III. RATE OF ACCUMULATION OF HEAT IN THE RESPIRATION 

 OF FRUIT UNDER ADIABATIC CONDITIONS. 



CAUSES OF SELF-HEATING. 



As stated in Part I (p. 7), two attempts to determine the effect of 

 temperature on the respiration of bananas failed because of the 

 very rapid increase in respiration which occurred, incident to the 

 processes of ripening, during the periods of observation at room 

 temperature. It was observed that the walls of the desiccators in 

 which the fruit was kept became wet on the inside. In attempting 

 to discover the cause of this, the bananas were found to be from 1.4° 

 to 1.9° C. warmer than the desiccators. Attention was thus drawn 

 to the phenomenon of self-heating exhibited by certain agricultural 

 products, many similar instances being readily found. The heating 

 of bananas has long been known to the shippers. Carrots, sugar 

 beets, corn and other grains, cotton seed, hayseed, hay, manure, 

 tobacco, and stover all heat readily, especially if stored when moist 

 and under such conditions that the heat as produced is not dissipated. 



An inspection of the literature shows that self -heating may be due 

 to several causes. Heating caused by physiological processes prob- 

 ably operates first and raises the temperature to the point at which 

 other causes, enzymotic or chemical, come into play. Oxidizing 

 enzyms are the active agents in many cases. They are, for example, 

 probably the dominating factor in the fermentation of tobacco, 1 

 working most actively at the high temperatures which may have 

 occurred as a result of respiration. The microorganisms also induce 

 oxidation or other chemical changes involving the liberation of heat. 

 Finally there is the chemical oxidation which often supervenes when 

 one or more of the other causes has raised the temperature to the 

 point at which chemical action is appreciable. The final result may 

 then be charring, or even combustion. The difficulties in deciding 

 which of the several causes last named are operative in spontaneous 

 heating are interestingly discussed by Rahn. 2 



The operation of the physiological processes in respiration seems 

 to be the general cause of self-heating. As the law expressing the 

 increase of the rate of respiration with temperature is now approxi- 

 mately known, it has seemed worth while to calculate the rate at 

 which the temperature would increase when adiabatic conditions 

 are assumed — that is, conditions under which there is no gain or 

 loss in heat from the outside. The results of such a calculation 

 should be of value in the study of self-heating. 



1 U. S. Dept. Agr., Report No. 59, Loew, Curing and Fermentation of Cigar-leaf Tobacco. 



2 Michigan Agricultural College Experiment Station, Technical Bui. 5, 1910. 



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