Systems of Three and More Components

For multicomponent systems in general, we shall follow Scatchard s (1946) formulation of the expressions for the activities of the components and their derivatives with respect to the masses of the components — that is, the coefficients which enter into equation (27). We shall use the subscript K to denote any component made up of small molecules or ionsx, and i to denote a small ion which is a constituent of one or more components, but is not itself a component. Again denoting the protein as component 2, we have, following Scatchard  

In the special case of a three component system, in which component 3 is a salt composed of one anion and one cation, we have ps — 2 In y3. From these relations, we derive the coefficients employed in equation 

1 A small component may be defined here as one which passes readily through membranes impermeable to proteins of molecular weight of the order of 30,000 or above. 

Here J denotes any diffusible component other than K. For the three component system containing one salt (component 3) with two ions, the summation denoted by 27,- includes only one cation and one anion, andj 3c = v3a — 1. From (25a) and (25b) we have r2C = — r2 = — ZJ ZC —Za), which becomes —Zj/2 if the ions denoted by c and a are both univalent. 

The value of s lies always between zero and unity, and it may be taken as unity when Z2m2 2 m3 2. 

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Alfrey. T., and G. Goldfinger Copolymerisation of systems of three and more components. J. Chem. Phys. 12, 322 (1944). 

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