84 Properties of Wood Ashes. 



7. Selecting magnesia as an article possessing physical proper- 

 ties somewhat similar to those of ashes, I erected a cone of this 

 material, and at the summit buried a partially ignited coal. In a 

 few minutes T was surprised to find the whole coal was alive 

 with fire. Shortly afterwards the magnesia beneath the coal be- 

 came ignited, and the bottom of the heap almost intolerably hot. 



8. Guided by the specific gravity and the compressibility of 

 the substances employed, I repeated the experiment with pulveri- 

 zed chalk instead of magnesia. The chalk soon became red hot, 

 beneath the coal ; and the base of the heap, heated beyond en- 

 durance. 



Thus discovering that these alkaline earths possessed the same 

 heat-preserving properties as ashes, and that the same downward, 

 centralizing tendency of caloric was shown in all, I was led to 

 the conclusion that the heat eliminated and diffused in the sifted 

 ashes was the result of the combustion of the single coal buried 

 in them ; and considering their low conducting and radiating 

 power, it appeared probable that the amount of heat apparent was 

 not very far from the absolute quantity generated daring the 

 combustion. In every instance, while the central parts of the 

 cones were red hot, the exterior of the ashes except at the apex 

 was cold throughout the experiment. The caloric is evolved 

 faster than it is diffused, and of course it accumulates within a 

 small sphere near the coal to an igniting temperature ; combusti- 

 ble matter lying at the circumference of this sphere, would ignite 

 and generate another ball of fire, and this produce another, and 

 so on indefinitely, or while the last ignited spheres reached new 

 combustible matter. In this manner I conceive the caloric trav- 

 elled in the fifth and sixth experiments, and I see no reason why 

 it should not under similar circumstances circulate through a bed 

 of ashes spread over the whole earth. 



Satisfying myself in this manner that the presence of pulveru- 

 lent charcoal was not essential to the phenomenon in question, I 

 submitted other powders to similar trials. 



9. Fine sand, scorified wood ashes, anhydrous sulphate of lime, 

 common earth, all thoroughly dried, and the earth and sulphate 

 reduced to subtle powders, were severally made the tenements of 

 a fully ignited coal ; but in spite of all the persuasion I could 

 command, the coal refused to be buried alive in such sepulchres 

 as these ; almost as soon as it was decently interred, it expired. 



