Si FARADAY 



takci place when we make different particles act together. 

 Now I can make these bodies act upon each other in several 

 ways. In this case I am going to apply heat to the mixture ; 

 but if I were to give a blow with a hammer, the same result 

 would follow. [A lighted match was brought to the mixture, 

 which immediately exploded with a sudden flash, evolving a 

 dense white smoke.] There you see the result of the action 

 of chemical affinity overcoming the attraction of cohesion of 

 the particles. Again, here is a little sugar ( 17 ), quite a 

 different substance from the black sulphuret of antimony, 

 and you shall see what takes place when we put the two to- 

 gether. [The mixture was touched with sulphuric acid, 

 when it took fire, and burnt gradually and with a brighter 

 flame than in the former instance.] Observe this chemical 

 affinity traveling about the mass, and setting it on fire, and 

 throwing it into such wonderful agitation ! 



I must now come to a few circumstances which require 

 careful consideration. We have already examined one of 

 the effects of this chemical affinity, but, to make the matter 

 more clear, we must point out some others. And here are 

 two salts dissolved in water ( 18 ). They are both colorless 

 solutions, and in these glasses you can not see any difference 

 between them. But if I mix them, I shall have chemical 

 attraction take place. I will pour the two together into this 

 glass, and you will at once see, I have no doubt, a certain 

 amount of change. Look, they are already becoming milky, 

 but they are sluggish in their action not quick as the others 

 were for we have endless varieties of rapidity in chemical 

 action. Now, if I mix them together, and stir them so as 

 to bring them properly together, you will soon see what a 

 different result is produced. As I mix them they get thicker 

 and thicker, and you see the liquid is hardening and stiff- 

 ening, and before long I shall have it quite hard; and be- 

 fore the end of the lecture it will be a solid stone a wet 

 stone, no doubt, but more or less solid in consequence 

 of the chemical affinity. Is not this changing two liquids 



1T The mixture of chlorate of potash and sugar does not require the same 

 precautions. They may be rubbed together in a pestle and mortar without 

 fear. One part of chlorate of potash and three parts of sugar will answer. 

 The mixture need only be touched with a glass rod dipped in oil of vitriol. 



18 Two salts dissolved in water. Sulphate of soda and chloride of calcium. 

 The solutions must be saturated for the experiment to succeed well. 



