GENERAL PHYSICAL CONSTITUTION OF LIVING MATTER 35 



electrical current be sent through a colloidal solution ; in this case, the 

 particles move in the direction of the negative or positive current, ac- 

 cording to the chemical character of the colloid. This charge of the 

 colloidal particles is generally held to be due to the formation of a 

 double layer of electricity at the surface, between particle and water. A 

 similar explanation was given to the charge of particles suspended in 

 water; and this is considered another argument in favor of the idea, 

 that colloidal solutions are diphasic systems. It is, however, possible, 

 as Freundlich * has already mentioned, that the charges of the col- 

 loidal particles are due to the electrolytic dissociation of the latter. It 

 had generally been noticed that the colloids of an acid character are 

 negatively charged when in solution, while colloids of an alkaline char- 

 acter are positively charged. This is exactly what should be expected 

 if the charges of the colloidal particles in solution are due to electro- 

 lytic dissociation. If the colloid is an acid, it will dissociate into one 

 or more positively charged hydrogen-ions and a negatively charged 

 colloid-ion; if the colloid is an alkali, it will dissociate into one or 

 more negatively charged hydroxyl-ions and a positively charged 

 colloid-ion. 



Hardy f has shown that dialyzed white of egg (from the white of 

 a hen's egg) is electro-positive when a trace of acid is added, while a 

 trace of alkali makes it electro-negative. He believes that in the for- 

 mer case, the hydrogen-ions are caught in the meshes of the colloidal 

 particles of the white of egg and carry the latter with them when they 

 migrate in an electrical field. When alkali is added, the hydroxyl- 

 ions are caught in the meshes of the particles and drag the latter with 

 them in an electrical field. I have called attention + to the fact that 

 Hardy's observations allow of a different interpretation, namely, that 

 they may be due to the electrolytic dissociation of the white of egg. 

 The proteins have an amphoteric character, i.e. they are able to give 

 off HO-ions, as well as H-ions, to the surrounding solution. If we add 

 a trace of acid to the solution of dialyzed white of egg, the degree of 

 dissociation of the acid part of the molecule is diminished, and it will 

 dissociate chiefly into HO-ions and a colloid cation, and the latter will 

 migrate in an electrical field to the cathode. If a trace of alkali, how- 

 ever, is added to the surrounding solution, for the same reason, the 

 white of egg will be prevented from sending as many HO-ions into 

 solution as H-ions, and the molecule will dissociate mainly into H-ions 

 and a colloid anion. Hence, the addition of a trace of acid will give 



* Freundlich, Zeitseh. fur physikal. Chemie, Vol. 44, 1903. 



t Hardy, Proceedings of the Royal Society, Vol. 66, p no, 1901. 



j Loeb, University of California Publications, Vol. i,p. 149, 1904. 



