348 CARNEGIE INSTITUTION OF WASHINGTON. 



Morse, H. N., Johns Hopkins University, Baltimore, Maryland. Measure- 

 ment of the osmotic pressure of solutions. (For previous reports see Year 

 Books Nos. 2-12.) 



The work of the past year has been mainly along three lines, and the 

 greater part of the more unportant results have already been incor- 

 porated with the earlier work and discussed in a monograph which was 

 issued as publication No. 198 of the Carnegie Institution, in June 1914. 



The measurement of the osmotic pressure of glucose solutions was 

 completed through 60°, and is now proceeding at 70°. It has been 

 found that between 30° and 60° and, as far as known, at 70°, all the 

 pressures of this substance conform to the law of Gay-Lussac and to 

 that of Boyle for gases. It is to be recalled in this connection that at 

 0° and 10° previous work had shown the osmotic pressures of glucose 

 solutions to be excessive in the sense that at these temperatures the 

 ratios of osmotic to the calculated gas pressures of the solute are all 

 greater than unity. This fact has been tentatively ascribed to a hydra- 

 tion of the solute at low temperatures, which would have the effect of 

 concentrating the solutions. 



The osmotic pressures of mannite solutions were measured at 10°, 

 20°, 30°, and 40°. Mannite was selected because the molecular depres- 

 sions of the freezing-points of its solutions are normal, i. e., about 1.85°. 

 The ratio of osmotic to the calculated gas pressure of the solute was 

 found in all cases to be unity, showing that, between 10° and 40°, the 

 osmotic pressure of mannite solutions obeys the gas laws. 



Much work has also been done during the past year upon certain of 

 the electrolytes, especially upon salts of potassium and lithium. Great 

 difficulty was experienced, as had been expected, from the injurious 

 effect of electrolytes upon the semipermeability of the membranes — an 

 effect which is apparently due to the destruction of their colloidal 

 structure by the cations. Nevertheless, the osmotic pressures of 

 lithium-chloride solutions, ranging in concentration from 0.1 to 0.6 

 weight-normal, were successfully measured. The pressures found were 

 somewhat in excess of those which could be accounted for by the prob- 

 able electrolytic dissociation of the solute. For example, the osmotic 

 pressure of the 0.6 weight-normal solution at 30° was 29.54 atmo- 

 spheres, which would call for a dissociation of the salt amounting to 

 99.2 per cent. Here again, as in the cases of glucose and cane sugar at 

 low temperatures, the excessive pressures are tentatively ascribed to 

 concentration of the solutions through hydration of the solute. 



Much time has been given to the building up and testing of new 

 membranes with a view to discovering, if possible, semipermeable 

 materials which resist the injurious influence of electrolytes more suc- 

 cessfully than the ferrocyanides of copper, nickel, and cobalt. 



Dr. J. C. W. Frazer and Dr. W. W. Holland have cooperated in the 

 work of the year; and Messrs. E. L. Frederick and A. S. Musselman, in 

 the capacity of volunteers, have rendered valuable assistance. 



