On SupcrpJtospliate of Lime. 



211 



as a manure were in any measure dependent on its retaining; its 

 composition and remaining in this highly soluble condition in 

 the soil, we could not expect to see its application productive of 

 any good result on soils which contain even a moderate quantity 

 of lime, much less on those of the chalk and limestone districts. 

 Professor Liebig, v/ho suggested the use of this manure in the 

 first edition of his ' Chemistry of Agriculture/ says, in speaking 

 of this point — In a few seconds the free acids unite with the 

 bases contained in the earth, and a neutral salt is formed in a very 

 fine state of division." In some cases the neutralizing base may 

 be potash or soda, and then an alkaline and highly soluble phos- 

 phate is formed, but the quantity of lime existing in most culti- 

 vated soils would tend to convert the soluble phosphate of lime 

 wholly into neutral phosphate of the same base. 



If the view now taken be correct, the sole advantage of adding 

 sulphuric acid to any substance containing phosphate of lime is 

 to produce a soluble comipound, not for direct use of the plants, 

 but which shall penetrate intimately a large portion of soil, and 

 there reproduce the phosphate in a state of the finest subdivision, 

 and more perfectly distributed throughout the particles of earth 

 than it could be by any mechanical process. 



There are two points to be attended to in relation to this part of 

 our subject. The first is the. suh division (by chemical not mecha- 

 nical means) of the phosphate of lime; the second, the dis- 

 tribution of this substance (also by chemical and not by mechani- 

 cal means) through the soil. Vv'^e will take a simple case for 

 illustration. Suppose that we are desirous of converting a certain 

 quantity of hard mineral phosphate of lime into a state in which 

 it will be readily serviceable to vegetation, and let it be granted 

 that although very finely powdered it is in its natural condition 

 of little use as manure — to this powdered phosphate we add 

 sulphuric acid, which converts, as we have before seen, the inso- 

 luble phosphate into bi-phosphate, the product being the well- 

 known "superphosphate." Supposing further, that we divide this 

 product into two portions — to the one we add lime or chalk, and 

 then incorporate it with the soil, whilst the other is dissolved in 

 water and so applied. In either case the same precipitated 

 phosphate of lime is the ultimate result ; but there is this great 

 difference between the two experiments — that whilst the solution 

 of bi-phosphate of lime distributes itself throughout the soil before 

 it meets with lime to saturate and solidify it, the quantity that has 

 been mixed with lime or chalk previous to use is already saturated 

 and rendered insoluble, and is entirely dependent on mechanical 

 processes for its perfect distribution through the soil. These facts 

 are, I contend, of the highest importance boih to the manufacturer 

 and consumer of superphosphate. Thev are important to the 



p 2 . 



