478 Mr. H. M. Vernon on 



of air has a certain amount of decomposing effect on the 

 solution. 



Other determinations of the rate of evolution of chlorine 

 were made at temperatures between the. extremes given above, 

 namely, at 32°, 43°, 48°% 57°, 59°, and 63°. The curves 

 were in all cases quite regular, until the last few cub. 

 centim. of gas were being evolved, when their form changed 

 suddenly in the same way as those given above. It was 

 accordingly not thought necessary to represent them here. 

 In the experiment at 59°, when only 3 cub. centim. instead 

 of 5 cub. centim. of hydrochloric acid were used, only about 

 3' 5 cub. centim. of residual gas were evolved. 



It is thus evident that when the tetrachloride solution 

 undergoes decomposition, no intermediate chloride as Mn 2 Cl 6 

 is formed, but it decomposes regularly into MnCl 2 and Cl 2 . 

 If it were possible that the sesquichloride were formed at one 

 temperature, and that it happened to be just as unstable as 

 the tetrachloride at this particular temperature, yet it is 

 scarcely possible that through a range of temperature of more 

 than forty degrees, the tetrachloride should always decompose 

 with formation of an intermediate chloride which possessed 

 just the same degree of stability as itself. 



The fourth curve in the figure represents the rate of evolu- 

 tion of chlorine from a specimen of manganese oxide contain- 

 ing 45*33 per cent. Mn0 2 and 10*9 per cent, water. It there- 

 fore consists chiefly of Mn 2 3 . It will be seen that the curve 

 representing the rate of evolution of gas is regular, and similar 

 to the former curves. If, now, it be supposed for the time 

 being that the sesquioxide on dissolving in hydrochloric acid 

 forms the sesquichloride, it would follow from the fact of this 

 curve being regular that no chloride as Mn 3 Cl 8 , intermediate 

 between Mn 2 Cl 6 and MnCl 2 , is formed in its decomposition. 



The two dotted-line curves represent the rate of evolution 

 of chlorine from a solution of manganoso-manganic oxide, 

 Mn 3 4 , in hydrochloric acid. This Mn 8 4 was prepared by 

 heating some of the precipitated dioxide in the blowpipe 

 flame for a considerable time. The form of these curves is 

 similar to that of the others, only that more residual chlorine 

 is evolved. This is due to the fact that more hydrochloric 

 acid was added ; for nearly three parts of this oxide have to 

 be dissolved to give the same volume of chlorine as one part 

 of the dioxide. Thus in the curve at 57°, where 8 cub. centim. 

 of hydrochloric acid were used, there are about 9 cub. centim. 

 of residual gas, while in the curve at 48°, with 7 cub. centim. 

 of hydrochloric acid, there are also about 9 cub. centim., or 

 nearly half of the total volume of gas evolved. It is thus con- 



