386 Decomposition of Iron Pyrites. 



itself with the sulphur of the iron pyrites to sulphuretted 

 hydrogen, from which the sulphur has finally separated itself/' 



The reactions suggested are given in the following formulae : 



2 molecules of pyrite Fe 2 S 4 , 

 plus 3 molecules of water H G O 3 , 



have yielded 

 1 molecule of iron oxide Fe 2 O 3 (afterward 



converted to hydrated oxide), 



3 molecules of hydrogen sulphide IF S 3 , and 

 1 molecule of sulphur S. 



However, on this subject, it appears extremely unlikely that 

 such a dissociation of the constituents of water could occur at 

 ordinary temperatures, without the intermediation of a free acid, 

 any more than in the case of the decomposition of water by me- 

 tallic zinc or iron, or that of artificial iron sulphide. It has been 

 shown by Stromeyer that, on the solution of pyrrhotite in dilute 

 hydrochloric and sulphuric acids, there is an evolution of hydro- 

 gen sulphide and a separation of sulphur in fine powder. I 

 would therefore suggest that we have probably, in these cases 

 of the natural production of sulphur, the indications of a reac- 

 tion with carbonic acid or some purely organic acid, very likely 

 one of the humus group, 42 decomposing the iron sulphide — per- 

 haps converting the iron into an organic salt, afterwards passing 

 into peroxide and eliminating the sulphur as hydrogen sulphide 

 and free sulphur, soon mechanically carried away in most cases. 



This hypothesis appears to be justified by the observations of 

 H. C. Bolton, who obtained a reaction for hydrogen sulphide, 

 on digestion of pulverized p} 7 rrhotite for twelve hours in a cold 

 concentrated solution of citric acid. He says : — 



" Three specimens of pyrite heated with citric acid gave no 

 traces of the gas, and three of pyrrhotite liberated it both in the 

 cold and freely on boiling. On the other hand, all the speci- 

 mens named are decomposed by hydrochloric acid, except one 



42 Proc. Am. Ass. Adv. Sci. (1879), XXVIII, 311. 



