PART V. GELATINE AND GLUE 



SECTION I. PROPERTIES OF GELATINE 

 AND GLUE 



MANY of the chemical properties of gelatine, especially those 

 which distinguish it from other proteins, have been described 

 in the Introduction to this volume, and need no further 

 comment. In this section its colloid nature and behaviour 

 will chiefly be considered, for these points have greatest 

 importance from the standpoint of industrial chemistry. 



It is hoped, moreover, that this section will be of interest 

 not only to the chemist concerned in the manufacture of 

 gelatine and glue, but that it will be of value also to those 

 concerned in leather manufacture. The difference between 

 the " collagen " which composes the hide fibre and the 

 high-grade gelatines is so small that for many practical 

 purposes it may be considered negligible. Thus the de- 

 scription of the behaviour of a gelatine gel is very largely 

 applicable to a hide gel also. 



Gelatine has been crystallized by von Weimarn by 

 evaporating a dilute solution in aqueous alcohol whilst in a 

 desiccator containing potassium carbonate, the temperature 

 being maintained at 6o-70 C. The carbonate takes up 

 water only, and the concentration of the alcohol therefore 

 slowly increases until the gelatine is no longer soluble. 

 Gelatine is usually found and known in the colloid state, 

 however, and its behaviour in this state only is of practical 

 importance. 



The fundamental idea of modern colloid chemistry is 

 that colloids are heterogeneous systems, usually two-phased, 

 in which one phase is liquid and the other phase either 

 liquid or solid. The latter phase, which is divided into smalj 



