PHOSPHORIC ACID SOLUBLE IN AMMONIUM CITRATE III 



alkalinity of the solvent on the amount of phosphoric acid dis- 

 solved. The materials subjected to experiment represented a wide 

 range of substances used as, or entering into the composition of, 

 phosphatic fertilizers such as bone meal, steamed bone, orchilla 

 guano, navassa rock, navassa superphosphate, Florida soft rock, 

 precipitated calcium phosphate, Pamunky phosphate, calcined 

 redonda, South Carolina rock, apatite, grand connetable, acid na- 

 vassa, South Carolina phosphate, dissolved bone-black, and cotton- 

 seed meal. 



The time of digestion extended from half an hour to 10 hours, 

 and in general the quantity of phosphoric acid dissolved by the 

 ammonium citrate solution increased as the time of digestion was 

 prolonged. 



The digestions were made at temperatures ranging from 30* 

 to 85. In general, the quantity of phosphoric acid dissolved in- 

 creased with the temperature. 



The quantity of sample used in its relations to the volume of 

 the solvent was also studied. The percentage of the total acid 

 dissolved increases very rapidly as the weight of the sample 

 diminishes. 



The addition of citric acid to the neutral ammonium citrate 

 increases its solvent power. On the other hand, the addition of 

 ammonia to the neutral solution of ammonium citrate diminishes 

 its solvent power. 



The finer the state of subdivision of the sample the more effi- 

 ciently the solvent acts. 



An examination of the original paper of Fresenius, Neubauer, 

 and Luck, on whose researches the citrate method is based, shows 

 that the temperature conditions are not carefully controlled. 82 An 

 attempt has been made to summarize in the above conclusions, 

 work made under well defined conditions which illustrate the 

 various points under consideration. While each authority of value 

 upon the subject is represented, no attempt has been made to dis- 

 cuss all the work done by any of them. One element that seems to 

 have been generally overlooked in discussing the problem is that 

 nearly all results have been obtained from a one-half hour treat- 

 82 Zeitschrift fur analytische Chemie, 1871, 10 : 133. 



