Manganese Tetrachloride. 483 



tated. The trace of tetrachloride remaining on the filter-paper 

 was estimated separately and allowed for. By this method at 

 5° and —9°, from a specimen of dioxide containing 4*2 per 

 cent. MnO, 54*2 per cent, and 53*8 per cent, were recovered. 

 With a specimen of dioxide containing 72*1 per cent. Mn0 2 

 and 12*5 per cent. MnO, 55*77 per cent. Mn0 2 was recovered 

 at 18°. At —20° this would correspond to the recovery of 

 about 58*77 per cent. When some of this dioxide was shaken 

 in a flask with hydrochloric acid and then poured into water, 

 56*49 per cent, was recovered; with hydrochloric acid satu- 

 rated with chlorine, 56*54 per cent, was recovered, the tem- 

 perature of solution being in both cases 18°. The reason of 

 this slight increase lies probably in the fact that when hydro- 

 chloric acid is dropped slowly on to the dioxide on a filter- 

 paper, the energy of the chemical action raises the tempera- 

 ture several degrees, and so more of the tetrachloride formed 

 is decomposed. 



With a specimen of dioxide containing 79*53 per cent. 

 Mn0 2 and 10*5 per cent. MnO, 55*5 per cent, was recovered 

 at 13°. With a specimen containing 45*33 per cent. Mn0 2 

 and 43*76 per cent. MnO, and consisting therefore mostly of 

 Mn 2 3 , 74*5 per cent. Mn0 2 was recovered, whilst with some 

 Mn 3 4 , 85*43 per cent, was recovered. These last two expe- 

 riments confirm Pickering's conclusions that the amount of 

 dioxide recovered is largely increased if molecules of MnCl 2 

 be present in the solution. 



It is thus seen that, instead of the amount of dioxide re- 

 covered being always slightly below fifty per cent., it is 

 always slightly above it, if the solution be performed at 

 ordinary temperatures. At the same time it is remarkable 

 that it is not possible to recover by any means, except the 

 introduction of MnCl 2 into the solution, a much larger pro- 

 portion of dioxide than fifty per cent. The same explanation 

 as was given before for this result, only more extended, 

 may be used here. In the solution of manganese dioxide in 

 hydrochloric acid at all temperatures, both low and high, it 

 must be considered that the molecules of MnCl 2 and the atoms 

 of chlorine are in a continuous state of recomposition together 

 to form molecules of MnCl 4 , and these are continuously de- 

 composing again. At no temperature will the number of 

 molecules of MnCl 4 , actually existing as such in the solution, 

 be much greater than half, unless, of course, additional mole- 

 cules of MnCl 2 are present. On precipitation of the solution 

 with water, therefore, only a little more than half the dioxide 

 will be recovered, the atoms of chlorine present merely com- 

 bining with one another to form molecules, which will dis- 



2M2 



