COMPOSITION AND CHARACTERS OF URINE 1129 



the ammonium urate precipitate into a beaker. To the ammonium urate precipitate, 

 suspended in about 100 c.c. water, add 15 c.c. strong sulphuric acid and titrate at once, 

 without cooling, with the potassium permanganate solution. At first every small 

 addition of the permanganate is decolorised before it diffuses through the liquid, but 

 towards the end the decolorisation is slower and the permanganate should be added 

 two drops at a time until a faint pink colour is seen throughout the whole solution. 

 The amount of uric acid can then be calculated, 1 c.c of the permanganate solution being 

 equivalent to -00375 grm. uric acid. 



CHLORIDES. The chlorides of urine are estimated by Volhard's method. The 

 principle of this method consists in precipitating the chlorides by excess of a standard 

 solution of silver nitrate in the presence of nitric acid. The excess of silver is then 

 estimated in an aliquot part of the filtrate with a solution of potassium or ammonium 

 sulphocyanate which has been previously standardised against the silver solution, a 

 ferric salt being used as indicator. 



The following solutions are required : 



(1) Standard silver nitrate solution either or so that 1 c.c. corresponds to -01 grm. 



NaCl. 



(2) Potassium sulphocyanate solution (8 grm. per litre). 



(3) Pure HNO 3 free from chlorides. 



(4) A saturated solution of iron alum. 



The potassium sulphocyanate solution must be standardised against the silver nitrate 

 solution. This is carried out as follows : Place 10 c.c. AgN0 3 solution with a pipette 

 in a beaker, add 5 c.c. pure HNO 3 , 5 c.c. iron alum solution, and 80 c.c. water. Now 

 run in the sulphocyanate solution from a burette until a permanent red tinge is obtained. 

 Note the amount required for the 10 c.c. AgN0 3 solution. 



The method of analysis is carried out as follows : Place 10 c.c. urine in a 100 c.c. 

 measuring flask with a pipette. Then add about 4 c.c. pure nitric acid and 10 or 20 c.c. 

 with a pipette of the standard silver nitrate solution. Now fill up to the mark with 

 distilled water, mix thoroughly, and filter into a dry vessel through a dry paper. Take 

 exactly 50 c.c. of the filtrate with a pipette and titrate with the sulphocyanate solution 

 until a permanent red colour is obtained, iron alum having been added before the titra- 

 tion is commenced. Calculation of results : 



50 c.c. filtrate = S c.c. KCNS 

 .-.100 c.c. = 2$ c.c. 

 Now x c.c. KCNS = 10 c.c. A g N0 3 



oo 10 x 2/Sf . AT ~ 

 .. 2$ c.c. = _ AgNO 3 



This is the excess not utilised to precipitate the chlorides 



.. (20 J = amount of AgNO 3 solution used. 



x ] 



Hence NaCl in grammes per 10 c.c. in the volume passed in twenty -four hours. 



ESTIMATION OF PHOSPHATES. The method depends upon the precipitation 

 of all the phosphates by a standard solution of uranium acetate or uranium nitrate in 

 the presence of sodium acetate and acetic acid as (UrO 2 )HP0 4 . The determination of 

 the end-point, when soluble uranium salt is in solution, is shown by means of potassium 

 ferrocyanide, or by cochineal tincture, which becomes green. 



The following reagents are required : 



(1) Acid sodium acetate solution (100 grm. NaAc, 30 grm. HAc, 1000 c.c. H 2 0). 



(2) Cochineal tincture (5 grm. cochineal extracted for several days with 150 c.c. alcohol 



and 100 c.c. water and then filtered). 



(3) Standard uranium solution (1 c.c. = -005 grm. P 2 5 or 5 mg.>. 



This must be prepared by standardising against a standard phosphate solution. 

 Generally sodium phosphate is employed ; about 12 grm. are weighed out and dissolved 

 in 1000 c.c. water ; 50 c.c. of this solution are evaporated to dryness, incinerated, and 



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