COMPOSITION AND CHARACTERS OF URINE 1261 



into a flask or beaker and diluted with five times its volume of water. Four or 

 five drops of phenolphthalein are then added and decinormal sodium hydrate 

 is run in until there is a slight permanent pink colour. The amount of alkaline 

 solution necessary to produce this colour is a measure of the acidity of the urine. 

 Ten cubic centimetres of formalin, diluted with three volumes of water and pre- 

 viously neutralised to phenolphthalein with decinormal alkali, are then added. 

 The colour disappears owing to the setting free of the acid radicals previously 

 combined with ammonia. Decinormal alkali is then run into the mixture until 

 a permanent pink colour is again obtained. The number of cubic centimetres 

 of the decinormal alkali required in this second case corresponds to the amount of 

 decinormal ammonia previously present in the 25 c.c. of urine. 



This method gives somewhat higher figures than the method of Folin just 

 described, owing to the fact that the small traces of amino-acids, which may be 

 present in the urine, react to formalin in a very similar way. The difference 

 does not exceed 10 per cent., so that the method is amply delicate for clinical 

 purposes. 



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 (Jaffe'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 



8-1 



10 x = 8-4 mg. creatinine. 

 9-5 



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

 modification 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. 



(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 allow the precipitate to settle. 

 This precipitate contains a niucoid substance (and phosphates) which, if not 



