COOLING, STORING, AND SHIPPING MILK. 



11 



During the test with the galvanized-iron tank the air temperature 

 ranged from 72° to 80° F. with an average of 76° F. At the end of 

 nine hours the temperature of the water was 58° F. and the tempera- 

 ture of the milk was 56.5° F. It will be noted that the minimum 

 temperature of the water was reached three hours after the ice was 

 added, and from that time on the temperature of the water rose slightly 

 for the next two hours, until all the ice was melted. From this point 

 the rise in the temperature of the water was more rapid. The tempera- 



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Fig. 8. — Rise in temperature of water during 9 hours in 4 types of cooling tanks, 

 tanks covered and exposed to direct rays of sun. 



All 



ture of the milk continued to fall until just before the sixth hour, 

 when the curves showed that the temperature of the milk dropped 

 below the water. This was due to the fact that about one hour before 

 all the ice was melted the temperature of the water began to rise 

 and rose faster than the temperature of the milk dropped. This is 

 caused by the fact that there is a double transfer of heat, first from the 

 air to the water, then from the water to the milk. 



