1178 PHYSIOLOGY 



CREATININE. In Folin's method for the determination of creatinine, which is 

 now universally employed, advantage is taken of the colour reaction given by creatinine 

 (and by no other normal urinary constituent) with picric acid in alkaline solution 

 (Jaffre's reaction), the colour being compared with that of a standard potassium 

 bichromate solution. The reagents employed are decinormal potassium bichromate 

 containing 24'55 grm. per litre ; saturated picric acid solution containing about 12 grm. 

 per litre ; and a 10 per cent, solution of sodium hydrate/ For the comparison of the 

 colours a Duboscq colorimeter is employed. 



Ten cubic centimetres of urine are measured into a 500 c.c. flask; 15 c.c. of picric 

 acid and 5 c.c. of sodium hydrate are then added and the mixture allowed to stand for 

 five minutes. Some of the potassium bichromate solution is placed into one of the 

 cylinders of the colorimeter and its depth accurately adjusted to the 8 mm. mark. 

 At the end of five minutes the contents of the 500 c.c. flask are diluted up to 500 c.c. 

 with water, and some of the mixture placed into the other cylinder of the colorimeter, 

 and the two colours are then compared. The calculation of the results is very simple. 

 If, for example, it is found that it takes 9-5 mm. of the unknown urine picrate solution 

 to equal the 8 mm. of the bichromate, then the 10 c.c. of urine contains 



8*0 



10 X = 8'4 mg. creatinine. 

 9*5 



ESTIMATION OF URIC ACID. The best method for this purpose is a slight modi- 

 fication by Folin of the method devised by Hopkins. 

 For this method the following reagents are required : 



(1) A solution of ammonium sulphate, uranium acetate, and acetic acid, made up as 



follows : 500 grm. ammonium sulphate, 5 grm. uranium acetate, and 60 c.c. 10 per 

 cent, acetic acid are dissolved in 650 c.c. water. The volume of this solution is 

 almost exactly 1000 c.c. 



(2) Ten per cent, ammonium sulphate solution. 



n 



(3) potassium permanganate solution made by dissolving 1-581 grm. pure potassium 



permanganate in one litre of water; 1 c.c. = -00375 grm. uric acid. 



Measure 200 c.c. urine with a pipette into a 500 c.c. flask and add 50 c.c. of the 

 ammonium sulphate and uranium acetate reagent. Mix the solutions and allow to 

 stand for about half an hour so as to let the precipitate settle. This precipitate 

 contains a mucoid substance (and phosphates) which, if not 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 ammo- 

 nium 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 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 



