CRYOSCOPIC AND OSMOTIC DATA. 8l 



calculation for 0.75 gram molecular solutions of cane sugar, using 

 the measurements of Berkeley and Hartley.^ Some of our de- 

 terminations of the freezing point of solutions of cane sugar 

 illustrate their peculiar osmotic behavior.^ 



For a gram molecular solution of cane sugar (342.2 grams per 

 liter of solution) we found A = — 2.775° C.; for ^ mol. (256.6 

 grams per liter) A = — 1.855°, — i-86° C; and for }4 mol. 

 (171. 1 grams per liter) A = — 1.15°, — 1.155° C. For these 

 three solutions the theoretical depression of the freezing point 

 would be to — 1.85°, — 1.387° and — 0.925° C, respectively. 

 Comparison of these figures shows how much in excess of the 

 theoretical osmotic pressure, that of these solutions really is. 

 Morse and Fraser have pointed out that the correspondence with 

 the theoretical expectations is greater, if "weight normal" 

 solutions are used, i. e., if the substance is present in a liter of 

 the solvent, instead of this volume of the solution. This does 

 not account, however, for the full amount of the discrepancy 

 found. To illustrate this: It was found in our experiments that 

 in making a gram-molecular solution by dissolving 17. 11 grams 

 of cane sugar in 50 c.c. of the solution (15° C), it was necessary 

 to add only 39.4 c.c. of distilled water; A was — 2.775° C. Had 

 50 c.c. of solvent been used to make the corresponding "weight 

 normal" solution, A would have been — 2.187° C.^ This figure 

 exceeds the theoretical A (— 1.85° C.) by 0.337° C., which is 

 probably to be accounted for by hydration of the sucrose molecule 

 (Callendar (6)). 



In the figures given above it is to be noted that the A of .75 

 mol. solution of sucrose ( — i .855° C.) is that which theory expects 

 of a gram molecular solution, and its osmotic pressure lies between 

 that of the sea water at Woods Hole and Pacific Grove. By 



' The measurements of Berkeley and Hartley were made using other concen- 

 trations. The original figures of these workers as also those of Morse and Fraser 

 et al. are given in the " Physikalisch-chemische Tabellen," Landolt, Bornstein and 

 Roth, 4th ed., Table 179, p. 787. Their original papers are referred to, ibid., p. 790. 



2 The sugar used in these experiments was free of all reducing sugars and had 

 been twice recrystalized from glass-distilled water with subsequent drying in 

 vacuo. 



^Calculation of the freezing point of a molecular "weight normal" solution, 

 based upon Morse's figure for the observed osmotic pressure (24.8 a. — 0° C.) 

 gave a slightly lower figure, viz.: A = — 2.048° C. 



