286 Mr. S. U. Pickering on the Hypothetical 



whereas if Mn 2 Cl 6 were formed, only 50 per cent, of it could 

 be recovered, 



2Mn0 2 + 8HC1 = Mn 2 Cl 6 + 01 2 + 4H 2 | 



Mn 2 Cl 6 + 2H 2 = Mn0 2 + MnCl 2 * + 4HC1 J ' ' (4) 



The maximum amount recovered was 47 per cent, at —20°, 

 the results plotted against temperature being represented by 

 a curve which had at this point become nearly parallel to the 

 axis. 



3. That the amount of higher chloride formed may be 

 very materially increased by adding a small quantity of 

 manganous chloride to the acid used to dissolve the dioxide ; 

 this might be the case if the higher chloride were Mn 2 Cl 6 , 



Mn0 2 + 4HC1 + MnCl 2 = Mn 2 C) 6 + 2H 2 0, 



but could not be the case if the higher chloride were MnCl 4 . 

 One molecular proportion of the manganous chloride increased 

 the amount of higher chloride from 45 to 80 per cent., and 

 there was a very marked change of curvature at this point, it 

 requiring another 4 molecules of the manganous chloride to 

 increase the amount of higher chloride by another 15 per cent. 



4. That the sesquioxide will dissolve in hydrochloric acid 

 with practically no evolution of free chlorine, and that nearly 

 the whole of the available oxygen which the former contains 

 may be recovered when the action is reversed by decomposing 

 the solution with excess of water. 



Mn 2 3 + 6HCl=Mn 2 Cl 6 + 3H 2 1 



\. . . (5) 



Mn 2 Cl 6 + 3H 2 = Mn 2 3 + 6HC1 J 



With one exception, which may be easily explained, Mr. 

 Vernon's experiments add confirmation to all these results. 

 I proceed to take them seriatim. 



1. The first half of the available chlorine is evolved much 

 more rapidly than the second half. On p. 476 of Mr. Vernon's 

 paper we find several determinations at comparatively high 

 temperatures. In one of them, for instance (that at 75°), 

 " more than half the gas comes off in the first minute," the 

 other half requiring 30 minutes for its evolution. At lower 

 temperatures (18°), the only experiment which was made to 

 ascertain whether the rates at which the two halves of the 

 chlorine were evolved were different (Experiment I. p. 473) 

 showed that a current of air carried off 45*9 per cent, in the 

 first hour, and only 24'5 per cent, more in the next three 



* Or a corresponding amount of MnO. 



