Determination of Molybdenum. 171 



replace the receiver, and to continue the distillation without 

 danger of admitting air to the distillation flask. 



In experiments to be described— (1) to (5) of the table — the 

 proportions of potassium iodide and molybdic acid, and the 

 strength of the hydrochloric acid recommended by Friedheim 

 and Euler were retained. The essential change of condition is 

 the removal of atmospheric air from the distillation flask before 

 the acid is admitted to contact with the other reagents. Potas- 

 sium iodide (3 grm.) and water (200 cm3 ) were put into the receiver 

 C, and a little of this solution was allowed to flow into the 

 trap g. Ammonium molybdate carefully weighed (0*3 grm.) 

 and potassium iodide (0*5 gm. to 0'75 grm.) were introduced 

 into the distillation-flask B, the apparatus was connected as 

 shown in the figure and carbon dioxide was passed freely 

 through the whole apparatus for some minutes. The stop- 

 cock d, between the bulb of the funnel A and the flask B, 

 was closed and hydrochloric acid (40 cm3 , sp. gr. 1*12) was 

 poured into the funnel ; the air above the liquid in the funnel 

 was displaced by carbon dioxide through the space between 

 the neck of the funnel and the loosely adjusted stopper carry- 

 ing the inlet tube ; the connection between the funnel and 

 inlet tube was tightened, the stop-cock opened, and the acid, 

 under the pressure of carbon dioxide, was permitted to flow 

 into the flask. In this way the acid, iodide and molybdate 

 were made to interact with little danger of the presence of 

 oxygen. The flask was heated by the Bunsen burner and the 

 iodine evolved, passing over quietly in the slow current of 

 carbon dioxide, collected in the receiver. The liquid was 

 boiled until fumes of iodine were no longer visible above the 

 liquid in the flask and connecting tubes backed by a ground 

 of white, and then a full minute more. At this stage, the 

 green color of the liquid having developed fully, the apparatus 

 was permitted to cool, the current of carbon dioxide was in- 

 creased, the cap of the receiver was loosened at y, the contents 

 of the trap were washed back into the receiver, the rest of the 

 apparatus was lifted bodily from the receiver, the liquid adher- 

 ing to the inlet-tube was washed off into the receiver and the 

 end of the tube was dipped immediately into a solution of 

 potassium iodide. The constant flow of carbon dioxide pre- 

 vented reflux of air during the transfer, and as soon as the end 

 of the tube had been submerged in the solution of potassium 

 iodide (which was employed not only as a water-seal, but to 

 catch any iodine still carried in the gas), it was possible to 

 reduce the rapidity of the current. 



After titrating the iodine in the distillate the receiver was 

 again placed in the train and the process of distillation was 

 resumed under the former conditions and continued until the 



