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a colourless, dense, nonflammable, highly stable liquid belonging to the family of organic halogen compounds. Tetrachloroethylene is a powerful solvent for many organic substances. By the mid-20th century it had become the most widely used solvent in dry cleaning (displacing carbon tetrachloride and trichloroethylene) and was also commonly used for cleaning metal objects in vapour-degreasing apparatuses. Its broad acceptance has been based upon its nonflammability and low toxicity. Small quantities are also employed as a vermifuge, particularly against hookworm (see ).