Roxan Guise, age 10, of Niagara Falls, Ontario, Canada, for her question:

HOW DO THEY MAKE SOAP?

Chief ingredients of soap are fats and chemicals called alkalies. Either animal fats or such vegetable oils as coconut and olive oil are used. Most manufacturers use as the alkali a chemical called sodium hydroxide, often called caustic soda or lye.

Until the 1940s most manufacturers used the kettle method of making soap which employed a three story tank that held more than 100,000 pounds of ingredients. Now the continuous process utilizes a hydrolyzes, a three foot stainless steel tube that measures 80 feet in height. Hot water under high pressure is pumped into the top as hot fat enters at the bottom. Because of the pressure, the fat splits into fatty acids and glycerol with the fatty acid rising to the top where it is removed, purified and mixed with alkali to make soap. The continuous process method makes as much soap in a few hours as can be made in several days by the kettle method.