678 THURAS: RECORDING SEA-WATER SALINITY 



3. Heating produced by the current in the cells. 



4. Temperature lag of the sealed cell when the temperature of 

 the bath suddenly changes . 



5. Flow of sea water through the open cell. 



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

 value when the sea water passing through the open cell changes 

 in salinity. 



7. Air bubbles in the cells. 



Different frequencies and wave forms, of alternating current, 

 were obtained from a machine giving a good sine wave form at 

 1000 and 500 cycles and a power circuit giving about 60 cycles. 

 Successive conductivity measurements on the same solutions 

 with these three frequencies gave readings none of which differed 

 by as much as 5 parts in 100,000. The open cell and sealed 

 cell in the two arms of the bridge contained sea water of a salinity 

 of 35 and 32 grams per 1000 grams of sea water. 



The electrical capacities of the cells were measured in a Wheat- 

 stone bridge circuit by use of a vibration galvanometer and a 

 variable inductance. Each cell was placed in one arm of the 

 bridge in series with a variable inductance which was used to 

 balance the capacity effect in the cell. Before making the meas- 

 urements the cells were carefully platinized with a 1 per cent solu- 

 tion of pure platinic chloride for three hours, reversing the 

 current every ten minutes. This covered the electrodes with a 

 firm gray coating of platinum black. The apparent series ca- 

 pacity of the sealed cell was found to be 11,000 microfarads and 

 the capacity of the open cell 14,000 microfarads. These large 

 series capacities are equivalent to small reactances and since 

 these reactances are in quadrature with the ohmic resistances 

 they only affect the balance of the dynamometer by reason of 

 second order terms and are therefore negligible. No variation 

 in capacity was obtained with sea water of different concentra- 

 tions. Increasing the current in the cell from 0.05 to 0.25 am- 

 pere increased the apparent capacity by 30 per cent. However, 

 since the capacities of the cells are large any change in capacity 

 may be neglected as may also the reactances of the capacities 

 themselves, for the accuracy required in this work. The Wheat- 



