132 



Poicer of Soils to absorb 3fajiiire. 



The following numbers give the per centage of ammonia 

 (NH3) in different samples as actually prepared : — 



First sample ., . . 4.51 



Second sample, . . . 5.64 



Third sample , 5.32 



The double silicate of alumina and ammonia is only very 

 slightly soluble in water, as the following experiments will 

 show : — 



26.64 grains of double silicate were digested in 16,000 grains of distilled 

 water — the filtered solution gave 0.2195 grains of ammonia, or 

 0,96 grains to the gallon. 



29.80 grains of double silicate were digested in 16,000 grains of distilled 

 water — the filtered liquid contained 0.265 grains of ammonia, or 

 1,160 grains to the imperial gallon. 



This is a very small degree of solubility, as will be seen when 

 it is remembered that carbonate of lime, which is considered an 

 almost insoluble substance, dissolves in water (free from carbonic 

 acid) to the extent of two grains in the imperial gallon. The 

 double silicate of alumina and ammonia loses ammonia at a tem- 

 perature considerably under the boiling point of water, and it is 

 entirely deprived of it by a red heat. 



The double magnesian silicate resembles those already de- 

 scribed, but has not yet been fully examined. 



I have avoided giving any detailed technical account of these 

 salts, and have only mentioned those particulars in their history 

 which bear upon the agricultural question. It is necessary, how- 

 ever, to notice some points in relation to them as a class. In 

 the first place, it will have been observed that there is a regular 

 order of decomposition between the silicates of each base and 

 ordinary salts of other bases : thus the soda silicate is decom- 

 posed by salts of either lime, potash, or ammonia ; the potash 

 silicate again is decomposed in its turn by lime or ammonia ; 

 and, lastly, the lime compound by ammonia. The different 

 bases may be arranged in the order in which they replace each 

 other from the silicate as follows : — 



Soda, 



Potash, 



Lime, 



Magnesia, 



Ammonia. 



That is to say, that from a silicate of alumina and any one of 

 these bases the base will be dislodged by a salt of any of those 

 under it in the list. Nitrate of potash, for instance, will turn 

 out soda from its silicate, and a potash silicate will be formed ; 

 whilst ammonia will replace any of the other bases. Of course 

 the reverse of this action cannot occur, and therefore the double 



