255 Contributions towards [Oct. 



has given origin to this assertion. This is a pretty good method 

 of separating the iron usually combined with manganese in its 

 natural state; for sulphate of iron, when exposed to a red heat, 

 becomes insoluble in water. 



Such is the action of sulphuric acid when the fire is raised 

 only high enough to redden the retort; but quite other affinities 

 take place when the heat is urged so as to melt the coated retort. 

 In that case the salt is decomposed, the protoxide takes a portion 

 of oxygen from the acid, and is changed into black oxide, while 

 the acid makes its escape in the state of sulphurous acid. I 

 repeated this experiment twice, and each time obtained in the 

 beak of the retort a portion of solid sulphuric acid, which dis- 

 lolved in water with the evolution of the heat, and the hissing 

 noise for which it is distinguished. We shall see hereafter that 

 when oxymuriatic acid is passed through a solution of muriate of 

 manganese it is very much disposed to crystallize. Can the metal 

 give occasion to this crystallization ? And supposing this conjec- 

 ture to be verified, can we 'from thence draw any conclusions 

 respecting the still enigmatical appearance of a fuming matter 

 in oil of vitriol? 



VI. Action of Sulphurous Acid on Manganese. 



Hitherto I have only examined the action of sulphurous acid 

 on carbonate of manganese. I made a current of pure sulphu- 

 rous acid gas pass through a vessel containing distilled water, 

 and thence into another vessel in which there was carbonate of 

 manganese mixed with water. A strong effervescence took place, 

 owing to the disengagement of carbonic acid. When the expe- 

 riment was finished I separated the solution smelling strongly of 

 sulphurous acid from a white granular powder lying in the bot- 

 tom of the vessel, which, as I shall show presently, was sulphite 

 of manganese. 



The filtrated solution being evaporated, the sulphurous acid 

 was gradually converted into sulphuric acid, and the solution 

 exhibited the properties of sulphate of manganese with an excess 

 of acid. 



Properties of Sulphite of Manganese. 



It appeared in the state of a white, granular powder, destitute 

 of taste, and insoluble in water and alcohol. 



It is not altered by exposure to the air, and therefore may be 

 examined without difficulty. I left a portion of this salt for 

 three weeks in a small open vessel in a room : but it did not 

 undergo the smallest alteration. 



Sulphuric, muriatic, and nitric acids, drive off the sulphurous 

 acid when the salt is exposed to their action, and we obtain sul- 

 phate, muriate, or nitrate of manganese. 



