ELECTROLYTIC REDUCTION 597 



acid. Three substances are obtained by the electrolytic reduction 

 of uric acid — puron, isopuron, and tetra-hydro-uric acid. The 

 manner in which the hydrogen is added on is seen clearly from 

 the following formulae. 



NH-CO NH-CH, NH-CH.. NH-CK, 



II II II' II' 



CO C-NH CO CH-NH CO C-NH-CONH.. CO CH-NH-CONH, 



I II > CO I I >C0 1 II II 



NH-C-NH NH-CH-NH NH-CH NH-CO 



Uric acid Puron Isopuron' Tetra-hydro-uric acid 



It will be noticed that puron and isopuron are isomeric, i.e. they 

 possess the same empirical formula, CjHs02N4. The former is 

 transformed to the latter by treatment with caustic alkali. 



The methyl derivatives of uric acid^ also yield a series of 

 corresponding methyl derivatives of puron and isopuron. In 

 no case, however, is a substance corresponding to tetra-hydro- 

 uric acid produced. 



The slightly higher super-tension of mercury than lead is 

 the cause of some substances being reduced better with a 

 cathode of the former metal than with one of the latter.^ 

 Examples are acetone and caffeine. In the case of camphor 

 no reduction whatever takes place at a lead cathode, while, with 

 a mercury cathode, borneol is obtained in good yield. 



It is to be expected that the electric current will come more 

 and more into use as a preparative method for the reduction 

 of organic substances. By varying the potential one can, as 

 Nernst expresses it, produce pressures whose amount varies 

 between very small fractions of an atmosphere, and many 

 million atmospheres ; and this is the reason why the electric 

 current accomplishes the reduction of some substances, such 

 as uric acid, which remain entirely unaffected by the ordinary 

 chemical reducing agents. 



The successful clearing away of the many preliminary 

 difficulties leaves the method a well-understood and compara- 

 tively simple one, besides which, electro-reduction possesses 

 the further advantage of the absence of other reagents, which 

 usually entail a more or less troublesome process of elimination 

 in the course of reduction by the usual chemical agents. 



' Tafel and Houseman, Ber. d. deut. cheni. Gesell. 40 (1907), 3743 (in press). 

 Houseman, Dissertation, Wurzburg, 1906. 

 * Ber. d. deut. chem. Gesell. 34 (1901), 279. 

 ^ Tafel and Schmitz, Zeitschr. f. Elcctroc. 8 (1902), 280. 



