ii.] FL0CCULAT10N 39 



of clay suspended in the liquid. The flocculating power 

 of a salt also varies with both the acid and the metal; 

 the following table shows approximately their com' 

 parative effect : — 



The alkalis and salts like phosphate of sodium, which 

 give rise to free alkalis on hydrolysis, instead of 

 flocculating have the opposite effect, and keep the 

 particles in their finest state of division without any 

 tendency to settle. 



It is y furthermore, possible to show that many 

 substances, however finely divided, will not assume the 

 condition of indefinite suspension in water so as to be 

 flocculated by salts ; in particular, suspensions of finely 

 divided quartz, ferric hydrate, and hydrated alumina 

 flocculate spontaneously and will not remain turbid for 

 many minutes, though in their turn they can be 

 deflocculated and made to remain in suspension by 

 adding a trace of free alkali to the liquid. 



Without going further into the details of a subject 

 which is still very obscure, the condition of free suspen- 

 sion in water and the Brownian motion of the 

 particles of clay seem to be associated with the presence 

 of the zeolitic double silicates which contain atoms of 

 potassium or sodium in their molecule, and which doubt- 

 less give rise to a little free alkali by their partial 

 hydrolysis when in contact with a large bulk of water. 



We may thus conclude that fineness of grain is 

 not the only factor in the constitution of clay, but that 

 the characteristic clay properties which are always 

 associated with the power of flocculation depend also 



