COMBUSTION IN DEFINITE PROPORTIONS. 99 



I meant this, that neither of them would com- 

 bine in different proportions with the other, for 

 you cannot get 10 of hydrogen to combine with 

 6 of oxygen, or 10 of oxygen to combine with 

 6 of hydrogen it must be 8 of oxygen and 1 

 of hydrogen. Now suppose I limit the action 

 in this way; this piece of cotton wool burns, 

 as you see, very well in the atmosphere ; and I 

 have known of cases of cotton-mills being fired 

 as if with gunpowder, through the very finely- 

 divided particles of cotton being diffused through 

 the atmosphere in the mill, when it has some- 

 times happened that a flame has caught these 

 raised particles, and it has run from one end of 

 the mill to the other and blown it up. That then 

 is on account of the affinity which the cotton 

 has for the oxygen ; but suppose I set fire to 

 this piece of cotton which is rolled up tightly ; 

 it does not go on burning, because I have limited 

 the supply of oxygen, and the inside is pre- 

 vented from having access to the oxygen, just 

 as it was in the case of the lead by the oxide. 

 But here is some cotton which has been imbued 

 with oxygen in a certain manner. I need not 

 trouble you now with the way it is prepared ; 

 it is called gun-cotton. ( 21 ) See how that burns 



H 2 



