Abstract
GELATIN, in the form of glue, has been so long known that, according to Dr. Bogue (J. Franklin Inst., 1922, vol. 193, p. 795), “we are unable to penetrate the archives of the human race to a date where we may say with assurance that glue was not^ yet discovered. Certain it is that this material was in use as an adhesive in the days of the great Pharaohs of Egypt.” As glue, or κóλλα, it has given us the term “colloid,” and at the time when this term was first used by Graham it was supposed that all colloids were substances of very complex constitution, such as is glue. This, however, is by no means the case, since what are known as the suspensoid colloids may consist of the elements themselves, e.g. colloidal gold and silver. The emulsoid colloids, however, consist to a large extent of very complex chemical substances, as, for example, the proteins, and it is to this class that gelatin belongs. Because of its complex constitution the chemical investigation of gelatin and of the processes which occur in its extraction from bones and hides is still in its infancy, and essentially progress has only been made in the direction of the examination of the degradation products. It is therefore not to be wondered at that the enormous literature on gelatin consists, to a very great extent, of accounts of results obtained in the investigation of its colloidal properties. Naturally, the earliest physical properties to be investigated were the viscosity of the sol and the swelling of the gel, and it was soon found that the relations were very complicated, depending on previous history, even in systems made up from gelatin and pure water alone. For example, shaking, or repeated passage through a viscometer, will decrease the viscosity of a gelatin sol; at ordinary temperatures the viscosity of a freshly made sol gradually increases, whilst that of a freshly diluted sol gradually decreases; in a freshly made gel the intensity of the Tyndall effect gradually increases; and so on, all indicative of the formation of a structure and of the attainment of an equilibrium of some kind.
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PRICE, T. Gelatin. Nature 110, 286–288 (1922). https://doi.org/10.1038/110286a0
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DOI: https://doi.org/10.1038/110286a0