1907.] On Globulins. 425 



•which form colloidal solutions because one of the radicles is of large size, is 

 ^almost or quite immiscible with the solvent, and therefore readily forms 

 molecular complexes which have the electric sign proper to the radicle when 

 ♦dissociated from its fellow in the salt molecule. 



Each colloid particle undoubtedly carries on its surface a charge, since, 

 without exception, they move in a uniform electric field. But in the system 

 formed by each particle there cannot be any free electricity, any resultant 

 ^charge. If there were, the system would, by Earnshaw's theorem, be 

 unstable, and settling would occur the more rapidly the greater the charge. 

 Experiment shows the opposite to be the case. The charge on each particle, 

 therefore, must be bound by an equal and opposite charge on the liquid face 

 opposed to it. The condition of double electric layers is therefore realised. 



It has been shown by Waymouth Keid* that in a solution of proteid no 

 osmotic pressure can be traced to the proteid, and I find that when a 

 -solution of globulin is dialysed against water until equilibrium is reached, 

 the dialysee and dialysate have exactly the same electric conductivity. These 

 facts, added to others already stated, afford overwhelming evidence that in 

 these solutions the chief portion of the proteid is, in effect, removed from 

 solution by being gathered into masses of more than molecular dimensions 

 which are separated from the rest of the solvent by a surface. The masses 

 -of probably hydrated proteid thus form an internal phase. In colloidal 

 salts such as soaps, solutions of globulin in dilute acid or alkali, solutions of 

 -caseinogen or of acid or alkali albumen, in which the internal phase is 

 bounded by double electric layers formed by ionic interaction with the 

 external phase, the stability of the system with reference to forces such 

 as gravity will depend, in part, upon the potential difference between the two 

 faces round each particle. The electric double layers will contribute to 

 stability, since any movement of a particle through the fluid will develop 

 free electricity in quantity proportional to the potential difference between 

 the layers.f 



Salts in small amount diminish the stability of these colloidal systems 

 and bring about concentration ; and salts, as has been shown experimentally 

 by Wiedeman, PerrinJ Burton,§ and others, diminish the potential difference 

 in the condenser system round each particle. 



The contribution which the electrification of the internal surfaces makes 

 to mechanical stability is seen in the high viscosity of these solutions as 



* ' Journ. of Physiology,' vol. 31, p. 438, 1904. 



t Helmholtz, ' Wied. Ann.,' vol. 7, p. 337, 1879. 



X 'Journ. de Chim. Physique,' vol. 2, p. 61, 1904 ; vol. 3, p. 50, 1905. 



% 'Phil. Mag.,' November, 1906. 



