CHEMISTRY. 



[CARBONIC ACID. 



4~. Iti production. Use the hydrogen 

 M. illustrated in 



1 1; and intrndm-i- 

 into it a quantity of 

 marble, or chalk, bro- 

 ken into small pieces, 

 but not powdered ; on 

 this pour a little water, 

 and add half as nm h 

 hydrochloric acid, so 

 as to half fill the bot- 

 tle. Fit in the bent 

 tube, and let it dip into a tall gloss jar, so as to reach to 

 the bottom, as in Fig. 52. The acid will take the lime 

 away from the marble, and the gas will pass into and 

 fill the jar. This gas is very heavy, and will not escape 

 until the glass is full : at the same time a small piece of 

 card may just bo placed over the mouth of the vessel, to 

 prevent the action of currents of air. 



f'xi>triment 48 Dip a lighted taper into the jar ; the 

 flame will be immediately extinguished. 



Ef)>triment 49. Into a glass jar put a small piece of 

 r>t . ss. Fig. M. taper or candle, by tying it to a 



wire (Fig. 53), and let the candle 

 rest at the bottom of the jar, after 

 having first lit it. Now take 

 another jar tilled with the gas, 

 and pour its contents into the first 

 one, in the same way as if water 

 were being poured out. Owing to 

 its great weight the gas will pass 

 into the vessel holding the taper, 

 and extinguish the flame (Fig. 54). 

 These two experiments illustrate 

 the deadly nature and weight of 

 the gas ; and suggest very simple means of prevent- 

 ing loss of life, to persons who have to descend into 

 mines, vats, or other places where this gas is often 

 bond. 



rimrnt 50. Half-empty a jar of this gas by tilt- 

 iiig it on one side for a few seconds ; then dip in a lighte.l 

 taper. It will be found that the taper will burn until it 

 reaches the part where the heavy gas is, when it will at 

 once go out This simple experiment shows how it often 

 occurs that human lives are lost, by persons descending 

 deep wells or vats, which frequently contain large 

 quantities of carbonic acid gas. In the upper part no 

 gas will be found ; whilst, owing to its density, it may 

 be in quantities in the lower part. Every deep vessel or 

 place should thus be tried by means of a lighted cainlle, 

 before any person is allowed to descend into it. If the 

 flame be not extinguished, then little danger can arise ; 

 on the other hand, if it be extinguished, no attempt 

 should be made to descend until some means have been 

 adopted to ventilate the place. This may be done 

 by letting down large chauffers of burning coal, which 

 will produce currents of air; or quantities of slak.-.l 

 lime may be cast in, so as to absorb the carbonic 

 acid gas. 



A very large amount of carbonic acid is produced by the 

 combustion of candles, coal, coke, and charcoal ; and that 

 produced from the last-named material has often been 

 employed for suicidal purposes. Lime-water is the best 

 test for the presence of carbonic acid, an the gas instantly 

 forms chalk, or carbonate of lime, on coming in contact 

 with the lime !> ', 1 in solution. Lime-water is readily 

 made by shaking up some fresh-burnt lime with cold 

 water, and decanting off the clear transparent solution, 

 which alone must be used. The following experiments 

 will illustrate the fact that carbonic acid is produced by 

 respiration and combustion. 



Erprrimrnt 51. Pour into a small glass a little lime 

 water, and then, by means of a glass tube, blow from 

 the mouth into the water. After a short time, the lim.- 

 water will become milky, owing to the carbonic acid 

 driven from the longs combining with the lime, and 

 forming chalk. 



Rzprriment 52. Arrange a piece of apparatus as in 

 the diagram, Fig. 55. On the right is a small furnel 



suspended over a candle ; the funnel is connoctwl with 

 the purifier used in making oxygen (see Fig. 15) ; acd 



o ML 



;. 



the air is drawn from over the lighted candle through 

 lime-water contained in the purifier, by sucking at the 

 small tube. The gas produced by the burning candle 

 will form chalk in the purifier with the lime-water ; and 

 thus the products of combustion are shown to be the 

 same as those obtained from the breath as expired from 

 the lungs. 



Similar results obtained as above from the pro- 

 ducts of respiration and combustion, may not at first 

 sight appear easy of comprehension by some of our 

 readers ; we, however, can readily explain them. The 

 candle contains carbon as one of its constituents; and 

 during combustion, that carbon becomes converted into 

 carbonic acid. The food wo partake of also contains 

 carbon ; and this, in the blood, comes in contact with the 

 oxygen of the air on the surface of the lungs. It there 

 undergoes a slow process of combustion, and produces 

 carbonic acid gas. Indued, there is every possible 

 analogy between the production of heat in our furnaces 

 and in our lungs, by an identical process carried on at 

 different degrees of intensity. The following experiment 

 will prove the presence of charcoal in sugar. 



Experiment 53. Make a strong solution of sugar in 

 hot water, and add to it some concentrated sulphuric 

 acid. The latter will seize the water in the sugar, and 

 set free its charcoal, as a dense, spongy, black moss. 



\Ve have already noticed that carbonic acid is present 

 in the atmosphere ; we may here, therefore, call attention 

 to the fact, that whilst poisonous to animals, it forms 

 the food of plants. The leaves of trees act as lungs, and, 

 by means of them, the carbon of the carbonic acid in the 

 air is absorbed into their structure. Thus, three-fourths 

 of a tree are gathered from the air. What is poison to 

 us, becomes the food of plants : they purify what we 

 poison, and return to us the oxygen, so essential to our 

 existence, from the carbonic acid which we have cast off 

 from our lungs. 



Carbonic avid is the cause of the effervescence of malt 

 liquors, sparkling wines, soda-water, Ac. ; and although 

 deathly to the lungs, acts as a healthy stimulant to the 

 stomach : hence arises the invigorating and freshening 



' of the beverages to which wo have referred. 

 l!y means of considerable pressure, carbonic acid may 

 bo liquefied, and even brought into a solid state. This 

 may be effected in a strong bent glass tube, by placing 

 the materials at one end, and receiving the gas at the 

 other. It is, however, more conveniently managed by 

 means of a strong metal apparatus, constructed for the 

 purpose ; which is illustrated in the following engraving. 

 It consists of two parts, joined by means of a pipe. The 

 vessel on the right-hand side of the cut is that into which 

 the materials are introduced ; and the gas passes thence 

 by means of the tube, into the receiver. 



If the gas IK- allowed to pass out of the receiver while 

 in a liquid state, it evaporates so rapidly as to be con- 

 verted into a powdery substance, resembling snow. If 

 this solid carbonic acid be mixed with ether, it produces 

 the most intense cold obtainable l-y any means, owiu? 

 to the rapid evaporation which takes place. 



