AN ELECTRICAL OXYGEN -TEMPERATURE 

 METER FOR FISHERY BIOLOGISTS 



By 



Kermit E. Sneed and Harry K. EXipree 

 Southeastern Fish Cultural Laboratory 

 Bureau of Sport Fisheries and Wildlife 

 Marion, Alabama 



ABSTRACT 



An oxygen -temperature meter, designed particularly for fishery 

 biologists, was constructed and tested. The oxygen circuitry was 

 modified from polarographic devices, and the temperature circuit 

 consists of a Wheatstone bridge and thermistor system driven by a 

 transistor controlled, constant current regulator. 



The platinum, silver -silver oxide electrode pair was imbedded 

 in epoxy and weighted for measurements in any depth of water . When 

 covered with a plastic membrane, the electrode response is not 

 influenced by mild acids, alkali, salts, or pollution that does not 

 dissolve or grossly foul the membrane. The increased hydrostatic 

 pressure due to depth did not appreciably affect the electrode's 

 linear response. 



The electrode is temperature sensitive and has a positive co- 

 efficient of 3 - 8 percent per degree Centigrade, varying with the 

 size of the working electrode and the thickness of the plastic 

 membrane . 



Circuitry, method of construction and directions for operation 

 are included. 



The polarographer has been familiar with Early devices (Saiia, 1955) for the deter- 



the typical wave form of oxygen since the advent mination of oxygen in natural waters consistedof 



of polarographic analysis in about 1920 (Lingane, bare electrodes which quickly became "poisoned" 



1958). The oxygen wave depends on the relation- due to the plating of the electrode with other 



ship between the current -voltage curve (fig- 1) metallic ions in the water. At best these devices 



obtained when the dropping mercury or platinum served only to compare oxygens in two or more 



electrode is operated at variable voltages to a samples of water and did not hold their calibra- 



standard non-polarizable reference electrode, tion more than a minutes. Too, they were 



such as saturated calomel, silver-silver chloride, highly movement dependent, requiring a rather 



or silver-silver oxide. The potential at which large circulation of water past the electrode, 

 the diffusion current remains relatively constant 



(the current -voltage plateau) serves to identify Better polarographic techniques for the 



the chemical (since this relation is constant, determination of oxygen in natural waters, blood, 



depending on the particular electrode reaction) urine, and other aqueous and non-aqueous solu- 



and the height (amount) of the diffusion current tions continued to be developed. Clark, Wolf, 



serves to identify the quantity of the chemical. Granger, and Taylor (1953) investigated certain 



