6 Mr. D. Forbes's Researches on the 



nickel, and manganese present by the use of succinate of am- 

 monia with the usual precautions. The succinate of iron, redis- 

 solved in hydrochloric acid and reprecipitated by ammonia, 

 afforded 11*78 grs. sesquioxide of iron, equal to 8*173 grs. iron, 

 or 34*47 per cent, in the mineral. 



The solution, or rather filtrate, separated from the oxide of iron 

 was now precipitated by sulphide of ammonium ; this precipitate, 

 collected, incinerated, dissolved in nitric hydrochloric acid, and 

 precipitated by potash, gave 0*19 gr. oxide of cobalt, nickel, and 

 manganese, which were arsenized and separated according to 

 Plattner's method by the blowpipe, giving 0*171 quadribasic 

 arsenide of cobalt, equal to 0*104 metallic cobalt, or 0*44 per 

 cent, in the mineral, and 0*09 quadribasic arsenide of nickel, 

 equal to 0*0056 metallic nickel, or 0*03 per cent., whilst the 

 manganese was estimated by the difference. The determination 

 of arsenic was attempted in precisely the same manner as that 

 of the sulphur, as described above ; but notwithstanding every 

 precaution, I could not have any confidence in the result, as 

 after three attempts I noticed in each case the smell of garlic 

 indicative of some evolution of arsenic. I therefore modified the 

 process as follows : — 20*05 grs. mineral in fine powder was placed 

 in a porcelain crucible and drenched with pure nitric acid until 

 no further oxidation took place. Carbonate of soda was added 

 to take up the superfluous nitric acid, and more carbonate of 

 soda along with nitrate of potash added to make up the same 

 quantities as those used in determining the sulphur. The whole 

 was heated to dryness, removed to a silver crucible and fused ; 

 the residue was digested with water as usual, and the arsenic 

 determined in the filtrate, after acidifying it by hydrochloric 

 acid, as arseniate of ammonia and magnesia, which, when ignited 

 with the usual precautions, gave 18*84 grs. 2MgO AsO 5 , equal to 

 9*116 grs. arsenic, or 45*46 per cent, arsenic in the mineral*. 



The results of this examination, when tabulated, will now stand 

 as follows : — 



Arsenic . . . 



. 45-46 



Sulphur . . 



. 19*53 



Iron .... 



. 34*47 



Manganese . . 



. 0*14 



Cobalt .... 



. 0*44 



Nickel .... 



. 0*03 



100*07 



* I had the curiosity to make a determination of the arsenic by simply 

 fusing with nitrate of potash and carbonate of soda as before mentioned, 

 and only obtained 38*59 per cent, of arsenic, a loss of 6*87 per cent., which 

 shows how unsafe this method is. 



