Book describing the discovery of thallium and six specimens, 1861.
© Science Museum / Science & Society Picture Library
Thallium was discovered spectroscopically in 1861 by William Crookes (1832-1919) who isolated it by its green line. It is a rare soft white metallic element, occurring naturally in zinc blende and some iron ores. The book is an article written by the Fench chemist C A Lamy, who independently also isolated Thallium, leading to a scientific controversy over who discovered the element first. The specimens are Crookes' and contain a sample of Thallium as well as five of its compounds.