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Named from the Greek word meaning "green twig" (a bright green line is present in the element's spectrum), thallium is a very soft, bluish-white metal that can be cut with a knife. It easily reacts with air, water (especially steam) and most acids. Thallium resembles lead in appearance, but chemically resembles aluminum. Thallium is used in photocells, infrared detectors, solders, and glass that melts at low temperatures. When amalgamated with mercury, thallium depresses mercury's freezing point by twenty degrees. It has been used as an insecticide and rodent poison, as well as in treating skin infections. These uses have been discontinued, due to thallium's high toxicity.