GELATIN 



By T. SLATER PRICE, O.B.E., D.Sc, F.I.C. 

 Director of Research to the British Photographic Research Association 



Although gelatin, in the form of glue, has been known at 

 least since the time of the Pharaohs of Egypt (Cf. Bogue, 

 Journ. Franklin Institute, 1922, 193, 795) the chemistry both 

 of its preparation from bones and hides, and of its constitution, 

 may still be said to be in its infancy. Belonging, as it does, 

 to those complex substances, the proteins, its chemical investi- 

 gation is a very difficult problem, and essentially progress has 

 only been made in the examination of its degradation products, 

 which consist mainly of amino-acids. Dakin {Journ. Biol. 

 Chem., 1920, 44, 524) has so perfected the methods of degrada- 

 tion and separation of the amino-acids that he has succeeded 

 in recovering 91-3 per cent, of the total nitrogen, as shown by 

 the following table : 



Glycine . 

 Alanine . 

 Leucine . 

 Serine 



Aspartic acid 

 Glutamic acid 

 Lysine 



There are still, however, unidentified bases in the hydrolytic 

 products of gelatin, as pointed out by van Slyke and Hiller 

 (Proc. Nat. Acad. Sci., 192 1, 7, 185). Attempts have been 

 made by Prof. Procter and by J. A. Wilson to deduce a formula 

 for gelatin, but as it has still to be proved that pure gelatin, 

 as a unitar}^ substance, has been obtained, such formulae have 

 very little significance. 



In view of the complex chemical nature of gelatin it is not 

 to be wondered at that the enormous literature on the subject 

 consists, to a very great extent, of accounts of the results 

 obtained in the investigation of its colloidal properties. 

 Actually the word " colloid " is derived from the Greek word 

 KoWa, meaning glue, and at the time when this term was first 

 used by Graham it was supposed that all colloids were sub- 

 stances of very complex constitution, just as is glue. As is 

 well known, however, this is by no means the case, since the 



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