Manganese Tetrachloride. 473 



solution into water. The precipitate was collected, washed, 

 and dried for sixteen hours at 75° C. Its composition was as 

 follows : — 



Mn0 2 = 90*77 per cent. 



MnO = 4-21 „ 



H 2 = 4-80 



99-78 



This and other specimens of dioxide were analysed by 

 heating a weighed quantity to redness for about thirty minutes 

 and reweighing on cooling. The amount of available oxygen 

 existing in the oxide, which consists chiefly of Mn 3 4 , is then 

 estimated in the usual way by heating with hydrochloric acid 

 and estimating the chlorine evolved. Separate values of the 

 total manganese and of the water present are thus arrived at. 

 The available oxygen in the dioxide is determined separately. 



I. To a weighed quantity ('3069 grm.) of hydrated Mn0 2 

 in a small flask were added 10 cub. centim. of concentrated 

 hydrochloric acid. The flask was immersed in water at 18° C. 

 In fifteen minutes, when *4 litre of air had been drawn through, 

 14*2 per cent, of the available chlorine was removed. In 

 forty-five minutes longer 31*7 per cent, more chlorine was 

 removed ; or, in the first hour 45*9 per cent, had been 

 removed. In this time 1*5 litre of air had been drawn 

 through the solution. In the next hour 14*1 per cent, more 

 chlorine was removed, and in the next two hours 10*5 per 

 cent. more. We thus see that, while half the available 

 chlorine had not been removed even after an hour, yet that the 

 amount removed is much greater in the first hour than in the 

 second, and this is greater than in the next two hours. The 

 reason of this will be made evident further on. It should be 

 noticed that, while the amount of chlorine removed is much 

 smaller in the second hour than in the first, yet that in the 

 next two hours it is smaller in about the same proportion; while 

 if Mn 2 Cl 6 and no MnCl 4 were formed in the solution, we should 

 expect the last half of the chlorine to come off at a more even 

 rate than it does here. Also the first half of the chlorine 

 cannot be said to have been evolved very quickly, as it took 

 over an hour to be removed from the solution. 



II. To a weighed quantity ("2819 grm.) of hydrated dioxide 

 in a small flask, surrounded by a freezing-mixture of ice and 

 salt, were added 10 cub. centim. of hydrochloric acid which 

 had previously been cooled to the temperature of the freezing- 

 mixture, viz. — 14° C. The air, before bubbling through the 

 liquid, was drawn through a worm-tube immersed in the 



