Discovery of thallium

Thallium was discovered in 1861 by the English chemist William Crookes in London, who found a bright green line in the spectrum of residues from a sulfuric acid plant while searching for tellurium. The French chemist Claude-Auguste Lamy independently isolated the metal in 1862, and a dispute followed over who had priority. The name comes from the Greek thallos, meaning green shoot or twig, referring to the colour of the spectral line. Thallium is a soft, heavy metal that tarnishes quickly in air. Its salts are tasteless and highly poisonous, and thallium was once used in rat poison and ant poison and gained a reputation as a poisoner's weapon, so that most countries have restricted its use. Modern uses include electronics and medical imaging.

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