The NaOH is a colorless transparent crystal, and its relative density is 2.130, the melting point is 318.4℃ and boiling point is 1390 ℃. There are two kings of NaOH in market: solid state and liquid state. The pure solid state NaOH is white, and has many shapes. The pure liquid state NaOH is colorless transparent liquid. The solid state NaOH has strong hygroscopic, it is easy to mix with water, and then release the heat.