RETENTION OF MOISTURE. G7 



Kinds of Earth. ^^^ rUso.Cc?"*" 



Humus, 190.0 



Garden earth, 89.0 



Arable soil, 52.0 



Arable soil, 48.0 



Retention of moisture. When soils become wet 

 with dew or rain they part with it by evaporation 

 with very different degrees of rapidity. Those 

 which absorb the most are generally the ones which 

 dry the slowest, and this quality constitutes the 

 difference between warm and cold soils, as seen 

 below : 



One hundred parts of the water contained in the soil loses in the course of 

 four hours, at GG^ Fahr., the following per centage: 



Kinds of Soil. Per cent, of Loss. 



Silicious sand, 88.4 



Calcareous sand, 75.9 



Gypsum, 71.7 



Sandy clay, ■ . . 52.0 



Stiffish clay, 45.7 



Stiff clay, 34.9 



Pure claj', . . . ' 31.9 



Calcareous soil, 28.0 



Garden earth, 24.3 



Humus, 20.5 



Thus it will be seen that those soils which absorb 

 the least moisture lose it the quickest by evapora- 

 tion. As the earth dries, it shrinks. This causes 

 the cracking of clays, which, as will be perceived in 

 the chapter on drainage, is such an important qual- 

 ity, because it permits the water to pass off through 

 these crevices, when tenacious earths would other- 

 wise be impervious. 



