720 



GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



The sample of vesicular speiss was made up of equal, parts of nine specimens, 

 collected, three at the American smelter, two at the Harrison, four at the Ohio and 

 Missouri. 



By sifting, it was separated into 



Speiss powder 90. 17 



Iron grains 9. 83 



Lead grains Trace 



Total 100.00 



The iron grains are also perfectly free from arsenic and very tough. The speiss 

 powder of this sample was not analyzed, as in all probability its composition is the 

 same as that of type No. 2 ; but it was assayed for gold and silver. (See speiss assay 

 No. 5.) 



Conclusions. The sieve examination of speiss shows: 1. That speiss type No. 1 

 contains no free iron and is a noil-saturated speiss. 2. That speiss type No. 2 contains 

 just enough iron in excess to indicate that it is saturated with iron. 3. Lastly, vesicu- 

 lar speiss type No. 3 contains a very large excess of free iron. It is a supersaturated 

 speiss, whose fusion has been prevented by this excess of infusible iron. 



The writer made three comparative experiments on the fusibility of the three 

 kinds of speiss. In each case the pulverized speiss was mixed with borax in a porce- 

 lain crucible, heated over the blast-lamp, properly regulated to operate as nearly as pos- 

 sible in the same conditions. Speiss types No. 1 and No. 2 melted easily, and no 

 appreciable difference could be detected in their melting point. Speiss type No. 3 was 

 melted with more difficulty than the preceding and formed a vesicular button, show- 

 ing incomplete fusion. 



ANALYSES XXXVII AXD XXXVIII. SPEISS. 



Discussion. The formula of the large crystalline speiss analyzed in XXXVII is 

 (FeM) 6 AsS, M designating the small quantities of metals accompanying iron, and the 

 rational formula is probably represented by Fe s As(FeM)S. 



The fine-grained speiss analyzed in XXXVIII is represented by the formula 

 (FeM) 9 AsS, and probably by the rational formula Fe 8 As(FeM)S. 



