PHYSIOLOGICAL CHEMISTEY 427 



EXPERIMENT V. Tests for Uric Acid in Urine. Apply Schifs 

 test to urine. The result is positive, but does not necessarily show the 

 presence of uric acid, as other reducing bodies are present in the urine. 

 The murexide test cannot be applied directly to urine, as urine yields a 

 red pigment on heating with nitric acid. In order to apply this test 

 take about 100 c.c. of urine, add ammonia until it is alkaline, and 

 saturate with ammonium chloride. A precipitate of ammonium urate 

 forms. This is filtered off, dissolved in a few c.c. of water, and employed 

 for the murexide test. 



ESTIMATION OF URIC ACID. 



The most rapid and accurate method is that of Hopkins as modified by Folin. 



In this method the mucoid substances and some of the phosphates of urine 

 are first of all precipitated by a strong solution of ammonium sulphate con- 

 taining uranium acetate and acetic acid, and the filtrate is then rendered alkaline 

 with ammonia ; on standing ammonium urate separates out. This is collected 

 on a filter, washed, and suspended in water and titrated with vi/20 potassium 

 permanganate. 



The method is carried out as follows : 



To 300 c.c. urine in a flask 75 c.c. of the uranium ammonium sulphate re- 

 agent is added (500g. ammon. sulph., 5gr. uranium acetate, 60 c.c. 10 per cent, 

 acetic acid, 650 c.c. water), and in five minutes the solution is filtered through 

 a dry thick filter paper into a dry 250 c.c. measuring cylinder, or into a dry 

 beaker. Two portions of the filtrate of 125 c.c. each are transferred to 

 beakers and 5 c.c. concentrated ammonia added to each. The beakers are 

 then set aside for twenty-four hours, at the end of which time the precipitate 

 of ammonium urate will be found on the bottom of the beaker. The clear 

 supernatant fluid is carefully poured through a hardened filter, after which the 

 sediment is shaken with a 10 per cent, solution of ammonium sulphate and care- 

 fully collected on the same filter and washed once or twice with the 10 per cent, 

 ammonium sulphate solution. It is unnecessary to transfer every trace of pre- 

 cipitate to the filter, and the washing with ammonium sulphate solution does not 

 require to be prolonged. The filter is then opened up and the precipitate washed 

 into the beaker in which the original precipitation was made by means of a spray 

 of distilled water from a wash bottle. As a result of this process about 100 c.c. 

 of fluid should have collected in the beaker. Then 15 c.c. H 2 S0 4 (cone.) is 

 added to the fluid, and while still hot from the mixing of acid and water, it is 

 titrated with w/20 potassium permanganate until a faint pink colour remains for 

 five seconds after mixing. The reading obtained, multiplied by 0*00375, gives 

 the grammes of uric acid in 100 c.c. of urine. 1 



Estimation of the Total Purine Bodies. Modified Camerer's Method. 

 Principle. Ammoniacal silver nitrate, in the presence of neutral salts, or, 

 better, of magnesium mixture, combines with all the purine bodies to form an 

 insoluble salt of definite composition (see p. 425). The nitrogen in this can be 

 estimated by Kjeldahl's method, and the result expressed as total purine nitrogen. 

 This result is exceedingly useful in studying the metabolism of purine bodies. If 



1 On account of partial solubility of ammonium urate in water, it is necessary 

 to add 3 mg. uric acid for every 100 c.c. of urine. 



