290 The Hypothetical Tetrachloride of Manganese. 



tions it was not possible to locate the point at which the 

 change of curvature occurred within about *1 molecule. 



Referring to the straightness of my curve up to the 

 addition of one molecule of manganous chloride, Mr. Yernon 

 remarks that "it can be shown mathematically that the form 

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

 not be a straight line." Had Mr. Vernon but favoured us 

 with the mathematics of this very complicated reaction, he 

 would have conferred a benefit on science and put its ablest 

 representatives into the shade. 



The increase in the amount of the higher chloride Mr. 

 Vernon attempts to explain by the latter being a dissociation- 

 product of MnCl 4 ; and, after reproducing an elementary 

 text-book expose of how the presence of excess of dissocia- 

 tion-products will reduce the amount of substance dissociated, 

 concludes that "if, therefore, a large excess of MnCl 2 is 

 present" there will be " much less decomposition." But he 

 forgets that my results show that it does not require a large 

 excess, but only one molecular proportion of manganous 

 chloride to increase the higher chloride present to double 

 its former amount, and that a large excess in addition to this 

 has but a small additional effect on the results. In order, 

 however, to remove the least chance of his explanation being 

 accepted, Mr. Vernon proceeds to show by experiment that 

 the presence of dissociation-products — or at any rate of the 

 other dissociation-product, the chlorine — has no appreciable 

 effect on increasing the amount of the higher chloride. 



4. Manganese sesquioxide dissolves in hydrochloric acid 

 without the liberation of any free chlorine, and nearly the whole 

 of the available oxygen in it can be removed on decomposing the 

 solution with water. Mr. Vernon confirms this, p. 483. 



Thus it will be seen that the only tittle of the evidence 

 adduced by Mr. Vernon which might at first sight appear to 

 militate against my conclusion as to the formula of the higher 

 chloride is based on experiments which are obviously faulty, 

 and leads to results diametrically opposed to even his own 

 experimental results, while in every other particular he simply 

 confirms my observations. 



I have refrained from criticising all the details of Mr. Ver- 

 non's paper ; but I venture to think that those who study 

 these details will certainly arrive at no other conclusion than 

 that to which a study of his main arguments leads, namely, 

 that whatever be the real nature of the higher chloride of 

 manganese, Mr. Vernon's results have thrown no fresh light 

 upon the subject, nor have they in any way invalidated the 

 existing evidence for considering it to be the sesquichloride. 

 July, 1891. 



