54 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



containiug zinc. (51043.) It consists essentially of sulphide of zinc of the follow- 

 ing composition : 



Per ceut. 



Zinc (Zu) 45.68 



Lead (Pb) 1.48 



Iron (Fe) 6.71 



Manganese ( Mu ) 0. 54 



Sulphur (S) '25.98 



Antimony (Sb) trace 



Arsenic (As) not present 



Copper Cu) not present 



Silica (SiO.) 8.13 



Lime(CaO) 6.20 



Silver (Ag) 0.0188 or 5.5 ounces per ton 



(3) Finely crystallized, nearly pure, sulphide of zinc. (50926.) 



(4) Furnace accretion, formed on the walls of the shaft furnace when smelting ores 

 containing zinc. (51042.) This sample contains considerable lead and is of the fol- 

 lowing composition : 



Per cent. 



Zinc (Zn) 38.99 



Lead (Pb) 37.48 



Iron (Fe) 0.94 



Lime (CaO) 3^ 



Sulphur (S) 19. 74 



Silica (SiOo) 0. 57 



Arsenic {As) not preseut 



Copper (Cu) not present 



Manganese (Mn) not present 



Antimony (Sb) 0. 12 



Silver (Ag) variable, from 15 to 36 ouuces per ton throughout piece 



When roastiug- thespeiss iu stalls previous to returniog it to the shaft 

 furnaces very beautiful and interesting sublimation products are 

 formed, consisting of the sulphides and oxide of arsenic. These are 

 illustrated by three specimens : 



(1) Yellow sulphide of arsenic (orpiment). (51040.) 



(2) Arsenious acid in octahedral crystals of great beauty. (51079.) 



(3) Oxide and sulphides of arsenic (arsenious acid, orpiment, and realgar). Four 

 specimens. (51038.) 



Refining Base Bttllion. 



The base bullion resulting from the tirst smelting operation is charged 

 into large reverberatory furnaces and melted. In some cases only a 

 single brand of pig lead is melted in the charge, but generally several 

 brands are mixed, rich with poor, and very impure with quite pure, the 

 object being to get a mixture containing the right proportion of silver 

 and also to assist the removal of impurities from the very impure ma- 

 terial. 



Ul^on becoming melted any residue of unmelted dross is drawn off 

 from the melted lead and the bath is submitted to an oxidizing action 

 to remove the imi)urities; as fast as these accumulate upon the surface 

 they are withdrawn. As soon as the bath is purified or softened sutii 



