Another opinion has been advanced by Bartholdi, to account for the spontaneous combustion in powder mills: namely, that charcoal sometimes contains phosphorus, combined with hydrogen, which, by the action of the pestle, is disengaged in the form of gas, and inflames, the moment it comes in contact with the air. Others again suppose, that it sometimes contains pyrophorus.
Pulverizing the charcoal, in the first instance, by itself, and adding water, during its mixture, from time to time, a measure proposed in 1808, by M. David, and now generally adopted, will prevent such accidents; for it appears, they have not occurred in France, since the adoption of this plan. Some remarks on spontaneous combustion, may be seen in the article on _artificial volcanoes_.
M. Sage, (_Journal de Physique_, vol. lxv, p. 423, or _Nicholson's Journal_, vol. xxiii, p. 277), has written on the spontaneous ignition of charcoal, and adduced some facts on the subject; by which it appears, that M. de Caussigni was the first, who observed, that charcoal was capable of being set on fire, by the pressure of mill stones.
Mr. Robin, commissary of the powder mills of Essonne, has given an account, in the _Annales de Chimie_, of the spontaneous inflammation of charcoal, from the black berry bearing alder, that took place the 23d of May, 1801, in the box of the bolter, into which it had been sifted. This charcoal, made two days before, had been ground in the mill, without showing any signs of ignition. The coarse powder, that remained in the bolter, experienced no alteration. The light undulating flame, unextinguishable by water, that appeared on the surface of the sifted charcoal, was of the nature of inflammable gas, which is equally unextinguishable.[17]
The moisture of the atmosphere, of which fresh made charcoal is very greedy, appears to have concurred in the development of the inflammable gas, and the combustion of the charcoal.
It has been observed, that charcoal powdered and laid in large heaps, heats strongly.
Alder charcoal has been seen to take fire in the warehouses, in which it has been stored.
About thirty years ago, M. Sage saw the roof of one of the low wings of the mint set on fire by the spontaneous combustion of a large quantity of charcoal, that had been laid in the garrets.