330 M. Affwedson on the Decomposition of [May, 



considered as completed, and the apparatus was allowed to cool, 

 still filled with hydrogen gas. The product of this experiment 

 was a light- green powder, which dissolved in muriatic acid, with 

 the evolution of sulphuretted hydrogen gas ; and the solution 

 was rendered only slightly turbid by the solution of barytes. 

 Thus it appears that the salt was completely decomposed : 

 1*484 gramme of sulphate of manganese thus treated lost 0*697 

 gr. in weight, or 46*97 per cent. In another experiment 0*553 

 gr. lost 0*263, or 47*56 per cent. x\ third experiment gave a 

 loss of 1*034 gr. from 2*195 grs. of salt, which amounts to 47*10 

 per cent. The mean of these three experiments gives 47*22 for 

 the loss of weight sustained by 100 parts of anhydrous sulphate 

 of manganese when thus treated. 



It becomes now a question of some difficulty to determine 

 the composition of the substance thus obtained. It is impossible 

 that it could contain the same quantity of sulphur as the salt 

 employed (Mn S a ), because a quantity of sulphurous acid had 

 made its escape : nor could it be manganese combined with an 

 atom of sulphur (Mn S) ; for on such a supposition the weight 

 lost by 100 parts of the salt should have been 52*32, which was 

 considerably greater than that found by experiment. I thought 

 it, therefore, likely that I had obtained a body analogous to the 

 crocus antimonii ; or that it consisted of a combination of sul- 

 phuret of manganese and protoxide of manganese. The simplest 

 proportion in which such a combination can take place, is one 

 atom of sulphuret with an atom of protoxide ; and in order to 

 obtain such a result from protosulphate of manganese it is 

 obvious that 100 parts of the salt must lose 47*09 ; or almost the 



loss sustained in the preceding experiments ; for 2 Mn S- : 



2 Mn & - (Mn -f- Mn S 2 ) :: 100 : 47*09. The reason of this 



combination may be thus explained, that the sulphate of manga- 

 nese is decomposed by hydrogen gas in such a way that half of 

 the salt is changed into Mn S 2 , while the other half loses its 

 acid and remains in the state of protoxide. In order to prove 

 the truth of this opinion, it was merely necessary to determine 

 the quantity of sulphur in the reduced body, the quantity of 

 manganese being already known from our knowledge of the 

 composition of the salt ; and the remainder wanting to make out 

 the complete weight must obviously be oxygen. I attempted 

 first to determine the sulphur by dissolving the body in aqua 

 regia in order to oxidize the sulphur, that it might be afterwards 

 thrown down by barytes ; but the evolution of sulphuretted 

 hydrogen gas which took place on the addition of the acid 

 rendered this method abortive. I next dissolved the matter in 

 muriatic acid, and made the sulphuretted hydrogen gas pass 

 through a solution of acetate of lead ; but even when this pro- 

 cess was followed, I obtained an uncertain and varying product : 





