428 



EXCRETION 



of 10 per cent, ammonium molybdate; a yellow precipitate of ammonium 

 phospho-molybdate is formed. Or, add acetic acid, then a few drops of 

 uranium acetate; a bright yellow precipitate of uranium ammonium phos- 

 phate is formed. These two reactions are used as the basis for a quan- 

 titative determination of phosphorus. 



10. The Preparation of Urea. Take 100 c.c. of normal urine, evap- 

 orate to one-half its quantity, and precipitate the phosphates and sulphates 

 by adding a mixed solution of barium hydrate and nitrate. Filter, evaporate 

 the nitrate to dryness, take up in warm 95 per cent, alcohol, and*refilter. 

 Crystals of urea separate out when the alcohol is evaporated off. 



FIG. 309. Doremus' Ureometer. 



Evaporate a large sample, 200 c.c., of urine to a syrupy mass, add nitric 

 acid. Crystals of urea nitrate are formed. Wash the crystals in dilute nitric 

 acid, then dissolve in water. The urea is set free by adding barium carbonate 

 until the carbon dioxide ceases to come off. Filter, evaporate over a water 

 bath to dryness, and dissolve the urea in 95 per cent, alcohol; decant, and 

 recrystallize by evaporating off the alcohol. (ij* 



11. Urea Determination by Doremus' Ureometer. Fill the ureom- 

 eter with hypobromite of sodium solution. Take a sample of urine in 

 the pipet which accompanies the instrument, drawing it exactly to the 

 mark. Insert the pipet past the bend of the ureometer and slowly and 

 carefully empty the urine so as not to lose any of the liberated nitrogen. 

 The instrument is graduated to read off the percentage of urea directly. 



12. Uric Acid. Concentrate over a water bath 500 c.c. of urine to 

 100 c.c. and boil with 10 c.c. or more of strong hydrochloric acid. Upon 



