URINE: QUANTITATIVE ANALYSIS. 391 



rate Fusion Method. Place 25 c.c. of urine in a large silver cru- 

 cible and evaporate to a syrup on a water-bath. Add 10 grams 

 of NaOH and 2 grams of KNO 3 to the residue and fuse the mass 

 until all organic matter has disappeared and the fused mixture is 

 clear. Cool the mixture, transfer it to a casserole by means of hot 

 water, acidify the solution slightly with pure nitric acid and evapo- 

 rate to dryness on a water-bath. Moisten the residue with a few 

 drops of dilute nitric acid, dissolve it in hot water and transfer to 

 a beaker. Now add an equal volume of molybdic solution 1 and 

 keep the mixture at 40 C. for twenty-four hours. Filter off the 

 precipitate, wash it with dilute molybdic solution and dissolve it in 

 dilute ammonia. Add dilute hydrochloric acid to the solution, being 

 careful to leave the solution distinctly ammoniacal. Magnesia mix- 

 ture 2 (10-15 c.c.) should now be added and after stirring thorough- 

 ly and making strongly ammoniacal with concentrated ammonia 

 the solution should be allowed to stand in a cool place for twenty- 

 four hours. Filter off the precipitate, wash it free from chlorine by 

 means of dilute ammonia (1:5), dry, incinerate and weigh, as 

 magnesium pyrophosphate, Mg 2 P 2 O 7 , in the usual manner. 



In this method the phosphoric acid of the urine is precipitated as 

 ammonium magnesium phosphate and in the process of incinera- 

 tion this body is transformed into magnesium pyrophosphate. 



Calculation. The quantity of phosphorus, expressed in terms 

 of P 2 O 5 , in the volume of urine taken may be determined by means 

 of the following proportion : 



Mol. wt. Wt. of Mol. wt. 



M VP 2 O 7 : Mg 2 P 2 O 7 : :P 2 Os : x (wt. of P 2 O 5 in grams), 

 ppt. 



If y represents the weight of the Mg 2 P 2 O 7 precipitate and we 

 make the proper substitutions we have the following proportion : 



221. i : y :: 140.9: x (wt. of P 2 O 5 , in grams, in the quantity of 



urine used. ) 



To express the result in percentage of P 2 O 5 simply divide the 

 value of x, as just determined, by the quantity of urine used. 



1 Directions for the preparation of the solution are given on p. 57. 



- Directions for the preparation of magnesia mixture may be found on p. 295. 



