ON ARTIFICIAL REFRIGERATION. 



925 



cylinder, are fixed in ])()siti()ii tlirouj;!! the cork. In older now to ])er- 

 form the exi)erimcnt, the cylinder (A) is nearly tilled witli -warm waterj 



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

 The 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 jiressure it liquefies in (&). 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 portion of the hot water is withdrawn from the cylinder by means of the 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 liquefied ammonia begins to evaporate, and is again absorbed 

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

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

 disturbed. The ammonia now i)asses 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 (/«) it is soon filled with ice." 



O.— THE PEOGRESSIVE STAGES IN" ICE-MAKIKG IKYEK- 



TIOXS. 



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

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



