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Crookes, Sir William

studied found chemistry light

(1832–1919) British chemist and physicist: discovered thallium; studied ‘cathode rays’; predicted need for new nitrogenous fertilizers.

The eldest of 16 children of a London tailor, little is known of his childhood. Crookes was a student in the Royal College of Chemistry from 1848, and became assistant. After two modest teaching jobs he inherited some money, returned to London and set up a personal chemical research laboratory. He was also editor and proprietor of the influential Chemical News from 1859–1906.

In 1861 he examined the spectrum of crude selenium and found a new bright green line. From this clue he was able to isolate a new element, thallium; he studied its rather strange chemistry and measured its relative atomic mass. The accurate weighings for this (done in a vacuum) led to his invention of the Crookes radiometer, in which four light vanes, each with one face blackened, are pivoted in a glass container with gas at a low pressure. In light, the vanes rotate; the device helped to confirm the kinetic theory of gases. He also studied electrical discharges in vacuum tubes, already studied by J Plücker (1801–68) and J W Hittorf (1824–1914). Crookes found that the ‘cathode rays’ travelled in straight lines, could cast shadows, heat obstacles and be deflected by a magnet; he concluded they were negatively charged particles but this found little support until studies (20 years later) firmly identified them as electrons. Crookes also invented the spinthariscope (1903; Greek for ‘spark-viewer’) to detect the alpha-particles (helium nuclei) emitted by radioactive elements. This consists of a screen coated with ZnS and viewed by a lens: each impacting particle causes a visible light flash. Crookes also studied a variety of problems in technical chemistry (sugar from beet; textile dyeing; electrical lighting; antiseptics; sanitation; diamond formation) and especially the need to produce fertilizer from atmospheric nitrogen if soil fertility was to be maintained (1898). He had much scientific imagination, and he also experimented in spiritualism, suggesting that telepathy resulted from wave communication between brains. His long, active life covered a most interesting period in science.

Cross [next] [back] Cromwell, Thomas, Earl of Essex (1485–1540) - BIOGRAPHY, CRITICAL RECEPTION

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