1824.] On the Decomposition of the Metallic Sulphates. 329 



Article III. 



On the Decomposition of the Metallic Sulphates by Hydrogen 

 Gas. By J. A. Arfwedson. 



Since it has become known that the fixed alkaline sulphates 

 may, by means of hydrogen gas, be reduced to metallic sulphu- 

 rets, it was natural to infer that the same method would be 

 equally successful with the different metallic sulphates. This 

 consideration induced me to undertake a set of experiments by 

 the above-mentioned method, in order to determine more accu- 

 rately the nature of the combination of sulphur and manganese; 

 concerning which chemists have been long of opinion that the 

 manganese in it is in the state of an oxide ; although several 

 circumstances, the most important of which is its property to 

 dissolve in acids with the evolution of sulphuretted hydrogen 

 gas, have led also to the opposite sentiment. The experiments 

 which I am going to relate had at first no other object than to 

 determine the nature of this compound of sulphur and manga- 

 nese ; but the unexpected results obtained led afterwards to the 

 experiments which will be related. 



To avoid unnecessary prolixity in the description of the follow- 

 ing experiments, I should state in the first place, that all the 

 reductions of which I shall have occasion to speak, were per- 

 formed in precisely the same kind of apparatus, consisting 

 merely of a piece of barometer tube, of rather difficultly fusible 

 glass, about the middle of which was blown a small globular 

 cavity, into which the substance destined for reduction was put. 

 The hydrogen gas was prepared from zinc and dilute sulphuric 

 acid. It was dried by passing it through fused muriate of lime, 

 before it entered the tube. In those cases where sulphuretted 

 hydrogen gas was employed, it was freed from the accompany- 

 ing moisture in exactly the same way. 



Reduction of Protosulphate of Manganese by Hydrogen Gas. 



Tn the little apparatus just described a portion of pure sulphate 

 of manganese was put, which, though previously deprived of its 

 water, was again heated in the apparatus till I was certain that 

 it retained no moisture : then the evolution of hydrogen gas was 

 set a-going, and when the whole atmospherical air had been 

 driven out of the apparatus, the salt was heated over an Argand 

 spirit-lamp. Till the matter became red-hot, it underwent no 

 alteration ; but at that temperature the salt began to become 

 dark, and at the same time sulphurous acid and water came 

 over together. When this extrication was at an end, and when 

 the hydrogen gas passed through unaltered, the reduction was 



