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 qualities to be regarded are the degree of fireproofness, 

 durability, strength, appearance, cost, etc. 



Construction 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. 1 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 

 space 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. Rept. for 1906, pp. 52-55. 



