216 CANADIAN DAIRYING. 



the butter. The two common methods of refrigera- 

 tion are, by the use of ice or by mechanical means, 

 such as applying pressure to gases. The first thing 

 is to have the room properly insulated, as outlined in 

 a previous chapter. 



Refrigeration is the production of cold. Cold is 

 produced by transferring heat from a warmer to a 

 colder body, or by extracting heat and rendering it 

 latent. Heat is rendered latent (of no effect) when 

 bodies are changed from a solid to a liquid, or from a 

 liquid to a gas. In the case of ice, cooling is the 

 result of heat being absorbed or rendered latent, as 

 it changes from a solid condition to that of a liquid. 

 This heat is taken from the surrounding bodies, hence 

 they become colder. If the water be evaporated, 

 heat is again rendered latent and cold is produced. 



In order to produce cold rapidly the ice should be 

 broken finely, as it will then produce cold more 

 quickly. If ice be mixed with salt, the degree of 

 cold is greater and it is produced more rapidly, be- 

 cause salt has a great affinity for water, and it attacks 

 the ice in order to get water to slake its thirst. In 

 doing this it is dissolved by the water, and we have 

 two solid bodies changing to a liquid, hence more 

 cold produced. To get the best results from ice and 

 salt, the mixture should be placed in galvanized iron 

 cylinders about one foot in diameter and as deep as 

 the cold-storage room. A sufficient number of these 

 should be placed in the cold-storage to give the 

 desired temperature. The liquid should be removed 

 to a drain, having a trap on it to prevent the warm 



