10 BULLETIISr 420, U. S. DEPAETMEISTT OF AGRICULTURE. 



described. Several experiments were carried out, using air at different 

 temperatures for cooling purposes. 



In figure 6 are shown the results of cooling by air at an average 

 temperature of 67.9° F. (19.9° C). A complete set of curves is 

 incorporated, principally to show the rate of cooling with air at this 

 high initial temperature. Curves 3 and 4 show the relative rate of 

 cooling between quart bottles of milk and water, respectively, when 

 placed side by side at the bottom of the stack. These curves agree 

 very closely with those in figure 2. Curves 5 and 6 show, respectively, 

 the rate of cooling between pints and quarts placed at the top, or 

 fifth, tier of crates. Curves 3 and 6 are plotted from temperature 

 readings taken in the lower quart of milk and the upper quart of 

 water, respectively. The average difference in temperature between 

 these bottles was 9.8° F. (5.4° C), while the maximum difference was 

 about 19° F. (10.5° C). Curves 5 and 6 are practically parallel 

 throughout the range, the curve showing the drop in temperature of 

 the pint remaining throughout about 5 degrees lower than that of 

 the quart. The average difference in temperature between curves 4 

 and 6, which are plotted from temperature readings taken in the 

 lower and upper quarts of water, respectively, is 10.5° F. (5.8° C), 

 while the greatest is 20° F. (11.1° C). 



The temperatures indicated by the curves in figure 7 were deter- 

 mined in a pint and a quart bottle at the top of the stack and also one 

 of each kind at the bottom. The temperature of the lower quart and 

 pint, as shown by curves 3 and 4, respectively, drops below that of 

 the outgoing air. It should be remembered, however, that the tem- 

 perature of the outgoing air was taken at the point where it left the 

 box; hence, the temperature of the air passing over the bottles was 

 lower than that indicated by the curves. Toward the end of the run 

 the temperature of the lower pint was reduced below that of the 

 incoming air. This was caused by the temperature of the outside air 

 rising so rapidly that that of the lower pint,^wliich had been cooled, 

 had not had sufficient time to adjust itself to the rising temperature 

 of the outside air. The average difference between the lower pint 

 and the upper quart, curves 4 and 5, was about 25° F. (13.9° C), 

 while the maximum difference in temperature was about 43° F. 

 (23.9° C). This difference becomes more marked when the tempera- 

 ture of the outside air is lower, consequently, when blowing air up 

 through the crates there is great danger of the top crates not being 

 cooled properly, while on the other hand the milk in the lower crates 

 may be frozen, provided the initial temperature of the incoming air 

 is below the freezmg point. By comparing temperature curves 3 and 

 6, lower quart and upper pint, respectively, it will be noted that the 

 temperatures in the two bottles were much nearer each other. The 

 maximum difference was about 12° F. (6.7° C), but the average was 



