A
caustic compound,
sodium hydroxide.
Also known as soda lye or
alkali. A very
useful substance -- though it is no longer used regularly for making
soap, it is used in making
hominy grits,
Drano, and
oven cleaner.
If you see "Cocoa processed with alkali" on any chocolate product, rest assured that this means the cocoa has been reacted with lye.