Studies on Glass XII. Some New Heat Capacity Data for Organic Glasses. The Entropy and Free Energy of dl-Lactic Acid

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Abstract
Heat capacity measurements by the Nernst method have been made upon samples of secondary butyl alcohol and 3‐methylhexane in the glassy and liquid condition and upon a sample of dl‐lactic acid (1) in an incompletely crystallized state, (2) in the form of an acid glass and liquid, and (3) in the form of a mixed glass and liquid. From these results the specific heats and heat of fusion of pure crystalline dl‐lactic acid also have been derived. The data for the several glasses and undercooled liquids show a rapid rise from the heat capacity characteristic of a crystalline solid to that for the liquid state within a transition region of about 10° and the nature of this transition region has been discussed. A calculation of the molal entropy and free energy of formation of liquid dl‐lactic acid at 298.1°K yields 45.9 (±1.0) e.u. and —124,300±(2300) cal., respectively.

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