22 
BULLETIN 420, U. S. DEPARTMENT OF AGRICULTURE. 
other hand the action of the milk as represented by curve 7 is very 
difficult, owing to complications produced by the physical properties 
of milk under changing temperature conditions. 
In curve 10 it will be noted that there was an increase in the differ- 
ence in temperature between the top and bottom layers of the water 
just after the fan was started. This may be explained by the fact 
that there was an air space between the top of the liquid and the 
paper-cap covering which acted as a heat insulator, protecting the 
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Fig. 16.— Relative drop in temperature of quart bottles of milk and water and incoming and outgoing air; 
also difference in temperature between top and bottom of quarts of milk and water. Air blown down- 
ward through stack. 
top layer of the water from the direct effect of the cold air, while the 
bottom layer, which was in direct contact with the bottom of the 
bottle, was chilled quickly, increasing the difference in the tempera- 
ture between the top and bottom layers. The upper terminal of the 
differential couple was placed in the center of the neck of the bottle; 
hence with the air space in the bottle neck the top layer of the water 
was cooled to a great extent by conduction from the sides. There 
