CHEMICAL HISTORY OF A CANDLE 129 



experiments with it as you please, at your own homes. Let 

 me here tell you why I am so careful to fill this phial nearly, 

 and yet not quite full. I do it because the evolved gas, which, 

 as you have seen, is very combustible, is explosive to a con- 

 siderable extent when mixed with air, and might 

 lead to harm if you were to apply a light to the end 

 of that pipe before all the air had been swept out 

 of the space above the water. I am now about to 

 pour in the sulphuric acid. I have used very little 

 zinc and more sulphuric acid and water, because I 

 want to keep it at work for some time. I therefore 

 take care in this way to modify the proportions of the 

 ingredients so that I may have a regular supply not 

 too quick and not too slow. Supposing I now take a 

 glass and put it upside down over the end of the tube, 

 because the hydrogen is light I expect that it will re- 

 main in that vessel a little while. We will now test the FlG> 7I 

 contents of our glass to see if there be hydrogen in it; I think 

 I am safe in saying we have caught some [applying a light]. 

 There it is, you see. I will now apply a light to the top of the 

 tube. There is the hydrogen burning. There is our philo- 

 sophical candle. It is a foolish, feeble sort of a flame, you 

 may say, but it is so hot that scarcely any common flame gives 

 out so much heat. It goes on burning regularly, and I am now 

 about to put that flame to burn under a certain arrangement, 

 in order that we may examine its results and make use of the 

 information which we may thereby acquire. Inasmuch as the 

 candle produces water, and this gas comes out of the water, 

 let us see what this gives us by the same process of com- 

 bustion that the candle went through when it burnt in the 

 atmosphere, and for that purpose I am going to put the lamp 

 under this apparatus, in order to condense whatever may 

 arise from the combustion within it. In the course of a short 

 time you will see moisture appearing in the cylinder, and you 

 will get the water running down the side, and the water from 

 this hydrogen flame will have absolutely the same effect upon 

 all our tests, being obtained by the same general process as 

 in the former case. This hydrogen is a very beautiful sub- 

 stance. It is so light that it carries things up; it is far 

 lighter than the atmosphere, and I dare say I can show you 

 H C VOL. xxx E 



