HISTORICAL INTRODUCTION 7 



low, and whether the isoelectric point is reached slowly or quickly, 

 and without or with mechanical agitation." 



In a preliminary note 1 on his work on globulins published in 

 1903 Hardy gives an interpretation of the influence of H and OH 

 ions on the direction of migration of protein particles in an 

 electrical field which was destined to play an important role in 

 colloid chemistry, since it suggested to the later workers that the 

 H and OH ions produced their influence on the electrical charge of 

 the protein particles through a process of adsorption. 



"The properties of globulins in solution seem to justify the following 

 view: They are not embraced by the theorem of definite and multiple 

 proportions. Therefore they are conditioned by purely chemical forces 

 only in a subsidiary way. A precipitate of globulin is to be conceived 

 not as composed of molecular aggregates but of particles of gel. I have 

 shown elsewhere that gelation and precipitation of colloidal solutions 

 are continuous processes. These particles of gel when suspended in a 

 fluid containing ions are penetrated by those ions. Let the fundamental 

 assumption be that the higher the specific velocity of an ion the more 

 readily it will become entangled within the colloidal particle. Then 

 as H and OH ions have by far the highest specific velocity the colloidal 

 particle will entangle an excess of H ions in acid and thereby acquire a 

 + charge and of OH ions in alkali and thereby acquire a charge. 

 These charges will decrease the surface energy of the particle and 

 thereby lead to changes in their average size." 



Perrin adopted the idea that H and OH ions confer their 

 electrical charge to colloidal particles on account of their rela- 

 tively large velocity of migration, whereby they were readily 

 adsorbed by the colloidal particle. The hypothesis of a prefer- 

 ential adsorption of H and OH ions by colloidal particles has 

 since played a great role in colloid chemistry. 



In 1904 the writer of this volume offered instead of this colloidal 

 a purely chemical view of the significance of the isoelectric 

 point and of the cause of the influence of acids and alkalies on 

 the direction of the migration of the colloidal particles. 2 



"It seems to the writer, however, that a different view of these 

 phenomena is possible whereby they appear in harmony with the view 

 of electrolytic origin of the charges of colloids. The proteids are known 



1 HARDY, W. B., J. Physiol., vol. 29, p. 29, 1903. 



2 LOEB, J., Univ. of Cal Publications, Physiology, vol. 1, p. 149, 1904. 



