THE PROPERTIES OF SOILS 197 



of the water as possible and examine the layer at the bottom. 

 It will be found to be scarcely gritty, but almost greasy to the touch, 

 indicating that it is made of very fine particles ; on drying it will 

 shrink and crack and form a hard cake. Now take the beaker 

 with the sand in it, put it in the oven, and when it is dry brush 

 out the sand (it will be quite loose and show no tendency to 

 cake) on to the fine sieve, and weigh the two portions, the 

 coarse sand which is retained and the fine sand which passes 

 through. Now tabulate the results : 



5 grams taken = 100 per cent. 



Coarse sand, 0*23 grams . . = 4-6 

 Fine sand, 3*61 grams . . = 72*2 

 Clay and silt (by difference) = 23*2 



Repeat this experiment for both soil and subsoil of the clay and 

 sandy arable land, and set out all the results side by side. 



The process just described is a rough version of the accepted 

 method of analysing a soil mechanically by grading it into its 

 constituent particles of clay and sand of various sizes. If even the 

 simple appliances required are not available, a good deal of infor- 

 mation can be got by adding a spoonful of each of the powdered 

 soils to separate tea-cups, rubbing them up with water as de- 

 scribed and pouring off the turbid water, using the finger as a 

 pestle, and finally collecting the sand remaining at the bottoms of 

 each cup on separate sheets of paper for comparison by the eye. 



On examining the results it will be seen that the sandy soil is 

 not all sand, but that a fair amount of clay and fine silt can be 

 washed away from it, also that the clay soil often contains a 

 considerable proportion of fine sand. We never find a purely 

 clay soil, and only on the most barren of heaths will the sandy 

 soils contain less than 10 per cent, of clay and silt. Next, we 

 shall see that the sandy soil and its subsoil are much alike as 

 regards the proportion of sand and clay they contain, but that 

 the surface layer of the clay soil is distinctly more coarsely 

 grained and contains a higher proportion of sand than the sub- 

 soil. This difference between soil and subsoil is due to the rain 

 washing away the finest particles and leaving the coarser ones 

 behind, just as we have seen the flint stones are left on the top 



