22 



BULLETIN 744, U. S. DEPARTMENT OF AGRICULTURE. 



relative time required for the milk to rise in temperature from 44° to 

 50° F. for the various cans was as follows : 



Hours. 



Can No. 1 8 



Can No. 2 10 



Can No. 3 3 



Hours. 



Can No. 4 4 



Can No. 5 2 



Can No. 6 £ 



While the high temperature of 99.5° F. would not be encountered 

 frequently in practice, it serves well to illustrate the efficiency of 

 different types of cans under extreme conditions. In curve No. 3 of 



Fig. 10. — Efficiency of various types of cans for holding milk. Room temperature, 74.5° F. 



figure 17, showing the rise in temperature of milk in the ice-com- 

 partment can, it will be noted that all the ice was not melted until 

 about 8 hours after the beginning of the test. The temperature of the 

 milk, however, rose to 50° F. within 3 hours. The rapid rise in 

 temperature of the milk in the can, even though the ice compartment 

 contained ice, is due to the large surface which was exposed to the 

 warm outside air as compared to the smaller surface exposed to the 

 ice. The absorption of heat by the milk from the air was much faster 

 than the absorption of heat by the ice from the milk. It will be 

 noted that after all the ice was melted the rise in temperature of 



