Directions: Give each child four copper coins. Give each child four containers, one containing ketchup, one containing lemon juice and salt, one containing soy sauce, and one containing vinegar and salt. Have the children dip only half the coin into the ketchup and hold it there for one minute. Wipe it off with a tissue and rinse it in water. Do the same with the other three mixtures. After finished, have the children compare the coins and decide which cleaned the coins the best.