ICE PRODUCED ARTIFICIALLY. 63 



take the necessary quantity of heat from some- 

 thing, and in this case it will take the heat from 

 the tray, and from the water underneath, and 

 from the other things round about. Well, a 

 little salt added to the ice, has the power of 

 causing it to melt, and we shall very shortly 

 see the mixture become quite fluid, and you 

 will then find that the water beneath will be 

 frozen frozen because it has been forced to 

 give up that heat which is necessary to keep it 

 in the liquid state, to the ice on becoming 

 liquid. I remember once, when I was a boy, 

 hearing of a trick in a country alehouse ; the 

 point was how to melt ice in a quart pot by the 

 fire, and freeze it to the stool. Well, the way 

 they did it was this r they put some pounded 

 ice in a pewter pot and added some salt to it, 

 and the consequence was, that when the salt 

 was mixed with it, the ice in the pot melted 

 (they did not tell me anything about the salt, 

 and they set the pot by the fire, just to make 

 the result more mysterious), and in a short 

 time the pot and the stool were frozen together, 

 as we shall very shortly find it to be the case 

 here. And all because salt has the power of 

 lessening the attraction between the particles of 



