26 ENGINEERING FOR LAND DRAINAGE. 



Sandy truck soil 37-29 per cent 



Wheat land 42 .72 



Barren clay 47. 19 



Gummy land 61.54 



Pipe-clay 65. 12 



i I 4 1 



a it 

 << it 



By comparing the fineness of the grains with the 

 volume of empty space, it is seen that the finer the 

 grains the greater the volume of empty space a soil con- 

 tains. That is, a clay holds or is capable of holding 

 27,8 per cent of volume of water more than the sandy 

 soil noted, while the grains of the clay are about five 

 hundred times smaller than those of the sandy soil. By 

 comparing the results of several analyses of soils and 

 subsoils, it is found that the results which appear in the 

 tables referred to, characterize all soils. 



These investigations show that clays are made up of 

 the smallest grains, and contain the greatest volume of 

 empty space, and from the results of other experiments 

 it appears that the volume of empty space of soils in 

 general is in direct proportion to the per cent of clay 

 which they contain. When this space becomes charged 

 with water, the rate of movement under a given head, 

 as would be readily and correctly inferred, is more 

 rapid through a sandy soil than through one composed 

 of a considerable per cent of clay. While the sandy 

 soil contains less total volume of space and hence will 

 hold a smaller volume of water than the clay soil, the 

 spaces are larger individually than those in the clay 

 and hence less resistance is offered to the flow of water 

 through them. 



Experiments were made at the Station with a num- 



