IN LEGHT IN THE PRESENCE OF OXYGEN. CREIGHTOX. 55 



it still possessed a slight colour, not unlike the colour produced 

 when Nessler's solution is added to a solution containing a min- 

 ute quantity of ammonia. About a week after the last of the 

 iodine had disappeared, this colour went also. In all solutions 

 of hydriodic acid, where the iodine disappears, this colour was 

 observed. 



Although it seemed absolutely certain, from the fact that 

 the seco'nd U-tube, B, in the above apparatus contained no 

 iodine, none of it could have escaped out of the latter into the 

 atmosphere, yet the objection arose that as the gas inside the 

 bottles was taken out, carrying with it iodine, some of the 

 iodine, although very unlikely, might have escaped. It was to 

 overcome this objection that the experiment to be described was 

 carried out. 



500 cc. of acid potassium iodide solution were placed in a 



reagent bottle provided 

 with a tightly fitting 

 rubber cork, through 

 which passed a glass 

 tube provided with a 

 stop-cock. This glass 

 tube went almost to the 

 bottom of the liquid as 

 shown in Fig. 2. This 

 tube was connected 

 with a gas holder con- 

 taining oxygen under pressure, the gas from which was first 

 purified and dried, by passing through wash bottles containing 

 sodium bicarbonate and concentrated sulphuric acid, before 

 being allowed to enter the iodide solution. 



The stop-cock was opened, the rubber cork loosened, and the 

 air in the bottle displaced by oxygen. The rubber stopper was 

 then tightly fitted, the oxygen in the bottle allowed to attain 

 the same treasure as that in the holder, and the stop-cock closed. 



