Thallium (Tl), chemical element, metal of main Group 13 (IIIa, or boron group) of the periodic table, poisonous and of limited commercial value. Like lead, thallium is a soft, low-melting element of low tensile strength. Freshly cut thallium has a metallic lustre that dulls to bluish gray upon exposure to air. The metal continues to oxidize upon prolonged contact with air, generating a heavy nonprotective oxide crust. Thallium dissolves slowly in hydrochloric acid and dilute sulfuric acid and rapidly in nitric acid. Rarer than tin, thallium is concentrated in only a few minerals that have no commercial value. Continue reading from Encyclopedia Britannica
The discovery of thallium was controversial. William Crookes of the Royal College of Science in London was the first to observe a green line in the spectrum of some impure sulfuric acid, and realised that it meant a new element. He announced his discovery in March 1861 in Chemical News. However, he did very little research into it.
Meanwhile, in 1862, Claude-August Lamy of Lille, France, began to research thallium more thoroughly and even cast a small ingot of the metal itself. The French Academy now credited him its discovery. He sent the ingot to the London International Exhibition of 1862, where it was acclaimed as a new metal and he was awarded a medal. Crookes was furious and so the exhibition committee awarded him a medal as well. Continue reading from Royal Society of Chemistry
Thallium is a malleable, soft element that can be sliced with a knife. It has a metallic luster that quickly tarnishes when exposed to air to a bluish-green color. Small amounts of thallium are found in manganese nodules on the ocean floor. Thallium is used in photoresistors, infrared optical equipment, low melting glasses and several other applications. Thallium sulfate has been used as a rodent and ant killer because it’s odorless and tasteless. However, the use of the product has been prohibited since 1972 in the United States. Continue reading from LiveScience
