DecmnposUioii of Iron Pyritec 



159 



'I'liese experiments broualit out the fdllowing facts : 

 First. The etfeet of oxidation, ,im-ing the first ten d.ys, ap- 

 I-eared to the eye to be confined to more or less loss of polish 

 caused by a gradually overspreading film of tarnish. A latent 

 process ot internal decomposition was however in progress, onlv 

 ;" one case suggested (No. 91), by the finely cracked surface". 

 1 he gradual disnitegi-ation and increasing strain produced by 

 the internally developed films ot vitriol finally resulted in sud- 

 den rupture, with explosion of the loose and bulky yitriol-pow- 

 der. Minute sharp sjilinters of fractured pyrite often 

 abounded through this powder. This reaction is markedly 

 characteristic of the marcasitic and lighter varieties of pvrite 

 toward the bottom of the series. The relationship is apparent! 

 between these miniature explosions under artificial conditions of 

 oxidation, and the well-known natural explosions of masses of 

 the m,ner,d during weathering. On the purer pyritio and 

 heavier varieties, the action differed by the formation of a thin 

 him or crust of vitriol on the outside of the crystal, and by the 

 retention of crystalline form, even when the vitriolic decom- 

 position became complete ; the attack was almost or entirely 

 external, and no internal strain or sudden rupture ensued. 



becondly. The presence of enclosed impurities was shown by 

 green, gray or black tints of the efflorescent vitriol, the latter 

 sometimes indicating the enclosure of carbon in the pyrite of 

 Coal-sha es (Nos. 84 and 91) and of carbonaceous argillyte (No 

 104 , and sometimes that of lead or other impurities (No 3)' 

 Such impurities have doubtless exerted an accessory influence 

 toward ready oxidation by facilitating the entrance of the cor- 

 rosive agent. The same experiment was repeated upon another 

 set of bright crystals, with the substitution of the vapors from 

 fuming nitric acid in place of those of bromine. 



