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What the name means: The name thallium derives from the Greek word thallos, meaning a “budding, green twig”.

Who identified thallium? In 1861, British chemist, Sir William Crookes analysed a sample of residue from an industrial plant that produced sulphuric acid. He had been given the sample because he was interested in finding out if it contained the elements selenium and tellurium. Spectroscopic analysis did not show either of these two elements as being present. However, Crookes saw a vivid green line that did not correspond to any known element at that time. He deduced that he had identified a new element that he called thallium on account of its spectrum. A year later, in 1862, a French chemist named Claude-Auguste Lamy used electrolysis to isolate thallium.

About thallium: Thallium is a soft, silvery-grey metal that tarnishes quickly in the air to form a grey-blue coating. It is a very toxic element that was once used in rat poisons but was considered to dangerous and its use has now been discontinued.