168 REFRIGERATION AND ITS USES 



heat from the water and continues to do so till the water is 

 frozen. As long as the compressor is kept running, the circu- 

 lation of the ammonia continues. 



196. Why Brine is Used and How the Temperature of the 

 Brine is Regulated. When studying the thermometer, we 

 saw that Fahrenheit got the temperature which he called 

 zero on his thermometer by mixing salt and crushed ice 

 (Art. 17). Now if just enough salt is mixed with ice to make a 

 saturated solution 1 when the ice melts, the melting point of 

 the mixture is a little lower than the lowest temperature 

 Fahrenheit obtained. It is about 7F. But it should 

 be carefully noted that the melting point of such a mixture is 

 also the freezing point of a saturated solution of salt and 

 water, just as the melting point of pure ice is exactly the 

 freezing point of pure water (Art. 16). The saturated solu- 

 tion of salt and water, then, can be frozen only by lowering 

 the temperature to about 7F., which is 39 below the freez- 

 ing point of water. 



In operating an ice plant it is customary to cool the brine 

 to about 16 or 18F. The temperature of the brine can 

 easily be governed by opening wider or partly closing the 

 regulating valve. It will be noticed that the compressor, 

 not only compresses the ammonia gas on the compression 

 side of the regulating valve, i.e., in the cooling coils, but 

 that at the same time it is reducing the pressure on the 

 other side of the valve, i.e., in the pipes in the brine vat. 

 It also becomes evident that if the regulating valve is nearly 

 closed the pressure becomes great on the compression side 

 while it is reduced on the exhaust side. On the other hand, 

 opening the valve wider permits the pressure to become some- 

 what nearer equal on the two sides. Hence we speak of the 

 HIGH SIDE and the LOW SIDE of the plant. The high side 

 comprises that portion of the ammonia pipes from the com- 



1 NOTE : A saturated solution of salt is one in which no more salt will dis- 

 solve in the water. At ordinary temperatures 2^ Ib. of water will 

 dissolve about 1 Ib. of salt. 



