84 MODERN HIGH FARMING. 



We have already seen liow most of the ingredients placed in the 

 soil are absorbed and made available for plant food. It will there- 

 fore be unnecessary to add that none of the manures are assimilated 

 in the form in which they are introduced. 



Thus acid phosphate, sold as soluble, and found upon analysis to 

 answer the required test, simply means that, so long as the sulphuric 

 acid maintains possession of the lime it has taken from the phosphoric 

 acid, the latter has only one base, which its own acidity enables it 

 to dissolve when immersed in the water ; but place these matters in 

 the ground where the carbonates are in excess and the sulphuric 

 acid is at once overpowered and the phosphoric acid set free. 



The latter element, being unable to exist in nature in a free state, 

 or in any other than a tribasic form, unites once more with the lime 

 and iron of the soil, and so at once practically reassumes the same 

 chemical form it originally wore when tipped into the mixers at 

 the factory. 



The question naturally arises, under these circumstances, whether 

 it is of any use continuing the employment of acid, soluble, or super- 

 phosphate, and whether it would not be wiser to at once adopt the 

 direct application of the raw material ? Some chemists having 

 declared that young rootlets are frequently destroyed by the cor- 

 rosive action of the sulphuric acid. ( ?) 



The original idea of mixing the acid with the phosphates in order 

 to render them more easily assimilable, arose from the impossibility 

 of reducing either bones or mineral phosphates to such a high state 

 of division and disintegration, as to make them easy to grapple with 

 and decompose by the chemical elements in the soil. 



The whole theory of Liebig, therefore, was, that what could not 

 be done mechanically, chemical means could easily effect. And the 

 best proof of the complete disintegration or dissociation of the 

 elements in the mixing process, is to be found in the formation of 

 sulphate of lime, and the consequent deprivation of the phosphoric 

 acid of two of its bases ; so that, while it is undeniable that tribasic 

 phosphate is immediately reformed in the soil, we consider it to be 

 reformed in such a conveniently disseminated manner, as to facilitate 



