88 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



composition of the clay particles undoubtedly influences the char- 

 acter of the soil. The term "Klay" has been proposed to dis- 

 tinguish the clay particles of a soil from the hydrated aluminium 

 silicate termed clay by the chemist. 



True clay is present in the soil in two forms. First, as colloidal 

 clay in a swelled condition; and second, as clay in non-colloid, 

 or shrunken condition. In the colloid condition, clay remains 

 suspended in water indefinitely. Small amounts of lime and other 

 substances coagulate the clay and cause it to separate out in flakes. 

 When the coagulating substance is removed, the clay again 

 becomes colloidal. This may be easily shown by washing a clay 

 soil with acid to remove lime, then with water, and shaking it 

 with ammonia. Clay will enter into suspension and remain sus- 

 pended a long time, but if ammonium sulphate, ammonium car- 

 bonate, or other salts are added, the clay quickly separates in 

 flakes. 



Colloidal clay was prepared by Schloesing. 1 He brought the 

 clay into suspension in water, as iri the mechanical analysis of a 

 soil, and precipitated the clay with a small quantity of acid, 

 collected the colloidal clay on a filter, and washed with distilled 

 water. The residue on the filter was treated with ammonia, and 

 diffused in a considerable quantity of distilled water. This was 

 then left until deposition ceased, which required several months. 

 The microscope could then no longer detect particles of visible 

 dimensions in the solution. The liquid was decanted off, and the 

 colloidal clay precipitated by the addition of a small quantity of 

 acid. It dried to a translucent, horn-like mass. According to 

 Schloesing, even the stiffest natural clays seldom contain more 

 than 1.5 per cent, of such true colloidal clay. 



Colloidal clay has much higher binding properties than shrunken 

 or coagulated clay. The tenacity of a soil containing colloidal clay 

 is greatly influenced by its condition. If the clay is in its fully 

 swelled condition, the soil exhibits its maximum cohesion, and if 

 a sufficient quantity of clay is present, it will be quite impervious 

 to water. If the colloidal clay is in a shrunken coagulated state, 

 1 Chimie Agricole, 1885. 



