40 RESOURCES OF TENNESSEE. 



temperature rose, the other combustible materials were oxi- 

 dized, and when it reached a certain temperature, the oil ig- 

 nited. Then all the combustibles burned and we had the phe- 

 nomenon of spontaneous combustion. 



In the complete oxidation or combustion of pyrite and mar- 

 casite, iron oxide or rust and the gas, sulphur dioxide, are 

 formed. This gas is largely the sulpfeur fumes given off in the 

 burning of the shale and is the same as that given off from a 

 burning sulphur match. It attacked the leaves of the trees, etc., 

 and caused the offensive odor of the burning shale. It is sol- 

 uble in water, and because there was a great deal of moisture 

 on the shale, this gas was dissolved, and caused all the shale to 

 have an acid taste. 



A small amount of sulphuretted hydrogen gas was formed 

 by the action, in the presence of moisture, of the sulphur diox- 

 ide, from the burned pyrite, on the pyrite of the shale, which 

 had not yet burned. This was the gas of the fumes which at- 

 tacked the white paint on the boats and changed some of the 

 white lead carbonate of the paint to black lead sulphide, thus 

 causing the dirty color. 



When the supply of oxygen is rather limited, as was the case 

 in some parts of this pile of shale, the marcasite and pyrite 

 are only partially oxidized. In this case iron sulphate and free 

 sulphur would be formed. The heat volitilized the sulphur, 

 which, on cooling at the surface, condensed, and was deposited 

 as crystals and yellowish whito. powder on the surface of the 

 pile of shale. The iron sulphate left behind in place of the py- 

 rite or marcasite, on cooling took up water and formed crystals 

 of green vitriol or copperas. These crystals, however, on ex- 

 posure to the air, lose some water and crumble to a white 

 powder, which was its form in the burned shale. 



The burning of shale is no ordinary occurrence but is possible 

 when there is a large amount of combustible material in it. 

 The spontaneous combustion of shale, however, is very rare, 

 and this phenomenon is worthy of record. 



