the sulphate was widely used as a rodenticide and ant killer. It is odourless and tasteless, giving no warning of its presence the electrical conductivity of thallium sulphide changes with exposure to infrared light, and so it is used in photocells thallium bromide-iodide crystals are used as infrared detectors used, with sulphur or selenium and arsenic, to produce low melting glasses which become fluid between 125 and 150°C originally used in treating ringworm and other skin infections. Its use was limited because of the narrow margin between toxicity and therapeutic benefits A mercury-thallium alloy, which forms a eutectic at 8.5% thallium, freezes at -60°C, some 20° below the freezing point of mercury