in Heraldry, signifies the wane of the moon from the full to the new. The moon in this state is called moon decrecent or in decours; and when borne in coat armour, she faces to the left side of the escutcheon, as she does to the right side when in the increment.

DECRIPITATION, in Chemistry, signifies the quick separation of the parts of a body, occasioned by a strong heat, and accompanied with a crackling noise. This effect is most frequently produced by water contained betwixt the parts of the decrepitating body, when these parts possess a certain degree of adhesion. This water being quickly reduced into vapour by the heat suddenly applied to it, rarefies and bursts the parts which compress it, with a crackling noise. The bodies most subject to decrepitation are certain salts, such as common salt, sulphate of potash, nitrate of lead, and the like, the decrepitation of all which proceeds from the water of their crystallization. Clays which are not perfectly dry, and flints, are also subject to decrepitation.