600 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 58. 



muth mineral was completely soluble in hot concentrated hydro- 

 chloric acid while the fresh clean pyrite was not appreciably at- 

 tacked. The portion taken for analysis was dissolved on the steam 

 bath with concentrated hydrochloric acid and the insoluble material 

 was caught and Avashed thoroughly on a Gooch crucible, dried at 105 

 degrees and weighed. It consisted mainly of pyrite which was later 

 proven free from any trace of lead or bismuth. The solution was 

 then analyzed by standard methods, yielding the results given below : 



Anali/sis of hismutoplagionite. 



Insoluble 18.88 



Lead (Pb) 26.15 



Iron (Fe) .58 



Antimony (Sb) 2.41 



Bismuth (Bi) 37.14 



Sulphur (S) (calculated) 14.17 



Total 99.33 



Because of the complications introduced by the large amount of 

 pyrite present, sulphur was not directly determined — an omission not 

 serious in view of the fact that the constituent bases, when calcu- 

 lated to their respective sulphides, bring the total reasonably close 

 to 100 per cent. On the assumption that the pyrite was attacked to 

 a slight extent by the acid, the iron found in solution is deducted 

 as pyrite (FeSj). The composition derived for the gangue free 

 bismuth mineral, in terms of 100 per cent, is given below, together 

 with the ratios derived from the percentage figures : 



Recalculated analysis and ratios of hismutoplagionite. 



Lead 



Bismuth. . 

 Antimony 

 Sulphur.. 



33.02 



46.90 



3.04 



17.04 



0. 1594 

 .2255 

 .0253 

 .5313 



These ratios indicate exactly the formula : 



Pb,(Bi,Sb)8Si„ or 5PbS.4(Bi,Sb),S3. 



or the compound is SPbS.lBi^Sa, with the Bi in small measure re- 

 placed by Sb, the molecular ratios of bismuth to antimony being 

 approximately as 9:1. This formula brings the mineral in line, 

 chemically, with plagionite and liveingite, the formulas for the 

 three minerals being : 



Plagionite 5PbS.4Sb=S3. 



Bismutoplagionite 5PbS.4BijS,. 



Liveingite 5PbS.4AsjSi. 



