Reading Selection, Lesson 16
Getting Taken to the Cleaners
Early forms of dry cleaning used petroleum solvents such as kerosene. But kerosene is flammable—it burns. After a series of explosions at dry cleaners, the solvent tetrachloroethylene was widely adopted, and it is still used today (along with other solvents). Tetrachloroethylene is not flammable, but its fumes can be toxic in enclosed spaces. That is one reason why, if dry-cleaned clothes smell strongly of solvent, you should drive home from the dry cleaners with your car windows open.
How does dry cleaning work? A dry-cleaning machine is like a giant washing machine. Clothes are placed in the machine. Tetrachloroethylene, mixed with a very small amount of water and a special detergent, is added. (Water is added to remove any stains caused by water-soluble substances.) The tetrachloroethylene flows continuously through the machine until the clothes are clean. Any solvent that remains in the clothes after the cleaning cycle eventually evaporates. All the remaining solvent is recycled. It is heated until it evaporates and then cooled until it condenses to produce a clean solvent that can be used again.
A new approach to dry cleaning has been developed. This method does not use any toxic dry-cleaning solvents. Special detergents and carbon dioxide, which is the solvent, clean the clothes. The carbon dioxide, which is normally a gas in air and is not harmful to the environment, is put under pressure during the cleaning process. This pressure keeps the carbon dioxide in a liquid state. Both the special detergents and the carbon dioxide can be recycled. Will this more environmentally friendly approach be the future of dry cleaning?
1. Why do people who own washing machines still go to the dry cleaners?
2. Can you suggest two advantages of recycling the solvents used in the dry-cleaning process?
3. Heat generally causes materials to expand. If this is true, why do some fabrics shrink when washed?