CHEMICAL AFFINITY 47 



therefore composed of two substances different to itself, 

 which appear at separate places when it is made to submit 

 to the force which I have in these wires; and if I take an in- 

 verted tube of water and collect this gas (H), you will see 

 that it is by no means the same as the one we collected in 

 the former apparatus (Fie. 24). That exploded with a 

 loud noise when it was lighted, but this will burn quite 

 noiselessly: it is called hydrogen; and the other we call 

 oxygen that gas which so beautifully brightens up all com- 

 bustion, but does not burn of itself. So now we see that 

 water consists of two kinds of particles attracting each other 

 in a very different manner to the attraction of gravitation 

 or cohesion, and this new attraction we call chemical affinity, 

 or the force of chemical action between different bodies; 

 we are now no longer concerned with the attraction of iron 

 for iron, water for water, wood for wood, or like bodies 

 for each other, as we were when dealing with the 

 force of cohesion; we are dealing with another kind of 

 attraction the attraction between particles of a different 

 nature one to the other. Chemical affinity depends entirely 

 upon the energy with which particles of different kinds 

 attract each other. Oxygen and hydrogen are particles of 

 different kinds, and it is their attraction to each other which 

 makes them chemically combine and produce water. 



I must now show you a little more at large what chemical 

 affinity is. I can prepare these gases from other substances 

 as well as from water,- and we will now prepare some oxy- 

 gen : here is another substance which contains oxygen chlo- 

 rate of potash; I will put some of it into this glass retort, 

 and Mr. Anderson will apply heat to it: we have here dif- 

 ferent jars filled with water, and when, by the application 

 of heat, the chlorate of potash is decomposed, we will 

 displace the water, and fill the jars with gas. 



Now, when water is opened out in this way by means of 

 the battery, which adds nothing to it materially, which takes 

 nothing from it materially (I mean no matter; I am not 

 speaking of force), which adds no matter to the water, it 

 is changed in this way the gas which you saw burning a 

 little while ago, called hydrogen, is evolved in large quantity, 

 and the other gas, oxygen, is evolved in only half th 



