168 FARADAY 



black substance; so that you have the entire proof of the 

 nature of carbonic acid as consisting of carbon and oxygen. 

 And now I may tell you, that whenever carbon burns under 

 common circumstances it produces carbonic acid. 



Suppose I take this piece of wood, and put it into a 

 bottle with lime-water. I might shake that lime-water up 

 with wood and the atmosphere as long as I pleased, it would 

 still remain clear as you see it; but suppose I burn the 

 piece of wood in the air of that bottle. You, of course, 

 know I get water. Do I get carbonic acid? [The experi- 

 ment was performed.] There it is, you see that is to say, 

 the carbonate of lime, which results from carbonic acid, and 

 that carbonic acid must be formed from the carbon which 

 comes from the wood, from the candle, or any other thing. 

 Indeed, you have yourselves frequently tried a very pretty 

 experiment, by which you may see the carbon in wood. 

 If you take a piece of wood, and partly burn it, and then 

 blow it out, you have carbon left. There are tilings that 

 do not show carbon in this way. A candle does not so show 

 it, but it contains carbon. Here also is a jar of coal-gas, 

 which produces carbonic acid abundantly; you do not see 

 the carbon, but we can soon show it to you. I will light it, 

 and as long as there is any gas in the cylinder it will go on 

 burning. You see no carbon, but you see a flame, and be- 

 cause that is bright it will lead you to guess that there is 

 carbon in the flame. But I will show it to you by another 

 process. I have some of the same gas in another vessel, 

 mixed with a body that will burn the hydrogen of the gas, 

 but will not burn the carbon. I will light them with a burn- 

 ing taper, and you perceive the hydrogen is consumed, but 

 not the carbon, which is left behind as a dense black smoke. 

 I hope that by these three or four experiments you will 

 learn to see when carbon is present, and understand what 

 are the products of combustion when gas or other bodies 

 are thoroughly burned in the air. 



Before we leave the subject of carbon, let us make a few 

 experiments and remarks upon its wonderful condition as 

 respects ordinary combustion. I have shown you that the 

 carbon, in burning, burns only as a solid body, and yet you 

 gerceive that, after it is burned, it ceases to be a solid. There 



