Salinity conductivity ratio

In 1978, the Joint Panel for Oceanographic Tables and Standards (JPOTS) decided that a new definition was needed for salinity that was based more on a salinity/conductivity ratio. 

Salinity was first rigorously defined by Knudsen (1902, p. 28) as the weight in grams of the dissolved inorganic matter in one kilogram of seawater after all bromide and iodide have been replaced by the equivalent amount of chloride and all carbonate converted to oxide. In 1978, the JPOTS decided that a new definition was needed for salinity that was based more on a salinity/conductivity ratio and was termed the practical salinity scale. 

Figure 1 The solubility of the principal atmospheric gases in seawater, as a function of temperature. Units are millilitres of gas contained in a litre of seawater of salinity 35 psu, assuming an overlying atmosphere purely of each gas. Note that salinity is defined in terms of a conductivity ratio of seawater to a standard KC1 solution and so is dimensionless. The term practical salinity unit , or psu, is often used to define salinity values, however. It is numerically practically identical to the old style unit of parts per thousand by weight...

Table 3.3 Equation Relating the Conductivity Ratio Measured by an Inductive Salinity to Practical Salinity, PSS 1978.

The PSS-78 is based on the measurement of a conductivity ratio and, hence, is technically unitless. Nevertheless, some oceanographers use a psu designation to represent a practical salinity unit and others report salinity in units of parts per thousand (%o). The latter convention has been adopted in this text. In any event, it is important to appreciate that the practical salinity is no longer directly traceable to the theoretical definition given in Eq. 3.1. 

This new relationship was termed the practical salinity scale and is based on a background paper by Lewis (1978). The practical salinity of a water sample is defined in terms of the conductivity ratio, F15, which is defined as follows ... 

Therefore, a standard seawater sample with a salinity (5) of 35 (with no %o units needed) has a conductivity ratio of 1 at 15°C and 1 atmosphere, using a standard KC1 solution of 32.4356 g in a 1 kg mass of solution. Finally, recent applications of microwave remote sensing have been used to determine surface water of gradients of salinity in coastal regions, particularly in river plume regions (Goodberlet et al., 1997). 

The samples were collected in December 1983 during different phases in the tidal cycles and at different depths. ((S) represents the samples collected at 05 m depth and (B) represents the overlying bottom samples). The 4 sampling stations (Fig. 1) were selected in order to obtain a range from fresh to brackish water. Samples were collected up-river (1,2, 3, and 4) at high tide, and down-river (4 , 3 , 2 , and 1 ) at low tide. The measures of pH and electrical conductivity ratios were measured on-board. The salinity of all samples was calculated from the electrical conductivity ratios [ 1 ]. ... 

Salinity is presently determined by measuring the conductance of seawater by using a salinometer. The modem definition of salinity uses the practical salinity scale, which replaces the chlorinity-salinity relationship with a definition based on a conductivity ratio (Millero, 1996). A seawater sample of salinity S= 35 has a conductivity equal to that of a KCl solution containing a mass of 32.435 6g KCl in 1 kg of solution at 15 °C and 1 atm pressure. No units are necessary on the practical salinity scale however, in practice, one often sees parts per thousand, ppt, or the abbreviation psu. New salinometers using this method are capable of extremely high precision so that the salinity ratio can be determined to 1 part in 40 000. At a typical salinity near 35 this procedure enables salinities to be determined to an accuracy of 35.000 0.001. This is much better than most chemical titrations, which, at best, achieve routine accuracy of 0.5 parts per thousand. 

Conductivity ratio of seawater to SSW pressure term Variable electrical resistances Scientific Committee on Oceanic Research Practical salinity (PSS78 scale)... 

In the early 1960s, bench salinometers were developed that allowed measurement of the electrical conductivity of a seawater sample relative to that of a standard with high precision. Cox et al. (1967) had related chlorinity and conductivity ratios of seawater to standard seawater at temperatures higher than 10 °C and tabulated their results (UNESCO, 1966). Following their work, the responsible international oceanographic organizations adopted a redefinition of salinity (Wooster et al, 1969). Firstly, it was assumed that salinity was proportional to chlorinity, to be consistent with the assumed constancy of the ionic composition. The constant was chosen so that for 5=35 %o, both the Knudsen formula (3-1) and the new relationship... 

