; 



G 2 



M 



■=?\w? 



G. S. ADAIR 



Station, Cambridge, where the protein solutions could be equilibrated 

 for many days at 0°C, confirmed the value of 66,000 for the molecular 

 weight of haemoglobin. 4 



The osmometers used for these experiments were essentially similar 

 to that shown in Figure 1 . T denotes a glass tube graduated in mm, 

 h = height of haemoglobin solution, M a collodion membrane of 

 diameter 1-1 cm and length 8 cm, which is tied by rubber string to a 

 piece of semipressure tubing into which a 5 mm glass tube G 2 is 

 inserted. W = level of buffer in tube of 35 mm diameter. 



Membranes are made from dry pyroxylin 

 dissolved in absolute alcohol and anhydrous 

 ether, and their permeability is adjusted by 

 the addition of varying amounts of ethylene 

 glycol. The texture of the membranes is of 

 significance. Thick membranes may slowly 

 adsorb protein and give pressures which fall 

 slowly over long periods. 



The diameter of the osmometer tube is 1-3 

 mm for pressures greater than 10 cm solution. 

 For more dilute protein solutions osmo- 

 meters of 3-3 mm bore are used so that the 

 correction for capillarity is smaller. Figure 1 

 also shows the method now used for the 

 determination of capillarity. Z is a small 

 open tube containing the protein solution, 

 h z and W z denote the levels of the protein 

 solution and of the buffer used as dialysate" 

 With osmometers of 3-3 mm bore, capillarity 

 readings indicate an apparent equilibrium 

 within one hour but then fall slowly at a 

 rate of approximately 0-1 mm per day for 

 about 6 days. If the membrane is of suitable permeability and surface 

 area, the time required for capillarity effects to reach equilibrium may 

 be much longer than the times required for osmosis and the diffusion 

 of salts. 



Recently, rapid and accurate measurements of the osmotic pressure 

 of haemoglobin have been made with toluene manometers in which 

 the capillarity effects usually reach equilibrium in a few seconds. 

 Paraffin, alcohol or toluene manometers have been used in osmometers 

 designed by Weber 5 , Oakley 6 , Bourdillon 7 , Bull 8 and Scatchard et al. 9 

 The experiments to be recorded have been made with toluene osmo- 

 meters simplified by omission of taps and joints. 



Capillarity effects at an oil-water interface within a glass tube may 



Figure 1. Osmometer 

 and capillarity measure- 

 ment/or small pressures 

 at 0°C. 



192 



