192 Gooch and Browning — Method for the 



An experiment differing from the last i?i that thirty times as 

 mnch arsenious oxide and iodine were taken, gave similar 

 results. 



It is plain, therefore, that the arsenious acid and arsenic acid 

 exert opposite effects under the conditions of these experiments, 

 and that one or the other prevails according to the proportion- 

 ate composition of the solution, the degree of dilution, and the 

 temperature. 



The experiments detailed in the following statement were 

 intended to determine the conditions best adapted to eliminate 

 the iodine from such quantities of potassium iodide as would 

 ordinarily be dealt with in the course of analysis. 



A solution of potassium iodide was placed in an Erlenmeyer 

 beaker of 300 cm 3 capacity, followed by a solution of potassium 

 arseniate and by dilute sulphuric acid [1:1], and the volume 

 of the liquid was diluted to about 100 cm 3 . A mark was put 

 upon the beaker to indicate the level to which the liquid was 

 to be reduced, a spiral of platinum wire was placed in the 

 solution to prevent explosive ebullition, and the contents of the 

 flask were boiled until the desired degree of condensation was 

 reached. Colorlessness of the liquid at this point, though a 

 fair indication of the absence of free iodine, is no indication 

 that the hydriodic acid has been completely decomposed, and 

 so, in the event of finding the liquid colorless, it was first cooled 

 and snaken with chloroform to prove or disprove the absence 

 of free iodine, and then tested for the presence of hydriodic 

 acid by shaking with nitrous acid and chloroform. 



An inspection of these results shows at once that when the 

 larger amounts of iodine are to be eliminated the proportion of 

 sulphuric acid to the final volume after boiling needs to be 

 increased somewhat beyond that which is necessary to set free 

 very small portions such as were dealt with in the experiments 

 of the earlier series. 



In Series D it appears that the proportion of sulphuric acid 

 increases from 8*3 per cent to 25 per cent of the whole volume 

 before the liquid is found to be free from iodine as such, and 

 even then there sometimes remain minute, though probably 

 insignificant traces of hydriodic acid. 



In the experiment of Series E the liquid was diluted after 

 concentration and the boiling repeated, and the volatilization of 

 the iodine was thus more nearly perfected than in the correspond- 

 ing experiments of the previous series — a proportion amount- 

 ing to 16*6 per cent apparently accomplishing the work done 

 by 25 per cent of the same acid in a single concentration. The 

 results of Series F, Gr, and H, are closely comparable with those of 

 the corresponding experiments of Series D. Throughout these 

 experiments it is again made evident that it is the proportion, 



