CARBONIC ACID

a term Bt erp to the hypothetical substance H2COs, but more often to the anhydrous form, carbon dioxide CO:, or C.A. gas. Carbon dioxide occurs in the atmosphere to the extent of four volumes in 10,000, though in towns the amount may be larger. It occurs also in solution in river and sea-water, being carried down by rain or liberated from decomposing carbonates in the soil. The gas is produced in large quantities in lime kilns, being formed by the decomposition of the chalk or limestone from which the chalk is made. Fermentation and putrefaction give rise to carbon dioxide, which may exert considerable pre ure if the proce es are carried out in closed ve els. In the laboratory, carbon dioxide is prepared by treating. marble or chalk with dilute hydrochloric acid, but it may generally be stated that all carbonates when treated with most acids yield the gas. O©.A. is a colorle gas about 1.5 as heavy as air, moderately soluble in water; it liquefies at 0° C. under a pre ure of thirty-six atmospheres. It is used in the preparation of aerated waters, quantities being di olved in water under pre ure to produce the sparkling effect when the pre ure is at length removed by releasing the stopper of the bottle.