with the Mercury Cathode. 375 



ments show that potassium cyanide used for solution of the 

 silver chloride cannot he washed out in a few seconds under 

 the tap but does practically all diffuse out upon long standing 

 in water. 



After the experiment last recorded in the previous para- 

 graph was performed, the silver (5*7 grams) on the anode used 

 was dissolved in half strength nitric acid. Some platinum, 

 finely divided, appeared in the beaker. The mixture was 

 evaporated on the steam bath and water added. A white pre- 

 cipitate was apparent. The addition of more nitric acid caused 

 the disappearance of the white precipitate. The liquid upon 

 evaporation was now noticed to have the reddish yellow color 

 of platinum chloride and did contain platinum in solution. 

 The writer would say that the solution of the platinum black 

 was due to the action of nitric acid and hydrochloric acid, 

 which latter could only have come from some silver chloride 

 left unattacked by the cyanide, and, consequently, that potas- 

 sium cyanide may not completely dissolve fused silver chloride 

 from the gauze anode. This experiment verified a previous 

 observation to the same effect. 



Cleaning with Ammonia. — It was attempted many times to 

 remove the fused silver chloride from the anode by solution in 

 ammonia. This was only partially successful, as a few selected 

 experiments will show. In one the anode covered with *72 

 grms. of fused silver chloride lost "52 grms. upon ten minutes 

 rotation in strong ammonia. 



In a second experiment the anode was rotated in one-half 

 strength ammonia four hours. Then, after heating to redness 

 again, rotated for 15 minutes in fresh ammonia and the solu- 

 tion evaporated. The residue showed silver chloride. The 

 anode after heating again to dull redness and still showing 

 silver chloride, was fused and rotated 17-J hours in ammo- 

 nia of half-strength and the liquid was evaporated. Silver 

 chloride was found in the residue. The anode, upon being 

 weighed, showed a loss of "0110 grms. in weight. Reduction 

 in hydrogen reduced the weight '0020 grms. more. 



It was evident from these and other experiments that com- 

 plete solution of the fused silver chloride in ammonia was 

 tedious if not impossible. 



Reduction in Hydrogen. — The reduction of the silver chlo- 

 ride on the anode by hydrogen was more satisfactory than the 

 cleaning with either cyanide or ammonia. The process as it 

 was carried out was briefly as follows : The anode after weigh- 

 ing, covered with fused chloride, was suspended in the porcelain 

 heating crucible previously described, the cover of iron or mica 

 snugly but lightly adjusted, hydrogen dried by sulphuric acid 

 introduced briskly, Rose fashion, through the cover and the 



