124 FARADAY 



I think you can see a little in this way. We had Just now 

 the case of a substance which acted upon the water in the 

 way that Sir Humphrey Davy showed us^ 13 ) and which I 

 am now going to recall to your minds by making again an 

 experiment upon that dish. It is a thing which we have to 

 handle very carefully; for you see, if I allow a little splash 

 of water to come upon this mass, it sets fire to part of it; 

 and if there were free access of air, it would quickly set fire 

 to the whole. Now this is a metal a beautiful and bright 

 metal which rapidly changes in the air, and, as you know, 

 rapidly changes in water. I will put a piece on the water, 

 and you see it burns beautifully, making a floating lamp, 

 using the water in the place of air. Again, if we take a 

 few iron filings or turnings and put them in water, we find 

 that they likewise undergo an alteration. They do not 

 change so much as this potassium does, but they change 

 somewhat in the same way; they become rusty, and show 

 an action upon the water, though in a different degree of 

 intensity to what this beautiful metal does; but they act 

 upon the water in the same manner generally as this potas- 

 sium. I want you to put these different facts together in 

 your minds. I have another metal here [zinc], and when 

 we examined it with regard to the solid substance produced 

 by its combustion, we had an opportunity of seeing that it 

 burned; and I suppose, if I take a little strip of this zinc 

 and put it over the candle, you will see something half way, 

 as it were, between the combustion of potassium on the 

 water and the action of iron you see there is a sort of com- 

 bustion. It has burned, leaving a white ash or residuum; 

 and here also we find that the metal has a certain amount 

 of action upon water. 



By degrees we have learned how to modify the action of 

 these different substances, and to make them tell us what 

 we want to know. And now, first of all, I take iron. It is 

 a common thing in all chemical reactions, where we get 

 any result of this kind, to find that it is increased by the 

 action of heat; and if we want to examine minutely and 



u Potassium, the metallic basis of potash, was discovered by Sir Humphrey 

 Davy in 1807, who succeeded in separating it from potash by means of a 

 powerful voltaic battery. Its great affinity for oxygen causes it to decompose 

 water with evolution of hydrogen, which takes fire with the heat produced. 



