A NOTE ON THE LABORATORY DETERMINATION OF THE HEAT OF TRANSITION OF St-I.FCII PAUL PORTER SUlTON North Carolim State College of Agriculture and Engineering, Raleigh, North Comlim ACCORDING to the First Law of Thermodynamics, the heat of transition from rhombic to monoclinic sulfur is exactly equal to the difference between the heats of solution of each species in a given solvent, pro- vided they are so measured that the resulting mixtures have in both cases the same composition. Since the dissolving of this substance in carbon tetrachloride is endothermic, i t is, in principle, possible to determine these heats of solution in this liquid with an ordinary vacuum type student calorimeter, such being the pro- cedure recommended by Daniels, Mathews, and Wil- liams.' Two factors, however, render such measure- ments unsatisfactory unless special equipment is avail- able: h t , the low solubility of the element in this medium, which makes for a small temperature change; ' DANIELS. M~rHsws, AND WILLIAMS, "Experimental physical chemistry." McGraw-Hill Book Company. New York, 1934, p. 93. and second, the fact that the solvent is so volatile that its rapid evaporation causes a greater temperature drop than the effect to be observed. In seeking for a modification of this experiment, the writer was able to eliminate both of the above-men- tioned objections by replacing the carbon tetrachloride with a carbon disulfide-water mixture. The water covers the carbon disulfide, largely preventing evaporation, without influencing its solvent properties. Using a Beckmann thermometer, it was found that once temperature equilibrium was reached the calorimeter could then be handled in the usual m a n ~ e r . ~ With 350 cc. of carbon disulfide and 50 cc. of water, 10-gram sam- ples of rhombic and monoclinic sulfur gave temperature depressions of the order of 1.4 and 1.3 degrees, respec- tively. These are easily measured, and a final value of the molar heat of transition within 10 per cent of the accepted can readily be obtained. - "bid., pp. 91-2

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Page 1: A note on the laboratory determination of the heat of transition of sulfur

A NOTE ON THE LABORATORY DETERMINATION OF THE HEAT OF TRANSITION OF St-I.FCII

PAUL PORTER SUlTON

North Carol im State College of Agriculture and Engineering, Raleigh, North C o m l i m

ACCORDING to the First Law of Thermodynamics, the heat of transition from rhombic to monoclinic sulfur is exactly equal to the difference between the heats of solution of each species in a given solvent, pro- vided they are so measured that the resulting mixtures have in both cases the same composition. Since the dissolving of this substance in carbon tetrachloride is endothermic, i t is, in principle, possible to determine these heats of solution in this liquid with an ordinary vacuum type student calorimeter, such being the pro- cedure recommended by Daniels, Mathews, and Wil- liams.' Two factors, however, render such measure- ments unsatisfactory unless special equipment is avail- able: h t , the low solubility of the element in this medium, which makes for a small temperature change;

' DANIELS. M~rHsws, AND WILLIAMS, "Experimental physical chemistry." McGraw-Hill Book Company. New York, 1934, p. 93.

and second, the fact that the solvent is so volatile that its rapid evaporation causes a greater temperature drop than the effect to be observed.

In seeking for a modification of this experiment, the writer was able to eliminate both of the above-men- tioned objections by replacing the carbon tetrachloride with a carbon disulfide-water mixture. The water covers the carbon disulfide, largely preventing evaporation, without influencing its solvent properties. Using a Beckmann thermometer, it was found that once temperature equilibrium was reached the calorimeter could then be handled in the usual m a n ~ e r . ~ With 350 cc. of carbon disulfide and 50 cc. of water, 10-gram sam- ples of rhombic and monoclinic sulfur gave temperature depressions of the order of 1.4 and 1.3 degrees, respec- tively. These are easily measured, and a final value of the molar heat of transition within 10 per cent of the accepted can readily be obtained. - "bid., pp. 91-2