384 The Floccnlation of So i/s. Ill 



1. Subsoils containing no organic matter and from which the absorbed 

 bases have been removed by dilute acid, show a decreased base absorbing 

 power after partial ifjnition. This is the simplest and most obvious case. 

 It has been previously argued that the power to absorb base rests chiefly 

 with the colloidal gel matter of the soil. This colloidal matter will be 

 dehydrated and its colloidal state (eventually) destroyed by ignition. In 

 accordance with the argument it is found that an early eSect of ignition 

 is the depression of the base absorbing power. 



2. Untreated subsoils, containing no organic matter, but containing 

 absorbed lime, show an increased base absorbing power after 5 minutes' 

 ignition. The inference is as follows. In the original uuignited material 

 the whole of the absorptive power of the surface colloids of the subsoil 

 aggregate is satisfied or nearly so. On ignition the aggregate is disrupted 

 by the .shrinkage of the colloids and in the first stages of such disruption 

 new surfaces, whose absorptive power is not satisfied, are exposed. Such 

 new surface will lose its absorbing power as ignition proceeds, but in the 

 first stages of ignition the development of new surface more than counter- 

 acts the destruction of its colloidal state. The subsoil aggregate may show 

 no lime requirement at all as an aggregate for the absorptive power of the 

 outer surface of the aggregate may be fully satisfied with lime. When the 

 aggregate becomes broken the surfaces of the particles are exposed and 

 their exposure takes place before their absorptive power is lost. After 

 a short ignition, therefore, a sub!5oil free from organic matter and 

 which originally has no base absorbing power shows a base absorbing 

 power. 



This consideration fully supports the earlier views that lime reacts 

 with the colloidal surface forming a precipitate which entangles and 

 binds the particles. The complete formation of such an absorption com- 

 pound will clearly take place only over the outer surface of the resulting 

 aggregate. 



This view is also in accordance with the fact that after ignition it is 

 the acid-salt-forming bases rather than the neutral-salt-forming bases 

 which dissolve to a greater extent in acid. 



3. Soils containing organic matter show a marked decrease in base 

 absorbing power after partial ignition. Now, humus undoubtedly plays 

 an important part in the absorption of lime by the .soil colloids. On 

 ignition its colloidal state will be destroyed very rapidly. Where humus 

 is present therefore the decline in base absorbing power on ignition will 

 at first be very rapid and may easily overbalance the increase due to new 

 surface exposure. Moreover, the lime absorbed by the humus will 



