716 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



ANALYSIS XXXV. ROASTED CHAMBER DUST Continued, 

 national. 



Discussion, Everything indicates that the dust was roasted at a very high tem- 

 perature, and this is proved beyond doubt by the fact that traces only of carbonic 

 acid are detected. 



Ou comparing this analysis with the average analysis (XXXIV) of unroasted 

 chamber-dust, it is found that the percentage of lead is considerably increased, but 

 that a considerable quantity of silver is lost. One notices, also that the quantity of 

 chloriue, bromine, and iodine is about half what it was in the average sample of dust. 

 Coupling this with the loss of silver, it may justly be inferred that silver is lost in the state 

 of chloro-bromo-iodide, and that some lead is also lost in the same form. The quantity 

 of phosphate of lead has also diminished instead of increasing, showing that lead is 

 also lost in this form. The percentage of arsenic and antimony is lower than in the 

 unroasted dust, but this appears to be the only advantage gained by roasting, and a 

 very slight one it is in these cases. Sulphur, instead of being driven off by roasting, 

 is concentrated in the form of sulphate of lead, amounting to 37 per cent., and repre- 

 senting 5 per cent, of sulphur instead of 2 per cent., as in the chamber-dust. Lastly, 

 about 9 per cent, of carbon is driven off at great expense. This carbon is so intimately 

 mixed with the original dust that by simple heating in the blast furnace there would 

 be more than enough of it to reduce all the lead of the fumes. In fact, everything in- 



