DECOMPOSITION OF HYDRIODIC ACID. — ^CREIGHTON. 



19 



beginning of the reaction, before the second reaction begins to 

 make itself felt, we should expect to find that the amount of 

 iodine set free is less when the solution is acted upon by 7 rays, 

 than when it is acted upon by /3 and 7 rays. At the end of 

 three hours, when the solution had been kept at 24°C., the 

 decomposition was found to be as follows : 



J25Q Na^ S., O.J solution 



No radium for 3 hrs. at 240C . 



..0.65 cc 



yS and 7 rays 



..0.85 " 



7 rays " " . 



..0.72 " 



Influence of Sunlight and Radium in the Absence of Oxygen. 



If a hydriodic acid solution such as was used in the pre- 

 ceding experiments be entirely freed from occluded air, and 

 placed in a tube from which all the air has been removed, it 

 was found that this tube could be placed in the sunlight for 

 any length of time, without the solution showing any decom- 

 position. In order to remove all occluded air before being 

 sealed off, the solution was kept in a vacuum in the dark for 

 twenty-four hours ; for otherwise it is found that extremely 

 minute quantities of dissolved air will slightl}^ decompose the 

 hydriodic acid. 



The same experiment was then tried with radium, instead of 

 sunlight. In order to keep the solution under a vacuum for 

 two or three days, without sealing up the radium in a tube with 

 the solution, the vessel containing the solution with the radium 

 was placed under a bell jar on a brass plate, connected by a 

 glass tube to a " Geryk " vacuum pump. The joint between the 

 bell jar and the brass plate was made 

 perfectly tight by sealing it with a 

 preparation made by heating together 

 equal parts of pure india rubber, par- 

 affin, and vaseline. When the vacuum 

 was made this tube was sealed off from 

 tlie pump. A delicate manometer con- 

 nected with the jar, showed no change 



to pur 





fi 



