Native Aneniuret of Manganese. 383 



A solution of ferro-cyanite of potassa tinged the liquor of a 

 light-blue, but did not produce any well- formed precipitate. 



Hydrosulphuret of ammonia precipitated it of a dirty yel- 

 lowish white. 



A portion of the ore having been heated in a glass tube, the 

 sublimed metallic crystals were separated for examination. 



They dissolved perfectly in nitric acid, and the solution 

 being concentrated to expel the excess of nitric acid, was found 

 to possess the following properties : — 



When a current of sulphuretted hydrogen was passed 

 through it, there was produced a yellow precipitate. 



When neutralized by potassa, and nitrate of silver added, 

 the well-known brick-red precipitate of arseniate of silver was 

 produced. 



With nitrate of copper the neutral solution gave a greenish 

 precipitate ; and with hydrosulphuret of ammonia, one of the 

 yellow colour of orpiment, when rendered slightly acid. 



After several preliminary trials I resolved upon employing 

 the following process for analytically determining the relative 

 proportions of the constituents. 



The ore was digested in nitric acid until it was entirely con- 

 verted into arseniate of manganese ; to it was then added an 

 excess of a solution of potash, and the liquors were boiled for 

 some tjme longer. The arseniate of manganese was thus de- 

 composed, and the protoxide eliminated, rapidly absorbing 

 oxygen, was converted into the brown deutoxide of that metal, 

 which being dried and weighed, the quantity of manganese 

 was calculated from it. 



The liquor thus freed from the manganese was accurately 

 neutralized by nitric acid ; then a solution of binacetate of lead 

 was added, as long as any white precipitate was produced. 

 The arseniate of lead, thus formed, was dried, weighed, and the 

 quantity of arsenic deduced from it. 



