A POSSIBLE EXPLANATION OF CERTAIN FOREST FIRES 

 OF UNKNOWN ORIGIN 



By Hi;nry Schmitz 



Laboratory of Forest Products, University of Idaho, Moscow 



Fires of unusual origin which might be the cause of forest hrcs are, 

 of course, of immediate interest to foresters and lumbermen. The 

 following record of a case of "spontaneous combustion"' in a single 

 dropping of horse dung is therefore reported. The circumstances sur- 

 rounding this case are briefly these : 



. On August 7, 1921, at approximately 4 p. m. it was observed ^ that a 

 single dropping of horse dung exposed to direct sunlight back of 

 Morrill Hall on the University of Idaho campus began to saioke faintly. 

 The volun:e of smoke steadily increased and the dung heap finally burst 

 into flame. The maximum temperature on this day was 91° F. 



Immediately after the flame was noticed a detailed examination of 

 the droppings was made in order to determine if the combustion may 

 not have been due to the action of the sun's rays striking a piece of 

 glass near the heap, or whether it was due to other causes. This 

 examination revealed the fact that there was no broken glass on or 

 near the heap and there was no evidence that the fire started through 

 any other means that through "spontaneous combustion." The evi- 

 dence also all pointed toward the fire having started in the interior 

 of the heap rather than on the surface. 



It is a well known fact that during the decomposition of vegetable 

 matter, particularly in the form of piles of horse dung, a quite high 

 temperature may be produced due, in part at least, to bacterial activity. 

 The present observation, however, deals with but a single dropping, 

 and with dung that was not over ten to fourteen days old, and probably 

 not over four. The horse had been feeding on green grass which would 

 influence the physical character of the dung. 



On account of the far reaching effects of forest fires started in a 

 manner as above described, it may not be amiss to briefly discuss the 

 physiological and physical factors obtaining in a pile of dung which 



' This observation was also made by at least six men of the faculty of the Col- 

 lege of Agriculture. 



769 



