166 FARADAY 



not know a finer experiment than this to show that carbon 

 burns with a spark. 



Here, then, is carbonic acid formed from its elements. It 

 is produced at once; and if we examined it by lime-water 

 you will see that we have the same substance which I have 

 previously described to you. By putting together 6 parts 

 of carbon by weight (whether it comes from the flame of a 

 candle or from powdered charcoal) and 16 parts of oxygen by 

 weight, we have 22 parts of carbonic acid; and, as we saw 

 last time, the 22 parts of carbonic acid combined with 28 parts 

 of lime, produced common carbonate of lime. If you were to 

 examine an oyster-shell and weigh the component parts, you 

 would find that every 50 parts would give 6 of carbon and 16 

 of oxygen combined with 28 of lime. However, I do not want 

 to trouble you with these minutiae ; it is only the general phi- 

 losophy of the matter that we can now go into. See how finely 

 the carbon is dissolving away [pointing to the lump of char- 

 coal burning quietly in the jar of oxygen]. You may say 

 that the charcoal is actually dissolving in the air round 

 about; and if that were perfectly pure charcoal, which we 

 can easily prepare, there would be no residue whatever. 

 When we have a perfectly cleansed and purified piece of car- 

 bon, there is no ash left. The carbon burns as a solid dense 

 body, that heat alone can not change as to its solidity, and 

 yet it passes away into vapor that never condenses into solid 

 or liquid under ordinary circumstances; and what is more 

 curious still is the fact that the oxygen does not change 

 in its bulk by the solution of the carbon in it. Just as the 

 bulk is at first, so it is at last, only it has become carbonic 

 acid. 



There is another experiment which I must give you before 

 you are fully acquainted with the general nature of carbonic 

 acid. Being a compound body, consisting of carbon and 

 oxygen, carbonic acid is a body that we ought to be able to 

 take asunder. And so we can. As we did with water, so 

 we can with carbonic acid take the two parts asunder. 

 The simplest and quickest way is to act upon the carbonic 

 acid by a substance that can attract the oxygen from it, 

 and leave the carbon behind. You recollect that I took 

 potassium and put it upon water or ice, and you saw that it 



