Tetrachloride of Manganese. 289 



some difficulty in reconciling this with the supposed results 

 of his previous experiments, which, he thought, showed that 

 " the tetrachloride and no free chlorine are originally formed," 

 and that at low temperatures the tetrachloride is scarcely 

 decomposed after two hours, in which case, of course, 100 per 

 cent, of the dioxide taken would be recoverable. His expe- 

 dient for reconciling these results may be ingenious, but will, 

 I fear, scarcely commend itself to scientific men. It is that 

 " at no temperature will the number of molecules of MnCl 4 

 be much greater than half"" of the maximum possible, the 

 other half being split up into manganous chloride and atoms 

 of chlorine, and that these atoms of chlorine at ordinary 

 temperatures unite to form molecules and are liberated as 

 such, whereas at low temperatures they are sufficiently accom- 

 modating as to " come less often into the positions necessary 

 for them in order that they may unite together/' and hence 

 they remain in the liquid as free atoms ! Mr. Vernon does 

 not see that, even if such a specious hypothesis could be 

 accepted, it entirely cuts the ground from under his feet. 

 His argument that the higher chloride is MnCl 4 depends on 

 all the chlorine liberated by the dioxide remaining combined 

 with the manganese. If he invents a method for retaining 

 some of it in the liquid without its being combined with the 

 manganese, what proof has he of any particular formula at all 

 for the higher chloride ? 



3. That the amount of higher chloride formed is largely 

 increased by dissolving the dioxide in the presence of a molecular 

 proportion of a manganous chloride. The amount which I 

 found, as mentioned above, was nearly doubled by the 

 addition of one molecular proportion, the rate of increase 

 being represented by a line "which differed little from a 

 straight line''' , up to about this point, after which it dimi- 

 nished very rapidly. Mr. Vernon concludes, as in the former 

 case, that I did not make allowance for the protoxide con- 

 tained in the dioxide taken, and that therefore the change of 

 curvature did not occur when 1, but when 1*132 molecules of 

 manganous chloride had been added. Why he should draw 

 such a conclusion it is impossible to say*, for I stated on 

 p. 657 that " the 9 per cent, of protoxide which the sample of 

 oxide used by me contained was allowed for in calculating 

 out the results wherever necessary ;". and I find, on reference 

 to my laboratory note-book, that this allowance was duly 

 made in the present case. Even had it not been, this would 

 not have weakened my argument, for with such determina- 



* Unless it is that a point is inserted in my diagram at the zero-point, 

 which is obviously incorrect. 



