in Heraldry, signifies the wane of Decrement; 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, faces to the left side of the escutcheon, as she does to the right side when in the increment.

DECREPITATION, 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 have a certain degree of adhesion together. This water being quickly reduced into vapour by the heat suddenly applied to it, rarefies and bursts with noise the parts which compress it. The bodies most subject to decrepitation are certain salts, such as common salt, sulphate of potash, nitrate of lead, &c., 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.