PHYSICAL PROPERTIES OF SOIL 



CHAPTER I 



PHYSICAL CONSTITUTION OF SOIL 



Physical Constitution of Soil Methods of Mechanical Analysis Relation of 

 Physical Constitution to Fertility Tenacity of Soil Cementing Materials 

 in Soil Coagulation of Clay Shrinkage on Drying Nature and Origin 

 of Tilth Specific Gravity of Soil Weight of Soil per Acre Colour of 

 Soil Odour of Soil. 



Physical Constitution. A soil is a mass of solid particles, 

 differing in their size, shape, and nature. In approaching 

 the subject of the physical constitution of soil it is simplest 

 to take, in the first instance, the case of an ideal soil, 

 consisting of uniform particles, having all the same size, 

 shape, and nature. In a system composed of solid spheres the 

 number of particles in any given volume will depend firstly 

 on the size of the particles, and secondly on their mode of 

 packing. If the spheres are all of the same diameter, there 

 will be a closest and a loosest mode of packing, in each of 

 which every particle is in contact with all those surrounding 

 it ; such arrangements are shown in Fig. I . 



In both these systems of spheres there is clearly a consider- 

 able proportion of empty space between the particles, which 

 only touch each other at certain points. With the closest 

 packing the interspaces form 25-95 per cent, of the total 

 *> B 



