Manganese Tetrachloride. 475 



was proved ' by passing chlorine into hydrochloric acid at 

 — 20° for some time, no chlorine hydrate being formed. 

 Indeed, it was found that the addition of even a small quantity 

 of hydrochloric acid to water containing chlorine-hydrate 

 crystals almost immediately destroyed them. Thus chlorine 

 was passed into 10 cub. centim. of water at 2°, chlorine 

 hydrate being very soon formed ; when, however, *5 cub. 

 centim. of hydrochloric acid was added to the .water, the 

 hydrate rapidly disappeared. Again, when a solution con- 

 taining water and HC1 in the proportion 6 : 1 was saturated 

 with chlorine at —9°, the hydrate was formed ; this quickly 

 disappeared when one part more of HC1 was added. Lastly, 

 it was found that, when a mixture of water and hydrochloric 

 .acid in equal proportions was saturated with chlorine at —19°, 

 no hydrate whatever was formed. 



It is therefore conclusively shown that when manganese 

 dioxide dissolves in hydrochloric acid, manganese tetrachloride 

 and no free chlorine are originally formed, and that the lower 

 the temperature the more stable does this tetrachloride solution 

 become. 



The Rate of Evolution of Chlorine from the Solution. 



It is now necessary to ascertain whether, on decomposition 

 of the tetrachloride solution, the sesquichloride or any other 

 intermediate chloride is formed. 



If an intermediate chloride, as Mn 2 Cl 6 , is formed on the 

 decomposition of the tetrachloride, we may reasonably expect 

 that this chloride should be more stable than the tetrachloride. 

 Consequently when a solution containing originally only tetra- 

 chloride decomposes, we should expect the first half of the 

 chlorine to come off considerably faster than the last half. At 

 ordinary temperatures the decomposition of the solution is so 

 slow that it would take a day or two before the greater part 

 of the chlorine would be evolved. The variations in the tem- 

 perature of the atmosphere, and also the impossibility of taking 

 a continuous series of readings of the volume of gas evolved 

 during this time, would render it impossible to arrive at a 

 satisfactory conclusion as to the rate of decomposition of the 

 solution. If, however, the temperature of the solution be 

 raised to above 30°, the rate of evolution becomes much more 

 rapid, and the greater part of the chlorine is evolved in a few 

 hours. 



Small weighed quantities (about '2 grm.) of the dioxide, in 

 both its anhydrous and hydrated forms, were placed in the bulb 

 of a Y. Meyer's vapour-density apparatus. This was surrounded 

 by an outer tube of water,, which was in turn surrounded by 



