22 The Phosphates of America. 



bonated water at high pressure), when in a very short time all 

 phosphoric acid will have disappeared from the solution and will 

 be found in the deposit as phosphate of iron and alumina. 



If the chemists alluded to had confined their statements to the 

 fact that phosphates of iron and alumina were not advantageous 

 materials for the manure manufacturer, they would have been per- 

 fectly correct ; but they took on themselves a vast responsibility 

 when they declared them to be useless as fertilizers, for of all 

 questions, that as to the form in which phosphoric acid offers the 

 best all-round advantage to the practical farmer is the most subtle 

 and most delicate. 



If we accept the generally-admitted and rational theory that no 

 element can penetrate into the interior of a plant unless it be in so- 

 lution, it naturally follows that preference will be invariably given 

 to those commercial phosphates which are most readily subject to 

 dissociation ; and this will entirely depend upon two conditions : 



(a) Their own degree of aggregation. 



(b) The nature and composition of the soil in which they are 

 employed. 



The first thing to be obtained is undoubtedly a fineness of 

 pulverization which will so divide the molecules as to render them 

 easily decomposable by the natural action of the elements con- 

 tained in the ground. Here we touch at once the real source of 

 our difficulty, for in the matter of pulverization only partial suc- 

 cess has so far been achieved by any sufficiently cheap mechanical 

 means, and we are not very much further forward now than we 

 were in 1857, when Liebig recognized the difficulty and proposed, 

 in order to solve it, to chemically perform the disintegration by 

 manufacturing superphosphates. 



From the standpoint of disintegration this method of Liebig's 

 has been entirely satisfactory, and has enabled agriculture to rap- 

 idly obtain results from the use of phosphoric acid which would 

 otherwise have been impossible. From a chemical point of view, 

 however, the whole theory fails. We have seen that superphos- 

 phates are only soluble in water so long as the sulphuric acid with 

 which they have been manufactured retains its ascendency, and 

 that when they reach the soil, especially where carbonates are in 

 abundance, the sulphuric acid is atpnce overpowered, and the phos- 

 phoric acid, instead of remaining combined with one molecule of 

 lime and two molecules of water, at once undergoes reversion. To 

 put it plainly, the issue revolves upon a matter of time and of 



