In principal this salinometer is a "battery" composed of a pair of dissimilar metals immersed in the brackish water of the field as an electrolyte. Between these dissimilar metals there exists a potential difference which is practically independent of the concentration of salts in the electrolyte over a very wide range. However, the salt concentration has a marked effect upon the conductivity of the electrolyte. If the measuring circuit has constant resistance, the only change of resistance in the total circuit is that due to the change of conductivity of the water in which the cell is immersed. Since the driving EMF is essentially constant, the current fl.owing in the circuit is a measure of the conductivity of the water sample.
Arx, William S.. 1947. "A salinometer for use in brackish water." Journal of Marine Research 6, (2). https://elischolar.library.yale.edu/journal_of_marine_research/633