200 Phelps — Determination of Nitrites in Absence of Air. 



The experiment numbered 9 is included to show a fact found 

 early in the investigation, namely, the necessity of boiling out 

 the nitrogen dioxide before titrating the residual arsenious acid. 

 It was made like 3 and 4 above up to that point, when in 

 stead of boiling out the nitrogen dioxide, cooling, and titrating, 

 it was treated with a slow stream of air bubbling through for 

 fifteen minutes and then titrated. Evidently the nitrogen 

 dioxide in oxidizing affects the arsenious acid slightly. 



When the sulphuric acid is being added to the alkaline solu- 

 tion containing the arsenite, iodide, and nitrite, iodine is set free 

 locally but is at once taken up by the alkaline arsenite, so that 

 finally, wheu the acid reaction is reached, there is only a small 

 amount of it free, no matter how much nitrite may have been 

 used. This condition reduces to a minimum the possibility of 

 a loss of iodine by volatilization. 



As might be anticipated, the two processes show slightly 

 different results, the process outlined above tending to give 

 results in excess of the theory on account of the action 

 of dissolved oxygen, while that of Kinnicut and JNef should 

 show a deficiency as compared with theory, since the loss of 

 nitrogen oxides is evidenced by the odor when even a very dilute 

 solution of a nitrite is acidified. 



