CHEMICAL HISTORY OF A CANDLE 



141 



1 

 Hydrogen 



8 

 Oxygen 



Oxygen . 



Hydrogen 



Water . 



I had better, perhaps, tell you now how we get this oxygen 

 abundantly, having shown you how we can separate it from 

 the water. Oxygen, as you will immediately imagine, exists 

 in the atmosphere; for how should the candle burn to pro- 

 duce water without it? Such a thing would be absolutely 

 impossible, and chemically impossible without oxygen. Can 

 we get it from the air? Well, there are some very compli- 

 cated and difficult processes by which we can get it from 

 H t ^ - t ^ ie a ' 1T ' but we have 



" better processes. There 

 is a substance called the black oxide of man- 

 ganese; it is a very black-looking mineral, 

 but very useful, and when made red-hot it 

 gives out oxygen. Here is an iron bottle 

 which has had some of this substance put 

 into it, and there is a tube fixed to it, and 

 a fire ready made, and Mr. Anderson will 

 put that retort into the fire, for it is made 

 of iron, and can stand the heat. Here is 

 a salt called chlorate of potassa, which is 

 IG ' 7S now made in large quantities for bleach- 

 ing, and chemical and medical uses, and for pyrotechnic 

 and other purposes. I will take some and mix it with 

 some of the oxide of manganese (oxide of copper, or 

 oxide of iron would do as well), and if I put these to- 

 gether in a retort, far less than a red heat is sufficient 

 to evolve this oxygen from the mixture. I am not pre- 

 paring to make much, because we only want sufficient for 

 our experiments; only, as you will see immediately, if I 



