12 



BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 



Table IV. — Influence of fine grinding on the solubility of Florida and Tennessee 

 phosphates in certain conventional solvents. 



[Analyses by R. F. Gardiner 



and J. 



A. Cullen.] 









Degree of fineness. 



Total 

 PsOs. 



Percentage of total P2O . 

 soluble according to — 



Amount 

 dissolved 

 by water 



Type of rock. 



Official 

 method. 



Wagner's Dyer's 

 method, method. 1 



satu- 

 rated 

 with 

 CO2. 



Florida pebble 



Between 60 and 130 mesh . . . 

 Between 130 and 180 mesh . . 

 180 mesh and finer 



Percent. 

 35.53 

 36.27 

 37.03 

 31.25 

 29.96 

 26.80 



Percent. 

 2.76 

 4.66 

 5.54 

 .83 

 2.34 

 3.80 



Percent. 

 11.54 

 16.10 

 18.66 

 8.16 

 8.85 

 17.60 



Percent. 

 2.55 

 2.59 

 2.57 

 2.51 

 2.62 

 3.11 



P.P.M. 

 2.0 



Do 



3.0 



Do 



4.0 



Tennessee brown rock 



Do 



Between 60 and 130 mesh . . . 

 Between 130 and 180 mesh. . 

 isn mpsh and finer . . . 



2.0 



4.0 



Do 



4.5 









^ The solubility determinations according to Dyer's method were made on new samples. 



Table IV shows that in nearly every instance the finest ground 

 material yielded considerably more phosphoric acid to the solvents 

 employed than the coarser material. 



Several concerns now producing ground phosphate rock claim that 

 their product is ground so that 80 per cent will pass a sieve of 200 

 meshes to the linear inch. While some tests run in this laboratory 

 seem to make it doubtful if a uniform product of this degree of fine- 

 ness can be placed on the market at present prices, the material 

 should at least be ground so that 90 per cent will pass a 100-mesh 

 sieve. Such rock will contain a large percentage of very much finer 

 material. 



EFFECT OF ORGANIC FERMENTATION. 



It is generally believed by those who favor the use of raw rock 

 phosphate as a fertilizer that the action of decaying organic matter 

 increases the availability or effectiveness of the phosphate in the 

 soil. While actual field experiments lend support to this conclusion, 

 efforts to prove this point in the laboratory have not been altogether 

 satisfactory. 



Lupton ^ mixed floats with cottonseed meal and allowed the mix- 

 ture to ferment. Citrate-soluble phosphoric acid was determined 

 at the beginning and from time to time during the three months of 

 the experiment. The results were inconclusive. McDowell ^ allowed 

 a mixture of floats and manure to ferment in a barrel for 13 months 

 and compared the water-soluble and citrate-soluble phosphoric acid 

 present at the beginning and at the end of that period. No increase 

 in the amount of citrate-soluble phosphoric acid was noted. In a 

 similar experiment Holdefleiss^ found but little increase in the 

 citrate solubility of phosphate rock which had been mixed with 

 various organic materials and inorganic salts and allowed to ferment 



lAla. Agr. Expt. Sta., Bui. No. 48, pp. 1-10 (1893). 

 2 Pa. Agr. Expt. Sta., Ann. Kept. 1907-8, p. 175. 

 ■ Heiden, Dungerlehre, 2, 509. 



