CARBON AND CARBONIC ANHYDRIDE. 



106. Carbonic Anhydride not a Supporter of Combustion. 

 A lighted taper introduced into a jar of this gas is extin- 

 guished as quickly as it would be if it were dipped into wa- 

 ter. This is simply because oxygen is absolutely necessary 

 to the continuance of the combustion. There is, it is true, 

 a sufficient quantity of oxygen in the carbonic anhydride, 

 but it is so thoroughly united with carbon that not a par- 

 ticle will quit it to unite with the carbon of the taper. A 

 very pretty way of showing that this gas is not a support- 

 er of combustion, and at the same time that it is heavier 

 than air, is to pour it, as seen in Fig. 24, 



from one jar down into another in which 

 there is a lighted taper. Notwith- 

 standing that carbonic anhydride does 

 not support ordinary combustion, a few 

 substances having a great attraction for 

 oxygen will burn in it. A piece of 

 magnesium wire lighted and plunged 

 into a jar of the gas burns brilliantly, 

 taking the oxygen to itself and leaving 

 the carbon, which appears as a black 

 powder on the sides of the glass jar. 

 The decomposition of the carbonic anhydride is thus ex- 

 pressed : 



Carbonic anhydride, Magnesium, Carbon, Magnesium oxide, 

 CO 2 " + 2Mg C + 2MgO. 



107. Effects of Carbonic Anhydride when Respired. As it 

 is with nitrogen ( 68), so with this gas no animal can live 

 in it. But it destroys life not merely because, like nitrogen, 

 it shuts out oxygen from the blood in the lungs, but it acts 

 also as a positive poison. It produces an effect upon the sys- 

 tem similar to that of some narcotics. Nitrogen is constant- 

 ly taken into the lungs in large quantities without doing any 

 harm, for about four fifths of the air is nitrogen; but if car- 



Fig. 24. 



