62 ANIMAL CHEMISTRY LECTURE III. 



Carb-anhyd. Lime . Water Chalk 



ro , H a Ca"O a or w n ( CCa"0 3 or 



iCaO.H 2 



If instead of absorbing it by lime-water in this manner, we were 

 directly or indirectly to weigh the resulting carb-anhydride, we 

 should find that its weight was exactly equal to that of the carbon 

 burnt, plus that of the oxygen which served to burn it. But, in 

 addition to carbonic anhydride, there was during the combination 

 an abundant production of light and heat. Now the axiom, that 

 out of nothing comes nothing, is just as true of light and heat 

 as of water and carbonic anhydride. We have no difficulty in 

 understanding the production of the carbonic anhydride ; what, 

 however, is the origin of the light and heat ? 



(65.) So much, then, for the formation of oxide of hydrogen 

 or water, and oxide of carbon or carbonic anhydride ; now for 

 their decompositions. By a variety of means we are able to 

 separate hydrogen and carbon from their respective combinations 

 with oxygen one of the most suitable materials for the pur- 

 pose being metallic sodium. If, for instance, we introduce under 

 this inverted jar of water a piece of metallic sodium, which, for 

 the sake of convenience, I have diluted with a little mercury, so 

 that the reaction may take place more slowly than it otherwise 

 would, we get, you perceive, a regular evolution of hydrogen 

 gas. The sodium combines with the oxygen of the water, whilst 

 its hydrogen is set at liberty ; and in a similar manner we may 

 liberate carbon from carbonic anhydride, as I will now endeavour 

 to show you. The carbonic anhydride that we produced by the 

 combustion of a piece of charcoal in oxygen was absorbed, you 

 will remember, by means of lime, whereby we obtained this pre- 

 cipitate of chalk, from which by treatment with hydrochloric acid 

 we may easily re-obtain the carbonic anhydride. Thus, if I transfer 

 our mixture of chalk and water into the narrow cylinder standing 

 over this mercurial trough, and then pass up a little hydrochloric 

 acid, you see that the chalk disappears with effervescence, while a 

 quantity of gas collects at the top of the cylinder, which is the 



