592 



SCIENCE PROGRESS 



current, having been of considerable theoretical and practical 

 importance. 



Amidophenol 

 r H /^'^= 



We turn now to the second class — the electrolytic reduction 

 of difficultly reducible substances. This subject is a more recent 

 one. The first such reduction was carried out by Tafel ^ on 

 strychnine in 1898, to be followed in rapid succession by a large 

 number of other compounds, so that the method has become one 

 of great importance not only as a preparative method, but also 

 in view of the many physico-chemical problems involved. 



The advantages of the electro-reduction of organic substances 

 — more particularly of difficultly reducible substances — will be 

 considered briefly at the conclusion of the article. 



A short description of the method and apparatus employed 

 by Tafel for the quantitative investigation of these reductions 

 must now be given.- Experiments must be made on a small 

 scale to see firstly if the substance is capable of being electro- 

 lytically reduced at all, and secondly to determine the influence 

 on the time required for the reduction of variations of current 

 concentration,^ current densit}^* etc. The time required is an 

 important factor, as man}^ of the products obtained are easily 

 decomposable. Such preliminar}' experiments are made in the 

 closed apparatus shown in fig. i. 



The lead beaker (a) serves as anode. The porous cell (b) 

 separates anode chamber from cathode chamber. The cathode 



* Annalen, 301 (1898), 285. 



* Ber. d. dent. chem. Gesell. 33 (1900), 2209 ; Zeitschr. f. p/tys. Chew. 34 

 (1900), 187. 



^ Current concentration = current per litre of cathode liquid. 



* Current density = current per square centimetre of cathode surface. 



