320 THE HANDBOOK FOR PRACTICAL FARMERS 



bottom of the tank to hold the cans off of the tank floor and to 

 allow cold water to reach the bottom of the cans. 



Size of tanks. — The size of the tanks should be suited to the 

 number of cans to be handled. However, as the quantity of milk 

 varies from season to season and from year to year, it is advis- 

 able to divide the tank into two compartments. Too large a tank 

 results in a waste of ice, while a tank that is crowded with milk 

 cans does not provide space for sufficient ice to cool the milk. The 

 tank should be placed in the milk house where it will be protected 

 from the sun in summer and from the extreme cold in winter. 



Use of ice. — Ice should be put in the cooling tank long enough 

 before milking to bring the water to a low temperature by the 

 time the milk is ready for cooling. The amount of ice necessary 

 to cool and hold each gallon of milk at fifty degrees F. will vary 

 from one and one-half to two and one-half pounds, provided the 

 milk was precooled and the water in the cooling tank was forty- 

 five degrees F. when the milk w^as put in. Where milk is not 

 precooled, about four pounds of ice will be required per gallon 

 of milk. 



Well or spring water for cooling milk. — If well water or 

 spring water is used for cooling milk, the water should be 

 pumped from the well or spring direct to the cooling tank ; other- 

 wise the water will be too warm when it arrives at the tank. 

 The inlet should be at the bottom of the tank, allowing the water 

 to flow around the milk cans and out of the top. 



Construction of tanks. — While wooden tanks have given good 

 results in cooling, an insulated concrete tank is much more desir- 

 able. Such a tank is easily built and can be set partly in the 

 ground. When the tank is set low, cans of milk can be lifted in 

 or out with very little effort. The total thickness of the walls 

 of an insulated concrete tank should be eight inches, divided into 

 two walls, the outside being two inches, then two inches of good 

 insulation, and the inside wall four inches thick. The concrete 

 mixture should consist of one part Portland cement, two parts 

 clean, sharp sand, and four parts broken stone or gravel. For 

 the purpose of waterproofing, hydrated lime equal to ten per 

 cent by weight of the cement, should be added to the mixture. 

 The insulation, which generally consists of some commercial 

 fibre insulator, should be coated with and set in hot asphalt, 

 which should be allowed to become thoroughly dry before the 

 inner walls of the tank are put up. The inside walls should be 

 very carefully troweled to insure a smooth surface without 

 projecting particles. 



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