C. T. JACKSON'S ADDRESS. 463 



to plants ; nor would their most soluble salts prove most eco- 

 nomical. 



Nature presents in sparingly soluble combinations her most 

 rare and precious fertilizers. The phosphates are the most 

 rare of all, and seldom do we find the phosphoric acid in com- 

 bination with any bases that form soluble salts with it, but on 

 the contrary, it is generally found in combination with lime, 

 alumina, and oxide of iron, and forming not more than three- 

 tenths per cent, of the soil. 



Sulphate of lime, or gypsum, is also a sparingly soluble salt. 

 It is slowly decomposed by the action of carbonate of ammo- 

 nia, and, little by little, sulphate of ammonia is produced, and 

 is ready to meet the wants of growing plants, while at the same 

 time, carbonate of lime is formed by the union of the carbonic 

 acid of the carbonate of ammonia, with the lime, of the sul- 

 phate of lime. 



This again is decomposed by the freshly forming organic 

 acids, produced by the decay of vegetable matters in the soil, 

 and carbonic acid gas is disengaged, and goes to decompose 

 the silicates of the alkalies, while the organic lime salts, are 

 absorbed and digested by the living plants ; so that there are 

 numerous combinations and decompositions always going on 

 around the roots of the plants ; chemical changes, which have 

 by some been attributed to the mysterious powers of life. 



