58 MANAGEMENT OF DAIRY PLANTS 



with a waterproof hot cement made from a mixture of pitch 

 and asphaltimi. As in the case of cork, it is finished in a smooth 

 cement plaster. 



5. Lith. — Lith is considered to be as satisfactory an insulat- 

 ing material as cork, except that it takes up moisture more 

 readily. It is cheaper than cork. The construction with lith 

 is the same as with cork.^ 



6. Other Materials. — Other insulators, such as hair felt, 

 might be mentioned; but this has not become of much impor- 

 tance for creamery-storage insulation. 



SYSTEMS OF REFRIGERATION 



Two systems of refrigeration exist — the "Natural" and the 

 "Mechanical." The natural system uses ice as its source of 

 refrigeration; while the mechanical system removes the heat by 

 merchanical methods. 



NATURAL REFRIGERATION 



Methods. — In natural refrigeration, the ice used for cooling 

 purposes must be stored, requiring an ice house more or less 

 insulated. In using that ice for chilling stored products, the 

 refrigerator may be cooled by any one of three different methods. 

 The temperature may be lowered by the use of ice placed in 

 an ice bunker located in the refrigerator, or by connecting the 

 refrigerator with a contiguous insulated ice house, or by in- 

 stalling a tank above the refrigerator from which ice-cooled 

 brine is circulated through the refrigerator in a system of pipes. 



I. Ice Bunker Method. — This is the oldest form of refrigera- 

 tion and is yet in most common use in the smaller creameries. 

 The ice is placed in a bunker overhead and usually at one end 

 of the refrigerator. The refrigerator is frequently built against 

 an outside wall through which a small refrigerator door admits 

 ice from outside to the ice bunker. By leaving this door open 

 during cool nights, the refrigerator may be kept in good condi- 

 tion without ice during a good portion of the year. 



' For mineral wool slabs and Lith metal lath should be used for holding the 

 plaster. 



