Caustic soda flakes, Density : 2.13 g/cm³

Sodium hydroxide is a highly caustic base and alkali, that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It is highly soluble in water and readily absorbs moisture and carbon dioxide from the air. It forms a series of hydrates NaOH· nH2O. The monohydrate NaOH· H2O cystallizes from water solutions between 12.3 and 61.8 °C. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of the anhydrous compound.