374 C. A. Peters — Electrolysis of Sodium Chloride 



Change of Color and Fusion of Silver Chloride. — It was 

 noticed that as the anode containing silver chloride darkened 

 by light was exposed to the higher temperatures of the various 

 ovens used, it became gradually lighter in color and finally 

 colorless. The change was most rapid as the melting point, 

 487°,* was approached. 



Silver chloride that had been rendered colorless by fusion 

 and weighed, turned dark on exposure to light without change 

 in weight and became again colorless upon refusion with no 

 detectable change in weight. 



Goldbaumf and other writers speak of distinguishing by 

 color the silver chloride darkened by light from the silver 

 oxide also deposited on the anode. This is not always the 

 writer's experience. There were times in the course of this 

 work when he could distinguish between them. At. other 

 times only reference to the treatment the anode had under- 

 gone could decide whether it was coated with oxide or chlo- 

 ride or both, and the color gave no correct indication of what 

 might be on the anode. These points are noted in progress of 

 the work, which, however, have no direct bearing upon it. 



Cleaning with Potassium Cyanide. — Gooch and Read:}: 

 have shown that the gauze electrode plated from potassium 

 cyanide is contaminated by the cyanide. Consequently even 

 for the solution of the silver chloride from the anode the use 

 of this reagent, for the most part, was avoided. 



The two exceptions where it was used gave the following 

 experience. In one the anode covered with the fused chloride, 

 from the electrolysis of salt equivalent to *1773 grms. of chlo- 

 rine, was rotated in 5 per cent potassium cyanide for \\ hours, 

 then rinsed in running water under the tap and rotated again 

 in fresh water in a beaker for 2 hours. The water in this 

 second beaker gave a white precipitate when silver nitrate was 

 added, showing that potassium cyanide had diffused into it. 



In the second experiment the anode, also covered with fused 

 silver chloride from salt equivalent to "1773 grams of chlorine, 

 was allowed to stand in 5 percent cyanide solution all night 

 and part of a day, then washed under the tap and placed in a 

 fresh beakflr of water, where it stood during the remainder of 

 the day and all night. The following day it w r as rinsed again 

 and allowed to stand four hours in a second fresh beaker of 

 water. The water in the first beaker of water gave a precipi- . 

 tate with silver nitrate solution and the second none, not even 

 upon evaporation to 5 cmS on the steam bath. These experi- 



*Kohlrausck, P. A. (2), xvii, 642 (Dammer). 



fL. c. 



% This Journal, xxviii, 550, Dec. 1909. 



