H. A. Tempany 321 



At the point of maximum plasticity the gel skeleton will ramify 

 throughout the soil block surrounding in its meshes each one of the 

 constituent soil particles. As the gel loses water by evaporation it 

 will contract, and in contracting w^ll tend to draw together the particles 

 of the soil in its meshes. 



In any event internal friction and the inertia of the soil particles 

 will exert a certain degree of resistance to contraction, but in the earlier 

 stages of drying, owing to the fact that the distances separating the 

 particles are relatively large and the colloidal films relatively thick, 

 the internal resistance will be very small and approximately constant. 



As contraction proceeds however the constituent particles will 

 approach nearer to one another and internal friction will in consequence 

 tend to increase. Eventually a point mil be reached when the effect of 

 internal friction will become sufficiently pronounced to exert a percep- 

 tible retarding effect on the contracting force due to the gel, and this 

 will be evidenced by a diminution in the rate of contraction in relation 

 to the corresponding rate of water loss, and by a progressive departure 

 from the straight line relationship. In the end the resistance due to 

 these causes will become equal and opposite to the pull of the con- 

 tracting gel, when further shrinkage will cease and the continuity of 

 the gel skeleton within the block will become ruptured. 



It is to be observed that in such an event, even after shrinkage has 

 ceased, the gel condition continues to be maintained inside the block 

 and will continue to lose water in the same way as previously, but as 

 the continuity of the gel skeleton throughout the block has become 

 broken no further shrinkage is evident. 



That this is the case is clearly brought out when the total moisture 

 contents of the soils are compared with the proportion of the total 

 water present which has been evaporated when shrinkage ceases. 



This is shown in the following figures which give the mean total 

 moisture contents of each of the soils examined per cent, on the dry 

 soil and the percentage of the total which has been evaporated at 

 the time when shrinkage ceases. 



