CHEMICAL AFFINITY 99 



will see whether that water can extinguish it; here it is 

 burning out of the water, and there it is burning under the 

 water; and so it will continue until exhausted, and all by 

 reason of the requisite amount of oxygen being contained 

 within the substance. It is by this kind of attraction of the 

 different particles one to the other that we are enabled to 

 trace the laws of chemical affinity, and the wonderful variety 

 of the exertions of these laws. 



Now I want you to observe that one great exertion of this 

 power which is known as chemical affinity is to produce 

 HEAT and light; you know, as a matter of fact, no doubt, 

 that when bodies burn they give out heat, but it is a curious 

 thing that this heat does not continue; the heat goes away 

 as soon as the action stops, and you see, thereby, that it 

 depends upon the action during the time it is going on. I* 

 is not so with gravitation; this force is continuous, and is 

 just as effective in making that lead press on the table as 

 it was when it first fell there. Nothing occurs there which 

 disappears when the action of falling is over; the pressure 

 is upon the table, and will remain there until the lead is re- 

 moved; whereas, in the action of chemical affinity to give 

 light and heat, they go away immediately the action is over. 

 This lamp seems to evolve heat and light continuously, but it 

 is owing to a constant stream of air coming into it on all 

 sides, and this work of producing light and heat by chemical 

 affinity will subside as soon as the stream of air is inter- 

 rupted. What, then, is this curious condition of heat ? Why, 

 it is the evolution of another power of matter of a power 

 new to us, and which we must consider as if it were now 

 for the very first time brought under our notice. What is 

 heat? We recognize heat by its power of liquefying solid 

 bodies and vaporizing liquid bodies; by its power of setting 

 in action, and very often overcoming, chemical affinity. Then 

 how do we obtain heat ? We obtain it in various ways ; most 

 abundantly by means of the chemical affinity we have just 

 before been speaking about, but we can also obtain it in 

 many other ways. Friction will produce heat. The Indians 

 rub pieces of wood together until they make them hot enough 

 to take fire; and such things have been known as two 

 branches of a tree rubbing together so hard as to set the tre 



