CHEMISTRY OF HEMOGLOBIN 353 



where "K" is a constant which is characteristic of the equilibrium, and 

 represents the ratio of the velocities of the opposed reactions. The 

 concentration of oxygen in the solution will, of course, be directly 

 proportionate to the partial pressure Po of oxygen in the atmosphere 

 above the solution and to the absorption-coefficient at of oxygen in 

 water at the particular temperature "t" which is employed. We 

 therefore have : 



b = Po.at 



and:. 



^ = Kat Po 



Hence in a solution of hemoglobin brought into equilibrium at any 

 given temperature with a mixture of nitrogen and oxygen, such as air, 

 by shaking or by exposure over a very extensive surface, as in the 

 capillaries of the lungs, the ratio of oxyhemoglobin to reduced hemo- 

 globin should be directly proportional to the partial pressure of oxygen 

 in the atmosphere to which it is exposed. 



This relationship was investigated by C. Bohr who found so many 

 irregularities which were apparently inconsistent with the equation 

 that he inferred the existence of several different compounds of hemo- 

 globin with oxygen. The whole question was, however, reinvestigated 

 by J. Barcroft and his collaborators with greatly improved technique 

 and it was ascertained that the irregularities observed by Bohr were 

 due to inconstant contamination of the hemoglobin by crystalloids 

 and that in properly dialyzed solutions the relationship deduced from 

 the mass-law holds good with exactitude. The origin of the irregulari- 

 ties in solutions containing inorganic electrolytes resides in the ten- 

 dency of hemoglobin to polymerize in such solutions, Roaf having 

 found that while hemoglobin in distilled water exerts an Osmotic 

 Pressure corresponding to a molecular weight of 16,000, in sodium 

 chloride solution the osmotic pressure corresponds to a molecular 

 weight of 32,000. On rendering this latter solution alkaline the molec- 

 ular weight of the hemoglobin again falls to 16,000, the weight 

 which is also indicated by the iron- and sulphur-contents, assuming 

 each molecule of hemoglobin to contain one atom of iron. 



The influence of Temperature upon the Equilibrium-constant of a 

 balanced chemical reaction is expressed by the well-known thermo- 

 dynamical equation: 



KT = K To e~T ^f) 



where KT is the value of the equilibrium-constant at the temperature T, 

 KT O is the value of the constant at temperature To, " q" is the heat given 

 out by the conversion of one gram-molecule of the substance and 

 "e" is the base of the natural or "Napierian" logarithms. The 

 validity of this equation for the reaction between oxygen and hemo- 

 23 



