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EXPLANATION OF EXERCISE VI 



On the average dairy farm, one of the most practical methods of 

 cooling milk is to set the can containing the milk in a tank of ice water. 

 For this purpose a cement tank is the most durable and in the long run 

 cheapest. The walls of the tank should be from four to six inches 

 thick and that side on which the milk is lifted in and out of the tank 

 should be faced with iron to prevent the cans from chipping the 

 cement. The tank will be most convenient if it is sunk in the floor 

 as this will make it easier to lift the cans in and out. The walls 

 should, however, extend about twelve inches above the floor to pre- 

 vent dirt working into the tank. An outlet should be made in the 

 bottom of the tank so that it may be easily cleaned as more or less 

 milk will be spilled, causing the tank to become unsanitary. 



A galvanized iron tank, useful in cooling milk and capable of hold- 

 ing four cans, may be purchased from dairy supply houses for from 

 eight to ten dollars. 



In order to have milk cool properly in a tank of this kind it is 

 necessary to frequently stir the milk in the cans. Unless milk is 

 stirred frequently it will not cool rapidly and rapid cooling is essential 

 in preventing an increase of germ life. 



The purpose of the following exercise is to show the effect of stirring 

 at different intervals on the rapidity with which milk cools. The 

 student should also draw conclusions regarding the frequency with 

 which milk should be stirred to get the best practical results. 



EXERCISE VI 

 COOLING MILK IN CANS 



1. Heat four cans of milk to 95 F. and place in a tank of ice 

 water. For this experiment about 135 pounds of ice will be required. 



Stir can No. I every five minutes and record the temperature. 



Stir can No. II every ten minutes and record the temperature. 



Stir can No. Ill continuously and record the temperature every 

 ten minutes. 



Do not stir can No. IV at all but record the temperature of the 

 milk in the center at ten minute intervals. 



2. Carry on the experiment for one hour and at the end of one 

 hour thoroughly stir can No. IV and record the temperature of the 

 mixed milk with that of the temperature of the milk before the 

 milk was thoroughly stirred. 



3 . Compare the temperature obtained in the four different cans. 

 Draw conclusions concerning the frequency with which milk should 

 be stirred, to get the best practical results. 



