EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 



13 



for eight months. Pf eiffer 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- 

 cism, since no blanks or checks (P2O5 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 (PaOg). 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 (PzOs) per million parts of the extracting 



solution. 









P2O5 



P2O5 











extra<>ted 



extracted 









P2O5 



from 150 



from 150 



P2O5 







extracted 



grams of 



grams of 



extracted 



Jar 

 No. 





from jars 



material 



material 



from 60 



Treatment. 



by 3 liters 



by 300 cubic 



by 300 cubic 



grams of 





of 



centimeters 



centimeters 



materia . 







distilled 



of 0.2 per 



of 0.2 per 



by 1 per 







water. 



cent citric 



acid in 24 



hours. 



cent citric 



acid in 8 



days. 



cant NaOH 







P.v.m. 



P. p.m. 



P. p.m. 



P. p.m. 



1 



Quartz and fl.oats 



1.5 

 88.0 



116.0 

 68.5 



149.0 

 99.0 



7.5 



2 



Quartz, floats, and grass 



11.0 



3 



Quartz and grass 



88.0 



26.0 



32.0 



8.7 



/^ 





71.0 



67.0 



88.0 

 66.5 



118.0 

 57.0 



12.5 



5 





9.3 









iLandw. Vers-Stat., 343 (1896). 



sWis. Agr. Expt. Sta., Research Bui. No. 20 (1912). 



