抄録
As often reported, if limited quantities of water and gelatin xerogel are brought into contact with each other there takes place a contraction in total volume. As to the dependence of this shrinkage on the pH value of the liquid that surrounds the gel, however, a group of investigators have found that the volume decrease attains to a maximum in a pH region about the isoelectric point of the gelatin, while another group say that it becomes minimal there; but any convincing theory seems to have not yet been put forward to resolve this antinomy.
The present author, intending to find a clue to the molecular events inducing the spontaneous wetting of extremely fresh fillet, examined as preliminaries the said contraction of a gelatin-water system and found that the contraction minimum in the isoelectric zone is just realized only at a lower temperature. He proposes, hereupon, a view that the apparent volume reduction may be caused by the resultant of two separate mechanisms, viz., (1) fixing of water molecules around rather stationary polar groups of gelatin, which reduces the space thermally swept by these molecules, and (2) migration of water molecules into oil-repellent gaps in the xerogel, which lessens the water remaining outside the gel. Results of the present experiment, in which the contraction dependence on pH of the immersion liquid was examined at different temperatures and with varying moisture-contents of sample, will serve by the help of this view to settle the pending antinomy about the contraction of a gelatin-water system.
