234 0. 8. Pidman — Determination of Uranium and 



that point a little more fully. The apparatus that was used is 

 shown in the accompanying figure. 



The same form of apparatus was 

 used in the preliminary experiments 

 just mentioned, except that in the 

 place of the stoppered funnel there 

 was a piece of glass tubing bent at 

 right angles. In the process finally 

 worked out for tlie determination of 

 the uranium a two-hole stopper was 

 used, instead of the one having three 

 holes, of which one served for carry- 

 ing the inlet tube connected with the 

 stopcock of the burette and the other 

 for carrying a bent glass tube, by 

 which the suction was applied. 



In the experiments carried out with 

 this form of the apparatus carbon 

 dioxide was passed through the receiv- 

 ing fi.ask until, by testing the escaping 

 current with a solution of sodium hy- 

 droxide, it was proved that only car- 

 bon dioxide was present. The ura- 

 nium sulphate solution was then passed through the reductor 

 with gentle suction, just as when no carbon dioxide was used, 

 and was followed by the dilute sulphuric acid used to wash out 

 the flask, 250^"^' of hot water, and finally by 200^°^' of water at 

 the ordinary temperature of the room, to cool down the solu- 

 tion somewhat and to bring up the volume to the dilution at 

 which it was ordinarily titrated. A strong current of carbon 

 dioxide was then turned on until the partial vacuum caused by 

 the suction had been entirely filled, and, by testing again, it 

 was found that carbon dioxide entirely filled the flask. An 



excess of a — potassium permanganate solution was next intro- 

 duced into the receiving flask by means of the stoppered 

 funnel without admitting any air. After the flask had been 

 gently shaken so that the permanganate was diffused through 

 the liquid, the apparatus was disconnected from the reductor 

 and the excess of permanganate destroyed by a small excess of 



n 

 a — solution of ammonium oxalate. The solution was still 

 10 



so warm that it was possible to tell fairly well when an excess 



of the ammonium oxalate had been added. The mixture was 



then heated to about 60° and the final end-point taken with a 



10 



potassium permanganate solution. 



