URINE ! QUANTITATIVE ANALYSIS. 4O/ 



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

 tent by means of the Kjeldahl method (see p. 381). 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. 



2. Salkowski's Method. Place 400-600 c.c. of protein-free 

 urine in a beaker. Introduce into another beaker 30-50 c.c. of an 

 ammoniacal silver solution 1 with 30-50 c.c. of magnesia mixture, 2 

 add some ammonium hydroxide and if necessary some ammonium 

 chloride to clear the solution. Now add this solution to the urine, 

 stirring continually with a glass rod, and allow the mixture to stand 

 for one-half hour. Collect the precipitate on a filter paper, wash 

 it with dilute ammonium hydroxide and finally wash it back into 

 the original beaker. Suspend the precipitate in 600-800 c.c. of 

 water, add a few drops of hydrochloric acid and decompose it by 

 means of hydrogen sulphide. Now heat the solution to boiling, fil- 

 ter while hot and evaporate the filtrate to dryness on a water-bath. 

 Extract the residue with 20-30 c.c. of hot 3 per cent sulphuric 

 acid and allow the extract to stand twenty-four hours. Filter off 

 the uric acid, wash it, make the filtrate ammoniacal and precipitate 

 the purine bases again with silver nitrate. Collect this precipitate 

 on a small-sized chlorine-free filter paper, wash, dry and incinerate 

 it in the usual manner. Now dissolve the ash in nitric acid and 

 titrate with ammonium thiocyanate according to the Volhard- 

 Arnold method (see p. 396). Calculate the content of purine bases 

 in the urine examined, bearing in mind that in an equal mixture of 

 the silver salts of the purine bases, such as we have here, one part of 

 silver corresponds to 0.277 gram of nitrogen or to 0.7381 gram 

 of the bases. 



XX. Allantom. 



Paduschka-Underhill-Kleiner Method. To 50-100 c.c. of 

 urine in a beaker add basic lead acetate until no more precipitate 

 forms. Filter and pass hydrogen sulphide gas through an aliquot 

 portion of the filtrate to remove the excess of lead. 3 Filter again, 

 drive off the hydrogen sulphide by heat and treat an aliquot por- 



1 Prepared by dissolving 26 grams of silver nitrate in about 500 c.c. of water, 

 adding enough ammonium hydroxide to redissolve the precipitate which forms 

 upon the first addition of the ammonia and making the balance of the mixture 

 up to i liter with water. 



2 Directions for preparation may be found on page 295. 



3 In the original method of Paduschka sodium sulphate is used for this 

 purpose. 



