62 SOILS. 



clay adheres to the tongue, so as to render the separation painful ; when 

 wetted it quickly bulges with great energy, and in a short time resumes 

 its former jelly-like condition. When moistened with less water it 

 assumes a highly plastic and adhesive condition, so that it is difficult to 

 handle and almost as sure to soil the operator's hands as so much 

 pitch. 



Effects of Alkali Carbonates upon Clay. The carbonate of 

 potash and soda, when in very dilute solution (.01 to .05%) 

 exert upon diffused clay an effect the reverse of the acids and 

 neutral salts. They destroy the flocculent aggregates formed 

 by precipitation with these, or naturally existing in the soil, 

 and tend to puddle the clay so as to render it impervious to 

 water. It is thus that in the alkali lands of the arid regions 

 we often find the soil or subsoil consolidated into a very re- 

 fractory " hardpan," difficult to break even with a sledge ham- 

 mer and impossible to reduce to tilth until the alkali carbonate 

 is destroyed by means of a lime salt, such as gypsum. (See 

 chapt. 23). Ammonia water also helps to cause the diffu- 

 sion of clay in water, but its effect of course disappears upon 

 drying. It is probable that this property of sodic carbonate 

 can be utilized in rendering earth dams firmer and more secure 

 against the penetration of water. 



