DIGESTION, in Chemistry, is an operation which consists in exposing bodies to a gentle heat in proper vessels, and during a certain time. This operation is very useful in favouring the action of certain substances upon each other; as, for example, of well calcined, dry, fixed alkali upon rectified spirit of wine. When these two substances are digested together in a matras, with a gentle sand-bath heat, the spirit of wine acquires a reddish-yellow colour and an alkaline quality. The spirit would not so well acquire these qualities by a stronger and shorter heat.