116 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



formula M = W 



22.488+0.0824* 



, in which oxygen is assigned an atomic 



weight of 16. 



The use of = 16 as a standard for the calculation of molecular 

 weights was continued only through the first series of measurements. 

 In this series, cane sugar is considered to have a molecular weight of 

 342.22. In all later work, H = 1 was employed as the standard, and the 

 molecular weight of sugar is 339.60. Accordingly, the formula given 



above becomes, in subsequent computations, M = W — : ~ , in 



which M is the molecular weight ; P the observed osmotic pressure; W 

 the weight of the substance which is dissolved in 1,000 grams of water; 

 22.265 the theoretical pressure (at 0°) of a gram-molecular weight of 

 a gas when its volume is 1 liter; and 0.0817 is the temperature coefficient, 

 either of a gas or of osmotic pressure. The values are based on the 

 weight of a liter of hydrogen as given by Morley, and corrected to the 

 latitude and altitude of the place of work. 



Table 11.- — Cane sugar, Series I. Variations in the temperature of the bath. 



The difference between the highest and lowest temperature of the bath 

 is given for each experiment in Table 11. At the present time, when 

 a variation of 0.05° in bath temperature is regarded as vitiating a reading 

 of pressure, these differences appear appallingly large. 



Judging by the non-appearance of solute in the water surrounding 

 the cells, and the ability of the cells to sustain considerable pressure, 

 it was concluded that the membrane had not leaked. Other possible 

 sources of dilution— of which much will be said hereafter — did not at 

 that time impress us as likely to affect materially the pressures devel- 

 oped in the cells. It was suspected, however, in the beginning that 

 the sugar might be subject to some inversion, for which it would be 

 necessary to correct the observed pressures. All the solutions, when 

 taken from the cells, were therefore examined for invert sugar by 

 the then most approved form of Fehling's method. Evidence of its 

 presence was found in all the solutions, but it was only in the more 



