Chemical Examination of Arsenical Pyrites, 85 



31. ARSENICAL PYRITES. 



I examined this mineral many years ago, and showed that 

 it contained iron, arsenic, and sulphur. But the art of analy- 

 sis was not at that time far enough advanced, or my skill in 

 it not sufficient to enable me to determine with accuracy, the 

 proportion of the constituents. It will be worth while, there- 

 fore, to state here the result of an analysis of it, lately made 

 in my laboratory. 



The specimen examined was from Sweden, in pretty regu- 

 lar detached crystals, consisting of elongated octahedrons. 



Fracture foliated. 



Color white. Lustre metallic and splendent. Some of 

 the crystals had a yellowish tarnish on the surface. 



Not scratched by the knife, but by quartz. 



Easily frangible. 



Specific gravity 6*920. 



Before the blow-pipe it emits a white smoke, having the 

 the smell of garlic, and leaves an iron-colored residue, 

 strongly attracted by the magnet. 



It was analyzed by acidifying the arsenic and sulphur, and 

 separating the iron in the state of peroxide. The arsenic and 

 sulphuric acids were both thrown down by barytes, and the 

 arseniate of barytes was separated from the sulphate, by means 

 of nitric acid. Its constituents determined in this way were, 



Iron, - - 33'98 



Arsenic, -_---,_ 45'74 



Sulphur, 19-60 



99-32 



This is obviously equivalent to, 



1 atom iron, ___-._ 3.5 



1 atom arsenic, _---__ 4.75 



1 atom sulphur, ------ 2 



10-25 



