54 METHODS FOR THE ANALYSIS OF URINE 



of a 10 per cent solution of copper sulphate and maintain the 

 temperature of the mixture at the boiling-point for at least three 

 minutes. Filter off the flocculent precipitate, wash it with hot 

 water until the wash water is colorless, and return the washed 

 precipitate to the flask by puncturing the tip of the filter paper 

 and washing the precipitate through by means of hot water. 

 Add water until the volume in the flask is approximately 200 c.c., 

 heat the mixture to boiling and decompose the precipitate of 

 copper oxide by the addition of 30 c.c. of sodium sulphide solu- 

 tion. After decomposition is complete, the mixture should be 

 acidified with acetic acid and heated to boiling until the separat- 

 ing sulphur collects in a mass. Filter the hot fluid by means 

 of a filter-pump, wash with hot water, add 10 c.c. of 10 per cent 

 hydrochloric acid and evaporate the filtrate in a porcelain dish 

 until the total volume has been reduced to about 10 c.c. Per- 

 mit this residue to stand about two hours to allow for the sepa- 

 ration of the uric acid, leaving the purine bases in solution. 

 Filter off the precipitate of uric acid, using a small filter paper, 

 and wash the uric acid, with water made acid with sulphuric 

 acid, until the total volume of the original filtrate and the wash 

 water aggregates 75 c.c. Determine the nitrogen content of the 

 precipitate by means of the Kjeldahl method (see page 33), and 

 calculate the uric acid equivalent. 



Render the filtrate from the uric acid crystals alkaline with 

 sodium hydroxide, add acetic acid until faintly acid and heat to 

 70 C. Now add 1 c.c. of a 10 per cent solution of acetic acid 

 and 10 c.c. of a suspension of manganese dioxide to oxidize the 

 traces of uric acid which remain in the solution. Agitate the 

 mixture for one minute, add 10 c.c. of the sodium bisulphite solu- 

 tion and 5 c.c. of a 10 per cent solution of copper sulphate and heat 

 the mixture to boiling for three minutes. Filter off the pre- 

 cipitate, wash it with hot water, and determine its nitrogen con- 

 tent by means of the Kjeldahl method (see page 33). Inasmuch 

 as the composition and proportion of the purine bases present in 

 urine is variable, no factor can be applied. The result as regards 

 these bases must therefore be expressed in terms of nitrogen. 



Benedict and Saiki report cases in which the total purine 

 nitrogen by this method was less than the uric-acid nitrogen as 

 determined by the Folin-Shaffer method. The inaccuracy was 

 found to lie in the Kruger and Schmidt method. To obviate 



