Thallium
. Thallium (Greek thallos, “young shoot”), symbol Tl, soft, malleable metallic element that acquires a bluish-gray color upon exposure to the atmosphere. Thallium is in group 13 (or IIIa) of the periodic table . The atomic number of Thallium is 81. Thallium was discovered spectroscopically in 1861 by the British chemist Sir William Crookes. It was isolated by Crookes and, independently, by the French chemist Claude August Lamy in 1862. PROPERTIES AND OCCURRENCE Thallium forms a hydroxide in water, and is soluble in nitric acid and sulfuric acid . It forms two series of salts, represented by thallous chloride, TlCl, and thallic chloride, which are univalent and trivalent, respectively. Thallous oxide, a black solid that, when molten, attacks glass and porcelain, is made by heating thallium in air at very high temperatures. Thallium has a high index of refraction and is therefore important in the manufacture of several types of optical glass. Thallium ranks 60th in abundance among the e