SOILS. 27 



ber of different soils with reference to this point. Tubes 

 were filled with the varieties of earth to be investigated, 

 and water passed through the soil under a constant free 

 head of two inches above the soil. The time which, 

 under these conditions, one inch of water passed through 

 three inches of soil was noted. The following are a 

 few of the results obtained : A sandy soil containing 

 3.9 per cent of clay, time 5 -J- minutes, A heavy red 

 clay with 28.8 per cent of pure clay, time 1 33 minutes. 

 A black gummy land with large grains of sand and 26 

 per cent of clay, 16 minutes. 



These experiments bring out the facts regarding the 

 mechanical structure of soils from which may be drawn 

 some very helpful conclusions. It must be kept in 

 mind, however, that natural soil conditions are often 

 different from those existing in the portion of soil which 

 has been experimented with. The ground beneath its 

 surface contains seams and channels made by the en- 

 trance and decay of plant-roots, or is changed by the 

 separation of joint clays into little cubes, or possibly 

 the surface has been puddled by some means, thereby 

 essentially changing the structure in such a way as to 

 give us quite different results. The outlet for water is 

 not always at hand as provided for in experiments. 

 The percolation of water through the surface soil is 

 affected by cultivation and by the application of fer- 

 tilizers, the latter having the effect of changing the 

 arrangement of the soil grains and making the soil 

 more retentive of moisture. 



