541 Gooch and Read — Determination of Chlorine. 



Art. LIII. — The Electrolytic Determination of Chlorine in 

 Hydrochloric Acid with the Use of the Silver Anode ; by 

 F. A. Gooch and H. L. Read. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccv.] 



In Yortmann's work* upon the electrolytic determination of 

 the halogens with the use of a silver anode, the determination 

 of iodine in iodides was demonstrated experimentally ; and the 

 statement was made, with the promise of future demonstra- 

 tion, that chlorides and bromides are susceptible of similar 

 treatment. It was shown that when a suitable electric current 

 is passed through a solution containing a moderate amount of 

 potassium iodide and a proper amount of sodium hydroxide, 

 iodine may be fixed upon the silver anode while potassium 

 hydroxide is formed at the platinum cathode. It was found 

 that the addition of an alkali tartrate (3 grm. of Seignette salts) 

 aided the fixation of the iodine as silver iodide upon the anode, 

 but excepting the cases in which the amount of iodide handled 

 was very small, good results were also obtained without the 

 use of the tartrate. In this work, a disc of silver 5 cm in 

 diameter was used as the anode and a similar disc of 

 platinum, or a platinum dish, served as the cathode ; the total 

 volume of the solution was 100 cm3 to 150 cm3 , containing 6 cm3 to 

 10 cm3 of a 10 per cent solution of sodium hydroxide ; and the 

 current, less than '07 ampere under a potential not exceeding 

 2 volts, was allowed to act for several hours. The end of the 

 electrolysis was determined either by testing a few drops of 

 the solution for iodine or by putting in fresh anodes until no 

 more silver iodide was formed upon the anode surface. To 

 determine the increase in weight of the anode due to fixation 

 of iodine, the anode was removed from the liquid, washed 

 with water and with alcohol, dried over a Bunsen name, and 

 finally heated to dull redness or to the fusing point of silver 

 iodide for the purpose of removing oxygen also fixed upon 

 the anode. It was noted that small amounts of silver (0*0010 

 grm. to 0*0015 grm.) were dissolved from the pure silver anode 

 and deposited to some extent upon the platinum cathode ; but 

 to completely deposit upon the cathode the dissolved silver it 

 is recommended to introduce a platinum anode after removing 

 the silver anode and to pass the current for an hour. The 

 sum of the increase in weights of both electrodes is the meas- 

 ure of the iodine fixed. 



Yortmann thus emphasized strongly two points : viz., that 

 the silver anode should be heated to a temperature sufficient 

 to break away oxygen (held according to Yortmann in the 



* Monatshefte f. Chemie, 15, 280 (1894) ; 16 3 674 (1895). 



