336 WATER. 



sorbed in limited quantity, like the majority of soluble substances 

 But if instead of administering them separately dissolved in water, 

 as was done in the physiological experiments, they are incorporated 

 with a loose and humid soil, these salts react upon the calcareous 

 matter almost always existing in the ground, and are transformed 

 into carbonate of ammonia, which exerts undeniably a favorable in- 

 fluence upon vegetation. From these facts it may be presumed 

 that the introduction of lime and marl is not merely to supply the 

 defective calcareous element, but likewise a principle, carbonate of 

 lime, which produces a particular action upon the manure, changing, 

 through double decomposition, the unassimilable ammoniacal salts 

 there present into a carbonate capable of being assimilated, which 

 transmits to the plant the azote of the organic matter of the dung 

 and the carbon contained in the calcareous rocks. 



These reactions which go on between soluble salts and one that 

 is insoluble under the peculiar conditions united in arable land, show 

 that we must not always conclude as to what passes in the ground 

 from phenomena observed in the laboratory of the chemist ; and it 

 is probable that by extending the study, of these singular reactions 

 to alkaline salts generally, we shall better understand the mode of 

 action and utility of saline substances in agriculture. Thus, for 

 example, the operation of common salt as a fertilizer is still very 

 obscure. Many skilful husbandmen question its efficacy ; neverthe- 

 less, when moderately employed it seems to do good. In plants 

 growing on the sea-coast soda is found in a great measure com- 

 bined with organic acids, and the chlorine deduced by analysis from 

 their ashes is nowise proportional to the alkali they contain. The 

 whole sodium does not enter the vegetable as a chloride, but very 

 likely as carbonate of soda, and that in virtue of a reaction analogous 

 to the one which calcareous matter has upon ammoniacal salts. 



It is quite certain that chloride of sodium in solution is not affect- 

 ed by carbonate of lime ; but then it was proved by Clouet that if 

 into sand moistened with this same solution powdered chalk be put, 

 and the mixture left in contact with air, an efflorescence of sesqui- 

 carbonate of soda ere long makes its appearance. Thus by the 

 conjoint effect of capillarity and the carbonic acid of the atmosphere, 

 common salt in the conditions above mentioned undergoes by contact 

 with chalk a partial decomposition, of which the result is carbonate 

 of soda, a salt, like carbonate of potash, most favorable to the growth 

 of plants. Accordingly, in furnishing sea-salt to a soil sufficiently 

 calcareous, we really enrich it with carbonate of soda. We more- 

 over perceive that the same salt diffused through land devoid of 

 carbonate of lime may not produce any fertilizing effect. 



OF WATER. 



Water is not only indispensable to the life of plants, but likewi** 

 promotes vegetation after the manner of a manure, on account of 

 the saline or organic substances it generally holds in solution. Rain 

 is the source of the soft waters which flow in rivers, spring from 



