PHOSPHATES 



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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 c.c. 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 filtrate add a solution of magnesium sulphate. This precipitates 

 the sodium and potassium phosphates as a triple phosphate of magnesium, 

 which is insoluble. Tests 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 



FIG. 309. Doremus' Ureometer. 



uranium acetate; a bright yellow precipitate of uranium ammonium phosphate 

 is formed. These two reactions are used as the basis for a quantitative de- 

 termination of phosphorus. 



10. The Preparation of Urea. Take zooc.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 filtrate to dryness, take up in warm 95 per cent alcohol, and refilter. Crys- 

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



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 

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