MINERAL CONSTITUENTS 137 



ing and wetting and drying will gradually restore the soil to its 

 granular condition. The time required for this depends somewhat 

 upon the organic matter and lime content of the soil. It is never a 

 wise plan to permit stock to run on a moderately heavy soil when 

 wet so late in spring that its granular condition will not be restored 

 again by freezing and thawing. In the corn belt considerable dam- 

 age is done to the soil by pasturing the cornstalks too late in the 

 spring. 



(e) Coagulation or Flocculation. The examination of a clay 

 soil usually shows it to be made up of fine particles cemented into 

 granules, crumbs, or grains. If a few grains of clay soil be pul- 

 verized and put into a liter of water and stirred and allowed to 

 stand for several weeks, some material will be found still in suspen- 

 sion. If some mineral acids or certain salts or lime water are added 

 to this liquid coagulation will occur and floccules may be seen form- 

 ing, which gradually settle to the bottom, carrying with them the 

 suspended clay particles. This may be well shown by putting a 

 drop of water with suspended clay under the microscope. Intro- 

 duce a drop of lime water under the cover glass. The particles will 

 at once begin to collect in groups, showing the formation of floccules. 

 This process takes place in soils due to the presence of certain sub- 

 stances in solution in tlie soil moisture that act as electrolytes. In 

 some cases, fertilizers when added produce this effect, and lime- 

 stone, which gives rise to the soluble bicarbonate, produces floceula- 

 tion. This is, however, a slow process and will not produce granula- 

 tion as quickly as is ordinarily supi>osd, although heavy acid soils 

 are undoubtedly benefited physically by the application of lime- 

 stone. Common salt produces the same effect and likewise many 

 other salts. Most alkaline substances, however, deflocculate clay 

 soils and produce a puddled condition. Ammonia and most of its 

 salts are good examples. The black alkali of the West is especially 

 detrimental because of the physical effect it has on soils in producing 

 a puddled, impervious condition. This, however, may be remedied 

 by the application of gypsum, calcium sulfate. The injurious effect 

 of sodium carbonate or black alkali is destroyed by this reaction 

 and sodium sulfate and calcium carbonate produced, the latter of 

 which has a flocculating effect on the soil and soon changes the 

 puddled condition entirely. It has been observed frequently that the 

 water of glacial streams is extremely muddy, while that coming from 

 limestone regions is characterised by clearness. The difference is 

 due to the lime content of the water from the two sources. In 



