PROCEEDINGS OF THE NATIONAL, MUSEUM 



VOL. 65 



appearance of the material. A specimen was then pohshed and 

 examined carefully by modern metallographic methods and, avoiding 

 molybdenite and the scattered large grains of pyrite, was found to 

 be homogeneous except for the small percentage of chalcopyrite. 

 Four analyses were made in all on separate specimens, each of which 

 was carefully selected and studied metallographically. In analysis 

 1 the presence of silver was not suspected and it was weighed with 

 the copper. In analysis 2, made a year later, a large error was made 

 by inadvertently filtering off a large part of the lead and weighing 

 it in the form of sulphate, with the quartz. The value for lead in 

 this analysis was adopted arbitrarily from the mean relation of lead 

 to bismuth in the other three and the insoluble matter and sulphur 

 were corrected in accordance. The results are given here because 

 the determinations of copper, silver, and bismuth are of value. The 

 analyses were made at intervals over three years and with variously 

 modified procedures. Each analyzed sample was a thin slice which 

 had been polished and examined metallographically and selected free 

 from pyrite and with a minimum of molybdenite. These were 

 crushed and screened to pass 100-mesh screens, the dust removed, 

 and the quartz floated out by a gravity separation with methylene 

 iodide. The quartz present in exceedingly thin veinlets yielded 

 mixed grains so that the samples could not be entirely freed from 

 quartz. The small chalcopyrite grains associated with the quartz 

 could not be avoided although in one case they were largely removed 

 magnetically. The results of the analyses are stated in detail, sepa- 

 rately, below. 



Analysis 1 of benjaminite. 



Constituent. 



Original. 



Deduc- 

 tions. 



Net. 



Recalcu- 

 lated. 



Quartz 



Lead 



Copper 



Silver 



Iron 



Bismuth 



Molybdenum 

 Sulphur 



Total- 



is. 46 



20. 77 



8. 17 



1.69 



38. 36 



.60 



14.26 



13.46 



1.92 

 1.69 



20. 77 

 6.25 



26. 87 

 8.09 



.60 

 2.35 



38.36 



"n'n 



49. 63 



"mil 



97.31 



20.02 



77.29 



100. 00 



The impurities deducted are the insoluble quartz and molybdenite 

 equivalent to the total molybdenum and chalcopyrite equivalent to 

 the total iron. These amount to quartz 13.46 per cent, molybdenite 

 1 per cent, and chalcopyrite 5.56 per cent. 



The results of analysis 2, recalculated as above noted, are as 

 follows : 



