1824.] the Metallic Sulphates by Hydrogen Gas. 331 



the cause of which was that the sulphuret of lead formed is partly 

 converted into sulphate during the drying. 



Still, however, the method remained of determining the quan- 

 tity of sulphur by roasting the compound. A portion of the 

 substance in question prepared just before, which I shall here- 

 after call oxisulphuret of manganese, was heated to redness in a 

 platinum vessel. The matter took fire before it became red-hot 

 and burnt, leaving behind brown oxide of manganese, or oxidum 

 manganoso-manga)iicuin. But in order to drive off the whole of 

 the sulphur, a long continued roasting was necessary. 



0*36 gr. of oxisulphuret gave by this treatment 0-347 gr. of 

 brown oxide of manganese ; equivalent to 9639 per cent. The 

 oxide of manganese thus obtained dissolved in muriatic acid 

 without any residue, and the solution was not rendered turbid 

 by muriate of barytes. Now if the oxisulphuret of manganese 



were a compound of Mn + Mn S : , then 100 parts of it would 



correspond with 96*58 parts of Mn + Mn : , or brown oxide of 



manganese ; and the result, as is obvious, corresponds very well 

 with this calculation. 



Meanwhile, in order to be certain of the accuracy of these 

 conclusions, I thought it necessary to make direct experiments, 

 in order to show the existence of protoxide of manganese in 

 body. 



For this purpose a portion of protosulphate of manganese 

 was reduced bv hvdrogen eras, in the way above described. 

 After this the apparatus was weighed in order to determine the 

 amount of the oxisulphuret remaining.* A stream of dry 

 sulphuretted hydrogen gas was then passed through the same 

 apparatus. It was clear that the protoxide of manganese, in 

 case it was present, would by this process be converted into 

 Mn S J ; consequently a certain portion of water would be 

 formed. This accordingly took place, and with so much rapi- 

 dity, that almost as soon as the gas entered the apparatus, and 

 before any heat had been applied, the whole interior of the small 

 glass globe in which the matter lay, was covered with small drops 

 of water. It is possible that the reduction in this case might be 

 accomplished without the application of any heat; but to make 

 sure of the reduction, it is expedient to apply the heat of a spirit- 

 lamp till the matter becomes of a low red heat ; and the process 

 must be continued as long as any moisture makes its appear- 

 ance. The apparatus is then to be allowed to cool. It is to be 

 wf i'jhed after the gas with which it is filled has been driven off, 

 and replaced by common air. 0*933 gr. oxisulphuret treated in 

 this way left 1*022 gr. of sulphuret. This corresponds to 100 

 parts of the former, and I09-.34 of the latter. This is just the 



* The diminution of weight was cjuitc the same as in the former experiment. 



