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

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.