300 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 13 



bedded in quartz or minute, deeply striated crystals in open cavities. 

 The streak is black on porcelain or brownish black when rubbed very 

 thin with a glass rod. The hardness is about 2.5. 



Material for analysis was secured free from impurities other than 

 quartz and a little pyrite, both of which remained unattacked 

 when the mineral was dissolved in hydrochloric acid. The ma- 

 terial was found to be free from other impurities by examination of 

 polished surfaces under the miscroscope. Standard methods of analysis 

 were used, the bismuth and lead being separated by the basic nitrate 

 method. It is noteworthy, however, that this method, which is the 

 one recommended by most textbooks, is one which gives satisfactory 

 results only when performed with extreme care. The major separation 

 was accomplished by precipitating the bismuth by means of hydrogen 

 sulfide in strongly acid solution, the precipitate being almost free from 

 lead while very little bismuth remained in solution. The separation 

 by the basic nitrate method was repeated several times on each pro- 

 duct of this separation before these two metals were obtained free 

 from each other. The material available for analysis was too small to 

 permit sulfur to be determined. The results of the analysis, recalcu- 

 lated after deducting gangue, are given in table 1. 



TABLE 1. 

 Analysis of Galenobismutite from Idaho 



Total _ 100.00 



The formula thus derived is: 



Pb Bi2 S4 or PbS.BisSs. 

 The copper, iron, and antimony, while present in minor amount, 

 merit note, f Copper and iron while probably not entirely isomorphous 

 with lead, can perhaps enter into solid solutions in limited amount, the 

 copper in all probability being in the cupric state. It is possibly sig- 

 nificant that copper and iron are molecularly roughly equivalent to 

 the antimony and may be combined with it. Such an amount of cop- 

 per and iron compounds might conceivably be present as submicro- 

 scopic inclusions in the galenobismutite. 



