H. A. Tempany 319 



of a series of readings and were the result of the increased tendency 

 of the blocks to stick to the supporting cage in the wet stage. This 

 objection was partly surmounted by rubbing the interior surface of 

 the cage with graphite but could not be completely got over. By 

 repeating the experiments a number of times the irregularities could 

 however be readily smoothed out. 



The results are given in the accompanying table ; they are expressed 

 in terms of the water per cent, on the weight of the wet brick and in 

 the corresponding linear contraction per cent. The results are also 

 displayed graphically in Diagram 3 (p. 320). 



The character of the results is striking and shows that in the earlier 

 stages of the process of evaporation and contraction the per cent, 

 water lost and the corresponding per cent, linear contraction is the 

 same in all cases, and takes the form of a straight hne ; as evaporation 

 proceeds however the straight line form is departed from and the curves 

 evince an upward tendency; the point of departure from the straight 

 line form varies in the case of the different soils occurring at a point 

 which is progressively nearer to the point of origin of the curve as the 

 total observed shrinkage diminishes. 



The reason underlying these occurrences appears fairly obvious 

 when the mechanism of the process of shrinkage is considered. The 

 effect in question is attributable to the action of soil colloids, which 

 when soil is moistened form a gel; successive additions of water to dry 

 soil resvdt in the more and more complete transition to the gel form, 

 until when the point of maximum plasticity is reached the gel is in 

 equihbrium. At the point of maximum plasticity it appears probable 



