879 



CHAPTER IX 



COMPOUNDS OP CARBON WITH OXYGEN AND NITROGEN 



CARBONIC anhydride (or carbonic acid or carbon dioxide, CO 2 ) was th J 

 first of all gases distinguished from atmospheric air. Paracelsus and 

 Van Helmont, in the sixteenth century, knew that on heating limestone 

 a particular gas separated, which is also formed during the alcoholic 

 fermentation of saccharine solutions (for instance, in the manufacture 

 of wine) ; they knew that it was identical with the gas which is pro- 

 duced by the combustion of charcoal, and that in some cases it is found 



FIG. 61. Dumas' and Stas' apparatus for determining the composition of carbonic anhydride. 

 Carbon, graphite, or a diamond is placed in the tube E in the furnace, and heated in a stream of 

 oxygen displaced from the bottle by water flowing from A. The oxygen is purified from carbonic 

 anhydride and water in the tubes B, C, D. Carbonic anhydride, together with a certain amount 

 of carbon monoxide, is formed in E. The latter is converted into carbonic acid by passing the 

 products of combustion through a tube P, containing cupric oxide heated in a furnace. The cuprio 

 oxide oxidises this CO into C0 2 , forming metallic copper. The potash bulbs H and tubes I, J, K 

 retain the carbonic anhydride. Thus, knowing the weight of carbon taken and the weight of 

 the resultant carbonic anhydride (by weighing H, I, J, K before and after the experiment), the 

 composition of carbonic anhydride and the equivalent of carbon may be determined. 



in nature. In course of time it was found that this gas is absorbed by 

 alkali, forming a salt which, under the action of acid, again yields this 

 same gas. Priestley found that this gas exists in air, and Lavoisier 

 determined its formation during respiration, combustion, putrefaction,, 

 and during the reduction of the oxides of metals by charcoal ; he deter- 

 mined its composition, and showed that it only contains oxygen and 

 carbon. Berzelius, Dumas with Stas, and Roscoe, determined its com- 



