CHEMICAL AFFINITY S7 



bfned with other substances. Here is a little chlorate of 

 potash containing the oxygen which we found yesterday 

 could be procured from it ; it contains the oxygen there com- 

 bined and held down by its chemical affinity with other 

 things, but still it can combine with sugar, as you saw. This 

 affinity can thus act across substances, and I want you to see 

 how curiously what we call combustion acts with respect to 

 this force of chemical affinity. If I take a piece of phos- 

 phorus and set fire to it, and then place a jar of air over the 

 phosphorus, you see the combustion which we are having 

 there on account of chemical affinity (combustion being in 

 all cases the result of chemical affinity). The phosphorus 

 is escaping in that vapor, which will condense into a snow- 

 like mass at the close of the lecture. But suppose I limit the 

 atmosphere, what then? why, even the phosphorus will go 

 out. Here is a piece of camphor, which will burn very well 

 in the atmosphere, and even on water it will float and burn, 

 by reason of some of its particles gaining access to the air. 

 But if I limit the quantity of air by placing a jar over it, as 

 I am now doing, you will soon find the camphor will go out. 

 Well, why does it go out? not for want of air, for there is 

 plenty of air remaining in the jar. Perhaps you will be 

 shrewd enough to say for want of oxygen. 



This, therefore, leads us to the inquiry as to whether oxy- 

 gen can do more than a certain amount of work. The oxygen 

 there (FiG. 30) can not go on burning an unlimited quantity 

 of candle, for that has gone out, as you see ; and its amount 

 of chemical attraction or affinity is just as strikingly limited: 

 it can no more be fallen short of or exceeded than can the 

 attraction of gravitation. You might as soon attempt to 

 destroy gravitation, or weight, or all things that exist, 

 as to destroy the exact amount of force exerted by this 

 oxygen. And when I pointed out to you that eight by weight 

 of oxygen to one by weight of hydrogen went to form 

 water, I meant this, that neither of them would combine in 

 different proportions with the other, for you can not get ten 

 of hydrogen to combine with six of oxygen, or ten of oxygen 

 to combine with six of hydrogen ; it must be eight of oxygen 

 and one of hydrogen. Now suppose I limit the action in this 

 way : this piece of cotton wool burns, as you see, very well in 



