24 BULLETIlSr 420, U. S. DEPARTMENT OF AGRICULTURE. 



The velocity of air calculated from the Pitot-tube readings is 

 997^ ' = 2,253 feet a minute, and the volume of air discharged 



each minute is 2,253x1.07 = 2,410 cubic feet. The readings, how- 

 ever, were taken in the discharge pipe after the air had been heated ' 

 by passing over the hot bottles; hence the volume of cold air supphed ' 

 should be corrected in the ratio of the absolute temperatures of the 



2 410 X499 



air at the inlet and outlet of the box, or — — =— = =2,326 cubic feet 



617 



of cold air supphed each minute. 



The time of operating was 148.5 minutes to cool to approximately 

 45° F. Therefore the total amount of air supphed for coohng was 

 148.5X2,326 = 345,411 cubic feet at an average temperature of 39.6'^ 

 F. (4.2° C), or a total weight of 345,411 X 0.07838 = 27,069 pounds. 



The heat required to raise the temperature of this amount of 

 air and perform the work of expanding the air, which was fur- 

 nished by the hquid, bottles, and crates inside the box, is 



27,069x0.169(58.1-39.6+^Xl8(357,785-345,411)=84,919B. T. 



U. in other words, 34,919 B. T. U. is the amount of heat absorbed 

 from the materials inside the box, and it is obvious that the heat 

 given up by these materials should theoretically equal or balance th& 

 amount absorbed by the air. 



Following are data and calculations of the amount of heat given 

 up by the hquid, glassware, and crates : 



Weight of water tised in experiments 677 pounds. 



Initial temperature of water J 137.4° F. (58.55° C). 



Final temperatine of water 45.7° F. (7.61° C). 



Difference 91.7 F. (50.94° C). 



Weight of glass 572 pounds. 



Initial temperature of glass 137.4° F. (58.55° C). 



Final temperature of glass 45.7° F. (7.61° C). 



Difference 91.7° F. (50.94° C). 



Weight of wood in crates 189 pounds. 



Initial temperature of wood 79.0° F. (26.11° C). 



Final temperature of wood 43.3° F. (6.28° C). 



Difference 35.7° F. (19.83° C). 



Weight of iron in crates 198 pounds. 



Initial temperature of ii'on 79.0° F. (26.11° C). 



Final temperature of iron 43.3° F. (6.28° C). 



Difference 35.7° F. (19.83° C). 



Average temperatm-e of air in room 70.0° F. (21.1° C). 



Average temperature of outgoing au- 58.0° F. (14.4° C). 



B. T. U.i extracted from water, 677 (137.4-45.7) =62, 080' 



B. T. U. extracted from glass, 572X0.1877 (137.4-45.7) = 9, 848 



1 Fabrenheit degrees were used in the calculations; hence results are in B. T. U. 



