Diameter changes of gelatinized coacervate drops of the complex coacervate gelatine-gum arabic resulting from a change in the pH of, or from the addition of neutral salts to the surrounding medium. I

1. A microscopic method is developed for the measurement of diameter changes of gelatinized coacervate drops. 2. The influence of the pH and with constant pH (3.7) the influence of neutral salts is investigated on the gelatinized complex coacervate gelatine (positive)-gum arabic (negative). 3. Upon variation of the pH the diameter passes through a minimum lying very close to the pH (3.7) at which, with the given ratio of mixing of gelatine and gum arabic, complex coacervation is optimum (where for example the water content of the coacervate is a minimum). 4. In the regions of smaller salt concentrations the diameter changes are reversible, at higher concentrations irreversible. 5. The reversible change due to the addition of a salt is a swelling. For this swelling the double valence rule holds: 3-1>2-1 > 1-1 and 1-3 > 1-2 > 1-1. 6. The position of the minimum of the swelling-pH curve, the swelling with salts and the thereby prevailing double valence rule are in agreement with the conception that in the gelatinization of the complex coacervate the typical complex relations (electrostatic attraction versus water content) have been retained. The complex gel which results is distinghuised from the complex coacervate only by the coherence of the positively charged gelatine to a gel structure.