APRIL 4, 1921 THURAS: MEASUREMENT OF SEA WATER SALINITY 161 



During the Ice Patrol of 1920 an opportunity was given to use the 

 electrical method of measuring sea water salinity on board ship. An 

 apparatus consisting of instruments and parts secured from the 

 Bureau of Standards was set up on shipboard and several hundred 

 determinations of salinity were made. The operation of the ap- 

 paratus was simple and convenient and at no time did weather condi- 

 tions interfere with the measurements. This apparatus consisted of: 

 a wheatstone bridge, a Leeds and Northrup alternating current 

 galvanometer, a specially constructed electrolytic cell designed for a 

 salinity recorder, ^ a hand regulated temperature bath, and a rebuilt 

 1/12 horse power direct current motor to give 120 volts, 60 cycles of 

 alternating current when connected to 110 volts direct current. This 

 machine was designed and built by Mr. A. J. Fecht of the Bureau of 

 Standards. 



All measurements were made at 25° C. and a table was prepared to 

 give salinities directly from the balanced bridge readings. The com- 

 plete apparatus was tested each day by standard sea water taken 

 from a supply which had been carefully measured both by a chemical 

 method and a density method^ before beginning the cruises. This 

 supply of sea water lasted throughout the cruises. The temperature 

 of the electrolytic cell bath could easily be held to within 0.03° C, 

 and the bridge, after balancing the moving coil of the galvanometer 

 so that the center of mass was fairly near the axis of support, could be 

 set to a value corresponding to 0.02 in salinity. No electrical capacity 

 or inductance was necessary for balancing the bridge, and variations 

 in the voltage and frequency of the generator had no appreciable effect 

 on the bridge setting. With the rough apparatus used the determina- 

 tions were accurate to 0.05 in salinity, or better than 0.02 of one per 

 cent. 



Since the electrical conductivity method may be satisfactorily used 

 at sea to measure the salt content of ocean water, attention is directed 

 to the references given in the foot notes which describe an apparatus 

 which will give a continuous record of sea water salinity from a moving 

 vessel. This instrument in conjunction with an instrument to record 

 temperature, which has been constructed, would give the three most 

 important physical variables of sea water, namely, temperature, 

 salinity and density. Such records taken regularly over the same 

 course would show monthly and yearly variations of these physical 

 properties which might be of much scientific value. 



2 See this Journal, 8: 145, 680. 1918. 

 » See this Journal, 7: 605. 1917. 



