Preliminary Remarks. Statement of the Problem

It is usually assumed that the diffusion coefficient is independent of the concentration. However, experimental data [64,120,272,388,393,439,491] show that the diffusion coefficients in liquids often strongly depend on the concentration. In dilute solutions, an increase in the concentration always produces a decrease in the diffusion coefficient. For example, two grams of sodium chloride dissolved in one liter of water decreases the diffusion coefficient by 10%. Often the diffusion coefficient linearly decreases with the increase of the diffusing substance concentration (sugar, raffinase, etc.) in the water solution [64]. 

In solutions of a number of monovalent salts (NaCl, KC1, KI, LiCl, etc.), the dependence of the diffusion coefficient on concentration (for C 0.1 mole/liter) is fairly well described by the expression [332, 393] 

Mass and Heat Transfer Under Complicating Factors 

For hemoglobin and gray albumin diffusing in salt solutions, we have [13, 393] 

Dissolving 0 to 2x 10-4 mole/liter of KMnC 4 in water decreases the diffusion coefficient by 25%. A very large change in the diffusion coefficient is observed in solutions of methylen-blue (the molecular weight m = 317) the presence of 6 x 10-4 mole/liter of this substance decreases the diffusion coefficient to half the original value at room temperature. 

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