results of ±0.02%o salinity are obtained. This method, however, has 

 several disadvantages. These are: 



1. Best results are obtained in a laboratory ashore. Water samples, 

 therefore, must be preserved carefully and stored to prevent changes 

 in concentration. 



2. The titration is tedious and time-consuming. 



3. Exact determination of the end-point is subject to 

 operator error. 



A recent modification of the Wenner- Smith- Soul e conductivity bridge 

 has proven extremely successful, and use of the bridge undoubtedly 

 will take the place of volumetric titrations in those laboratories which 

 can obtain the equipment. 



B. FIELD INSTRUMENTS 



Oceanographers have recognized for a long time that it would be 

 highly desirable to measure salinity in situ . The problems of sample 

 stowage, tedious and time consuming titrations, and personal error 

 thus would be eliminated. 



In industrial and laboratory chemistry, instruments have been 

 devised which can be referred to as analysis and/ or concentration 

 instruments. These instruments depend upon either the chemical or 

 physical properties of the unknown. 



In situ , instruments for oceanography make use of the physical 

 properties of salt water and have been designed or proposed around 

 the measurement of: electrical conductivity, specific gravity, and 

 refractivity. Of the physical properties of sea water used to determine 

 salinity, electrical conductivity has received the most attention and 

 has been used for this purpose by a number of investigators. Conduc- 

 tivity varies nonlinearly with both temperature and salinity, increasing 

 with increased salinity, and increasing with increased temperature. 

 Therefore, both conductivity and temperature must be measured 

 simultaneously to obtain an accurate salinity. The two main difficulties 

 in using conductivity are polarization of the electrodes and the large 

 variation of conductivity with temperature. 



Polarization is an electrode surface effect and can be considered 

 as an additional resistance and capacitance in series with the cell. 

 The additional polarization resistance depends upon many factors, 



IV- 2 



