HISTORICAL INTRODUCTION 3 



particles (ultramicrons) have the same significance for colloidal solutions 

 as the isolated molecules have for crystalloidal solutions." 1 



The idea that the ultimate unit of the colloidal solution is not 

 the molecule or ion of the solute but an aggregate induced colloid 

 chemists to propose a new type of chemistry in which the laws of 

 classical chemistry were replaced by laws peculiar to colloid 

 chemistry. It seemed improbable to them that the stoichio- 

 metrical laws of classical chemistry should hold for colloidal 

 solutions in which the ultimate units were larger aggregates of 

 molecules, since they argued that only the surface of such aggre- 

 gates should be capable of reacting with other substances. The 

 stoichiometrical relations valid in classical chemistry were as a 

 consequence replaced in colloid chemistry by an empirical 

 formula, Freundlich's so-called adsorption formula, which was 

 supposed to account for surface action. 2 Recent investigations 

 by Langmuir 3 have furnished the proof that Freundlich's adsorp- 

 tion formula does not hold for the reaction of gases with mica, 

 glass, and platinum possessing a smooth surface, and Langmuir 

 was able to show that the forces which act in these cases are the 

 purely chemical forces of primary or secondary valency. Like 

 most empirical formulas the adsorption formula may hold within 

 a limited range of observations, but not throughout the whole 

 range of variation, and Langmuir states that this was also true 

 for the adsorption formula in his experiments. 



John A. Wilson and Wynnaretta H. Wilson 4 have made a most 

 important contribution towards the question of the applicability 

 of the adsorption formula to colloidal problems, in which they 

 were also led to a rejection of the adsorption formula and to the 

 adoption of a purely chemical interpretation. Their discussion 

 is based on the experiments of Procter and Wilson on gelatin 

 and the facts to be given in this book fully support their skeptical 

 attitude towards the adsorption formula. 



Even if we assume that the protein solutions contain no free 

 protein ions or molecules which is contradicted by the experi- 



1 ZSIGMONDY, R., "Kolloidchemie," 2nd ed., Leipsic, 1918. 



2 FREUNDLICH, H., " Kapillarchemie," Leipsic, 1909. 

 'LANGMUIR, I., J. Am. Chem. Soc., vol. 40, p. 1361, 1918. 



4 WILSON, J. A. and WILSON, W. H., J. Am. Chem. Soc., vol. 40, p. 886, 

 1918. 



