COAGULATION OF CLAY 31 



various substances to the water will however speedily bring 

 about the coagulation of the clay, which then completely 

 separates from the water as a flocculent precipitate. If this 

 precipitate is collected, and the precipitating agent separated 

 from it, the clay will be found to have regained its power 

 of permanent suspension in water. This behaviour of colloid 

 clay distinguishes it sharply from the various extremely fine 

 particles with which it is associated, and which are so difficult 

 to separate from it. 



If a clay containing fine silt is diffused through water and 

 the clay then coagulated, the whole of the suspended matter 

 falls together, the colloid clay carrying the silt down with it. 

 If the silt is separated, and purified from clay by the methods 

 already described, and is then diffused in water alone, it does 

 not exhibit the phenomena of coagulation when treated with 

 the reagents which precipitate true clay. 



The substances which determine the coagulation of clay 

 when diffused in water are very numerous. Acidification with 

 a mineral acid is very effective, and a great number of salts 

 produce this effect. According to Schloesing, who has made 

 a special study of these phenomena (Chimie agricole, 62), 

 lime, either as lime water or as salts of calcium, is especially 

 effective, 02 gram of lime being sufficient to cause a speedy 

 precipitation in a litre of clay water. Magnesia, according 

 to the same authority, is nearly as effective as lime. The 

 salts of potassium are less effective, and must be used in five 

 times greater quantity than the corresponding calcium salts. 

 The salts of sodium are still less active ; common salt is 

 however a very effective precipitant of clay if used in 

 sufficient quantity. 



Sachsse and Becker (Landivirth. Versuchs-Stationen, xliii. 1 5) 



