Action of Iodine iipon Sulphides. 155 



action is increased, but the decomposition appears to be in- 

 complete. 



Niceolite is strongly attacked in the cold, yielding a green 

 solution, which turns brown on heating with excess of iodine. 



Smaltite is strongly attacked in the cold, forming a brown- 

 red solution ; heat increases the action. 



Chalcopyrite * yields a deep-red solution in the cold ; the 

 action is increased by boiling, but no precipitate forms. 



Tetrahedrite, ullmannite, and arsenopyrite behave ■ like 

 chal copy rite. 



Boxirnonite yields a deep-red solution in the cold ; and on 

 heating, a heavy precipitate falls, which is evidemlv a 

 mixture of plumbic iodide with yellowish-white cuprous 

 iodide. 



From the preceding notes, it appears that molybdenite is 

 the only one of the seventeen sulphides examined which 

 resists the action of an aqueous solution of iodine. The reac- 

 tions of galenite and cinnabar are characteristic and beautiful • 

 that of bournonite discloses its composition very satisfactorily. 

 The difference of behavior between bornite and chalcocite is 

 marked. 



The results obtained with pyrite and pyrrhotite require 

 some explanations. Professor Henry Wurtz,f in 1858 em- 

 ployed iodine- water to separate pyrrhotite from pyrite* he 

 states that pulverized pyrite digested for 48 hours in the dark 

 with a brown solution of iodine (pulverized and washed 

 repeatedly to remove all free acid), "did not remove the 

 brown color of the liquid, and the latter had dissolved but a 

 trace of iron." We repeated this process, observing all the 

 precautions mentioned, and found that pyrites (from Colorado 

 and from Saxony), was decidedly attacked. Possibly the 

 discrepancy is only one of judgment as to the amount of de- 

 composition which ensues, but under ordinary circumstances 



* Meusel has studied the behavior of chalcopyrite with hydriodic acid ; Ber. ohem. Ges 

 m, 123; 1870. 



t On some Improvements in the Preparation of Hard Minerals for Analysis, read before 

 the A. A. A. S. at the Baltimore meeting. Am. J. Sci., [2] Vol. XXVI, p. 190. 



