26 SCIENCE PROGRESS 



electrolytes. His conception of the structure of the electrical 

 double layer is somewhat similar to that of Freundlich. The 

 electrical charge on the colloidal particle is assumed to be due 

 to ions which are firmly fixed by chemical forces, the average 

 distance between each ion being large compared with molecular 

 dimensions. The process of neutralisation of these ions is the 

 first step in coagulation. If a solution of an electrolyte is 

 added to the colloidal solution the " fixed " ions attract those 

 ions with an opposite charge, and the number of " fixed " 

 ions which are neutralised at any moment is dependent upon A, 

 the work necessary to separate an ion from the surface and 

 the concentration of the electrolyte. It is assumed that when 

 the kinetic energy of the oppositely changed ion of the elec- 

 trolyte exceeds W, then it is no longer held by the " fixed " 

 ions on the surface ; the fraction of the ions in the active state 



is given by ^"kt' By applying the theory of adsorption 

 developed by Langmuir, the author shows that the fraction of 

 the fixed ions which are neutralised is a function of the valency 

 of the oppositely charged ion of the electrolyte and its mobility. 

 For a negative surface it is derived that the order of adsorption 

 of cations will be Th > Al > Ba > Sr > Ca > Mg > H > 

 Cs, Rb > K > Na > Li, an order which is found experimentally 

 for the precipitating power of cations. 



Porter (p. 135) has put forward a proof of the Helmholtz 

 equation for the flow of liquid in electroendosmosis, which 

 removes some of the difficulties of the Helmholtz proof and has 

 derived a similar equation for the velocity of a colloidal particle 

 in an electric field. 



Loeb (p. 153) points out that many of the anomalies ob- 

 served in the relative effects of anions on the precipitation, 

 swelling and other properties of proteins, disappear if these 

 properties be studied at a constant hydrogen ion concentra- 

 tion. The order which, according to Pauli, represents the relative 

 efficiency of different acids on the viscosity of blood albumens is 

 HCl > monochloracetic acid > oxalic acid > dichloracetic 

 acid > citric acid > acetic acid > sulphuric acid > trichlor- 

 acetic acid, an order which lacks any chemical character. 

 Loeb shows that gelatine with a pH > 4-7 can only combine 

 with cations forming metal gelatinate and at pH < 4'7 can 

 only combine with anions forming gelatine hydrochloride, etc. 

 Thus when a protein is placed in a solution of NaCl it will 

 combine with Na to form sodium proteinate as soon as the pH 

 is higher than that of the isoelectric point of the protein, and 

 when the pH falls below this value the Na is given off and protein 

 chloride is formed. The amount of acid required to bring 

 isoelectric gelatine to the same pH depends only on the basicity 

 of the acid and its degree of ionisation. The influence of acids 



