ELEMENTARY CHEMICAL PHYSIOLOGY 263 



CHAPTER XVI 



URINE (Continued) 



Inorganic Constituents of Urine. Deposits 



Chlorides. The amount of chloride excreted varies largely with 

 the amount present in the diet. Variation also takes place in 

 certain pathological conditions. 



EXPERIMENT I. Add to urine a few drops of nitric acid and then 

 silver nitrate solution. A white precipitate of silver chloride forms 

 which is soluble in ammonia. The nitric acid prevents the pre- 

 cipitation of other silver salts such as phosphate. 



Estimation of Chloride. There are two methods which are 

 commonly employed, Mohr's and Volhard's. The latter is the more 

 accurate of the two, but the former, which gives excellent results 

 although slightly too high because other substances like purines 

 combine with the silver before chromic acid does, is the more rapid. 



Mohr's Method.Take 10 c.c. of the urine, dilute with six or 

 seven times its volume of water, add 5 drops of a cold saturated 

 solution of potassium chr ornate. Then run in from a burette 

 standard silver nitrate solution (1 c.c. = 0-01 grm. NaCl), stirring 

 constantly until a permanent faint red colour of silver chromate 

 appears. 



c.c. AgN0 3 sol. usedxO-01 = grms. NaCl in 10 c.c. 

 Sometimes a correction is used on account of the too high value 

 referred to, viz., the deduction of 1 c.c. from the actual number of 

 c.c. AgN0 3 used in the titration. (See p. 288.) 



Phosphates. These are found in the urine as : 



(i) Earthy phosphates, i.e. combined with calcium and magnesium. 

 (a) Render the urine alkaline by means of caustic soda. Earthy 

 phosphates are precipitated. (6) Render alkaline with ammonia, 

 allow to stand, then examine by means of microscope the precipitate 

 of triple phosphate (feathery phosphates). 



(ii) Alkaline phosphates, i.e. combined with sodium and potassium. 

 Precipitate the earthy phosphates with NaOH, filter off the pre- 

 cipitate, acidify filtrate with acetic acid, then add uranium acetate 

 solution and warm. A precipitate of uranium phosphate forms. 



EXPERIMENT II. Boil some solution of ammonium molybdate in 

 nitric acid in a test tube and add drop by drop boiling urine acidified 

 with nitric acid. A yellow precipitate indicates the presence of 

 phosphate. 



Estimation of Phosphates. Place 25 to 50 c.c. urine in a porce- 

 lain basin with 5 c.c. acid sodium acetate solution 1 and heat it until 



1 Acid sodium acetate solution ; 100 grms. sodium acetate, dissolved in 

 water, 100 c.c. glacial acetic acid made up to 1,000 c.c. 



