[OLD] Water activity & osmotic coefficients

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From: James Cleverley

Subject: water activity & osmotic coefficients

The 'h2o' blocks of the GWB datafiles are tabulated coefficients for calculating the osmotic coefficients and thence the water activity (see eqs. 7.7 and 7.8 in Bethke, 1996). I have a few questions about this data and its calculation:

a) The a, b, c and d parameters tabulated in Bethke (1996) are for 25, 100 and 200oC, however in the thermo.dat datafile these values are tabulated at 25, 100 and 150oC. Which is correct?

Where is the publication that contains these parameters and there derivation?

c) When I calculate the osmotic coefficient at 100oC using the A parameter from Table 2 in Helgeson (1969) and the equation and a,b,c,d parameters in Bethke (1996) the answer is 1.086 which is different from the 0.935 in Helgeson's table. Why the difference?