228 BOARD OF AGRICULTURE. [Pub. Doc. 



this. Sufficient it must be to simply state the fundamental 

 principles of these several mechanical processes, for such 

 they are in every instance, for producing cold air in a given 

 space. 



Artificial refrigeration is produced, first, by transferring 

 heat from a warmer body to a colder one, as refrigeration by 

 cooled brine, which is one of the most practical and common 

 methods in use ; second, by the consumption of heat, brought 

 about by mechanical work or action ; third, by the evapora- 

 tion of liquids having a low l)oiling point. The governing 

 principle in this is that the latent heat of evaporation repre- 

 sents the amount of cold that can be produced in this way. 

 To these mechanical processes for cooling the atmosphere 

 should be added that by melting or dissolving solid bodies, 

 like the melting of a cake of ice, or the solution of salt in 

 water, making a brine. 



In practically all refrigerating systems, except that of 

 melting ice, a series of coils of pipes is used. These are 

 called expansion pipes, and those in the brine system are 

 placed in separate tanks containing the brine, which is cooled 

 to the desired degree. The brine, so cooled, is then con- 

 ducted by means of force pumps through pipes located in the 

 rooms to be cooled. This method of refrigeration is a safe 

 and sure one, though its efficiency may not be so great as 

 that of the vaporization of certain properties. 



Perhaps the most generally used of the mechanical proc- 

 esses for refrigeration, except it be the brine system, is that 

 called the ammonia compression system, which may be ac- 

 complished either by absorption or direct expansion. The 

 refrigeration in this system is brought about by the evap- 

 oration of liquid anhydrous ammonia, which takes place in 

 coils of pipes called the expander, or refrigerating coils. The 

 ammonia occurs in practical refrigeration in three dififerent 

 forms, as the liquid anhydrous ammonia, the gaseous an- 

 hydrous ammonia and solutions of ammonia in water of 

 various strengths. Anhydrous ammonia is such as has been 

 wholly freed from water. At 28 degrees below zero it is a 

 vapor or gas, just as water turns into steam or vapor at 212 

 degrees above zero. At a temperature of 30 degrees below 

 zero ammonia becomes a liquid by the ordinary pressure of 



