necessity of precise temperature control at a specific value and, 

 instead, depend upon maintaining the identical temperature for the 

 reference cell and the sample being analyzed. Sufficient data are at 

 hand to indicate that these instruments attain an accuracy of ±0.005%o 

 of salinity and a repeatability of ± 0.001 %o of salinity. 



An Australian device of recent design was demonstrated at Woods 

 Hole Oceanographic Institution during the summer of I960 by Mr. N. L. 

 Brown. Accuracy and repeatability seem to be as good as, or better 

 than, the modified Wenner-Smith-Soule conductivity bridge. It has the 

 additional important advantages that it is much smaller and far less 

 expensive to build. A conductivity bridge built in South Africa seems 

 to be as accurate and falls between the two as far as size and cost 

 are concerned. 



2. Radio frequency salinity measuring instrument 



Another recent development is a technique based on the measure- 

 ment of the absorption of radio frequency energy by the solution 

 undergoing analysis. This method of analysis seeks to avoid the 

 difficulties encountered with usual conductivity methods while retaining 

 the advantages of speed and flexibility. The distinguishing feature 

 of the radio frequency method is that the "electrodes" are on the 

 outside of the vessel containing the water sample, thus eliminating 

 the problem of electrode fouling. In this method it is necessary only 

 to pass the sample through the radio frequency field; no electrodes 

 come in contact with the sample being analyzed. The radio frequency 

 equipment can be used in the laboratory on individual water samples, 

 or at sea on a continuous stream of sea water pumped through it. 

 This latter application is limited by the depth which can be sampled 

 by such techniques. 



In radio frequency salinity measuring instruments, the principal 

 technical problem is that of precisely measuring radio frequency 

 voltage and current. The principle employed in this type of instrument 

 consists of passing a high frequency radio current (14 megacycles) 

 through a column of solution, rectifying the radio frequency current, 

 and measuring the amount of direct current which results. The amount 

 of direct current obtained is related to the impedence presented by the 

 column of solution, and the impedence in turn is determined by the 

 salinity of the solution. 



At the end of two years (1952-54) of developmental work by the 

 Texas Agricultural and Mechanical College, the results were summa- 

 rized as follows: "The objective of the research was an instrument 



IV- 8 



