COOLING HOT-BOTTLED PASTEURIZED MILK. 



21 



except tliat the velocity of air in the latter case was consideiably 

 greater than in the former. 



This experiment was repeated several times mider different condi- 

 tions, but the same general form of curve was obtained each time. 

 Just after the fan supplying the cold air was started the difference in 

 temperature between the top and bottom layers of milk was increased 

 by a degree or two, after which it gradually fell. This slight increase 











































































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-Variation in top and. bottom of same bottle. — Diflerence in temperature between top ^xid bottom 

 of quart bottle of milk when cooled by air blown upward through stack. 



just after starting was probably caused by a quick cooling of the 

 bottom layer which remained at the bottom on account of its greater 

 density, while the top layer gradually fell, its place being taken by a 

 warm layer. These results show the advantage of cooling by blowing 

 air downward through the crates. 



The curves in figure 16 show the results obtained when either milk 

 or water was cooled by cold air blown downward through the stack, 

 the average tenfperature of the incoming air being 19.8° F. (—7.7° C.) 

 and the velocity of air 1,707 feet a minute. It will be seen in the 

 figure that curves 2 and 8 show the variation in temperature of the 





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]JiG. 15.— Variation in top and bottom of same bottle.— Diflerence in temperature between top and bottom 

 of quart bottle of milk when cooled by air blown downward through stack. 



incoming and outgoing air, while curves 5 and 6 show the drop in 

 temperature of a quart bottle of milk and one of water, respectively. 

 Curve 7 shows the difference in temperature between the top and 

 bottom layers of milk, and curve 10 shows similar temperature differ- 

 ences taken in a quart of water. The solid line marked " ' ' is intended 

 to represent the point where there is no difference in temperature 

 between the top and bottom layers and is drawn on the temperature 

 scale at 39.1° F. (3.9° C), representing the maximum density of 

 water. Readings below the zero lino as a matter of convenience are 

 considered as minus, and tliosc al)ove as plus. Curve 10, represent- 

 ing the action of water, is not so difficult of interpretation, but on the 



