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A chemical reaction in which an ester compound is reacted with a metal alkali to form a metal soap and an alcohol. Saponification reactions have been used since ancient times to make soap from fats and oils. In this process, melted fats or vergatable oils are placed in the kettle, and caustic soda or lye, solution is added gradually. As the saponification reaction slowly takes place, the heated mixture gradually thickens or emulsifies as the caustic soda reacts with the fat to produce soap and glycerol. The soap is purified in salt bath, rinsed in water then separated into two layers. The top layer, called kettle soap, is composed of about 70% soap and 30% water. The botton layer, called nigre soap, contains soap (15-40%) mixed with the denser impurities such as dirt, ash, salt and excess alkali.

Synonyms and Related Terms

saponify; soap; kettle soap; nigre soap

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