A Rapid and Accurate Method for the 

 Measurement of the Osmotic Pressure of 



Haemoglobin 



G. S. ADAIR 



A description is given of a simple toluene osmometer adapted 

 for rapid measurements of osmotic pressures of dilute protein 

 solutions. Determinations of osmotic pressures of 0-24 to 

 3 per cent horse CO haemoglobin solutions at 1-0° C have not 

 yielded evidence of dissociation of the molecule. The mean 

 molecular weight determined was 66,400 ; the mean deviation 



was 400. 



Sir Joseph Barcroft 1 was greatly interested in the suggestion that 

 the degree of aggregation of haemoglobin depends on the salt con- 

 centration. In 1920 he asked me to attempt to measure the osmotic 

 pressure of haemoglobin solutions so that we might obtain direct 

 experimental evidence as to the relationship between particle size and 

 salt concentration. At that time we had no facilities for carrying out 

 experiments at a low temperature, and as haemoglobin tends to 

 denature at room temperature, we tried to devise osmometers that 

 allowed osmotic equilibrium to be reached rapidly. 



In the simplest method, a modification of that described by S. P. L. 

 Sorensen 2 , the protein was contained in a cylindrical collodion mem- 

 brane of 6 mm diameter and 5 to 15 cm length, which was fitted to a 

 capillary tube of 0-7 mm bore. The membrane was immersed in a 

 large volume of salt solution, and readings of the rate of osmosis or 

 dV/dt were made with the column of protein solution adjusted at 

 different heights above the level of the salt solution. 



The osmotic pressure n s in cm solution was computed by formula 1. 



dV/dt = I nd 2 dh/dt = -(h -c - tv s )AQ ... .(1) 



d = diameter of capillary h = height of column of protein 



c = correction for capillarity A = area of membrane 

 Q = permeability constant V = volume of protein solution 



Mercury manometers, or a compensating device in which air was 

 compressed by mercury, were used if the pressures were greater than 

 70 cm water. 



This work has been described in a thesis 3 but it was not published 

 elsewhere. Experiments made subsequently at the Low Temperature 



191 



