8 THEORY OF COLLOIDAL BEHAVIOR 



to be amphoteric in their reaction. If they be slightly dissociable they 

 will send H as well as OH ions into the solution. When the particles 

 send more H ions than OH ions into the solution they will have a 

 negative charge while they will have a positive charge when more OH 

 ions are given off than H ions. If acid is added to the solution in suffi- 

 cient concentration the amphoteric colloidal particle will send more OH 

 ions into the solution than H ions and hence, will assume a positive 

 charge. The reverse will be the case in an alkaline solution. It 

 harmonizes with this idea that, as Hardy found, neutral salts do not 

 influence the sign of the electrical charge of the globulins." 



We shall see later on that this suggestion explains the source of 

 the electrical charge of isolated protein ions but explains only 

 indirectly the charge of larger aggregates. 



In his famous paper on " Colloidal Solution" published in 

 1905, Hardy 1 abandons the physical view which he expressed in 

 1903 and adopts "a frankly chemical standpoint." 



" Globulin therefore is an amphoteric substance and its acid function 

 is much stronger than its basic function. As an acid it is strong enough 

 to form salts readily with bases so weak as aniline, glycocoll, and urea; 

 acting as a base it forms salts with weak acids, such as acetic, and boracic 

 acids, which are very unstable in presence of water." 



While Hardy accepts the idea of an electrolytic origin of the 

 charges of proteins, he does not seem to be ready to concede that 

 the reactions of proteins with acids and alkalies are purely 

 stoichiometric, as the following quotations indicate. 



" Though one may speak of the colloid particles as being ionic in 

 nature they are sharply distinct from true ions in the fact that they are 

 not of the same order of magnitude as are the molecules of the solvent, 

 the electric charge which they carry is not a definite multiple of a fixed 

 quantity and one cannot ascribe to them a valency, and their electrical 

 relations are those which underlie the phenomena of electrical endosmose. 

 To such ionic masses I would give the name 'pseudo-ions' and I propose 

 to treat globulin solutions from the standpoint of a hypothesis of 

 'pseudo-ions.' 2 



And in 1910 Wood and Hardy 3 express the view that proteins 



1 HARDY, W. B., J. Physiol., vol. 33, p. 251, 1905-06. See also, 

 HARDY, W. B., Proc. Roy. Soc., vol. 79, p. 413, 1907. 



2 HARDY, W. B., J. Physiol., vol. 33, pp. 256-257, 1905-06. 



3 WOOD, T. B. and HARDY, W, B., Proc, Roy. Soc., vol 81, p. 38, 1909, 



