12 BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 
TaBLe IV.—Jnjfluence of jine grinding on the solubility of Florida and Tennessee 
phosphates in certain conventional solvents. 
[Analyses by R. F. Gardiner and J. A. Cullen.] 
| 
Percentage of total P.O :| Amount 
soluble according to— _— dissolved | 
Type of rock. Leste of fineness. P20. 
i | 
Official |Wagner’s| Dyer’s | ra 
method. | method. method.! CO 
j 
Per cent. |Per cent. Ee cent.|Per cent.|P.P. M. 
Florida pebble. ...-...-...- Between 60 and 130 mesh...} 35.53 2.76 1.54] 2.55] 2.0 
IDO Sao be ee Oe es Between 130 and 180 mesh... 36. 27 4.66 16.10 | 2.59 3.0 
1B Ye eae ia Sele a SON Bee 180 mesh and finer...._..... 37.03 5.54 18. 66 | Pay | 4.0 
Tennessee brown rock...... Between 60 and 130 mesh...) 31.25 - 83 8.16 | 2.51 2.0 
APQM SST eet Ae es Between 130 and 180 mesh. -| 29.96 2.34 8.85 | 2.62 4.9 
3.80 ivé eT! 4.5 
DOS ah heey Se ee 180 mesh and finer........_- | 26.80 
1 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 fioats 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 Holdefieiss* 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 
1Ala. Agr. Expt. Sta.. Bul. No. 48, pp. 1-10 (1893). 
2Pa. Agr. Expt. Sta.. Ann. Rept. 1907-8, p. 175. 
* Heiden, Dungerlebre, 2, 509. 
