CHEMICAL HISTORY OF A CANDLE 127 



another glass jar, empty of all but air: if I examine it with 

 a taper I shall find that it contains nothing but air. I will 

 now take this jar full of the gas that I am speaking of, and 

 deal with it as though it were 

 a light body; I will hold both 

 upside down, and turn the one 

 up under the other; and that 

 which did contain the gas pro- 

 cured from the steam, what does 

 it contain now? You will find 

 it now only contains air. But 

 look! Here is the combustible 

 substance [taking the other jar] 



which I have poured out of the one jar into the other. It 

 still preserves its quality, and condition, and independence, 

 and therefore is the more worthy of our consideration, as 

 belonging to the products of a candle. 



Now this substance which we have just prepared by the 

 action of iron on the steam or water, we can also get by 

 means of those other things which you have already seen act 

 so well upon the water. If I take a piece of potassium, and 

 make the necessary arrangements, it will produce this gas; 

 and if instead a piece of zinc, I find, when I come to exam- 

 ine it very carefully, that the main reason why this zinc can 

 not act upon the water continuously as the other metal does 

 is because the result of the action of the water envelops the 

 zinc in a kind of protecting coat. We have learned in con- 

 sequence, that if we put into our vessel only the zinc and 

 water, they, by themselves, do not give rise to much action, 

 and we get no result. But suppose I proceed to dissolve off 

 this varnish this encumbering substance which I can do 

 by a little acid; the moment I do this I find the zinc acting 

 upon the water exactly as the iron did, but at the common 

 temperature. The acid in no way is altered except in its 

 combination with the oxide of zinc which is produced. I 

 have now poured the acid into the glass, and the effect is as 

 though I were applying heat to cause this boiling up. There 

 is something coming off from the zinc very abundantly, 

 which is not steam. There is a jar full of it; and you will 

 find that I have exactly the same combustible substance re- 



