Pnvir:2 



1/ 



Specific gravity of soil minerals: 2.6-2.75. 



1/ From Lyon, Buclman and Brady. The nature and properties of 

 soils. 5th Ed. 1952. 



Soils differ markedly in the kind of pore space they have. I have illus- 

 trated in Figiire 1 some information about pore size and distribution. I 

 have to admit that soil physicists will say that there is not a good 

 method of measuring or evaluating pore size. One method vxe do have is 

 to find out hoxj much tension is necessary to drain a certain amount of 

 water out of the soil. This can be equated to the amount of tension 

 required to draw capillaries of Imovm diameters. This method does give 

 sorae idea of pore size and distribution, although it has a lot of short- 

 comings. 



In the first graph in Figure 1 you will notice data for fine, sandy loam 

 are e^q^ressed on the basis of the total soil volume (100 cc.) being 

 occupied with solids (50 cc.) and with pore space (50 cc). In the 

 sandy loam soil there are very few pores smaller than 0.02 microns in 

 diameter. The large pores in the soil greater than 20 microns in diame- 

 ter constitute quite a large portion of all the pore spaces. In the 

 other illustration, Loam Soil, there are veiy fevr pores that are greater 

 than 20 microns in diameter. These are only two illustrations; in 

 between them are to be foiind all gradations and some that, perhaps, are 

 different. 



I think the next illustration (Figure 2) vrill give you another idea 

 about pore sizes. The author of these particialar data did not provide 

 enough information to enable us to use the same type of illustration 

 that we had in the first figure, but these diagrams will give an idea 



