The properties of colloidal systems. I.-The osmotic pressure of congo-red and of some other dyes

Abstract

Experiment made in 1895 by Linder and Picton upon solutions of arsenious sulphide indicated that colloidal solutions possess a real osmotic pressure, although the authors themselves claim no quantitative value for their results. In 1905 further experiments were made, but again great difficulties were met with, and, although it seemed evident that osmotic pressure was present, the numerical values obtained were irregular and small. The first definite proof that certain colloidal solutions are able to exert a not inconsiderable osmotic pressure was given by Starling in the case of the colloids of blood-serum. When separated by a gelatin membrane from a solution obtained by filtration of some of the same serum through Martin’s gelatin filter, the pressure rose to about 30 mm. Of mercury.