An acid composed of oxygen and carbon. It abounds in great quantities in nature, and appears to be produced in a variety of circumstances. It composes forty-four hundredths of the weight of limestone, marble, and other natural specimens of calcareous earth, from which it may be extricated by the simple application of heat, or by the superior affinity of some other acid, most acids having a stronger action on bodies than this. It is composed of 72 parts of oxygen, and 28 of carbon, and its spec. grav. is 1.5236, that of atmospheric air being 1.0000. See Aerated Waters.