G. S. ADAIR 



Table II 

 Effect of haemoglobin on activity coefficients and the excess of ions. 



y/y° ratio for NaCl 0-958 



y/y ° ratio for Na, HP0 4 and H 2 P0 4 0-928 



m, total molality of ions in L 0-2699 



m° total molality of ions in L° 0-2552 



Total excess in L 0-0147 



Theoretical excess in L 0-0002 



Corrected excess in L 0-0145 



b t excess coefficient 1-9000 



b H excess of H ions 4-0000 



- db H /dpH (approx) 8-0000 

 a° total activity of ions in L° 0- 1 800 



- log a° H = pH° 7-2550 



Table II shows the effects of the protein on the mean activity co- 

 efficients of the salts. These coefficients are independent of assumptions 

 concerning hydration or liquid junction potentials. The ratio y/y° for 



NaCl="^ a m ° a 



The ratio y/y° for sodium phosphates is an approximation, com- 

 puted by taking the mean valence of the anions as 1-75. 



The most important terms included in Table II are the excess co- 

 efficients b t and b H , required for the application of formula 3, and the 

 total activity of ions a° t . The total activity was calculated from the 

 total molality m° on the assumptions that sodium dihydrogen phos- 

 phate has the same activity coefficient as sodium chloride, and 

 disodium phosphate the same activity coefficient as sodium sulphate. 



The experimental data in Table I refer to ox haemoglobin which is 

 highly soluble. A few experiments made on supersaturated solutions 

 of horse haemoglobin and ammonium phosphate buffer mixtures 

 showed an excess of salts inside the membrane, comparable with 

 results obtained from more soluble species of haemoglobin. 



A series of measurements of the type exemplified in Table I is 

 required for the integration of formula 3. Table III gives a series of 

 values of pH°, a° and b, for 20 per cent solutions of sheep haemo- 

 globin, dialysed against ammonium phosphate buffer mixtures at 0°C. 

 The ionic strength of the buffer mixtures was varied by altering the 

 total phosphate, keeping the percentage of each salt constant at 

 50 per cent of (NH^ HP0 4 and 50 per cent of NH 4 H 2 P0 4 . The 



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