DECOMPOSITION OF HYDRIODiC ACID. CREIGHTON. 3 



who has done a lot of this work, used acid solutions of potassium 

 iodide for the production of hydriodic acid. He found that the 

 best results are obtained when the solution of potassium iodide 

 used has a concentration of 1 grain per litre. It was a solution 

 of this strength that was used in all the following work. The 

 hydriodic acid was set free from the iodide by a solution of 

 sulphuric acid consisting of one pirt of acid (sp. g. 1.84) tc 

 five parts of water. 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 ^ sodium thiosulphate 



solution. 



It was found that the end point could be determined very 

 quickly and accurately hy 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. 



The potassium iodide used was the chemically pure guaran- 

 teed reagent supplied by C. F. Kahlbaum. 



By carrying out the titration in the above manner, the error 

 was found to be about ± 0.08 cc. sodium thiosulphate solution. 



Five milligrammes of radium bromide of activity of about 

 1,000,000 were employed. The radium was enclosed in a small 

 glass tube, so that only the yS and 7 rays were used. 



The starting point in the investigation was to determine 

 whether radium exerted any influence on the oxidation of 

 hydriodic acid. For this purpose, the radium was placed over 

 a vessel containing the acid solution of potassium iodide, of the 

 concentration mentioned above, and allowed to bombard the 

 solution for a certain time ; at the end of that time the amount 

 of decomposition was compared with that of a similar solution 

 that had not been acted upon by radium. The vessels used to 

 contain the solutions were ordinary wide-mouthed reagent 

 bottles, with a capacity of about 1 25 cc. The small glass tube 



