218 CANADIAN DAIRYING. 



means of mechanical refrigeration. In this method 

 a gas is put under heavy pressure, which changes 

 it to a liquid and heat is given off. When the press- 

 ure is released in the cooling pipes or brine tanks, it 

 returns to a gaseous form and absorbs as much heat 

 as was given off by it when pressure was applied. 

 This heat is taken from the pipes or brine tank, the 

 air of the room, and from the substances in the room, 

 thus cooling them. The two most common gases used 

 are carbon dioxide (carbonic acid gas) and ammonia. 

 Manufacturers of both types of machines claim theirs 

 is the best. Both have advantages and disadvantages. 

 Three systems are in use for creameries : 



1. Direct expansion, where the cold is produced 

 by the expansion of the gas in pipes placed in the 

 room, in water, or in connection with the cream vat. 

 The advantage of this plan is that it saves the cost of 

 a brine tank, and it is less wasteful of the cold gas. 

 The disadvantage is that the compressor has to be 

 run for a longer time each day to produce the results 

 aimed at 



2. In the brine system the expansion coils are 

 placed in a brine tank, and the cold brine is pumped 

 through pipes where required. This method reduces 

 the time required for operating the compressor, but 

 is more expensive to install and requires the operation 

 of a brine pump. 



3. A combination of the foregoing is sometimes 

 used where the direct expansion is operated while 

 the creamery machinery is in operation, and the cold 

 brine for that portion of the day when the machinery 

 is not running. 



