic weight he made delicate weighings in vacuum and the small eratic swayings of the balance led him in 1875 to devise the radiometer - a set of pivoted light vanes blackened on one side which turned spontaneously in a vacuum under the action of light. The device was patented in 1876. Though not much more that a toy, its motion, caused by the stronger recoil of air molecules from the heated dark side of the vanes, supported the kinetic theory of gasses. His interest in vacuums led him by 1875 to produce an improved vacuum tube, with a much better vacuum than before, to study the effects of electric discharges in rarefied gases. This tube came to be known as a Crookes tube in the English speaking world. In a series of spectacular and ingenious experiments he significantly advanced knowledge of the properties of so-called cathode rays (streams of electrons), proving that they travel in straight lines, are deflected by a magnet, and therefore consist of charged particles rather than electromagnetic radiation. In later years he studied the radioactivity of Uranium and devised the spinthariscope, a device which made visible the impact of individual alpha particles emitted by radioactive materials.
In 1859 Crookes founded the journal Chemical News and Journal of Industrial Science and edited it to 1906. Other journals that he editied were The British Journal of Photography (1854-) and The Journal of Science (1864-1870). He produced numerous publications on a variety of scientific topics, including his Practical treatise on metallurgy (1869), Select methods in chemical analysis (1871), and Dyeing and tissue-printing (1882). His interests included economic and practical problems. For example, in 1898 he delivered an important address on "The wheat problem", arguing that nitrogen famine was a danger to the world and suggesting that it could be avoided by the fixation of atmospheric nitrogen - a practice soon widely applied. His studies included Researches in the phenomena of spiritualism (1874), while he held rather mystical views with regard to the origin of the elements and some other phenomena.
Crookes visited South Africa for the first time in 1896, as an expert witness in the famous legal proceedings relating to the MacArthur-Forrest cyanide process for gold recovery on the Witwatersrand. On 22 February 1896 he addressed the Chemical and Metallurgical Society of South Africa in Johannesburg, describing the latest experiments in Britain on the liquifaction of air and offering some comments on the newly discovered roentgen rays. He also used the opportunity to visit the diamond mines. After his return to England, in November and December 1896, he delivered two lectures on the diamond mines of Kimberley at the Imperial Institute (published in Nature, 1896/7). In June 1897 he delivered a detailed lecture on "Diamonds" before the Royal Institution of Great Britain. It was published in the Institution's Proceedings and dealt with the methods of recovery of diamonds in South Africa, theories of their formation, and their quality. An important prediction made was that iron, at a high temperature and great pressure, will act as a solvent for carbon and will allow it to crystallize out in the form of diamonds.
In 1905 Crookes again visited South Africa, this time as a member of the British Association for the Advancement of Science, which met jointly with its South African counterpart this year. He delivered an evening lecture on "Diamonds" in Kimberley, describing how a blue colour can be induced in colourless diamonds (thus increasing their value) by covering them with radium bromide for a year. The colour was said to persist after heating to a red heat. He published a book on diamonds in 1909, based partly on his two visits to South Africa. During his 1905 visit he and several others were awarded honorary Doctor of Science (DSc) degrees at a special graduation ceremony of the University of the Cape of Good Hope on 17 August.
Crookes was elected a Fellow of the Royal Society in 1863, was knighted in 1897, and received many other honours. He served as president of the British Association (1898), the Chemical Society (1887-1889), the Institute of Electrical Engineers (1890-1894), the Society for Psychical Research (1897), the Society of Chemical Industry (1913), and the Royal Society of London (1913-1915). He was elected an honorary member of the Chemical, Metallurgical and Mining Society of South Africa.