The Influence of Electrolytes on the Cataphoretic Charge of Colloidal Particles and the Stability of Their Suspensions

1. This paper gives measurements of the influence of various electrolytes on the cataphoretic P.D. of particles of collodion coated with gelatin, of particles of casein, and of particles of boiled egg albumin in water at different pH. The influence of the same electrolyte was about the same in all three proteins. 2. It was found that the salts can be divided into two groups according to their effect on the P.D. at the isoelectric point. The salts of the first group including salts of the type of NaCl, CaCl(2), and Na(2)SO(4) affect the P.D. of proteins at the isoelectric point but little; the second group includes salts with a trivalent or tetravalent ion such as LaCl(3) or Na(4)Fe(CN)(6). These latter salts produce a high P.D. on the isoelectric particles, LaCl(3) making them positively and Na(4)Fe(CN)(6) making them negatively charged. This difference in the action of the two groups of salts agrees with the observations on the effect of the same salts on the anomalous osmosis through collodion membranes coated with gelatin. 3. At pH 4.0 the three proteins have a positive cataphoretic charge which is increased by LaCl(3) but not by NaCl or CaCl(2), and which is reversed by Na(4)Fe(CN)(6), the latter salt making the cataphoretic charge of the particles strongly negative. 4. At pH 5.8 the protein particles have a negative cataphoretic charge which is strongly increased by Na(4)Fe(CN)(6) but practically not at all by Na(2)SO(4) or NaCl, and which is reversed by LaCl(3). the latter salt making the cataphoretic charge of the particles strongly positive. 5. The fact that electrolytes affect the cataphoretic P.D. of protein particles in the same way, no matter whether the protein is denatured egg albumin or a genuine protein like gelatin, furnishes proof that the solutions of genuine proteins such as crystalline egg albumin or gelatin are not diaphasic systems, since we shall show in a subsequent paper that proteins insoluble in water, e.g. denatured egg albumin, are precipitated when the cataphoretic P.D. falls below a certain critical value, while water-soluble proteins, e.g. genuine crystalline egg albumin or gelatin, stay in solution even if the P.D. of the particles falls below the critical P.D.