613 



CARBONIC ACID. 



CARD-MAKING. 



614 



decomposed by heat ; but the carbonates of potash and o soda do not 

 suffer any alteration by exposure to it. For the various carbonates see 

 the different alkaline, earthy, and metallic bases. 



CARBONIC ACID (CO,). There are two inorganic compounds of 

 carbon and oxygen, namely, carbonic oxide, consisting of one equiva- 

 lent of each of its elements, or six parts of carbon and eight of oxygen ; 

 and carbonic acid, formed of one equivalent of carbon and two equiva- 

 lents of oxygen. 



Carbonic acid was long known and observed to exist in various 

 forma, and to be produced in different circumstances, before its nature 

 was understood and its composition ascertained. Van Helmont recog- 

 nised it as a peculiar matter, and called it gas syheslre ; Hales supposed 

 it to be spoilt common air ; Black gave it the name of fixed mr, and 

 made many curious and original experiments upon some of its com- 

 pounds, showing that the causticity of the alkalies and lime depended 

 upon its absence ; Bergmann proved that it was an acid, and called it 

 aerial acid ; but Lavoisier first pointed out its true nature, and in 

 consequence of his discovery it received the name of carbonic acid, 

 which it still retains. 



Carbonic acid exists largely in nature. It is in comparatively small 

 quantity in the gaseous state in the atmosphere ; it is in solution in 

 most spring water, and in some called mineral waters to a considerable 

 degree ; but it is in solid combination that carbonic acid is found in 

 the largest quantity, forming nearly 44-100ths of all limestones and 

 marbles, besidr-s occurring in less amount united with other earths and 

 metallic oxides. 



Carbon and oxygen do not appear to combine, or, if at all, very slowly 

 at common temperatures, by direct action ; but certain compounds 

 which contain carbon, when undergoing the process of fermentation, 

 yield a large quantity of carbonic acid. [FERMENTATION.] 



It is also produced during the process of respiration ; by animal and 

 vegetable putrefaction; and by combustion, whether of oil, wax, 

 tallow, vegetable matter, or coal. 



Carbonic acid may be formed by the combustion of either charcoal 

 or the diamond in oxygen gas ; and it is found, that when 100 cubic 

 inches of oxygen have combined with as much carbon or diamond as 

 this quantity of gas is capable of taking up by combustion, there 

 remains precisely as much in volume of carbonic acid gas as there was 

 of oxygen employed. Thus 100 cubic inches of oxygen, weighing 

 84'4 grains, combine with 12'9 grains of carbon without any alteration 

 of volume, and consequently 100 cubic inches of this gas weigh 47'3 

 grains, or its density is to that of atmospheric air as 1'526 to 1. By 

 some chemists it is hypothetically regarded as composed of one volume 

 of oxygen gas and one volume of the vapour of carbon, condensed 

 into one volume. By weight it consists of 



2 equivalents of oxygen = 16 

 1 carbon = 6 



Equivalent = 22 



It contains twice as much oxygen as the bases which it saturates to 

 form neutral carbonates. 



When carbonic acid is required for experiment, it is usual to 

 evolve it by decomposing a carbonate, rather than to form it by the 

 combination of its elements as above described. For this purpose 

 carbonate of lime, or chalk, or marble, may be put into a retort, and 

 dilute hydrochloric acid being poured upon it, carbonic acid is plenti- 

 fully given out; and although this gas is to a certain extent 

 soluble in water, it may be received in jars filled with and inverted in 

 water. 



Carbonic acid gas is colourless and transparent, and therefore in- 

 visible ; it has an acid and slightly astringent taste ; it reddens litmus 

 paper, but the blue colour returns as the acid volatilises. It extin- 

 guishes burning bodies, and is fatal to animals. On account of its 

 great density, it diffuses slowly in the air, and hence it is apt to remain 

 long in fermenting vats, old wells, &c., and has frequently produced 

 fatal effects upon persons descending into them. Atmospheric air 

 may however contain l-20th of its volume of this gas, and be respired 

 without becoming hurtful. On account of its great weight, it may be 

 poured from vessel to vessel, as is shown by its extinguishing a taper 

 repeatedly. 



Carbonic acid, though gaseous at common temperatures and pres- 

 sures, may be compressed into a liquid state, as shown by Mr. Faraday ; 

