A microscopic study of the freezing of gel

Abstract

The curious spheres described by Moran, consisting as they do of a succession of shells, afford unmistakable proof that the formation of the ice phase inside a gel may not only vary in rate but actually intermit. This study was undertaken in the hope of throwing some light upon this phenomenon. It has revealed two unexpected facts, namely, that, save in very dilute gels, the course of internal freezing is usually intermittent, and that, instead of pure ice, a solid solution of gelatin and ice separates. Pure ice can and does sometimes form in the shape of rounded crystals scattered throughout the gel, but in the common type of freezing, by spheres or rays spreading from centres of crystallisation, it is always a solid solution which separates. The current conception that the spongy structure found in gels after being frozen and thawed is due to crystals of ice wrong. It is due to the de-solution on rise of temperature and fall of pressure of the solid solution mentioned above. Actually, so far as my observations go, when crystals of pure ice melt, the water is re-absorbed at once by the surrounding gel, leaving only a tiny cleft.