THALLIUM

Thallium was discovered in 1861 by Sir William Crookes (and independently by Claude-Auguste Lamy a year later) and occurs in the lithosphere at 0.7 ppm. The name thallium is in reference to the particularly bright green spectral lines seen in the spectra resultant from a flame spectroscopy test (from Greek thallos, meaning a green shoot or twig), the one used in its discovery. Thallium is a heavy metallic element that exists in the environment mainly combined with other elements (primarily oxygen, sulfur, and the halogens) in inorganic compounds.