Caustic Soda is the chemical Sodium Hydroxide (Chemical Formula), also known as lye. In its purest form, the caustic, highly toxic, crystalline solid is an inorganic compound that is soluble in water and insoluble in ether and other non-polar solvents. Caustic soda has many industrial applications that include the manufacture of pulp and paper, textiles, drinking water, soaps, detergents, and drain cleaner.