(also known as lye, caustic soda). Comes in fine granule form, sometimes called sodium hydroxide pearls. 99% pure.
Used in soapmaking to turn fats and oils into soap.
WARNING: Sodium hydroxide is a very dangerous chemical.
You must wear safety glasses and gloves at all times.
If sodium hydroxide touches your skin it will sting. Flush the area with cold running water until the stinging has gone. Vinegar and lemon juice remove the sting too.