EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 13 
for eight months. Pfeiffer and Thurmann? found that the compost- 
ing of decaying organic matter and phosphates produced but a 
slight increase in the citrate solubility of phosphate rock and actually 
decreased the solubility of acid phosphate. 
Truog,? however, states that these experiments are open to criti- 
Ycism, since no blanks or checks (P,O; determinations) were run on 
the organic materials mixed or composted with the phosphates. This 
author carried on a number of laboratory experiments to study the 
effect of decomposing organic matter on the solubility of finely 
ground rock phosphate. This solubility, however, was determined 
in nearly every instance in a 0.2 per cent solution of citric acid, 
which can not be considered a proof of, nor necessarily an index to, 
the availability of the phosphatic material. 
In his first experiment Truog made up the following mixtures in 
1-gallon glazed jars, each provided with a hole in the bottom: 
No. 1: 2.7 kilograms sand, 25 grams floats. 
No. 2:2.7 kilograms sand, 25 grams floats, 300 grams grass. 
No. 3:2.7 kilograms sand, 300 grams grass. 
No. 4:2.7 kilograms sand, 26 grams floats, 300 grams manure. 
No. 5:2.7 kilograms sand, 300 grams manure. 
The sand used in this experiment analyzed 97.9 per cent silica; 
the floats consisted of a high-grade finely ground rock phosphate 
containing 34 per cent phosphoric acid (P,O;). The grass was fresh 
fine grass finely chopped, and the manure was fresh cow dung 
without any litter. 
The contents of each jar were thoroughly mixed and an optimum 
amount of water was maintained in the jars for a little over four 
months. Both the water-soluble and citric-soluble phosphoric acid 
present in the mixtures were then determined. The results of these | 
analyses are given in Table V. 
TABLE V.—Parts of phosphoric acid (P20s) per million parts of the extracting 
solution. 
P.O; P.O; 
extracted | extracted 
P.O; from 150 from 150 P.O; 
extracted | grams of grams of | extracted | 
J from jars | material material from 60 | 
ar Treatment. by 3 liters |by 300 cubic|by 300 cubic] grams of 
No. of centimeters| centimeters} materia | 
distilled of 0.2 per | of 0.2 per by 1 per 
water. cent citric | cent citric jcant NaOH 
acid in 24 | acidin8 
hours. days. 
P.p.™m. P.p.m. P.p.™m. P.p.m. _ 
fein@uantaand Moats: so. 2.0.) e eee eel ees. s ee a5 116.0 149.0 7.5 
PPO uArtZ MOAtS ANG STASS.\- 2. - cs. sccce ose se == 88.0 68.5 99.0 11.0 
el ROUMATEZAMGsSTASS sso. 82 ee lee ccewisecieloce so =i=|> 88. 0 26.0 32.0 8.7 
AO vartzetoatsyand manures... 2..2+---------=- 71.0 88. 0 118.0 12.5 
Sa MOUMALGAAM GemVAMUTE 2.2 42/22 )os es cil selec = #12) == 67.0 66.5 57.0 9.3 
| 
ea ISS Pee ee 
1Landw. Vers-Stat., 343 (1896). 
2 Wis. Agr. Expt. Sta., Research Bul. No. 20 (1912). 
