Mineral Sulphides of Iron. 



189 



over a range from 400° to 600°. The curve was perfectly 

 smooth. When a similar charge of marcasite was heated in 

 the same way, an acceleration of the temperature was plainly 

 seen on the curve between 500° and 600°. (See fig. 5.) The 



Fig. 5. 



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Fig. 5. Thermal curves showing evolution of heat when marcasite is 

 changed into pyrite. (Curves 3, 4 and 5.) Curves 1 and 2 are thermal 

 curves of pyrite. 



