Soap
The alkalies used for soap-making are potash and soda. They must be in a caustic state, and this is produced by dissolving them and passing the solution through newly slacked lime, which takes away the carbonic acid. In this caustic lye the fats are boiled, their glycerine set free, and the soap formed in a state of solution in the water. The soap is obtained in the solid form by boiling this solution until the soap ceases to be soluble and rises to the surface, when it is drawn off into moulds. Castile-soap is composed of olive-oil and soda; oxide of iron is the cause of its mottled appearance. See OILS; PANS; SOAP-KETTLE.