148 WEIBEL AND THURAS: RECORDING SALINITY 



bridge circuit containing the two electrolytic cells, using either 

 a telephone at 500 cycles per second or an alternating current 

 galvanometer at 60 cycles per second as a detector. 



2. The temperature compensation is sufficient. For the maxi- 

 mum difference in salinity the lack of compensation did not ex- 

 ceed 0.03 in salinity (0.03 gram of solids per kilogram of water) 

 for a change of 10°C. 



3. No appreciable change in balance due to the flow of the sea 

 water through the open cell was obtained. 



4. To obtain a continuous record of salinity an alternating- 

 current galvanometer similar t o the usual direct-current galvan- 

 ometer is needed to operate tlie recorder. This galvanometer 

 was constructed of the electromagnet moving coil type,^ and 

 had a sensitivity and other operating constants as good as those 

 of the direct-current galvanometers now used. After these 

 preliminary experiments on some temporary cells had shown the 

 feasibility of the method a more careful study was made of cer- 

 tain sources of error in order to obtain data upon which to base 

 the design of the final cells. These effects are : 



1. Heating effect of the current in the cells; 



2. Temperature lag of the sealed cell when the sea- water 

 temperature in the bath suddenly changes; 



3. Time necessary for the resistance ratio to reach its true 

 value if the sea water passing through the open cell changes 

 in salinity. 



In the ordinary conductivity measurements performed in a 

 laboratory the heating effect of the current can be made negligi- 

 ble l)y using a sufficiently sensitive galvanometer or telephone 

 receivei', but with the less sensitive recording galvanometer this 

 current must be much larger and consequently requires a spe- 

 cially designed cell to dissipate the heat developed. From ex- 

 ]:)ei-iments on differently shaped cells the heating coefficients, 

 i.e., temperature rise per watt dissipated in the cells, were found 

 to l)e approximately inversely proportional to the diameters 

 and lengths of the cells. Since the length of cell is limited by 



*Weibel, E. E., Bureau of Standards Sci. Paper No. 297 p. 23. 1917. 



