54 MANAGEMENT OF DAIRY PLANTS 



materials and form of construction, the walls should be vermin- 

 and germ-proof and should give no inducement for mice and 

 rats to nest within them. Insulation should be not only moisture- 

 proof, but also elastic and of light weight to prevent settling. 

 Other quahties to be regarded are the degree of fireproofness, 

 durability, strength, appearance, cost, etc. 



Constructioii for Insulation. — All refrigerators should be 

 constructed with a vestibule. When the door of the vestibule 

 is open, the door of the refrigerator should be kept closed, and 

 vice versa. 



1. Dead Air Space. — This is the oldest form of insulation. 

 Although the air itself is a good insulator, it should be divided 

 into small air cells to be most efficient. In a large space, heat 

 is carried readily from one side of the wall to the other by convec- 

 tion, and the slightest crack or even nail hole will tend greatly 

 to reduce insulating power. 



The inefficiency of this form of construction is demonstrated 

 by Ruddick.' A refrigerator thus constructed with a 6-inch 

 dead air space melted 1,879 pounds of ice. During the same 

 time and under the same conditions, a refrigerator of the same 

 size and of same construction, except that the 6-inch hollow 

 sp'ace was filled with sawdust, melted 1,328 pounds of ice. The 

 third type of refrigerator, similarly constructed with 6 inches 

 of shavings, melted 1,055 pounds of ice during the same time 

 and under the same conditions. The average temperature held 

 in the refrigerators was 42° F. for the one built with air spaces, 

 41° F. for the one insulated with sawdust, while the temperature 

 was reduced to 37.6° F. in the one insulated with shavings. 



2. Sawdust and Shavings. — As already stated, both are effi- 

 cient insulators; but they must be kept dry. Sawdust absorbs 

 moisture more readily than shavings. When damp, both lose 

 greatly in efficiency; and sawdust will then not merely become 

 a most excellent conductor of heat, but will also settle and leave 

 an empty space on top. Shavings, if properly packed, will not 

 settle. They are, as a whole, the most satisfactory of the two 

 materials. 



1 Canada Dairy Commr. Kept, for 1906, pp. 52-55. 



