Decomposition of Iron Pyrites. 215 



of coal after winning is especially its accumulation without ven- 

 tilation, in stock-piles of great magnitude at mines, points of 

 shipment, or upon the premises of dealers, so as to admit of re- 

 tention of the heat developed and to promote the process of 

 oxidation under the influence of meteoric water and the heat of 

 the sun. Coals of certain kinds or in certain conditions, ex- 

 posed in this manner to the weather, are well known to develop 

 heat, even to the point of spontaneous ignition, while other 

 kinds of coals, especially those low in pyrites, may develop the 

 greatest quantity of heat under protection from the weather.'' 



In explanation of these facts, Richters has recently upheld 

 the view that such heat has been developed during the absorp- 

 tion of oxygen, both by its physical condensation within the 

 pores of the coal, and by its chemical combination, resulting in 

 the oxidation of the organic constituents of that substance. 



In accordance with this view, it was found that ordinary 

 coals, free from pyrites, experienced the strongest absorption of 

 oxygen when in a dry condition, and could therefore be best 

 protected from a development of heat by preservation in damp 

 , places, even with exposure to the atmosphere. On the other 

 hand, the older view attributed the elevation of temperature in 

 loose bodies of coal to the oxidation of its commonly enclosed 

 accessory, pyrites, and, as Kimball points out, with the addi- 

 tional heat produced by the hydration of the sulphuric anhyd- 

 ride, during vitriolization, and by the hydration and further 

 oxidation of the resulting salts. Even with a low average con- 

 tent of pyrites throughout a coal of this kind, the local concen- 

 tration of this accessory may obviously suffice to produce decom- 

 position and even spontaneous ignition. Accordingly dampness 

 has been found to promote the decomposition of a pyritic coal, 

 and its preservation is best ensured by keeping it in a dry con- 

 dition and place, with protection from the weather. 



There is a difference, however, in facility of decomposition 

 between the two important classes of coals, bituminous and an- 

 thracite, which is plainly connected with some peculiarity in 

 their pyritous contents, and Kimball remarks : 



** Some of the anomalies observed in coals of transition types, 

 in respect to resistance to weather, are perhaps as much due to 

 differences in their accessory pyrites as to the quantity contained 



