480 Mr. H. M. Vernon on 



cent, of the original Mn0 2 was recovered, When one mole- 

 cule of MnCl 2 was added, 80 per cent, of Mn0 2 was recovered; 

 and with six molecules of MnCl 2 , 95*5 per cent, was recovered. 

 When the results of ten determinations with proportions of 

 manganese chloride varying between these limits were repre- 

 sented diagrammatically, it was found that up to the addition 

 of one molecule of MnCl 2 the curve representing the amount 

 of Mn0 2 recovered was a straight line ; after this point the 

 form of the curve changed suddenly, the ratio of Mn0 2 re- 

 covered to molecules of MnCl 2 added being considerably less 

 than before. Pickering considers this to conclusively show 

 that the tetrachloride has no existence, and also that the 

 higher chloride formed is Mn 2 Cl 6 . 



On examination it will be found that this argument neither 

 proves the non-existence of the tetrachloride nor the existence 

 of the sesquichloride. Thus, it can be shown mathematically 

 that supposing MnCl 2 and the solution of the dioxide in 

 hydrochloric acid react as Pickering supposes, the form of 

 the curve up to the addition of one molecule of MnCl 2 will 

 not be a straight line, but will be to a certain extent curved. 

 Also, he says that the form of the curve changes suddenly 

 after one molecule of MnCl 2 has been added. He forgets, 

 however, that there is not one molecule of MnCl 2 present, but 

 1*132 molecule, for the specimen of dioxide used he showed 

 to contain 85*15 per cent. Mn0 2 and 9*36 per cent. MnO : 

 this MnO, on addition of hydrochloric acid, would of course 

 form MnCl 2 , and this was not taken account of when the rest 

 of the MnCl 2 was added. He found that the addition of one 

 molecule of MnCl 2 raised the amount of Mn0 2 recovered from 

 45 per cent, to 80 per cent.; the addition of *132 molecule would 

 accordingly raise it 4*62 per cent. He found the form of the 

 curve to change, therefore, after a point where 80 per cent, 

 of the dioxide was recovered, while according to his argument 

 it should have been after 75*36 percent, was recovered. Also 

 he would only have recovered 40^36 per cent, of the original 

 Mn0 2 , if pure dioxide had been used. These discrepancies 

 may be due to the conditions of solution and precipitation of 

 the dioxide not being kept quite the same for different expe- 

 riments. It would seem, therefore, that all that this curve can 

 with certainty be taken to show is, that the amount of Mn0 2 

 recovered is increased by the addition of MnCl 2 to the solution, 

 the amount of this increase being in proportion less and less 

 with each addition of MnCl 2 . This does not, however, show 

 that when the dioxide dissolves in hydrochloric acid, the sesqui- 

 chloride and free chlorine are formed ; it only shows that 

 manganese tetrachloride is more stable in the presence of 



