The Phosphates of America. 127 



+ 2(H 3 PO 4 ) + 12H 2 = 3 Ca 2 H 2 (P0 4 )2(H 2 O)4. 



2 insoluble tri- + 2 phosphoric + 12 water =3 crystallized neutral 



calcic phos- acid phosphate, soluble in 



phate neutral citrate of am- 



The advantages offered by the cheap production of such an 

 article as this in commercial form are, of course, too manifest to 

 need any elaborate explanation, but it may nevertheless not be out 

 of place to mention a few of them. 



In the manufacture of superphosphates we have seen that the 

 desired solubility, either in water or in citrate of ammonia, is at- 

 tained at the cost of doubling the bulk of the raw material by the 

 addition of an acid which practically serves no other purpose and 

 has no other value than as a dissolvent. If the original material, 

 therefore, contain sixty per cent, of tricalcic phosphate, the " super ' r 

 can only contain thirty per cent., and this, from the agricultural 

 consumers' standpoint, is certainly an anomaly, and, apart from 

 any question of solubility, must remain so for two reasons : 



1. A ton of sixty-per-cent. phosphate of lime, finely ground but 

 insoluble in water or citrate of ammonia, can be purchased at some 

 central point for, say, $10. 



2. A ton of superphosphate, containing only thirty per cent, 

 phosphate of lime, cannot be purchased at the same spot for less- 

 than $15. 



In the one case, freight is paid upon only forty per cent, of inert 

 material, whereas in the other it is paid upon seventy per cent. 



Apart from the perfectly legitimate profits attached to the 

 manipulation and transformation of a sluggish into an active body, 

 those who at present derive the greatest benefit from the trade in 

 fertilizers are the railroad companies. If it were for no other 

 object than the reduction of freight charges to a minimum limit, it 

 is consequently worth while to consider the advisability of substi- 

 tuting for the old method of manufacture, the one which we shall 

 now attempt to describe. 



The details of superphosphate mixing, and the reactions involved 

 in the process, have been gone over in a sufficiently ample manner 

 to prepare the way for the statement, that the cheapest and best- 

 known method of producing phosphoric acid is by displacing it from 

 its combination with phosphates of lime by means of oil of vitriol. 



The proportion of phosphoric acid contained in the raw material 

 being a matter of only relative importance, the adoption of such a 



