The Phosphates of America. 23 



money. The farmer buys a ton of raw phosphates, ground as finely 

 as possible and containing, let us say, twenty-five per cent, of phos- 

 phoric acid, for $10. If his land be tolerably acid he will get a 

 rapid return, but if it be not, the phosphate will not decompose, and 

 he will have to wait perhaps several years before obtaining any ap- 

 preciable results for his outlay. On the other hand, he buys a 

 ton of superphosphates, containing only fourteen per cent, of phos- 

 phoric acid, for $20, and applying it to a phosphate-barren soil, 

 produces the desired results on his very next crop. Hence it is 

 apparent that the phosphoric acid of the latter is more readily as- 

 similable than that of the former case ; and this assimilability can 

 only be due to its absolute state of division, which enables the 

 phosphate to come into contact with the acid sap of a greater num- 

 ber of root hairs and thus to be dissolved and absorbed by the 

 plant. We therefore repeat, that to define with scientific accuracy 

 the exact merit or intrinsic value of any specific phosphate is a 

 matter of very serious difficulty ; since besides that of its own phys- 

 ical condition, so much depends upon the nature and composition 

 of the soil in which it is to be employed. 



Dr. Charles Graham, of University College, London, was one of 

 the first to realize the facts we have noted, and writing upon the sub- 

 ject some ten years ago, said that " the vitriolating process, whereby 

 soluble phosphate is formed, was of value where nothing but bones 

 was employed, since it gave agriculture a convenient means of 

 distributing over the land an easily soluble substance in the place 

 of the pieces of bone previously used. With coprolites the same 

 thing was supposed to hold, and as years rolled on acid was more 

 and more used in the preparation of phosphatic materials, until at 

 last these have become rather vitriol -carriers to the profit of the 

 manure manufacturer than to the benefit of agriculture. Analyti- 

 cal chemists attached so high a value to the soluble phosphates 

 that the factor 30 became with many the multiplier in calculating 

 the commercial value from the centesimal composition of the 

 superphosphates. Some, indeed, went beyond this ; and in time 

 analytical chemists came to think of soluble phosphates as the only 

 test of vitriolated phosphate minerals the insoluble being regarded 

 as of little or no use." 



The same subject, received much attention at the International 

 Congress of the Directors of Agricultural Experimental Stations, 

 held in Paris in June, 1881, and the result was a general approval 

 of the efficacy of the undissolved forms. 



