Efflorescence

Efflorescence. Many hydrated substances on exposure to air lose some or all of the contained water with the formation, on their surface, of a powdery deposit. This phenomena is known as efflorescence, and a familiar example is met with in the case of ordinary soda crystals, Nn ,Co3 x 10 OH2, but if exposed to air loses one half of its water of crystallisation. The formation of nitre and sodium carbonates upon the soil in certain localities is also a case of efflorescence.