THE CATHODIC PRECIPITATION OF CARBON. 



By WILLIAM! BLUM and EDGAR F. SMITH. 



(Read January 4, 1907.) 



(Contribution from the John Harrison Laboratory of Chemistry.) 



Some years ago^ one of us (S) called attention to the electrolytic 

 precipitation of iron, by the current, from citrate and tartrate solu- 

 tions. In doing so, mention was made that on dissolving the de- 

 posited metal '' in dilute, cold sulphuric acid a strong odor of hydro- 

 carbons was perceptible." Later,^ reference was again made to 

 this fact and conditions given, observing which, the contamination 

 of the metal by carbon might be avoided. In electro-analysis, the 

 question of the contamination of metals by carbon, if the metals 

 have been precipitated from organic electrolytes, has been quite 

 freely discussed. However, the contamination in nearly all in- 

 stances has been regarded as a result of carelessness in manipulation 

 and may be avoided. 



During the past summer we made observations, on the conduct 

 of certain organic acids under the influence of the current, which 

 seem of value, hence a brief account of them is submitted in this 

 communication. 



To begin, it was tried to ascertain the degree of reduction of 

 oxalic acid at the cathode. The gasometric method was called into 

 use, e. g., a comparison of the volume of hydrogen evolved in the 

 cell, with that liberated in a voltameter in the same period. It soon 

 became evident that this procedure would not be delicate enough 

 to detect any such reduction. However, while occupied in this way 

 with an ammoniacal tartrate solution, a black deposit made its ap- 

 pearance on the cathode. When held in the flame it burned off 

 completely from the platinum plate. The latter had an area of 100 

 sq. cm. Several actual trials may be here introduced. Thirty-seven 



^ Am. Chem. Jr., 10, 330 and Jr. Analyt. and Applied Chemistry. 5. 48S. 

 * Smith's " Electrochemical Analysis," 3d edition, p. 100. 



59 



