CHEMISTRY. 357 



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

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

 Books Nos. 2-13.) 



The monograph on "The Osmotic Pressure of Aqueous Solutions," 

 which was issued by the Carnegie Institution of Washington (Publica- 

 tion 198) in June 1914, contained a brief account of all the work of the 

 author which had been brought to a definite conclusion up to that time. 

 At the close of the paper it was announced that the work of the inune- 

 diate future would consist in the measurement of the osmotic pressure 

 of glucose, cane-sugar, and mannite solutions at temperatures above 

 and below those which had been previously employed with these sub- 

 stances; also that the measurement of the osmotic pressure of levulose 

 solutions would be undertaken. The work of the past year has been 

 mainly along the hues thus indicated. 



It had been shown in the monograph referred to: (1) that at low 

 temperatures (under 25°) the ratio of osmotic to calculated gas-pressure 

 is greater than unity in solutions of glucose; (2) that at temperatures 

 between 30° and 50° the ratio is unity when the weight-normal system 

 of making solutions is employed. In other words, it had been estab- 

 lished that within the latter temperature-interval the osmotic pressure 

 of glucose solutions obeys the laws of Gay-Lussac and Boyle for gases. 

 The excessive ratios of osmotic to gas pressure which were observed 

 at the lower temperatures were ascribed, provisionally, to a concentra- 

 tion of the solutions through hydration of the solute; and it was sug- 

 gested that the observed subsequent dechne in all ratios to unity is due 

 to a dehydration of the solute at the higher temperatures, by which 

 process the solutions would necessarily suffer some dilution, that is, 

 an increase in the proportion of solvent to solute. The validity of such 

 explanations depends, in a great measure, however, on the ratio of 

 osmotic to calculated gas pressure at still higher temperatures, ^. e., 

 at temperatures above 50°. If the ratio, having once decUned to unity 

 at some temperature (30° in the case of glucose), persistently maintains 

 that value at all higher temperatures, the correctness of the explanation 

 of the excessive ratios observed at the lower temperatures (as due 

 to hydration of the solvent) would seem to be fairly well estabhshed. 



Very great importance is therefore to be ascribed to the measure- 

 ment of osmotic pressure at high temperatures; since it is through such 

 observations that we shall probably arrive at the correct explanation 

 of the fact that at low temperatures the ratios of osmotic to gas pres- 

 sure are as a rule excessive, i. e., greater than unity. The difficulties 

 which are experienced in measuring osmotic pressure correctly are very 

 great, even at low temperatures; but at high temperatures they 

 become almost insuperable, and the progress of the work is sometimes 

 for several months almost imperceptible. Nevertheless, we have suc- 

 ceeded, since the publication of the monograph referred to above, in 

 completing satisfactorily a long series of measurements of the osmotic 

 pressure of glucose solutions at 60°. Ten concentrations of solution 



