190 THE CHEMISTRY OF CREATION. 



On the contrary, if we cause air to expand, as 

 in the air-pump, we can produce a great degree 

 of cold, because the expanded air absorbs heat 

 into itself from all surrounding bodies. By the 



little contrivance 

 represented in the 

 cut we may readily 

 manufacture a small 

 quantity of ice. A 

 little water must be put into a watch-glass, 

 supported by a triangle of wire, over a saucer 

 of strong sulphuric acid, or oil of vitriol, placed 

 over the plate of an air-pump, and covered 

 by a flattened receiver; the pump, being then 

 worked, the water will in a few minutes be 

 converted into a solid mass of ice! Sir John 

 Leslie actually formed an apparatus for making 

 ice artificially on a large scale by the adaptation 

 of this principle ; and large ice-making machines 

 have been sent out to India with this view. 

 The facility with which we can now procure the 

 beautiful lake-ice of America, renders these 

 contrivances no longer interesting except as 

 curiosities. * 



It is partly in consequence of this increased 



* Recently a machine has been patented in America for 

 making ice by the expansion of previously compressed air. 

 It is a kind of steam-engine, and at every stroke produces a 

 shower 'of snow ! The idea is, however, not altogether new. 



