THURAS: RECORDING SEA-WATER SALINITY 677 



is a continuation of the work on this instrument and concludes 

 with the measurement of the specific conductivity (conductivity 

 per cm. cubed) of sea water, in reciprocal ohms, throughout 

 the range of concentration found in the open ocean. 



The author wishes to express his profound sorrow at the 

 death of his associate, Captain Weibel, who was recently killed 

 at the Front in France, while engaged in special scientific work. 

 The loss of his advice and inspiration has been keenly felt in 

 this development of his suggestions. His perseverance and 

 encouragement in the preliminary work showing the feasibility 

 of the method has been of great value to me in carrying out this 

 work. 



DESCRIPTION OF THE METHOD 



The method consists in measuring the ratio of the resistances 

 of sea water in two similar electrolytic cells; one cell is sealed 

 and contains sea water of average salinity and the other cell has 

 flowing through it the sea water to be measured. This ratio is 

 obtained with a Wheatstone bridge, using an alternating current 

 galvanometer and recorder. A calibration of the apparatus 

 can be made at any time by using sea water of a known salinity 

 in the open cell. A compensation for the temperature coefficient 

 of sea water is made by placing both cells close together in a 

 temperature bath through which sea water continuously flows. 



SOURCES OF ERROR 



The preliminary experiments indicated several effects which 

 might produce errors in measurement. The extent of these 

 errors has been determined by use of the new multi-tubular 

 cells in a Wheatstone bridge circuit. A sensitive alternating 

 current galvanometer, designed by Weibel, greatly facilitated 

 the balancing of the bridge. An enumeration of the disturbing 

 effects is given below and is followed by a discussion of the ex- 

 perimental data obtained. 



1. Change in frequency and wave form of the current. 



2. Change in the electrical capacity of the cells with change 

 in current and concentration of the sea water. 



