182 PEOFESSOR H. B. DIXON AND MR. E. C. EDGAR 



collected and dried in vacua over solid calcium nitrate, which was frequently 

 changed. The iodine was then intimately mixed with 5 per cent, of its weight of 

 purified barium oxide, and distilled to remove the last traces of water and hydrogen 

 iodide. The wet iodine, in the second portion, was dissolved in a strong, cold 

 solution of purified potassium hydrate until the solution had acquired a per- 

 manent light yellow tinge. The solution was then evaporated to dryness on 

 a water bath. The mixture of potassium iodide and iodate so obtained was 

 then placed in a large platinum crucible, fitted with a platinum hood, and 

 heated to dull redness for six hours. The resultant potassium iodide was re- 

 crystallised five times from water and dried in vacuo over calcium nitrate, which 

 was frequently changed. It was pure white in colour, and contained no trace of 

 potassium iodate ; its solution in water was neutral and remained colourless when 



exposed to light. 



Standard Solution of Iodine in Potassium Iodide. In a small weighing bottle, 

 carefully cleaned and dried, iodine, purified as described, was placed. This was 

 kept in a desiccator until ready for weighing. The details of the weighing are given 

 below : 



Temperature at start 16'5 C., Barometer at start 759 -8 millims., 



Temperature at end, 15'5 C., Barometer at end 757 '0 millims., 



Weight of bottle and iodine 52-28137 grammes. 



Weight of bottle 23-70084 



28-58053 

 Vacuum correction + -00279 



28-58332 



The weight of iodine dissolved was therefore 28 '58332 grammes. 



This iodine having been dissolved in a solution of potassium iodide, the iodine 

 solution was brought into a 2-litre flask through a drawn out funnel, and the residual 

 solution carefully washed in. 



The flask was calibrated by means of a burette previously calibrated, the neck of 

 the flask being drawn out in the blowpipe flame. After cleaning and drying, the 

 flask was filled with pure water from the burette, at the same temperature as that at 

 which the burette had been calibrated. The last drops were allowed to run into the 

 flask by contact with the glass surface immediately above the water, which stood in 

 the constricted part of the neck. A circular line was etched on the glass to mark 

 the exact level of the liquid in the constriction. 



The iodine solution was brought up to the etched mark by slowly adding pure 

 water, the solution being shaken after each addition of water. The final tempera- 

 ture of the solution was almost identical with the temperature at which the volume 



