Gelatin: Colloid and Conductivity

In recent years there has been a revival of interest in the micellar theory of structure proposed by N~tgeli in 1852 as a theory for the structure of protoplasm. This theory has been taken over by colloid chemists and applied to the structure of many colloids as a result of the work of Zsigmondy (1), Pauli (2), McBaln (3, 4) and their co- workers. Laing and McBain (4) have further extended the micellar theory to the sol-gel transformation by proposing that the micellar unit of the gel state is identical with that in the sol. According to these authors: "All that is necessary is to assume that the particles become stuck together or oriented into loose aggregates, which may be chance granules or, more probably threads." This conception is based on a study of sodium oleate, for which they found that in spite of the enormous change in viscosity involved in the change from sol to gel, such properties as electrical conductivity, lowering of the vapor pressure, refractive index, and sodium ion concentration remained identical in both the sol and the gel state. In support of their theory,
Laing and McBain point out that Arrhenius (5) found the conductivity in gelatin-water-salt systems to be the same in both sol and gel.
This aspect of the micellar theory has been extended by Gelfan (6) to protoplasm because he found that the conductivity of protoplasm remained independent of changes in viscosity and by Gelfan and
Quigley (7) to the blood coagulation process since their experiments showed that during the coagulation process there is no change in the conductivity of shed whole blood or plasma, in spite of the almost infinite increase in viscosity during coagulation.
In view of the concentration of excess electrolytes in the gelatin experiments of Arrhenius, as well as in protoplasm and in blood, the question arises whether the generalization from the findings on sodium oleate to all gelling systems, particularly among