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- 
acidulated coprolites and apatite practically valueless to crops. 
- Jordon? found in some greenhouse work (which is discussed else- 
wgrhere 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 60-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 LV. 
TaBLE III.—Relation of size of particles of the availability of the phosphoric 
acid contained therein, as measured by 60-day oats. 
| Phosphate | * 
Pot number. Added! Degree of fineness. Grain. Straw. 
Grams. Grams. Grams. 
11 (i Bee ea 2AGa|PSOibO OU MeSH s 2 nn aeRO Cte oe eRe ee es 5.9 | 6.8 
ose Se So AR er eee DIG Sone OnE a SR eee EE a ee oe TEA] 10.1 
Tb Ay Pe eee eee 250" 0060-200 mesh? <= 2a sank SS eee eee 5.8 hie 
7. Ue a Seem ae eee JAG Sse GOes ke hs See Cee. Ce ea is) ea es 7.7 11.4 
Ud ba 3 et ee oe 2.6 | DMonmeshiand Hersey sss aeons wee eee 8.7 Tit 
Fad Et Na ne Pe Pae IAW KGB Se Oe ees ee es = eS ee eee 2 Re 7.2 13ED 
Table IIT 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 (8) 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. 
1 Jour. Royal Agr. Soc.. 4, 176-196 (1868). 
2N. Y. Agr. Expt. Sta. (Geneva), Bul. No. 358 (1918). 
2 Jour. Agr. Research, 6, pp: 507-508 (1916). 
