A deliquescent substance is a material that readily absorbs water out of the air. Deliquescent substances keep absorbing water until they dissolve themselves into liquid solutions. This process is called deliquescence.
Soluble salts are examples of deliquescent substances. These include aluminum chloride, sodium nitrate, calcium chloride and potassium oxide. In order for deliquescence to occur, there must be sufficient humidity in the air, and the vapor pressure of the air must exceed the vapor pressure of the saturated solution. Packets containing deliquescent substances are used as desiccants to keep other substances dry. They also serve in chemical applications to remove water formed during chemical reactions.