SCIENTIFIC RECREATIONS. 



solution of ammonia at zero. This is in communication with another and 

 an air-tight vessel, of which the centre is hollow, The first process is to 

 heat the solution, and the gas escapes into the second " vase," w hich is sur- 



Fig. 358. Liquefaction of ammonia. 



rounded by cold water, and quite unable to escape. A tremendous pressure 

 is soon obtained, and this, added to the cold water, before long liquifies the 



Fig. 359. Carre's refrigerator (first action). 



ammonia, and when the temperature indicates 130 the hot vessel is sud- 

 denly cooled by being put into the water. The gas is thus suddenly con- 

 verted into a liquid, the water in the second hollow vase is taken out, and the 



