Tetrachloride of Manganese. 285 



I raised against those arguments which had previously been 

 used to support this formula (see Chem. Soc. Trans.' 1878, 

 p. 409). Mr. Vernon's paper has recently appeared in eoctenso 

 in this Magazine (vol. xxxi. p. 439). 



The evidence adduced by me (Chem. Soc. Trans. 1879, 

 p. 654) in favour of the formula Mn 2 Cl 6 was : — 



1. That the dissolution of manganese dioxide in hydrochloric 

 acid results in the (almost) immediate liberation of two 

 atoms of free chlorine for every two of loosely combined 

 chlorine present in the higher chloride formed, according to 

 the equation 



2Mn0 2 + 8HCl = Mn 2 Cl 6 + Cl 2 + 4H 2 0, . . . (1) 



instead of resulting in the liberation of no free chlorine, as 

 might be the case if the tetrachloride were formed: 



2Mn0 2 + 8HCl = 2MnCl 4 + 4H 2 0. ... (2) 



This fact was established by finding that of the total available 

 (i. e. free + loosely combined) , chlorine present, one half 

 might be removed from the liquid very quickly (in about half 

 an hour) by a rapid current of air, whereas many days are 

 required to remove the remaining half in the same way, this 

 second half being evidently present not as free chlorine, but 

 as the result of the gradual decomposition of the higher 

 chloride : 



Mn 2 Cl e =2MnCl 2 -+Cl 2 . 



2. That although a lowering of temperature increases the 

 stability of the higher chloride, the amount formed tends 

 towards a limit which no further lowering of temperature will 

 modify, this limit being that at which every two atoms of 

 manganese present as the higher chloride retain 2 and not 

 4 atoms of loosely combined chlorine, 



Mn 2 Cl 4 ,Cl 2 , not Mn 2 Cl 4 ,Cl 4 . 



The amount of loosely combined chlorine was estimated by 

 decomposing the higher chloride with excess of water : if 

 MnCl 4 were formed, the whole of the dioxide taken might be 

 recovered, 



2Mn0 2 + 8HCl=2MnCl 4 + 4H 2 -, 



2MnCl 4 + 4H 2 = 2Mn0 2 + 8HCl J ' 



Phil. Mag. S. 5. Yol. 33. No. 202. March 1892. X 



