168 Combustibility/ of Wood Ashes. 



of danger, while the box and its contents continued undisturbed? 

 With this inquiry in my mind, I made a memorandum of the 

 event in my common-place book, and left the subject for future 

 reflection and research. Years passed, and the memorandum fre- 

 quently met my eye as I occasionally turned over the leaves of 

 my manuscripts ; but it did not obtain any particular attention. 



4. A few months ago, however, I had cause to congratulate 

 myself for having made a careful record of the phenomenon re- 

 ferred to. Our domestic informed me, perhaps two months since, 

 that the ash-box, (a transverse section of the trunk of a very 

 large sycamore,) had "burnt through near the bottom." The 

 former occurrence of the same kind, presented itself vividly 

 to mind, and I eagerly repaired to the late scene of combustion to 

 pursue my original inquiry, believing the cause, whatever it might 

 be, to be the same in both instances. The domestic had poured 

 a large quantity of water upon the ashes in the morning when 

 she detected the fire, and she supposed every spark had been ex- 

 tinguished. I found, however, that the ashes were now, in the 

 evening, insupportably hot ; and by means of a spade, I ascer- 

 tained that the heat extended throughout the mass ; the blade 

 when drawn out, hissed when spit upon. I thoroughly drench- 

 ed the ashes, and then sat down to reflect upon the phenomenon. 



It soon occurred to me, as highly probable, that ashes, when 

 taken from the fire-place, contain a considerable quantity of car- 

 bonaceous matter in a state of minute division ; that ignition of 

 these particles might exist without being apparent to the eve ; 

 that this ignition might be communicated very slowly to the car- 

 bonaceous powder in surrounding cold or extinguished ashes, and 

 thus fire be conducted gradually to large coals, and to the wood- 

 en vessel containing the ashes. 



To determine the correctness of my conjecture, I sifted through 

 the finest Chinese sieve I could procure, some ashes which had 

 been taken from the fire-place the day before, and weighing 642 

 grs, subjected them to heat in a Hessian crucible. In a short 

 time the crucible became red hot ; but no redness was visible in 

 the ashes. At this stage of the process, I thrust a beech splinter 

 into the ashes, (being careful not to touch the crucible,) and it 

 immediately took fire. After allowing the crucible to cool, I 

 weighed the contents, and found they had lost 12 grs. The 

 quantity of comminuted carbon no doubt varies in different par- 



