ABSORPTIVE fOWEll OF THE SOIL. 350 



form. Dung liquor, rich in carbonate of potash, on the 

 other hand, would dissolve silica from the soil. 



Sulphuric acid, existing in considerable quantities in 

 dung liquor as a readily soluble salt of ammonia or potash, 

 would be partially retained by a soil rich in carbonate of 

 lime by conversion into sulphate of lime, which is com- 

 paratively insoluble. 



Absorption of Bases, from their Hydrates, Carbonates 

 and SilicateSi — 1. Incidentally it has been remarked that 

 free bases, among which ammonia, potash, soda and lime 

 are specially implied, may be retained by combining with 

 undissolved silica. Potash, soda (and ammonia?) may 

 at once form insoluble compounds if the silica be in large 

 proportion ; otherwise they may produce soluble silicates, 

 wliich, however, in contract with lime, magnesia, alumina 

 or iron salts, will yield insoluble combinations. As is 

 well proved, gelatinous silica and lime at once form a 

 nearly insoluble compound. It is probable that gelatinous 

 silica may remove magnesia from sobxtion of its bicarbon- 

 ate, forming a nearly insoluble silicate of magnesia. 



2. It has long been known that hydrated oxide of iron 

 and hydrated alumina may unite with and retain free 

 ammonia, j^otash, etc. Rautenberg experimented with 

 both these substances as freshly prepared by artificial 

 means, and found that, under similar conditions, 



10 j,'rm9. ofbytlrated 10 grms. of hydrated 

 oxide of iron. alumina. 



Absorbed of free ammonia 0.046 grm. 0.066 grm. 



" " free potash - 0.U7 " not det. 



Long continued washing with water removes the alkali 

 from these combinations. That oxide of iron and alumina 

 commonly occur in the soil in quantity suflicient to have 

 appreciable effect in absorbing free alkalies is extremely 

 improbable. 



Liebig has shown {Ann. Ch. u. Fh. 105, p. 122,) that 

 hydrated alumina unites with silicate of potash with great 



