PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 631 



rapidity of the process. The heat miiy be sufficient to ignite the 

 inflammable gases, as is not unfrequently shown by the spontane- 

 ous combustion of large heaps of coal, and by the fires in the 

 mines themselves; that the decomposition was the same in the 

 interior of the heaps as on the surface, it being equally rapid at 

 both points; that the action was most rapid during the first few 

 weeks of exposure, the heat generated by decomposition reaching 

 its maximum about the third or fourth week; that one-half the 

 oxygen absorbed was taken up during the first fourteen days. 

 The well known fact that coal long mined is far less liable to 

 spontaneous combustion may be adduced as corroborative evidence 

 of this. That a coal originally poor in oxygen, decomposes more 

 rapidly than one rich in it. That coal, dried at a temperature of 

 212° Fahrenheit till its weight remains constant, can be heated up 

 to 392° Fahrenheit (200° C.) without further loss of weight. 

 Hence, w^ater is an active element in the decomposition. That 

 large coal, exposing less surface to the action of the air and mois- 

 ture than small coal, is much less rapidly decomposed. The ten- 

 dency, however, of large lumps, having joints, to fall to pieces on 

 exposure is well known. 



The analysis of freshly mined coal of several heaps gave the 

 following composition : 



I. II. III. 



Carbon 71.51 per cent. 78.32 per cent. 82.21 per cent. 



Hydrogen 5. .32 per cent. 5.04 per cent. 6.38 per cent. 



Nitrogen 0.92 per cent. 0.88 per cent. 0.89 per cent. 



Oxygen 5.83 per cent. 8.08 per cent. 5.72 per cent. 



Sulphur 1.08 per cent. 0.66 per cent. 0.77 per cent. 



Ash 10.34 per cent. 7.02 per cert. 6.03 per cent. 



Total 100. 100. 100. 



The result of the experiment is as follows : 



Small Coal in Heaps, 



I. II. III. 



Absolute loss of weight 33.08 per cent. 44.61 per cent. 42.19 per cent. 



Loss of value as fuel 47.60 per cent. 56.81 per cent. 56.38 per cent. 



Loss of value as gas 45.61 per cent. 47.95 per cent. 60.29 per cect. 



Large Coal kept Under Cover. 



I. II. III. 



Absolute loss of weight 10.69 per cent. 6.;^ per cent. 3.19 per cent. 



Loss of value as fuel 12.59 per cent. 9.04 per cent. 4.66 per cent. 



Loss of value as gas 23.93 per cent. 16.32 per cent. 14.24 per cent. 



The great mass of coal consumed in this part of oui- country 

 being anthracite, the majority of consumers are not directly inter- 



