The inductive salinometer is a commonly accepted tool used to provide the data required for calculating chlorinity and salinity. It must be kept in mind however, that differences may arise between titrated chlorinity (according to Knudsen or Hermann) and chlorinity from conductivity. Furthermore the chlorinity-conductivity relationship is not defined explicitly below chlorinity about 3 per thousand. In that area a new polynomial acts as reference for chlorinity from conductivity. In this paper the difference between the two kinds of chlorinity will be called DCLY. Several authors already established the existence of variable DCLY in waters like the Baltic Sea. Measurements indicated a correlation with calcium and carbonate contents. The salinity in the Rhine-estuary near Rotterdam varies between almost zero and 25 per thousand. Samples were taken from this natural "salt-gradient" as well as from the most important Dutch rivers. Analyses were made for conductivity, chlorinity (titrated), sulfate, sodium, calcium, magnesium, pH and suspended solid matter. The most important mutual relations are investigated. A correlation of DCLY with excess calcium and sulfate is found. The pH is already known to have a small effect on the difference between the two kinds of chlorinity. With increasing chlorinity the DCLY diminishes. An example: for chlorinity about 2 per thousand the difference in chlorinity may be as large as + 0.060 per thousand, provided that DCLY is defined as chlorinity (cond) - chlorinity (titr). All samples were made double, only one was filtrated. The relative conductance of both samples was always the same. It seems there is no correlation of relative conductance with suspended solid matter under the used conditions. Probably the adsorption of the most important constituents by the solid matter is not significant, or easily undone by the shaking before the actual measurement. Of course nothing can be said about minor components. At the end of this paper the results are presented of analyses conductivity measurements and the estimated DCLY-range for each chlorinity in the Rhine-estuary based upon the analysed samples. |
