Properties isopiestic method

The isopiestic method measures a difference in vapour pressure while the isothermal distillation technique depends upon a difference in volume. Despite the specific changes being measured in the techniques each change is proportional to the colligative property of the solution - the lowering of the vapour pressure. 

The thermodynamic properties of 2-deoxy-sugars in water have been measured by microcalorimetric and isopiestic methods and compared to those of their parent monosaccharides. 

Because polyelectrolytes are nonvolatile, the most important thermodynamic property for vapor + liquid phase equilibrium considerations is the vapor pressure of water above the aqueous solution. Instead of the vapor pressure, some directly related other properties are used, e.g., the activity of water a, the osmotic pressure 71, and the osmotic coefficient < . These properties are defined and discussed in Sect. 4. Membrane osmometry, vapor pressure osmometry, and isopiestic experiments are common methods for measuring the osmotic pressure and/or the osmotic coefficient. A few authors also reported experimental results for the activity coefficient y i of the counterions (usually determined using ion-selective electrodes) and for the freezing-point depression of water AT p. The activity coefficient is the ratio of activity to COTicentration ... 

I now wish to report new measurements on the osmotic properties of aqueous strong electrolyte-strong polyelectrolyte mixtures conducted using the isopiestic vapor pressure comparison technique. [12] This method for determining osmotic coefficients is not as sensitive as the membrane osmometer, but it is much more accurate. It is not... 

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