Ko. 4.] COLD STORAGE. 229 



the atmosphere, and at higher temperatures if higher press- 

 ures are employed. Anhydrous ammonia dissolves in water 

 in varying proportions, and forms the aqua ammonia of com- 

 merce. When the anhydrous liquor is used for refrigeration, 

 it is called the compression system ; and when ammonia 

 proper is used, it is styled the absorption system. 



In the practical operation of the ammonia compression 

 system the coils of pipes are placed in the rooms to be re- 

 frigerated. The ammonia, after having expanded, is com- 

 pressed again by means of a compression pump, called the 

 compressor, into another system of pipes, called the con- 

 denser. The condenser is cooled off by running water, 

 which takes away from the ammonia in the coils the heat 

 which it has acquired through the compression, as well as the 

 heat which it has absorbed while having evaporated in the 

 expander. Owing to both pressure and withdrawal of heat, 

 the ammonia assumes its liquid form again, to pass into the 

 pipes, thus repeating its circulation over and over again, 

 thus embodying a perfect cycle of operations. Refrigeration 

 by the expansion or volatilization of the liquid ammonia is 

 accomplished to an astonishing degree, as it also is by the 

 brine system. It is possible to run the temperature down to 

 16 and more degrees below zero, and to freeze solid, meat, 

 poultry, butter or whatever else it is desired to keep for an 

 indefinite time. As these systems of artificial refrigeration 

 require power, and as this power must be kept in operation 

 all of the twenty- four hours in the day, the location of such 

 plants is not everywhere practicable. But the threading of 

 the highway wnth the electric wire and the increasing adapt- 

 ability of the gas engine make more and more possible the use 

 of these extremely efficient means of artificial refrigeration. 



The use of ice in cold-storage depots is yet by far the 

 most common means for refrigeration, and for ordinary cold- 

 storage purposes it will doubtless so remain for years to 

 come. In cities where great quantities of all kinds of farm 

 products are held for a better market, or to retard the ripen- 

 ing process, or to prevent a high temperature from injuring 

 them, cold-storage plants are oftentimes huge buildings of 

 ela])orate construction. Many if not most of these have 

 been built as investments, their owners renting space therein, 



