Manganese Tetrachloride. 479 



clusively proved that the change in the form of the curves is 

 due to the evolution of this residual gas, and not to the 

 decomposition of a more stable higher chloride of man- 

 ganese. 



These results, therefore, show that when any of the oxides 

 of manganese, Mn0 2 , Mn 2 3 , and Mn 3 4 , dissolve in hydro- 

 chloric acid, the only higher chloride produced is manganese 

 tetrachloride. The equations for the solution of manganese 

 sesquioxide and manganoso-maaganic oxide in hydrochloric 

 acid must therefore be : — 



Mn 2 3 -f 6HC1 = MnCl 4 + MnCl 2 + 3H 2 0. 

 Mn 3 4 + 8HC1 = MnCl 4 + 2MnCl 2 + 4H 2 0. 



Discussion of the Results obtained by Pickering. 



It is now necessary to see if it is possible to reconcile these 

 results with those obtained by Pickering. 



The first of his two arguments for the existence of man- 

 ganese sesquichloride and the non-existence of the tetra- 

 chloride, is, that if the chloride formed by the solution of the 

 dioxide in hydrochloric acid is MnCl 4 , then it can make no 

 difference to the amount of this chloride obtained whether the 

 solution be performed in pure hydrochloric acid, or in acid 

 containing a quantity of manganous chloride ; whereas, if the 

 chloride be Mn 2 Cl 6 , then by performing the solution of the 

 dioxide in the presence of a sufficient quantity of manganous 

 chloride we might succeed in converting the whole of the 

 oxide, together with some of the dichloride added, into the 

 higher chloride ; so that on decomposing it with water, we 

 should get as much dioxide precipitated as was dissolved, 

 thus : — 



Mn0 2 + 4HCl + MnCl 2 = Mn 2 Cl 6 + 2H 2 0, 



Mn 2 Cl 6 + 2H 2 = Mn0 2 + MnCl 2 + 4HCl. 



Otherwise, if no dichloride were added to the acid, we should 

 not be able to obtain in the precipitate more than half of the 

 dioxide dissolved, thus : — 



2Mn0 2 + 8HC1 = Mn 2 Cl 6 4 4H 2 + Cl 2 , 

 Mn 2 Cl 6 + 2H 2 = Mn0 2 + MnCl 2 + 4HCl. 



Accordingly, Pickering made a series of experiments in 

 which given weights of the dioxide were dissolved in hydro- 

 chloric acid in the presence of varied proportions of man- 

 ganese dichloride, and the solutions thus formed precipitated 

 with water, and the dioxide in the precipitate estimated. He 

 found that when no manganese chloride was added, 45 per 



