URIC ACID 



451 



phates split off from the organic radicle and may be precipitated by the 

 addition of barium chloride in hot solution. 



9. Phosphates. The phosphates of urine consist of the earthy and 

 alkaline salts, the latter predominating. Take a 50 cc. sample of urine, 

 add strong ammonia, and heat. The phosphates of calcium and magnesium 

 separate out, as they are insoluble in alkaline solution. Filter. 



To the nitrate add a solution of magnesium sulphate. This precipitates 

 the sodium and potassium phosphates as a triple phosphate of magnesium 

 which is insoluble. Test for phosphates in general are: 



Add nitric acid to a sample of urine, warm gently, then add a few drops 

 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 quantitative determination of phosphorus. 



10. The Preparation of Urea. Take 100 cc. of normal 

 urine, evaporate 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. 



Evaporate a large sample, 200 

 cc., of urine to a syrupy mass, add nitric 

 acid. Crystals of urea nitrate are formed. 

 Wash the crystals in dilute nitric acid, then dis- 

 solve in water. The urea is set free by adding bar- 

 ium carbonate until the carbon dioxide ceases to 

 come off. Filter, evaporate over a water bath to dry- 

 ness, and dissolve the urea in 95 per cent, alcohol ; de- 

 cant, and recrystallize by evaporating off the alcohol. 



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 cc. of urine to 

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

 cooling, crystals of uric acid are formed. Decant the supernatant liquid and 

 wash the crystals with a few cubic centimeters of 10 per cent, hydrochloric 

 acid. Dissolve the crystals and test. 



FIG. 309. Doremus' 

 Ureometer. 



