THE BEHAVIOUR OF SOLUTIONS OF HYDKIODIC ACID IN LIGHT 

 IN THE PRESENCE OF OXYGEN.* By H. Jermain M. 

 Creighton, M. A., Dalhousie University, Halifax, 2sT. S. 



Read 13th April, 1908. 



It is well known that solutions of hydriodic acid and acid 

 solutions of potassium iodide readily change into free iodine 

 and water. These reactions are accelerated by light, and also, 

 as the author 1 has shown, by radium. While investigating "the 

 influence of radium on the decomposition of hydriodic acid" 

 the author 2 observed that the iodine set free by the oxygen 

 increased with the time, reached a maximum and then grad- 

 ually fell off again, under certain conditions. It was also 

 observed that solutions of iodine placed in the sunlight slowly 

 became colourless. It was to try to account for the disappear- 

 ance of this iodine that this investigation was undertaken. 



The hydriodic acid used in these experiments, was set free 

 from solutions of potassium iodide by means of a sulphuric 

 acid solution consisting of one volume of acid (sp. g. 1.84) to 

 five volumes of water. The solutions of potassium iodide used 

 had a concentration of 1 gram per litre. The proportion of acid 

 to iodide solution was one to eight. 



The amount of oxidation was determined in the usual way, 

 by titrating the liberated iodine with T -^ sodium thiosulphate 

 solution. 



It was found that the end point could be determined very 

 quickly and accurately by highly illuminating the solution by 

 means of an electric light placed behind it, and reflecting back 

 the rays through the solution by placing a piece of white paper 

 around the beaker on the opposite side. 



Contributions from the Science Laboratories of Dalhousie University [Chemistry]. 



1 Creighton, Proc. and Trans. N. S. Inst. Science, vol. xii, 1, 1. 



- Loc. cit. Also Creighton and Mackenzie, Amer. Chem. Jour., 1908. 39, 4 (April). 



PKOC. & TRANS. N. S. INST. Sci., VOL. XII. TRANS. 4. 



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