IOWA ACADEMY OP SCIENCES. 
11 
vapor of iodine was not observed to rise above the bulb of 
the flask, but the complete conversion of the iodine into 
hydriodic acid required at room temperature three or four 
hours. If, however, the bulb of the flask was immersed in 
water kept at 50° it was found that the reaction went on 
much more rapidly and was completed in about one hour. 
Even at this temperature very little iodine came over, and 
this small quantity was, near the end of the experiment, 
returned to the flask by removing the flask from the water 
so that the liquid in the test tube and the wash water 
sucked back into the flask. The experiment was allowed 
to continue till all trace of the color due to iodine had dis- 
appeared and the liquid showed only the clear, light green 
color due to ferrous iron. 
In the five following experiments the hydriodic acid 
formed was determined, after oxidizing the iron in solution 
to the ferric condition, by titration with a twentieth nor- 
mal solution of silver after the method of Volhard. The 
silver solution was added in excess, the silver iodide was 
filtered off and the excess of silver was determined in the 
filtrate, with sulphocyanate. 
(1) 10 c.c. iodate solution required 20.00 c.c. silver solu- 
tion. 
(2) 10 c.c. iodate solution required 19.90 c.c. silver solu- 
tion. 
(3) 20 c.c. iodate solution required 40.07 c.c. silver solu- 
tion. 
(4) 20 c.c. iodate solution required 40.10 c.c. silver solu- 
tion. 
(5) 20 c.c. iodate solution required 39.75 c.c. silver solu- 
tion. 
The solution obtained on oxidizing the iron was not per- 
fectly colorless, and the color interfered somewhat with 
the titration with sulphocyanate. The best results were 
obtained when the solution was boiled to free it from 
nitrogen oxides and then allowed to stand till quite cold. 
Since it is questionable whether by Volhard’s method it is 
permissible to determine halogens by titrating the excess 
