EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 



11 



As early as 1868, Voelcker^ recognized the importance of fine 

 grinding in facilitating the solubility of bones, but considered un- 

 aci'dulated coprolites and apatite practically valueless to crops. 

 Jordon^ found in some greenhouse work (which is discussed else- 

 where in this bulletin) that pots of quartz sand treated with " floats " 

 produced greater yields of peas, barley, and rape than those receiv- 

 ing the same amount of phosphate in somewhat coarser particles. 

 Burlison ^ in a similar experiment with GO-day oats employed Ten- 

 nessee brown-rock phosphate of three different degrees of fineness 

 in a series of pots containing relatively pure sand, to which were 

 added also the other fertilizer elements. The results of this experi- 

 these experiments are given in Table IV. 



Table III. — Relation of size of particles of the availadility 

 acid contained therein, as measured by 60-day 



of the phosphoric 

 oats. 



Pot number. 



Phosphate 

 added. 



Degree of fineness. 



Grain. 



Straw. 



17 



Grams. 

 2.6 

 2.6 

 2.6 

 2.6 

 2.6 

 2.6 



80 to 100 mesh 



Grams. 

 5.9 

 7.0 

 5.8 

 7.7 

 8.7 

 7.2 



Grams. 



6.8 



18 



do 



10 1 



19 



100 to 200 mesh 



11.1 



20 



do 



11 4 



21 



200 mesh and finer 



11.1 



22 



do 



13.2 









Table III shows that there was considerable difference between the 

 average yields of oats treated with the coarser and those receiving 

 applications of the more finely ground phosphate rock. 



While the value of the conventional availability tests is seriously 

 questioned, the solvents employed serve fairly well to determine the 

 effect of fine grinding on the solubility of a given phosphate. In the 

 following experiments two of the most widely used phosphates pro- 

 duced in this country, namely, the pebble phosphate of Florida and 

 the brown-rock phosphate of Tennessee, were employed. 



Samples of these types of rock were ground to three different de- 

 grees of fineness, as follows: (1) Between 60 and 130 mesh, (2) be- 

 tween 130 and 180 mesh, and (3) 180 mesh and finer. The solubility 

 of the three grades of each type was then determined according to 

 the official method of the American Association of Official Agricul- 

 tural Chemists (solubility in ammonium citrate), according to Wag- 

 ner's method (solubility in 2 per cent citric acid), and according to 

 Dyer's method (solubility in 1 per cent citric acid) . In addition to 

 these conventional determinations the solubility of the material in 

 water saturated with carbon dioxide was determined. The results of 

 these experiments are given in Table IV. 



iJour. Royal Agr. Soc. 4, 176-196 (1868). 



SN. Y. Agr. Expt. Sta. (Geneva), Bui. No. 358 (1913). 



■Jour. Agr. Research, 6, pp. 507-508 (1916). 



