470 Mr. H. M. Vernon on 



then it is probable that the reverse action of water upon 

 manganese tetrachloride is represented by the equation 



MnCl 4 + 2H 3 = Mn0 2 + 4HC1, 



while the action of potassium iodide upon manganese tetra- 

 chloride will be represented by the equation 



MnCl 4 + 2KI = MnCl ? + I 2 + 2KCl; 



so, from the amount of iodine liberated from the potassium 

 iodide, and the amount of manganese dioxide precipitated, 

 the ratio in which the manganese and available chlorine exist 

 in the brown solution is obtained. This ratio, which from the 

 above equations is required to be 1 : 2, was found experi- 

 mentally to be almost exactly 1 : 2. Fisher showed that the 

 same ratio of manganese to available chlorine likewise held 

 good for the solution of manganoso-manganic oxide in hydro- 

 chloric acid, the reaction taking place on the solution of this 

 oxide in HC1 being presumably 



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



and, arguing from analogy, the action of hydrochloric acid 

 upon manganese sesquioxide would be 



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



S. U. Pickering (Chem. Soc. Journ. 1879, p. 654) repeated 

 Fisher's experiments, and in addition made a mimber of 

 experiments of his own upon the subject. He pointed out 

 that Fisher's experiments only showed that the solution con- 

 tained a higher chloride of the form Mn M Cl 2n+2 , and did not 

 prove that this chloride was the tetrachloride. He also 

 showed that it cannot be argued that the chloride Mn 2 Cl 6 is 

 not formed on solution of the corresponding oxide in hydro- 

 chloric acid, because the oxide precipitated from the solution 

 by water is Mn0 2 and not Mn 2 3 ; for if it is possible to 

 obtain from the sesquioxide a chloride corresponding to the 

 dioxide, so it is just as possible that the dioxide should be 

 obtained from a chloride corresponding to the sesquioxide, 

 thus — 



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



Pickering then endeavours to show that the higher chloride 

 formed by the reaction of manganese dioxide and hydrochloric 

 acid is manganese sesquichloride, and that therefore man- 

 ganese tetrachloride has no existence. His two arguments 

 for the existence of manganese sesquichloride will be discussed 

 further on. 



It appeared to me that, although Pickering in his paper 



