The swelling of isoelectric gelatin added to various volumes of acid of different concentration at 5°C. has been determined. The swelling is determined only by the concentration of the supernatant solution at equilibrium and is independent of the volume of acid.
Similar experiments with unpurified gelatin show that in this case, owing to the presence of neutral salts the swelling is a function of the volume as well as the concentration of acid.
Both results are predicted by the Procter-Wilson-Loeb theory of the swelling of gelatin.