164 OXIDATION-REDUCTION POTENTIALS 



back titration of excess reagent with water a small current is passed between the 

 electrodes. In a moist solution the electrodes are polarised and a potential difference 

 characteristic of the system can be measured, bub immediately there is a slight excess 

 of reagent present the cathode is depolarised and the potential difference disappears. 

 The sudden fall in potential can be observed with the aid of a galvanometer or by the 

 " magic eye " of a cathode ray tube. 



TOXICOLOGY 



In view of the possibiUty of detecting traces of compounds the polarograph is 

 valuable in toxicology. As an example it may be mentioned that aromatic nitro- 

 compounds give characteristic polarograms and in nitro-poisoning investigations may 

 be made directly on the serum of patients or on ether extracts. 



The polarographic half-wave potentials of nitrobenzene derivatives have been 

 studied by Dennis, Powell and Astle (1949). Toxic oxidation products of the chemo- 

 therapeutic drug arsphenamine have been detected with the polarograph. 



SUMMARY 



The general theory of polarographic methods is briefly described together with 

 some experimental considerations. Applications of the polarograph to systems of 

 biological interest such as dissolved oxygen, cysteine, proteins, enzymes, vitamins, 

 hormones, chemotherapeutic agents and antibiotics, are discussed. 



