314 LETTERS ON NATUEAL MAGIC. 



was possessed by many volatile oils when mixed 

 with spirit of nitre. 



Every person is familiar with the phenomena 

 of heat and combustion produced by fermenta- 

 tion. Ricks of hay and stacks of corn have been 

 frequently consumed by the heat generated during 

 the fermentation produced from moisture ; and 

 gunpowder-magazines, barns, and paper-mills 

 have been often burned by the fermentation of 

 the materials which they contained. Galen in- 

 forms us that the dung of a pigeon is sufficient 

 to set fire to a house ; and he assures us that he 

 has often seen it take fire when it had become 

 rotten. Casati likewise relates, on good authority, 

 that the fire which consumed the great church of 

 Pisa was occasioned by the dung of pigeons that 

 had for centuries built their nests under its roof. 



Among the substances subject to spontaneous 

 combustion, pulverized or finely-powdered char- 

 coal is one of the most remarkable. During the 

 last thirty years no fewer than four cases of the 

 spontaneous inflammation of powdered charcoal 

 have taken place in France. When charcoal is 

 triturated in tuns with bronze bruisers, it is re- 

 duced into the state of the finest powder. In 

 this condition it has the appearance of an unctu- 

 ous fluid, and it occupies a space three times less 

 than it does in rods of about six inches long. In 

 this state of extreme division it absorbs air much 

 more readily than it does when in rods. This 

 absorption, which is so slow as to require several 

 days for its completion, is accompanied with a 

 disengagement of heat which rises from 340 to 

 360 nearly of Fahrenheit, and which is the true 

 cause of the spontaneous inflammation. The in- 



