344 THE APPLE 



tanks of galvanized iron are provided. These are filled with ice 

 and salt for the purpose of reducing the temperature still lower 

 than is possible with the ice alone. 



The Dexter system. The Dexter patents cover a much more com- 

 plicated apparatus than any system of earlier invention using ice as 

 a refrigerant. It consists of a series of air flues between the exterior 

 and interior walls of the cold-storage room. The cold air from the 

 ice chamber flows down through one set of flues, and as it is warmed 

 returns through another set located outside of the first set. This 

 effectually prevents the penetration of outside heat, and makes the 

 regulation of temperature comparatively easy, even in warm weather. 

 This is practically like putting one cold-storage room inside of an- 

 other. To bring down the temperature to the desired point, Dexter 

 also uses the galvanized tubes or tanks filled with ice and salt. 



Other systems. Some houses are cooled entirely by the gal- 

 vanized-iron tanks. These are built in a variety of shapes and 

 sizes, and are usually placed around the sides or through the center 

 of a room and filled with ice and salt from above. Sometimes the 

 ice is stored above, but usually in a separate building, and hauled 

 up to the floor above the storage room as needed. This system is 

 not adapted for houses of more than one story, although in some 

 cases the tanks are filled from a corridor of the upper floor. 



Mechanical refrigeration. The ammonia system. A great variety 

 of machinery is being patented and manufactured for use in refrig- 

 eration. The aim of all these machines is practically the same — 

 to produce a given temperature at a lessened cost. The ammonia 

 process (which is being used in very large plants with satisfaction) 

 is, briefly, as follows : 



i. Ammonia gas (not the "ammonia" of commerce) is lique- 

 fied by high pressure in a condenser surrounded by cold water. 



2. The liquid ammonia is run into pipes where it is under less 

 pressure ; it then becomes a gas again, producing intense cold. 



3. These pipes are surrounded by double pipe coils containing 

 brine, which is cooled by the ammonia and is then run through 

 the storage room. The temperature is easily controlled by increas- 

 ing or decreasing the brine flow. 



4. The gas is either pumped back to the condenser by an air 

 pump (compression system) or run into a tank of water in which it 



