-0 5 -06 -07 -08 -09 



Figure 1: — The current-voltage wave of 

 oxygen with a platinum working elec- 

 trode, a silver-silver oxide refer- 

 ence electrode and potassium hydrox- 

 ide electrolyte. The ctirrent -voltage 

 plateau with KOH occurs between -0.75 

 and -l.l5 volts. 



plastic films to cover the electrodes and pre- 

 vent "poisoning" . These allowed continuous 

 recording of oxygen over long periods of time. 

 A symposium on the subject was held by the 

 Federation of the American Society of Experi- 

 mental Biology in 1957 and several specialists 

 in the field summarized the existing knowledge 

 and suggested new approaches. By this time the 

 polyethylene covered electrode was in general 

 use and was being used in blood and urine 

 analyses . 



Most of the techniques developed before 

 1959 were for laboratory analyses and employed 

 microelectrodes, the current output of which 

 was low and had to be amplified. Recently, 

 several instruments of this type have appeared 

 on the market and most of these are equipped 

 with the Clark electrode or some modification 

 of it. The great need for similar systems 

 adapted for measurements in the aquatic en- 

 vironment led to the development of suitable 

 electrodes (Carritt and Kanwisher, 1959; 

 Kanwisher, 1959). These workers have shown 

 that such electrodes respond linearly to oxygen 

 tensions, are highly stable, very sensitive, have 



rapid resppnse, and are not influenced by pH, 

 salts, most pollution, and changes in osmotic 

 pressures. 



The Carritt-Kanwisher system employs 

 a large (1-2 centimeters) platinum disc for the 

 working electrode and a pure silver tube (about 

 1-1 1/4 inches long and 3/4-inch in diameter) 

 for the silver- silver oxide reference electrode. 

 The electrodes are electrically insulated from 

 each other by lucite or epoxy cement. The whole 

 electrode assembly is covered by a polyethylene 

 or Teflon membrane behind which is a 0.5N KOH 

 electrolyte. A thermistor embedded with the 

 electrode can serve both as a temperature 

 measuring device or for partial temperature 

 compensation of the electrode reaction, which 

 is highly temperature sensitive (5 to 6 percent 

 per degree centigrade) . The mechanical details 

 of construction of an electrode assemble similar 

 to that of Carritt and Kanwisher are shown in 

 figure 2. 



PLASTIC FORIVI 



LEAD SHOT 



GASKET 

 CAP 



THERMISTOR 

 THERMISTOR RECESS 

 0-RING GROOVE 



SILVER 



PLATINUM 



Figure 2: — Longitudinal section of 



oxygen-temperature electrode assembly 

 suitably weighted for deepwater 

 measTorements . 



Virtually none of the publications by 

 electrochemists gives electrical circuitry 

 (except in a theoretical way) that can be used 

 by the average fishery biologist, who is usually 

 unfamiliar with polarography. However, one 

 company has developed an instrument, based 



