Osmotic Pressure of Haemoglobin 



measurements of the height of solution in the capillary tube. All 

 measurements recorded here were carried out at 3-4°C. 



The horse and human haemoglobin samples were prepared by 

 laking red cells, after repeated washing in 1 per cent sodium chloride 

 solution, with ether and separating the stroma by centrifugation. 

 These stock solutions of horse and human haemoglobin were, after 

 prolonged dialysis against distilled water, equilibrated with 0-2M 

 phosphate (0-1M Na 2 HP0 4 and (MM KH 2 P0 4 ; this mixture will 

 be referred to as 0-2M phosphate throughout this paper) before 

 dialysis against any of the other salt solutions used during this 

 investigation. 



RESULTS AND DISCUSSION 



The results of all the osmotic pressure measurements of horse and 

 human haemoglobin in solutions of varied composition, salt and 

 protein concentration are recorded in Tables I — VI. C is the con- 

 centration of dry haemoglobin in grams per 100 ml of solvent, and 

 P is the osmotic pressure in cms of water. The apparent molecular 

 weight, M, can be calculated from each measurement by the equation 



M=10R77^ ••••( 1 ) 



where R is the gas constant and T the absolute temperature. 



At 3°C M = 234000/^ 



and for M = 66700, which is the most accurate estimate for the 



p 

 molecular weight of haemoglobins (from iron analysis) -=, = 3-5. 



Discussion of the data presented here will be concerned with the 



p 

 examination of the deviations from the value of - = 3-5. 



Insertion of the computed values for the molecular weight from 

 each measurement would be misleading as changes in the value for 

 P/C can have other causes besides variation of the molecular weight 

 of haemoglobin. If zero overall surface charge of the colloidal solute 

 and thus equal concentration of the non-colloidal components in the 

 dialysate and the solution are assumed, deviations from the ideal 

 solution law 



P = mRT ....(2) 



(where m is the molar concentration of the protein) at finite protein 

 concentration are due to 



199 



