514 PHYSIOLOGICAL CHEMISTRY 



oxide and the subsequent decomposition of this precipitate by means 

 of sodium sulphide. The uric acid is then precipitated by means of 

 hydrochloric acid and the purine bases are separated from the nitrate 

 in the form of their copper or silver compounds. The nitrogen content 

 of the precipitates of uric acid and purine bases is then determined 

 by means of the Kjeldahl method (see page 483) and the correspond- 

 ing values for uric acid and purine bases calculated. 



Procedure. To 400 c.c. of albumin-free urine 1 in a liter flask 2 , add 24 

 grams of sodium acetate, 40 c.c. of a solution of sodium bisulphite 3 and heat 

 the mixture to boiling. Add 40-80 c.c. 4 of a 10 per cent solution of copper sul- 

 phate 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 precipi- 

 tate of copper oxide by the addition of 30 c.c. of sodium sulphide solution. 6 

 After decomposition is complete, the mixture should be acidified with t acetic 

 acid and heated to boiling until the separating 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. Permit this 

 residue to stand about two hours to allow for the separation 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 483), and calculate the uric acid equivalent. 6 



Render the filtrate from the uric acid crystals alkaline with sodium hydroxide, 

 add acetic acid until faintly acid and heat to 7oC. Now add i c.c. of a 10 per 

 cent solution of acetic acid and 10 c.c. of a suspension of manganese dioxide 7 

 to oxidize the traces of uric acid which remain in the solution. Agitate the mix- 

 ture for one minute, add 10 c.c. of the sodium bisulphite solution 8 and 5 c.c. 

 of a 10 per cent solution of copper sulphate and heat the mixture to boiling for 



1 If albumin is present, the urine should be heated to boiling, acidified with acetic acid, 

 and filtered. 



2 The total volume of urine for the 24 hours should be sufficiently diluted with water to 

 make the total volume of the solution 1600-2000 c.c. 



3 A solution containing 50 grams of Kahlbaum's commercial sodium bisulphite in 100 

 c.c. of water. 



4 The exact amount depending upon the content of the purine bases. 



5 This is made by^saturating a i per cent solution of sodium hydroxide with hydrogen 

 sulphide gas and adding an equal volume of i per cent sodium hydroxide. 



Ordinarily the addition of 30 c.c. of this solution is sufficient, but the presence of an 

 excess of sulphide should be proven by adding a drop of lead acetate to a drop of the solution. 

 Under these conditions a dark brown color will show the presence of an excess of sodium 

 sulphide. 



6 This may be done by multiplying the nitrogen value by three and adding 3^ mg. 

 to the product as a correction for the uric acid remaining in solution in the 75 c.c. 



7 Made by heating a 0.5 per cent solution of potassium permanganate with a little alco- 

 hol until it is decolorized. 



8 To dissolve the excess of manganese dioxide. 



