438 M, Berzelius on the [June, 



granular, but the grains are less equal ; the structure is by this 

 rendered less compact ; it has then the appearance of a cobalt 

 ore, it decrepitates less, gives sulphuret of arsenic by distilla- 

 tion, and leaves a silver-white residuum. 



It appears that it is the first of these varieties which was 

 examined by M. Psaff. The two first analyses which I am now 

 going to describe were made on the first variety, and the 

 remainder on the second, as may be seen by the results. 



(A.) Analysis hi/ Means of Nitric Acid, 



a. Forty parts of the pulverized mineral were treated with pure 

 nitric acid until the undissolved portion appeared to be merely 

 sulphur. The residuum weighed 1*38 part. The sulphur was 

 burnt, and left 0*27 part of sihca, or at least of an earthy pow- 

 der. The weight of the burnt sulphur was, therefore, I'll part. 



h. The solution precipitated by muriate of barytes ^ave 28*77 

 parts of sulphate of barytes, equivalent to 3*96 of sulphur, which,^ 

 added to 1-11 before obtained, make a total of 5*07 parts, or 

 12*675 per cent. 



c. The barytes added in excess was separated by sulphuric 

 acid ; and afterwards a current of sulphuretted hydrogen gas 

 was passed through the solution, as long a sulphuret of arsenic 

 was formed, which was washed upon a weighed filter ; it was 

 well dried, and was weighed while inclosed in a covered platina 

 crucible, in order to prevent the attraction of moisture during its 

 cooling. It weighed 36*87 parts. It was afterwards treated 

 with caustic ammonia upon the same filter ; the ammonia dis- 

 solved the sulphuret of arsenic, leaving as a residuum the sulphur 

 which was separated from the sulphuretted hydrogen during the 

 experiment by atmospheric air, and the peroxide of iron of the 

 liquid, which was reduced to protoxide. This sulphur was white, 

 and weighed, when well dried, 1*17 part. The 36*87 parts, 

 therefore, contained only 35*7 parts of sulphuret of arsenic, equi- 

 valent to 21*75 parts of metaUic arsenic, or 54*38 per cent, of 

 the weight of the mineral. 



d. The solution deprived of arsenic, and heated to reoxidize 

 the protoxide of iron, ammonia was afterwards added to it in 

 great excess. It occasioned a precipitate of an olive-green 

 colour; this was separated, and dissolved in muriatic acid : this 

 solution was neutralized as nearly as possible, and the iron was 

 precipitated by succinate of ammonia. The succinate of iron 

 decomposed by heat in an open vessel gave 1*83 part of oxide 

 of iron, which, when treated with soda by the blowpipe, smelled 

 strongly of arsenic. 



€. The ammoniacal solution was mixed with that from which 

 the iron had been precipitated by the succinate of ammonia ; 

 subcarbonate of potash was poured into it, and the ammonia 

 was evaporated. The oxide of nickel thus separated weighed 

 15*32 parts. 