Only lAPSO recognized SSW provides a reliable standard for conductivity ratio measurements. It should be used to standardize each bench salinometer before being used for sample salinity measurements and to detect and eventually trace any drift. The use of so-called substandards for standardization is not recommended, as it will significantly decrease accuracy (see Section 3.5.7 for exceptions if a decrease in accuracy is acceptable). 

All reference conductivities are derived from reference salinity values and calibrated CTD temperature and pressure by numerical back iteration of Eqs. (3-7) to (3-10). Traditionally, the measured conductivity ratio R is converted to conductivity assuming... 

The definitions of 1902 and 1969 give identical results at a salinity of 35 %c and do not differ significantly for most applications. The definition of salinity was reviewed again when techniques to determine salinity from measurements of conductivity, temperature, and pressure were developed. Since 1978, the Practical Salinity Scale defines salinity in terms of a conductivity ratio ... 

The next two series of experiments were conducted at a much higher di monosulfonate ratio, approximately 40 60 by weight. The results in entries 10 and 11 and 12-14 (Table 10) indicate that the IFT between saline AOS surfactant solutions and Kern River stock tank oil follow the same trend of decreasing IFT value with increasing hydrophobe carbon number. 

This standard seawater has since proven problematic because it is based on real seawater, whose conductivity is influenced by concentration variations in the nonconservative ions and subtle fluctuations in the ratios of the major ions. To eliminate these issues, a practical salinity scale (PSS-78) was adopted by international agreement in 1978. As a... 

There are two types of conductometric procedures commonly used. Firstly, a Wheatstone Bridge circuit can be set up, whereby the ratio of the resistance of unknown seawater to standard seawater balances the ratio of a fixed resistor to a variable resistor. The system uses alternating current to minimise electrode fouling. Alternatively, the conductivity can be measured by magnetic induction, in which case the sensor consists of a plastic tube containing sample seawater that links two transformers. An oscillator establishes a current in one transformer that induces current flow within the tube, the magnitude of which depends upon the salinity of the sample. This in turn induces a current in the second transformer, which can then be measured. This design has been exploited for in situ conductivity measurements. 

Figure (3) shows the solubilization parameters as functions of water concentration for SDS/2- entanol ratios of 0.25 and 0.40 at 25 C. The solubilization parameters are defined as Vo/Vs and Vw/Vs, where Vo, Vs and Vw are the volumes of organic phase, surfactant and aqueous phase in the microemulsions. The parameters are related to the drop size and also interfacial torsions f7.23). The bicontinuous phase is located around the composition range corresponding to equal values of solubilization parameters. The solubilization parameters are dependent on the initial surfactant and/or cosurfactant concentration. Similar dependence has been observed in other systems as a function of salinity and pH (7.231. Conductivity measurements performed as a function of water content indicate an S-shaped curve as shown in Figure (4). This is typical of microemulsions showing transition from oil-continuous to bicontinuous to water-continuous microstructure with increasing water content. 

As mentioned earlier, we sometimes conduct an alkalinity scan by changing alkali concentration while the salinity is fixed. Then the activity map can be presented by alkali concentration versus oil volume percent or the ratio of oil volume percent to surfactant volume or weight percent, schematically shown in Figure 12.5. 

Figure 15 indicates the variations of the emulsion electrolytic conductivity vs. formulation (aqueous phase salinity) at different constant water-to-oil ratios, indicated by the water volume fraction/. (83). When/ ranges from 0.4 to 0.7, the conductivity exhibits the typical pattem, already mentioned in the previou.s section. Suboptimum salinity (SAD < 0) is associated to O/W emulsions, while overoptimum salinity results in W/0 ones. There is, however, a slight change in... 

Since the major ions are present in seawater at constant ratios to one another, it is normally not necessary to measure the concentrations of all the ions since the concentration of one will allow the prediction of the others. Thus, chloride has traditionally been measured using a silver nitrate titration, and from this the salinity (i.e., total dissolved salt concentrations) can be derived. Now, however, conductivity is the routinely measured parameter and this is converted to salinity by a relationship agreed internationally with interlaboratory agreement ensured by the distribution of standard seawater samples for instrumental calibration. The use of modern inductively coupled conductivity measurements with careful temperature controls allows salinities to be determined with accuracy and precisions of the order of +0.01% or better. 

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