Decomposition of iron Pyrites. 



139 



ently from a subsequent deoxidation of the ferric chloride in the 

 })resence of the iron disulphide. The tube was hung up by a 

 south window and remained at the temperature of the labor- 

 atory for ninety days ; then, on opening by breaking under 

 water, not a trace of either iron or sulphur was detected in the 

 colorless fluid. The other tube, containing the lump, remained 

 colorless, even after several weeks. These experiments proved 

 tliat the variety, though stable, became unstable in fine powder, 

 and that it was impossible to obtain sufficiently accurate results 

 from analyses of the marcasite in the finely divided condition. 

 This was probably caused by the condensation of oxygen upon 

 the enormously increased surface, the addition of its weight and 

 Its partial combination Avith the iron and sulphur. The exper- 

 iments also proved the absence of any trace of iron protosul- 

 ])hide, of oxygen, or of other soluble impurities, which have 

 been suggested by some investigators. On the ground of these 

 experiments, the method of quantitative analysis was therefore 

 again modified by taking a rapidly weighed lump of the min- 

 eral, in the analysis whose results are headed No. 3. The pro- 

 cess of solution was of course considerably slower than in the 

 case of the fine powder. 



Analysis of crystalline marcasite from Folkestone, Eng. 

 Sp. Gr. =4.887. 



Iron 

 Sulphur 



Fine powder. 



47.310 



52.780 



100.090 



Fine powder. 

 46.807 

 52.464 

 99.271 



3 

 Lump. 



46.705 



53.359 



100.064 



Theoretical 

 Constitution. 



46.667 



53.333 



100.000 



A qualitative analysis of the mineral also showed the absence 

 of other metallic bases and of arsenic. The close approximation 

 of the last analysis (No. 3) to the theoretical composition is of 

 course partially accidental, as every chemist will understand, 

 but justifies the conclusion that the marcasite of Folkestone 

 contains no iron protosulphide. The surfaces of some of the 

 crystals in its groups are encrusted by a film or coating of 

 orange-colored iron-ochre, which indicates its liability to slow 



