Pure sodium hydroxide Alias:caustic soda is a white solid, easily soluble in water, and the aqueous solution has astringency and a greasy feel. Sodium hydroxide easily absorbs water when exposed to the air, the surface is wet and gradually dissolves, and its relative density is 2.130. Melting point 318.4 ºC. Boiling point 1390 ºC. There are two kinds of solid and liquid: pure solid caustic soda is white, in block, flake, rod, granular, and brittle; pure liquid caustic soda is colorless and transparent liquid. Solid caustic soda has strong hygroscopicity. Easily soluble in water, exothermic when dissolving, the aqueous solution is alkaline and has a greasy feeling; soluble in ethanol and glycerol; insoluble in acetone and ether. It is extremely corrosive and has a corrosive effect on fibers, skin, glass, ceramics, etc.