122 Gooch and Gruener — Iodometric Determination, etc. 



spondingly dangerous. We modified the apparatus, therefore, 

 so that onl} T glass should occur where by any possibility rubber 

 connections might act upon the free halogen. In place of the 

 ordinary retort we adopted a form of apparatus made use of 

 formerly by one of us in the quantitative distillation of boric 

 acid under the action of methyl alcohol — a pipette bent and 

 fitted as shown in the figure. To this apparatus was sealed a 

 Yarrentrapp and Will nitrogen bulb, the exit tube of which 

 was drawn out so that it might be pushed well within the inlet 

 tube of the second receiver — a Will and Varrentrapp absorp- 

 tion flask — and held in place by an outside rubber connector. 

 The third receiver acts simply as a trap to exclude air from the 

 absorption apparatus proper. In conducting the experiment 

 the receivers were charged with solutions of potassium iodide, 

 the first containing three grams, the second one gram, and the 

 third only a fraction of a gram for every tenth of a gram of 

 nitrate used. The first receiver was kept cool during the 

 process by immersion in water. The introduction of the 

 nitrate and manganous mixture following it was made easy and 

 safe by applying gentle suction to the end of the absorption 

 train. The current of carbon dioxide was started immediately 

 after putting in the manganous mixture, and after a suitable 

 time had elapsed for the removal of air heat was applied to 

 the retort and the distillation was continued until nearly all the 

 liquid had passed over. Finally the contents of the receivers 

 were united, the washing of the bulbs was effected easily and 

 expeditiously by passing the wash-water directly through retort 

 and receiver (the introduction of the manganese chloride into 

 the distillate being not at all prejudicial to the accuracy of the 

 titration), and the estimation of free iodine made by sodium 

 thiosulphate as described. The results of the experiments con- 

 ducted in this manner are given in Table III. 



These results are fairly satisfactory. The mean error of the 

 entire series is practically nothing. The manipulation is easy 

 and rapid. 



In brief, the process which gives us these results consists in 

 the distillation of the mixture of the nitrate with a saturated 

 solution of crystallized manganous chloride in strong hydro- 

 chloric acid in an atmosphere of carbon dioxide, the passage of 

 the products of action into potassium iodide, and the titration 

 of the liberated iodine by sodium thiosulphate. It is important 

 to take precautions to prevent the contact of the free halogen 

 with rubber stoppers or connectors, and any apparatus, suitable 

 for ordinary quantitative distillation and absorption, which 

 meets this condition will probably answer the requirements of 

 the process. Our own preference is for the apparatus described 

 and figured. 



