CLAY. 101 



bricks and pottery. When strongly heated 

 clay loses this property. 



The operations of tillage are partly 

 directed toward breaking up the masses of 

 clay, admitting air into the soil, and increas- 

 ing the si/e of the capillary spaces. They also 

 increase the tendency which the fine particles 

 have to gather into masses, thus permitting 

 a freer circulation of water. Lime has a 

 similar effect in causing the particles to col- 

 lect or flocculate, and is therefore often used 

 as a dressing for stiff, clay lands, in order to 

 make them lighter, and more easy to till. 

 Kneading and trampling have the opposite 

 effect : breaking up the little collections, groups 

 or floccules of clay and thus closing the small 

 openings. Hence it is that brick-makers and 

 potters, who require firm, compact masses, 

 thoroughly knead the clay they use before 

 working it into shape. The cultivator, on the 

 other hand, desires to bring his clay into a floc- 

 culent condition so as to permit the circulation 

 of air and water ; he thus, at intervals, digs, 

 forks, or ploughs the soil, admitting the air 

 and causing the clay to become flocculent, 

 while he is careful to prevent, as far as possible, 

 any trampling or walking over the soil which 

 he has tilled. 



