384 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



founded on the same principle as that we have explained already, 

 namely, the cold produced by rapid evaporation. 



A cylindrical boiler, partly filled with a solution of ammonia, is 

 placed on a furnace till a temperature of 130 C. is attained, which is 

 ascertained by a thermometer whose stem passes through the cover. 

 The ammoniacal gas is disengaged, and passes by a conducting tube 

 into a refrigerator or vessel in the form of an inverted truncated cone, 

 plunged in a tub of cold water. In the inside of this refrigerator is 

 placed a cylindrical vessel containing the water to be frozen, and this 

 is the way in which the result is obtained. The ammoniacal vapours 

 which are incessantly disengaged from the boiler are cooled by the 

 water in the tub, and are in addition submitted to an increasing 



FIG. 264. Carre's apparatus for the artificial manufacture of ice. 



pressure, they condense, the gas liquefies and remains inclosed in 

 cups fitted to the sides in the annular space surrounding the central 

 cylinder. The furnace is now replaced by a tub of cold water the 

 water in the boiler, on cooling, becomes able again to dissolve the 

 ammoniacal gas, which rapidly returns to its gaseous state. This 

 evaporation necessitates an absorption of heat which takes place at 

 the expense of the central vessel and of the water which it contains, 

 a block of ice can then be soon taken out of it. 



The apparatus just described, which is represented in Fig. 264, is 

 tor domestic use, as the quantity of ice it can produce is small. 

 The larger apparatus constructed by the same inventor for the 

 commercial manufacture of ice is arranged differently. 



