CLOVER CULTURE. 89- 



the oil and thrown into a heap of some considerable size, fire is very 

 liable to occur from the heat generated within the pile. In this condition, 

 slow oxygen ation of the oil take.s place, favored by the comparatively 

 enormous oil surfaces presented to the air included within the mass r 

 while at the same time escape of heat is prevented by the non-conducting 

 quality of the substance. As the heat accumulates, chemical combina- 

 tion takes place with still greater energy, the stored heat favoring the 

 process, and the process constantly contributing to increase the degree 

 of temperature. If now, the supply of air continues sufficient, as it will 

 be when the mass is sufficiently porous, and the physical conditions are 

 such as to continuously retain the generated heat, the time will come 

 when the temperature will be raised high enough to enkindle the mass. 

 Should an abundant supply of fresh air suddenly reach this over-heated 

 and inflammable material an outburst of flame may result. 



" Just the same result has been known to occur in many other sub- 

 stances, as charcoal still having condensed within its pores the inflamma- 

 ble gases separated in the process of manufacture, and reduced to a pul- 

 verized state; bituminous coal containing sulphur, and stored in very 

 large quantity. 



"Now what of moist vegetable substances? Commonly we should; 

 infer that moisture would prevent combustion. In order to burn, such 

 things must be dry. Hay in a barn is no exception to this rule. In fact, 

 if spontaneous combustion does occur in a haymow, you may be assured 

 that the igniting portion is dry at the time. What "takes place before 

 combustion is possible? At best it is hard to make all conditions such 

 that spontaneous combustion can occur. Hence one requisite is very in- 

 flammable material. Green grass or partially dried grass cannot possibly 

 ignite in this way. In truth such material has not the slightest tendency 

 o become warm on its own account. Familiar as the phenomenon is, 

 green vegetation thrown into a heap does not spontaneously heat. If 

 there were any way of keeping living organisms out of such a mass there 

 would be no generation of heat whatever. Green stuff would keep cool 

 just as certainly as the most thoroughly dried material. But under all 

 ordinary conditions, minute living things are abundant on grass when 

 ever cut and collected. They must have moisture to live. When, how- 

 ever, moist nutrient material is present, they do possess the peculiar 

 power of forming what we call fermentation. In this process heat is one 

 of the results, the chemical changes being fairly equivalent to, though not 

 identical with those of combustion. Under favorable conditions the degree 

 of temperature due to these organisms may rise until it becomes injurious 

 to their physiological functions, when it can rise no higher. If the mass 

 still continues moist, no other means are known whereby this tempera- 

 ture can be increased through any internal combinations or changes 

 whatever. Spontaneous combustion is an impossibility. Hence, no silo 

 filled with material containing water enough to keep moist through the 

 fermenting process can possibly burn. The upper limit of temperature 

 for these micro-organisms is pretty definitely ascertained, viz. about 145 

 degrees Fahr. is about the upper extreme if the bodies are immersed in 

 water. The micro-organisms referred to, are minute plants, and though 

 not killed by temperature fatal to grass and beans, are just as effectually 

 prevented from development at a given degree of heat. Now 145 degrees 

 Fahr. is scalding hot, but it lacks a long way of being sufficient to ignite 

 such fairly combustible matter as dry hay. In other words, heat due to- 

 f errrlentation by living organisms is never sufficient to cause the ignition 

 of vegetable matter, whether moist or thoroughly dry. 



1 ' Let us see, however, what else occurs. As true fermentation pro- 

 gresses, water is consumed as well as the nutrient material in which the 



