1824.] the Metallic Sulphates by Hydrogen Gas. 341 



was so small that it cannot be estimated. Whether this cobalt 

 originated from the matrix, or whether it was really a constitu- 

 ent of hair pyrites, cannot be determined. The second conjec- 

 ture is not improbable, as all other nickel-minerals contain 

 cobalt. 



Another solution of the oxide of nickel in muriatic acid was 

 mixed with the liquid remaining after the precipitation with 

 caustic potash in c. Then a current of sulphuretted hydrogen 

 gas was passed through this liquid after it had been mixed with 

 a slight excess of muriatic acid. No precipitate fell, but the 

 liquid assumed a tint of yellow indicating the presence of a trace 

 of arsenic. If we subtract the O006 gr. of quartz from the 

 0*222 gr. of hair pyrites, subjected to analysis, there will remain 

 0*216 gr. which is composed of 



Sulphur « 0-002 



b 0-072 



0-074 or 34-26 

 Nickel c 0-139 64-35 



0-213 98-61 



An atom of nickel weighs 739-51, and two atoms of sulphur 

 402-32 ; but 739-51 : 402-32 :: 64-35 : 35-02. Thus it appears 

 that hair pyrites is a compound of one atom of nickel and two 

 atoms of sulphur. It is not in the least affected by the magnet. 



Protosulphate of Iron. 



A determinate portion of pure protosulphate of iron, which 

 nad previously, by the cautious application of heat, been 

 deprived of its water, was treated with hydrogen gas. The salt 

 exhibited the very same appearances as sulphate of nickel under 

 the same circumstances. Sulphurous acid and water first came 

 over, and at last sulphuretted hydrogen gas. When the process 

 was concluded there remained a dark-grey agglutinated pulve- 

 rulent matter, which was strongly attracted by the magnet, and 

 dissolved in muriatic acid with the evolution of sulphuretted 

 hydrogen gas. The solution was not altered by muriate of 

 barytes. 0-858 gr. of anhydrous sulphate of iron, gave 0*396 gr. 

 of the new substance : 0*367 gr. of this new product were treated 

 with sulphuretted hydrogen gas. The weight was increased to 

 0-474 gr. ; but not the smallest portion of water was formed, 

 showing that sulphate of iron is changed by hydrogen gas into 

 a substance which contains no oxygen. 



The experiment with the hydrogen gas was repeated on 

 1*012 gr. of sulphate of iron, and the residual matter amounted 

 to 0-479 gr. The residue in the first experiment was 46-15 per 

 cent, and in the second 47-33 ; the mean of which is 46*74. The 



