306 



SMITH S INTERMEDIATE CHEMISTRY 



water to ice. The same principle is also largely used for cooling 

 air (in storage rooms for meat, etc.). 



The machinery is represented diagrammatically in Fig. 80. 

 The ammonia, first admitted from a bomb of liquefied ammonia, 

 is driven by the pump F along the tube E and condenses to liquid 



form in the tube coiled in the tank AB. 



Cold water circulates through AB, and 

 removes the heat produced by the com- 

 pression and liquefaction of the gas. The 

 liquid ammonia is allowed to drip through 

 the stopcock G into the lower coil. This 

 is kept exhausted by the compresser F, 

 and the liquid ammonia evaporates. In 

 doing this, it takes heat from a 30 per 

 cent solution of calcium chloride in water, 

 which does not freeze even at 12. 

 This cooled brine leaves the tank at D, 

 circulates through another tank (not 

 shown) in which the water-filled ice 

 moulds are suspended, and returns to C. 

 When used for cooling refrigerating 



chambers, the brine passes through a system of pipes suitably 

 placed in the cold-room. The whole machinery is made of iron, 

 as copper and brass are corroded by the ammonia. 



Ammonium hydroxide solution is sold under the name of 

 household ammonia, and is used, in washing and cleaning, to 

 soften the water. 



Exercises. 1. Classify the reactions shown by equations in 

 this chapter. 



2. How could you recognize the nitrogen and the hydrogen 

 obtained in the decomposition of ammonia (p. 304)? 



3. Why can we not dry ammonia gas with concentrated sul- 

 phuric acid or with phosphorus pentoxide? 



4. How could you separate a mixture of oxygen and ammonia? 



