triple Sulphuret, of Lead , Antimony, and Copper. 69 
These proportions, I have reason to believe, are tolerably 
exact ; for I did not observe any essential variation in the results 
of two other analyses* which I made of this substance, with 
every possible precaution . 
The loss may be principally ascribed to the oxide of antimony 
and sulphate of lead ; but especially to the former, which has a 
great tendency to adhere to filters and glass vessels. 
In some of the preliminary experiments, I obtained a small 
portion of zinc ; but, having received, through the kindness of 
Mr. R. Phillips, of Lombard-street, some pure crystals of the 
ore, I found that the zinc had proceeded from blende, which 
was imperceptibly mixed in the specimens which I had first 
examined. 
