51 Brown — Work on the Interaction of Hydrochloric Acid. 



nous chloride and sulphate the " KMn0 4 found" is slightly 

 greater than with the hydrochloric acid alone, due probably to 

 a lesser formation of the more volatile and indefinitely react- 

 ing product chlorine, more permanganate going to form the 

 more definitely reacting oxides of manganese than in the 

 digestion with hydrochloric acid alone. The amount of man- 

 ganese oxides represented by " oxidizing material not CI " in 

 the above table is seen to vary widely. This is in accordance 

 with Volhard's* assertion that acids hinder the reaction 

 between manganous salts and permanganate to give higher 

 oxides of manganese. This action, rather indefinite under 

 even the most favorable conditions, might be expected to be 

 especially so in the presence of the large amount of acid used 

 in these experiments. 



With all the salts above used, and especially with cadmium 

 chloride, the " total KMn0 4 found " is less than the perman- 

 ganate added before digestion. The natural supposition 

 seemed to be that this deficiency was due to the escape of 

 chlorine during the digestion. On adding potassium iodide 

 solution, however, to the Yoit flask during the hour's digestion, 

 no appreciable escape of chlorine was noticeable, while the 

 oxidizing material showed the same values as in Table V. 

 This was true whether the digestion was made with hydro- 

 chloric acid alone or in the presence of any one of the salts 

 used in Table V. It appeared evident, therefore, that the 

 chlorine disappeared in the digestion liquid, and that the 

 greater or less extent of this disappearance accounted for the 

 greater or less amount of chlorine found to be present in the 

 digestion liquid at the close of the hour's heating. Thinking 

 that possibly these various salts might interfere in some way 

 with the iodine liberated by permanganate from potassium 

 iodide in the presence of hydrochloric acid, experiments were 

 made to ascertain whether any of the observed differences 

 were due to such interference. These experiments were con- 

 ducted as follows: Into a flask were introduced 100 em3 of 

 normal hydrochloric acid, and in addition either 9*90 cm3 of 

 tenth-normal hydrochloric acid, or 9 - 90 cm of one of the tenth- 

 normal salt solutions there indicated. An excess of potassium 

 iodide was then added, 9*90 cm3 of permanganate run in and the 

 iodine liberated estimated with sodium thiosulphate. 



These experiments showed that normal values are obtained 

 by titrating iodine by thiosulphate in the presence of hydro- 

 chloric acid and any one of the various salts used, thus exclud- 

 ing the possible inference that the large amount of acid or 

 possibly the metallic chlorides interfered in the reaction. 



* Ann. Chem., cxcviii, 337 (1879). 



