ON ARTIFICIAL EEFRIGERATION. 



925 



cylinder, are fixed in position tlirougli the cork. In order now to per- 

 form the experimcut, the cylinder (A) is nearly filled with warm water; 



the glass stop-cock (h) is opened, and the tube (b) placed in ice-cold water. 

 Tlie water contained in the flask is now quickly boiled, and thus the 

 water in (A) is rapidly heated to 100°, and the ammonia gas driven out 

 of solution until by its own x^ressure it liquefies in (b). As soon as the 

 condensation of liquid ammonia ceases, the ebullition is stopped, and a 

 portion of the hot water is withdrawn from the cylinder by moans of the 

 syphon (g) ; cold water is allowed, to enter the cylinder, and after awhile 

 this is replaced by ice-cold water. The cylinder (B) is now removed, 

 when the li(piefied ammonia begins to evaporate, and is again absorbed 

 by the alcohol, though only slowly. But on. closing the stop-cock (/^) the 

 gas above the alcohol is quickly absorbed, and thus the equilibrium is 

 disturbed. The ammonia now passes rapidly through the tube {m m), 

 and is absorbed so quickly that the liquid ammonia in {h) begins to boil, 

 by which the temperature is so much lowered that if a test-tube contain- 

 ing water is placed outside {h) it is soon filled with ice." 



O.— THE PEOGEESSIYE STAGES 



TIO^^S. 



IX ICE-MAKIXG IITV^EI^. 



After Cullen's efforts to freeze water in the receiver of a vacuum-immp, 

 by the rapid vaporization of ether, we have to skip to the second quar- 



