Sodium hydroxide, the chemical formula for NaOH, commonly known as caustic soda, caustic soda, caustic soda, to have a caustic alkali, generally to flake or granular form, soluble in water, soluble in water heating) and formation of alkaline solution, otherwise deliquescence, easy to absorb water vapor in the air (deliquescence) and carbon dioxide (bad), can be in a hydrochloric acid test of whether metamorphism.