 and by the more recent experiments of M. Thilorier, it has been 

 rendered even solid. Mr. Faraday's method of operating may be seen 

 in the 'Phil. Trans.' for 1823. The liquid carbonic acid produced is 

 limpid, colourless, extremely fluid, and refracts light less than water 

 At 32 it requires a pressure of thirty-six atmospheres to retain 

 it in a liquid state ; in endeavours to open the tubes at one end, they 

 always burst into fragments with a powerful explosion. M. Thilorier 

 found that a jet of liquid carbonic acid received in a glass vial expanded 

 to about 400 times its own volume, and by this produced so great a 

 degree of cold, that one part of the carbonic acid congealed into a white 

 powder, adhered to the glass, and retained its solidity for some 

 minutes without pressure. Solid carbonic acid is now frequently made 

 in large quantities by this process, and is employed for producing in- 

 tense cold : by its aid mercury may be almost instantly frozen, even in 



a red hot vessel. [FREEZING MIXTURES.] It has already been men- 

 tioned that carbonic acid gas is soluble in water, and various contrivances 

 have been adopted for impregnating water and saline solutions with it, 

 to imitate natural mineral waters. Among these, Dr. North's appa- 

 ratus is well known, and is described in most works on chemistry. At 

 the average temperature and pressure, water takes up its own volume 

 of carbonic acid gas, and xinder a pressure of two atmospheres it 

 dissolves twice its volume, and so on. The water thus impregnated 

 becomes brisk and tart, and reddens litmus paper : when the water is 

 boiled, the carbonic acid is expelled. Carbonic acid is detected by the 

 properties of extinguishing flame, proving fatal to animals, reddening 

 litmus paper, but not permanently, and giving a precipitate with lime 

 water ; this precipitate is carbonate of lime, which is re-dissolved by an 

 excess of carbonic acid, and re-appears when that excess is expelled by 

 heat. 



Carbonic acid, though in small quantity, always exists in the 

 atmosphere, as may be shown by exposing lime-water to the air ; the 

 proportion does not usually exceed about one 2000th of the volume of 

 the air ; it is produced by the processes ,o respiration, combustion, and 

 animal and vegetable decomposition, as already alluded to. 



CARBONIC ETHER. [ETHYL.] 



CARBONIC OXIDE (00), commonly called also oxide of carbon, 

 was first obtained by Dr. Priestley, but its nature and composition 

 were determined by Mr. Cruikshaiik. Carbonic oxide may be pre- 

 pared in various modes : first, by direct action ; if charcoal be made 

 red-hot in a gun-barrel, and oxygen gas from bladders be repeatedly 

 passed over it, the oxygen is converted into oxide of carbon. Dr. 

 Priestley procured it by heating together chalk and iron filings ; in this 

 case the iron takes half the oxygen from the carbonic acid of the chalk, 

 and thus from a compound of two equivalents of oxygen and one 

 equivalent of carbon, the residual gas, which is carbonic oxide, is 

 constituted of one equivalent of each element. 



Another mode of obtaining it with great facility, is to heat oxalic 

 acid in a retort with sulphuric acid. Oxalic acid is a compound of 

 three equivalents of oxygen and two of carbon ; by the action of the 

 sulphuric acid it is separated into carbonic acid and carbonic oxide, 

 which are both evolved in the gaseous state ; if the mixed gases be 

 then passed through a solution of potash, the acid, being soluble ill 

 this liquid, is dissolved, and the carbonic oxide remains nearly pure. 

 The best mode of procuring carbonic oxide is to heat a mixture of one 

 part of ferrocyanide of potassium and nine parts of concentrated 

 sulphuric acid in a capacious flask or retort ; pure carbonic oxide soon 

 begins to be evolved in very large quantity. Carbonic oxide is also 

 produced, along with hydrogen, when steam is passed over ignited 

 charcoal or coke; it is also an invariable constituent in coal gas, 

 which contains on an average about 10 per cent, of this gas. The 

 properties of this gas are, that it is colourless and insipid ; it is but 

 slightly dissolved by water; it is fatal to animals, and extinguishes a 

 taper if immersed in it ; but when it meets with oxygen gas it burns 

 on ignition, and is converted into carbonic acid. It has no action upon 

 blue vegetable colours ; and, unlike carbonic acid, it does not occasion 

 any precipitation in lime water. 



Carbonic oxide is composed of 



1 Equivalent of oxygen = 8 

 1 carbon = 6 



Equivalent = 14 



It is hypothetically considered as constituted of 100 volumes of the 

 vapour of carbon and 50 volumes of oxygen gas, condensed into 100 

 volumes. One hundred cubic inches weigh 30'1 grains ; its density is 

 therefore to that of atmospheric air as '971 to 1. When electric sparks 

 are passed through carbonic acid gas, confined over mercury, a portion 

 of it is converted into carbonic oxide and oxygen gases. 



CARBOVINIC ACID. [ETHYL.] 



CARBUREIC ACID. A synonym for allophanic acid. [ALLOPHANIO 

 ACID.] 



CARBURET, or CARBIDE, a term designating a compound of 

 carbon with certain other bodies, as nitrogen and some of the 

 metals, &c. 



CARBURET OF IRON. [STEEL.] 



CARBURET OF NITROGEN. [CYANOGEN.] 



CARBURETS OF HYDROGEN. [HYDROCARBONS.] 



CARCASS, a shell, or hollow ball of iron, perforated in three places 

 at equal distances from each other, within one hemisphere of the shell, 

 and filled with a composition which burns with violence during eight 

 or ten minutes. When discharged from a mortar or howitzer, the 

 flames issuing from the perforations or fuze-holes set fire to any 

 building on which the carcass may happen to fall. 



CARD-MAKING. The name of cards is given to two kinds of 

 manufactured commodities, so utterly unlike each other that it is 

 difficult to conceive how it came to be so appropriated. One kind of 

 card is a flat piece of pasteboard applied to many purposes of business 

 or pleasure ; the other is a series of sharp metal spikes set into a 

 leather support, for carding or opening the fibres of cotton in the 

 cotton manufacture. We shall describe the manufacture of both these 

 kinds of cards, keeping them distinct, on account of their possessing no 

 other connection than that due to the similarity of name, 



