MODIFICATION OF JORGENSEN 8 



Using these corrections, the estimation of phosphoric acid be- 

 comes one of the most accurate of known analytical methods. 

 CORRECTION FOR PHOSPHORIC ACID DETERMINATION. 



Found, Lost. Found, Lost. 



Mg 2 P 2 O 7 milligrams Mg 2 P 8 O 7 milligrams 



in grams. Mg 2 P 2 O 7 . in grams. Mg 2 P 2 O 7 . 



o. 10 0.6 0.24 4.0 



o. 12 0.8 0.25 4.2 



0.14 1.2 0.26 4.6 



0.15 1-4 0.27 5.0 



0.16 1.6 0.28 5.5 



0.17 .4 0.29 6.T 



0.18 2.6 0.30 6.8 



0.19 3- 2 0.31 7.6 



0.20 3.5 0.32 8.6 



0.21 .36 0.33 9.6 



0.22 3.8 0-34 10.6 



85. Modification of Jorgensen. Jorgensen has submitted to a 

 renewed detailed study the standard methods of precipitation 

 of phosphoric acid as magnesium ammonium phosphate for the 

 purpose of determining whether any errors have crept into the 

 usual methods. 50 He used as the basis of his test for accuracy bv 

 preference a preparation of sodium ammonium phosphate in a 

 crystalline state, NaNH 4 HPO 4 H 2 O. He selected this salt as 

 the one best suited for testing the accuracy of the method and 

 the purity of reagent because it can be prepared easily in a state 

 of purity by recrystallization out of ammoniated water. The crys- 

 tals are subsequently exposed in the air until dry. It is also a 

 salt which has little tendency to efflorescence, and its purity can 

 be determined without reference to its phosphoric acid content 

 by determining the loss of weight upon ignition and by deter- 

 mining its content of ammonia. If these two determinations show 

 a pure salt the content of phosphoric acid may be left out of con- 

 sideration, since this is the material upon which methods and solu- 

 tions are to be tried. 



Aside from the variation in the standard of comparison, there 

 is little new in Jorgensen's work. He makes a few changes in 

 the composition of preparations which he uses, but the change in 

 no case is great enough to introduce any appreciable difference in 

 the manipulation. 



56 Zeitschrift fiir analytische Chemie, 1906, 45 : 273. 



