Carbonic acid is rapidly evolved, and may be collected, with some loss, over water in the pneumatic trough. If required dry, the gas must be passed over fragments of fused chloride of calcium, placed in a large tube, or through a small quantity of concentrated sulphuric acid, and collected by displacement or over mercury.
From oil of vitriol, 1 part; water, 6 parts; and chalk or whiting, 11⁄4 part; mixed in a suitable vessel, applying agitation.
Prop. Under ordinary conditions carbonic acid is a colourless, non-inflammable, irrespirable gas, possessing a slightly pungent odour, and an acidulous taste. Water absorbs its own volume of this gas, and by pressure may be made to take up enormous quantities, forming carbonated or aërated water. Its sp. gr. is 1·520; hence it may be poured from one vessel to another like water. By a pressure of thirty atmospheres at 32° Fahr. it is liquefied, the pressure required decreasing as the temperature gets lower. At -94° Fahr. it solidifies into a vitreous transparent mass.
Carbonic acid, even when greatly diluted with air, cannot be inhaled without insensibility following. An atmosphere containing more than its natural quantity of gas (1 part in 2500 parts by measure) acts upon the system as a narcotic poison; hence the danger of over-crowded rooms. It is a non-supporter of combustion, at once extinguishing a lighted candle, gas-jet, or even a piece of burning phosphorus, when these are placed in a jar of the gas.
Tests. It feebly reddens litmus paper, extinguishes the flame of a burning taper, and forms a white precipitate in aqueous solutions of lime and baryta, which is soluble in acetic acid. By the last test a very small quantity of this gas may be easily detected in the atmosphere of rooms, &c. A lighted candle is generally used to test an atmosphere suspected to contain carbonic acid: but it is found that
air that will support combustion will contain sufficient of this gas to cause insensibility.
Ant., &c. The patient should be immediately removed into the open air, and placed on his back with the head slightly raised. Cold water should be dashed over the body, hot water or mustard poultices applied to the feet, and ammonia (carefully) to the nostrils. Brandy-and-water and other stimulants may be administered. Continued friction on the surface of the body is also very useful. If the patient has ceased to breathe artificial respiration should be attempted. This may be done by gently pressing down the ribs, and forcing up the diaphragm, and then suddenly withdrawing the pressure. The inhalation of air, mixed with very little chlorine gas, has also been recommended. Wells, cellars, or other underground apartments, containing carbonic acid in poisonous quantities, may be freed from this gas by pumping it out in the same way as water, observing to allow the suction hose to fully reach the floor or bottom of the place. Fresh slaked lime or milk of lime, copiously thrown in, will have a like effect, by absorbing the gas. Free ventilation, whenever it can be established, is, however, not only the cheapest, but the most efficient remedy. See Asphyxia.
CARBON′IC OXIDE. CO. Syn. Protoxide of carbon, Carbon monoxide, Ga′seous oxide of carbon; Oxy′dum carbon′icum, L. A gaseous compound of carbon and oxygen, containing less oxygen than is contained in carbonic acid.
Prep. 1. From carbonic acid gas passed over fragments of charcoal, heated to redness in a tube of porcelain or iron.
2. From crystallised oxalic acid, gently heated with 5 or 6 times its weight of strong sulphuric acid in a glass retort.