1907 



SMITH— CATHODIC PRECIPITATION OF CARBON. 61 



rapidly took on a yellow color, a distinct odor of acetamide was 

 evolved and a black deposit appeared upon the cathode. It both 

 burned on heating and generated carbon dioxide with a chromic acid 

 mixture. It may be added that the solution was not heated from 

 without as it developed a great deal of heat during the passage 

 of the current. 



Similar results were obtained on electrolyzing a like solution 

 with out a diaphragm. 



Other experiments were as follows : 



1. Five grams of sodium citrate and one gram of citric acid 

 were dissolved in 150 c.c. of water and electrolyzed at 60° C, 

 for five hours, with a current of 4 amperes and 1 1 volts. There was 

 a brass-like deposit on the cathode. It weighed 0.0018 gram, while 

 the anode had lost 0.0014 gram. 



2. Fifteen grams of citric acid, neutralized with ammonia and 

 diluted to 150 c.c, were electrolyzed at 60° C, for four hours, with 

 a current of 4 amperes and 6 volts. A grayish black deposit separ- 

 ated on the cathode. It equaled 0.0014 gram, which represents 

 carbon. The anode lost in all 0.0103 gram in weight. 



In the many trials made, the solutions gradually acquired first 

 a pale yellow color which in turn passed to brown and at times 

 almost black without becoming turbid. However, it must be said 

 that solutions of ammonium oxalate, ammonium formate, ammonium 

 acetate and ammonium succinate did not yield black deposits to 

 the cathode. In solutions of ammonium lactate and benzoate they 

 appeared as readily as in tartrate and citrate solutions. 



This deposition of carbon upon the cathode is extremely interest- 

 ing. In 1896, Coehn (Z. /. Elektrochcmie (1896), p. 541) called 

 attention to the fact that when carbon was made an anode in the 

 electrolysis of sulphuric acid, the latter became at first yellow, and by 

 prolonging the experiment, dark red and reddish brown in color. 

 If this meant a solution of carbon the latter must presumably be 

 in the form of ions, c. g., in a form directable by the current. It 

 must be in a form, which, as it does not decompose water, would 

 appear at the anode. With these thoughts before him, Coehn elec- 

 trolyzed sulphuric acid of varying concentration with an anode of 

 carbon and a cathode of platinum. The result was a splendid depo- 

 sition of carbon on the cathode. It burned away completely on 



