Direct Determination of a Third Derivative of Gibbs Energy for Aqueous Solution

We built the apparatus for measuring the third derivative of G directly. The target quantity is "the partial molar entropy-volume cross fluctuation density of solute i " SVδi in aqueous solution. See Fig. 1. The two identical cells (Photo 1) contain sample solutions with slightly different mole fractions. The cells were encased in a stainless-steel can immersed in water bath maintained at 25oC. The hydraulic pressure was applied concurrently to the cells and the difference of the heats of compression between the two sample solutions was measured directly by a thermo-module sandwiched between the two cells. The result for 2-butoxyethanol (Fig. 2) indicates SVδi is determined with high accuracy.

(by K. Yoshida & Y. Koga & A. Inaba)

	Fig 1. Schematic diagram of apparatus. Two identical cells are filled with solutions with a small mole fraction difference. A hydraulic pressure is applied concurrently to the twin cells. The difference in heats of compression between two cells is determined by a thermo-module.
	Photo 1.
	Fig. 2. Comparison of the values and error bars of SVδBEby graphical differentiation and those directly determinated by the present apparatus. The error bar of this work is about the size of filled symbols.