166 



REFRIGERATION AND ITS USES 



From this table we see that to change ammonia from a gas 

 to a liquid at the ordinary temperature of 70F. requires a 

 pressure of about 130 Ib. per sq. in. We also see that at the 

 pressure of 1 atmosphere, or 15 Ib. per sq. in., the ammonia 

 will be in the liquid form if the temperature is below 29F. 

 and in the gaseous form if the temperature be above 29F. 

 (Fig. 125). 



NOTE : It is important that we remember that the ammonia used 

 in refrigerating plants is the pure, dry ammonia; never the water 

 solution of ammonia, or aqua ammonia. 



Temjoerafur-e ^ Jbr-fne. 



FIG. 125. Curve showing the properties of ammonia. 



195. How the Water is Frozen. The ammonia to be used 

 in the plant is received from the manufacturing chemist in 

 strong metal containers. It is highly compressed and, there- 

 fore, is in the liquid form. This ammonia is fed into the 

 system through the opening, A, Fig. 124. As the ammonia 

 escapes from the high pressure, it boils violently and changes 

 to the gaseous form. As the compressor is running, the 

 ammonia is drawn directly through the lower valve into the 



