Thallium: historical information
Thallium was discovered spectroscopically in 1861 by Crookes. The element was named after the green spectral line, which identified the element (Greek "thallos", green twig). The metal was isolated both by Crookes and Lamy in 1862. They had been expecting to isolate tellurium after removing selenium from the byproducts from a commercial sulphuric acid factory but instead foundthe new element thallium.