D. A. Kreider — Iodine Titration Voltameter. 



bottom of the tube, cathode above. The size of the electrodes 

 was, in the small cell, 1*6 X 2'7 cm ; in the large cell, 2*5 X 6 cm . 

 In the latter case the cathode was somewhat smaller and corru- 

 gated. These electrodes were bent into cylindrical form and 

 arranged coaxially with the tube. The smaller 

 cell had a diameter of 2 cm , length, 12 cm , length of 

 capillary, T cm . Its capacity was about 30 cc ; about 

 7 CC being required to cover the anode. The larger 

 cell was made in the same way, of a tube 3 cm in 

 diameter and about 15 cm in length, with a capil- 

 lary about 18 cm long. With the distance of 5 cm 

 between the nearest edges of the electrodes, the 

 total volume required to cover the cathode was czz 

 about 60 cc , about 20 cc sufficing to cover the anode. 



The apparatus was filled by raising the ground 

 glass rod and by diminished pressure, effected 

 through the side neck, drawing up through the 

 capillary successively the required amount of 

 hydrochloric acid and then the strong solution of 

 potassium iodide in water. In this way the anode 

 is completely submerged in the concentrated solu- 

 tion of iodide without the use of excessive quan- 

 tities. The hydrochloric acid serves as an elec- 

 trolyte, permitting the separation of the electrodes 

 sufficiently to preclude the possibility of any 

 interaction of the electrode products. 



By this method of filling the cell the iodide is 

 sufficiently acidified, and if not too rapidly drawn in, a sharp 

 line will mark the junction of the two solutions of different 

 density. The electrolysis results in a quantitative liberation of 

 iodine unless the current density is too great. In the latter 

 case oxygen is evolved along with the iodine. With the per- 

 missible current densities indicated in Table I, so long as the 

 potassium iodide is not impoverished about the anode, not a 

 trace of oxygen appears and the action is entirely satisfactory. 

 As the iodine is liberated it sinks along the electrode and by 

 its convection effect renews the iodide at the surface of the 

 electrode without the slightest disturbance of the supernatant 

 acid. In all cases where the current density has not exceeded 

 the indicated maximum, or where the duration of the current 

 has not been such as to exhaust the iodide (so that no oxygen 

 is evolved) the supernatant liquid remains perfectly colorless 

 and free of iodine, and continues to show a sharp line of 

 demarcation between the iodine solution and the acid. 



Table I shows the possible current densities, potential 

 change, and permissible time of run, under the given condi- 

 tions. In the first column, the first figure represents the num- 



