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XII. On the Chemical Composition of white e^orescent Pyrites. 

 7?j/ M. J. Berzelius*. 



XT is well known that the ciystalline form of white pyrites 

 differs so essentially fi'om that of yellow pyrites, that M. Haiiy 

 thought he ought to class them as two different mineral species. 

 No difference in the composition of the two substances, how- 

 ever, can be discovered by chemical analysis ; which adds one 

 more to the exceptions to the general rule, furnished by the 

 diversity in the two forms of carbonated lime, and that more 

 recently observed by M. Mitscherlich in two fonns of the sur- 

 phosphate of soda. 



White pyrites consists of two varieties ; one of which, per- 

 fectly crj'stallized, stands the air; while the other, which pre- 

 sents a confused crystallization, effloresces on exposure to the 

 au", and falls into a powder evidently vitriolic. This phoeno- 

 menon proves, then, a difference of composition between the 

 two varieties; a difference which deserves to be studied, in 

 order that we may see whether it can explain the difference 

 between them and yellow pyrites. 



I allowed a piece of white pyrites to effloresce for two years 

 and a half; and when it was entirely reduced I subjected it to 

 examination. Its bulk was almost doubled ; and it fell into 

 pieces on the slightest touch. A part of the mass was con- 

 verted into a white powder, of a styptic taste, and this powder 

 had begun to grow yellowish towards the edges. Viewed 

 through a microscope it presented a mass full of small cavities 

 filled with a white and effloresced salt, the interstices between 

 which appeared to be of white pyrites in an entire state, and 

 more or less crystalline. 



I then tried a portion of it with water; and separated the 

 dissolved part fi-om the indissoluble residue. The latter con- 

 sisted partly of a rough powder, which was composed of small 

 crystals of pyrites, and partly of a powder finer and lighter 

 and of a grayish colour approaching to black. \'icwed tlnoiigh 

 the microscope, this powder presented nothing but brilliant 

 particles of jijTites v/idiout any trace of sulphur eitliei- sci)a- 

 ratc or mingled with the pyrites. 



(«.) The solution deposited on being brought ijito contact 

 with the air, a yellow ochre; it was then entirely neutral. 



I treated this'solution with nitric aciil in orilcr to oxidate the 

 excess of iron, and I afterv/ards decomposed it by means ol 

 muriate of barytcs and caustic aunnonia. The jiroduct was 

 2.03 gr. of sulphate of barytes ; ami after se})arating the ex- 



* I'roni <lic Amalcs dv C/iimic for April 1822. 

 \u].r.(). X.). 'i!)l. Jail/ ]H'22. I CCSS 



