Appearance and Characteristics
Harmful effects:
Thallium and its compounds are highly toxic. The average oral lethal dose is estimated to range from 10 to 15 mg of thallium per kg of body weight.
Agatha Christie made use of thallium’s toxicity in her novel The Pale Horse. One symptom the victims experienced, including one of the amateur investigators, was that their hair came out in clumps.
Characteristics:
Thallium is a very soft, malleable, lustrous low-melting, silvery metal that tarnishes in air to the bluish-gray oxide. In appearance it resembles lead. The metal can easily be cut with a knife. In the presence of water, the poisonous thallium hydroxide (TlOH) is formed. Thallium dissolves slowly in hydrochloric acid and dilute sulfuric acid and dissolves rapidly in nitric acid.
Uses of Thallium
Thallium sulfate, which is odorless and colorless, was used as a rat poison and as an insecticide. This use has been discontinued in some countries, including the USA.
Thallium sulfide is used in photocells because its electrical conductivity increases on exposure to infrared light. Thallium oxide is used to make glass that has a high index of refraction. Thallium is also used in gamma radiation detection equipment.