CARBONATED WATER, is water either pure, or holding various saline matters in solution, impregnated with carbonic acid gas. For general sale in this country, the water usually contains a little soda, which being charged with the gas, is called [Soda water]; see this article for a description of an excellent machine for the manufacture of this fashionable beverage.
CARBONATES. Saline compounds in definite proportions, of carbonic acid, with alkalis, earths, and the ordinary metallic oxides.
The carbonates principally used in the arts and manufactures are those of [ammonia], [copper], [iron], [lead], [lime], [magnesia], [potash], [soda]. Native carbonate of copper is the beautiful green mineral called [Malachite].
Carbonates are easily analyzed by estimating either by weight or measure the quantity of carbonic acid which they evolve under the decomposing action of somewhat dilute sulphuric, nitric, or muriatic acid; for as they are all compounds of acid, and base in equivalent proportions, the quantity of acid will indicate the quantity of base. Thus, as pure limestone consists of 56 of lime and 44 of acid, in 100 parts, if upon examining a sample of limestone we find it to give out only 22 per cent. of carbonic acid gas, during its slow solution in muriatic acid, we are sure that there are only 28 parts of lime present. I have described, in the Annals of Philosophy, for October, 1817, a simple form of apparatus for analyzing the carbonates with equal readiness and precision. The simple rule by measure to which I was led, may be thus stated: From the bulk of evolved gas, expressed in cubic inches and tenths, deduct 1⁄20, the remainder will express the proportion of real limestone present in the grains employed. Pure magnesian limestone yields very nearly a cubic inch of the gas for every grain in weight.
CARBONATE OF AMMONIA. A salt called in modern chemistry sesquicarbonate, to denote its being composed of one and a half equivalent primes of carbonic acid, and one of ammonia. It consists by my analysis of 55·89 carbonic acid, 28·86 ammonia, and 15·25 water, in 100 parts. It is generally prepared by mixing from 11⁄4 to 11⁄2 parts of well-washed dry chalk, with 1 of sal-ammoniac, introducing the mixture into an earthen or cast-iron retort, or subliming pot, and exposing it to a heat gradually raised to redness. By double decomposition, the ammonia is volatilized in combination with the carbonic acid of the chalk, and the vapours are received in a condensing receiver made either of glass, stone ware, or lead. The chlorine of the sal-ammoniac remains in the retort, associated with the basis of the chalk in the state of chloride of calcium. Some ammonia gas escapes during the process.
The saline mass thus sublimed is purified by a second sublimation in glass, or salt-glazed earthen vessels. The salt may be obtained, by the above method carefully conducted, in rhomboidal octahedrons, but it is generally made for the market in a compact semi-crystalline white cake. It has a pungent ammoniacal smell, a hot, pungent, alkaline taste, a strong alkaline reaction, and dissolves in two parts of cold water. It must be kept in well-closed vessels, as by exposure to the air a portion of its ammonia exhales, and it passes into the state of the scentless bi-carbonate. It is employed much in medicine, chemical analysis, and by the pastry-cooks to give sponginess to their cakes in consequence of its volatilization from their dough in the oven. See [Sal-Ammoniac].
For the other carbonates used in the arts, see their respective bases; copper, lead, lime, &c.
CARBONIC ACID (Acide carbonique, Fr.; Kohlensäure, Germ.), consists of 1 prime equivalent of carbon = 6·125 + 2 of oxygen = 16·026, whose joint sum = 22·151, represents the atomic weight or combining ratio of this acid, in the neutral or protocarbonate salts. Its composition by volume is stated under [Carbon]. Its natural form is a gas, whose specific gravity is 1·5245, compared to atmospheric air 1·000; and being so dense, it may be poured out of one vessel into another. Hence it was called at first aërial acid. From its existing copiously, in a solid state, in limestones and the mild alkalies, it was styled fixed air by its proper discoverer, Dr. Black. About one volume of it exists in 1000 volumes of common atmospheric air, which may be made manifest by the crust of carbonate it occasions upon the surface of lime water. Carbonic acid gas is found accumulated in many caverns of volcanic districts, and particularly in the grotto dei cani at Pausilippo, near Puzzuoli; being disengaged in such circumstances by the action of subterranean fire, and, possibly, of certain acids, upon the limestone strata. It often issues from fountains in copious currents, as at Franzensbrunn, near Eger, in Polterbrunnen; near Trier; and Byrreshorn. This acid gas occurs also frequently in mines and wells, being called choke damp, from its suffocating quality. Its presence may, at all times, be detected, by letting down a lighted candle, suspended from a string, into the places suspected of containing this mephitic air. It exists, in considerable quantities, in the water of every pump well, and gives it a fresh and pleasant taste. Water, exposed some time to the air, loses these aerial particles, and becomes vapid. Many springs are highly impregnated with carbonic acid gas, and form a sparkling beverage; such as the Selterswasser, from Selters upon the Lahn, in the grand duchy of Nassau; of which no less than two millions and a half of bottles are sold every year. A prodigious quantity of a similar water is also artificially prepared in Great Britain, and many other countries, under the name of aërated or soda water.
Carbonic acid occurs in nature, combined with many salifiable bases; as in the carbonates of soda, baryta, strontia, magnesia; the oxides of iron, manganese, zinc, copper, lead, &c. From these substances it may be separated, generally speaking, by strong ignition, or, more readily, by the superior affinity of muriatic, sulphuric, or nitric acid, for the earth or metallic oxide. It is formed whenever vegetable or animal substances are burned with free access of air, from the union of their carbonaceous principle with atmospheric oxygen. It is also formed in all cases of the spontaneous decomposition of organic substances, particularly in the process of fermentation; and constitutes the pungent, noxious, heavy gas thrown off, in vast volumes, from beer vats. See [Distillation] and [Fermentation]. Carbonic acid is also generated in the breathing of animals; from 4 to 5 per cent., in volume, of the inhaled oxygen being converted, at each expiration, into this gas, which contaminates the air of crowded apartments, and renders ventilation essential to health, and even to life: witness the horrible catastrophe of the Black-hole at Calcutta.