Osmotic Behavior at Higher Concentrations

The rise of the osmotic pressure with the amount of substance dissolved at higher concentration ranges has been the subject of many experiments. The osmotic behavior of moderately concentrated solutions has been examined experimentally, in proteins by Adair,Pauli and Pent and 

Sorensen, in cellulose derivatives by Buchner,Dobry, Herz, Duclaux, Obogi and Broda and in rubber by Caspar and an excessive increase in osmotic pressure with concentration invariably foimd. 

A series of data obtained in these investigations is recorded in Fig. 77 to give an idea of the experimental effect. In all cases a steeply ascending curve expresses the relation between osmotic pressure and concentration and the question arises, whether this relation can be evaluated to get additional information on the state of high polymers in solution. If we expand the osmotic pressure as a function of concentration into a series in powers of Cs, we get 

At extremely low concentrations, all terms containing higher powers of c than 

The interpretation of the first coefficient, -4, of the series in equation (52) is unambiguous it is directly connected with the number of particles which move independently in the solution and, since the total weight of dissolved material is known, is also connected directly with the molecular weight, M2j of the dispersed substance. 

---