Power of Soils to absorb Manure. 



131 



plete. The composition of the double silicate of alumina and 

 lime in 100 parts is — 



Silica . ... . 53.33 

 Alumina .. . . .30.21 

 Lime . . . . 16.46 



100.00 



Like the corresponding salt of soda the lime double silicate 

 yields to water small quantities of the silicate of lime, but does 

 not dissolve as a whole. 



Double Silicate of Alumina and Potash. — This salt may either 

 be formed directly in the same way as the double silicate of 

 alumina and soda, by using silicate of potash instead of soda in 

 the precipitation, or it may be obtained by digesting either of 

 the two salts already described in sulphate or nitrate of potash, 

 when the soda or lime is dissolved out and replaced by potash. 



Its composition in 100 parts is — 



Silica 47 . 97 



Alumina . . , .27.17 

 Potash . . . .24.86 



100.00 



From this salt 1 gallon of water was found to dissolve 2.27 

 grains of potash. 



Double Silicate of Alumijia and Ammonia. — When any of the 

 foregoing compounds are digested in sulphate or muriate of 

 ammonia, an absorption of the ammonia takes place whilst the 

 alkali previously in the double silicate dissolves out. The 

 ammonia double silicate is very conveniently formed from the 

 double soda silicate ; it is, like the other salts, a fine white 

 powder, which theoretically should have the following com- 

 position : — 



Silica 53.96 ^ 



Alumina . , . .30.57 

 Ammonia* . . , .15.47 



100.00 



It should, however, be stated that this theoretical composition 

 has not yet been attained. Very many different quantities of the 

 ammonia silicate have been prepared, but the proportion of 

 ammonia has fallen much short of that mentioned above, after 

 due allowance has been made for the water of combination, which 

 always reduces the proportion of the different ingredients. 



* The chemical reader will understand that by ammonia here is meant the oxide 

 of amnionium (NH4O.) ; the per centage proportion of avimonia (NH3) will be 

 theoretically considerably less — namely, 10.01. 



k2 



