December, 1844.] 163 



Professor Johnson exhibited specimens of coal coke, cinders, and 

 lumps of pyrites, from a heap of about 250 tons of bituminous coal, 

 from the line of tho summit portage Railroad, in Cambria county, 

 Pennsylvania. This coal had been lying for five or six months in 

 the coal yard of Mr. Nathan Middleton, south west corner of Ridge 

 Road and Willow street, and was yesterday morning (December 2, 

 1844,) found to be on fire from spontaneous combustion, burning 

 through a board fence between the coal yard and the adjoining pre- 

 mises, very near the ground. The height of the pile, above the 

 point where combustion commenced, was about nine or ten feet. 

 On applying a thermometer at three feet distance, in a horizontal 

 direction from the fire, the temperature was found to be only 70 

 degrees ; but by digging down over the same point to within four 

 feet of the level of the fire, the temperature was 160 degrees. 



One of the specimens exhibited, on a surface of deposition, a yel- 

 lowish while pellicle of pyrites, which, from the minuteness of the 

 crystals, resembles frost-work ; another has distinct plies or scams 

 of the sulphuret continued through the lumps; a third is a nodular 

 lump of nearly pure pyrites ; and a fourth is a fragment of a reni- 

 form mass of the same material, weighing upwards of three pounds, 

 with a film of adhering coal. The interior of the mass is some- 

 what porous, with slight intermixture of carbonaceous matter; while 

 the exterior is a shell of much more compact structure. Clusters 

 of crystals, of considerable magnitude, are here and there seen. On 

 the part coated with coal are seen films or dissepiments, penetrating 

 the coal at right angles to the surface of the kidney-shaped mass. 

 On one side the coal has been polished, apparently by sliding under 

 immense pressure over some hard substance, giving it the appear- 

 ance of " slickensides." In this part, the projecting partitions of 

 sulphuret of iron, as well as the coal, have been broken down, 

 crushed and flattened, and the direction in which the folia have been 

 bent, marks that of the motion which had occurred in the bed. 



Professor Johnson also exhibited the peroxide of iron adhering to 

 the coke formed in this spontaneous ignition, and referred to the de- 

 composition of sulphate of iron, without access of air, as capable of 

 producing that oxide. Also, to the simultaneous development of 

 anhydrous sulphuric acid and sulphurous acid as the volatile pro- 

 ducts. The latter acid, when generated in the combustion or dis- 

 tillation of bituminous coal, passes off in combination with ammonia, 



