72 On the Ciranmtances produchig Ignlt'iun 



situations. As large quantities of charcoal are used in gun- 

 powder manufactories and in other works, its spontaneous com- 

 bustion in such places would manifestly endanger, not only much 

 property, but a number of lives. The subject is, therefore, 

 worthy of attention ; since, if the cause could be assigned, the 

 danger might be averted. 



If 20 or 30 cwt. of charcoal, in a state of minute division, 

 be put together in a heap and left undisturbed, spontaneous 

 combustion generally ensues. The fact has been long known ; — 

 but no investigation, with the exception of that to which I have 

 referred, has, to my knowledge, been instituted. 



Spontaneous combustion does not often take place in what 

 the manufacturers call round charcoal; that is to say, in frag- 

 ments of considerable size ; unless when large quantities are 

 laid together, under which circumstances it is not very unusual. 

 In this case the phaenomenon is generally ascribed by the 

 makers to the charcoal not having been sufficiently cooled after 

 its production. This reason is, no doubt, sometimes, but not 

 always, correct. On the contrary, T have known charcoal, 

 which has been freely exposed to the atmosphere, when, though 

 closely watched, it presented in the interval no appearance of 

 the kind. 



In one case charcoal was loaded in Manchester and con- 

 veyed by a cart to a distance of twenty miles. No combustion 

 appeared during the loading:, nor could the carter, though he 

 carefully examined, perceive any indication of it, when, at 11 

 o'clock, he left it for the night. At 5 o'clock on the following 

 morning, however, he was called up to save his cart, which he 

 found on fire and nearly consumed. 



This charcoal had been made three days before the acci- 

 dent. Care had been taken that it should be sufficiently cool 

 before it was loaded, as a similar event had previously occurred 

 to the same parties, who ascribed it to the charcoal being 

 too new, when, as they conceived, fire lurked in it unextin- 

 guished. 



These two instances may, I should think, be accounted for in 

 the following manner : — 



When large quantities of charcoal, as in the tirst example, 

 are laid together, it is evident that the lower parts must be ex- 

 posed to pressure, and, by the motion of the cart, to friction 

 from the parts above ; in this way, therefore, a portion of the 

 charcoal is pulverised, forming a compact mass at the bottom, 

 where it enters into spontaneous combustion. 



In the second instance, pressure and friction had still greater 

 influence. The carter, while he was loading, beat down the 

 charcoal with a large hammer, to force it into a smaller com- 

 pass. Conveyed for twenty miles in a cart, the pieces would rub 



