1262 PHYSIOLOGY 



thus removed, renders the subsequent filtration and washing of the ammonium 

 urate precipitate very slow. Filter off the supernatant liquid through a dry 

 filter into a dry vessel, and measure out 125 c.c. (= 100 c.c. urine) of this with 

 pipettes into a beaker. Add 5 c.c. concentrated ammonia, mix well, and allow 

 to stand covered with paper for twelve to twenty -four hours. 



Carefully decant the supernatant liquid upon a filter, wash the precipitate 

 of ammonium urate on to the filter with 10 per cent, ammonium sulphate, and 

 wash this once or twice with the same reagent to remove the chlorides as 

 completely as possible. 



Remove the filter from the funnel, open it, and with a fine stream of water 

 wash 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 per- 

 manganate 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 grin, 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 : 



71 



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



01 grm. Nad. 



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



(3) Pure HN0 3 free from chlorides. 



(4) A saturated solution of iron alum. 



The potassium sulphocyanate solution must be standardised against the 

 sulphocyanate solution. This is carried out as follows : Place 10 c.c. AgNO 3 

 solution with a pipette in a beaker, add 5 c.c. pure HN0 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. 

 AgNOj 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.o. 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 titration is commenced. Calculation of results : 



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

 .-. 100 c.c. = 28 c.c. 

 Now x c.c. KCNS = 10 c.c. AgN0 3 



10 * 



This is the excess not utilised to precipitate the chlorides 



.. (20 - : - \ = amount of AgNO 3 solution used. 

 x / 



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



