Precipitation is the process of separating solid particles from a solution by the action of either heat, light, or chemical substances. The solid particles separated are called the precipitate, and the liquid remaining the supernatant liquid. A precipitate may either fall to the bottom or rise to the top of the supernatant liquid. Precipitation caused by the action of heat is illustrated by the coagulation and precipitation of albumin, when albuminous fluids, such as the white of egg, are heated; precipitation of silver salts by light as in photography illustrates precipitation by light; and precipitation by chemical reaction occurs in many instances when salts are mixed in solution.

The objects of precipitation are: (1) to convert solid substances into the form of powder; (2) to purify liquids; (3) to test chemicals; and (4) to separate chemical substances.

There is a distinct difference between a sediment and a precipitate; a sediment is a solid matter separated merely by the action of gravity from a liquid in which it has been suspended. A precipitate, on the other hand, is a solid matter separated from a solution by chemical means.