202 ANIMAL PROTEINS 



gelatine sol (like other lyophile systems) contains chiefly 

 amicrons, but submicrons are also observable. 



i. THE CONTINUOUS PHASE 



Owing to the contractile force of surface tension, it is 

 concluded that the surface layer of a liquid is under very 

 great pressure, much greater than the bulk of the liquid. 

 Any extension of the surface of the liquid naturally causes 

 a corresponding extension of the proportion of liquid which 

 is thus compressed. If in a beaker of water there be placed 

 a porous substance, such as animal charcoal, there is a great 

 extension of the surface of the water, and a corresponding 

 increase in the amount of compressed water. If instead 

 there be substituted a large number of very small particles 

 of a substance, a still further increase in the amount of com- 

 pressed water is involved. As the specific surface of the 

 substance inserted is increased, and its amount, the propor- 

 tion of compressed and denser water increases also, until it 

 is a practically appreciable percentage of the total volume. 

 It is clear also that the extent of the zone of compression 

 will be determined also by the nature of the substance with 

 which the water is in contact at its surface, i.e. by the extent 

 to which it is hydrophile, and this indeed may be the more 

 important factor. 



Now in a gelatine sol we have the necessary conditions 

 for a system in which the compressed water bears an un- 

 usually large ratio to the total, owing to the enormous 

 surface developed by the minute particles of the disperse 

 phase (amicrons) and to the unusually wide zone of com- 

 pression surrounding each particle caused by the strongly 

 hydrophile nature of gelatine. It should be pointed out 

 that these zones of compression do not involve any abrupt 

 transition from the zone of non-compression, the layer 

 nearest the particle is under the greatest pressure, and the 

 concentric layers under less and less pressures, the actual 

 compression being thus an inverse function of the distance 

 from the particle. Now if there be a gradual increase in the 

 concentration of the sol, the time will come when these 



