112 ACTION OF SALTS. 



chemical possibility, but of a high degree of probability, that 

 the carbon, under the influence of growing plants, may unite 

 with oxygen or hydrogen, that is, with the elements of 

 water, and form thus food for plants. Hence, on such soil, 

 the mere application of salts, or of mineral manures, has 

 produced, yea, and does produce, marked and wonderful 

 effects. This would be the effect of salts, applied to soil 

 produced by the decomposition of slate ; even gneiss soil, 

 which occurs occasionally in extensive patches, would be 

 benefited, but much less by such application. But such soil 

 forms an exception, both to the general law which has been 

 stated, of the uniformity of mineral composition, and to the 

 necessity of applying salts and geine in conjunction. These 

 remarks may explain a seemingly possible anomaly to the 

 principle, that the base of all salts acts in one uniform man- 

 ner upon geine, and that peculiarities of action depend on 

 the acid of the salt. The effects of the first part of this 

 proposition (145), have been explained; the effect of the 

 second, is now to be considered. 



156. Perhaps no principle in agriculture is better estab- 

 lished than that an excess of any salt in the usual accepta- 

 tion of that term, is a cause of barrenness. Yet it is quite 

 as well established that the quantity of diflferent salts admits 

 of some latitude, and that some salts do produce better 

 results than others. Referring to the acid constituents of 

 these salts, it will be found that some acids are organic. 

 They consist of hydrogen, carbon, oxygen, all which, under 

 the influence of the living plant, may be dissociated, and 

 their elements form geine. Other acids consist of oxygen 

 and nitrogen, essential constituents of plants ; others consist 

 of chlorine ; others of sulphur and oxygen, and others of 

 carbon and oxygen. In other words, the acids are composed 

 of elements which form food for plants, or of elements 



