ESTIMATION OF PURINE BASES. 715 



Quantitative Estimation of Purine Bases according to SALKOWSKi. 1 

 400-600 cc. of the urine free from protein are first precipitated by mag- 

 nesia mixture, and then by a 3-per cent silver-nitrate solution as described 

 on page 710. The thoroughly washed silver precipitate is decomposed 

 by sulphuretted hydrogen after being suspended in 600-800 cc. of water 

 with the addition of a few drops of hydrochloric acid. It is heated to 

 boiling and filtered hot, and finally evaporated to dryness on the water- 

 bath. The residue is extracted with 20-30 cc. of hot 3-per cent sul- 

 phuric acid and allowed to stand twenty-four hours; the uric acid is 

 filtered off, washed, the filtrate made ammoniacal, and the purine bodies 

 again precipitated by silver nitrate, the precipitate collected on a small 

 chlorine-free filter, washed thoroughly, dried, carefully incinerated, 

 the ash dissolved in nitric acid, and titrated with ammonium sulpho- 

 cyanide according to VOLHARD'S method. The ammonium-sulphocyanide 

 solution should contain 1.2-1.4 grams per liter, and its strength should 

 be determined by a silver-nitrate solution: 1 part silver corresponds 

 to 0.277 gram nitrogen X)f purine bases, or to 0.7381 gram purine bases. 

 By this method the uric-acid and purine bases can be simultaneously 

 determined in the same portion of urine. 2 



MALFATTI 3 determines the nitrogen of the purine bases in the hydrochloric- 

 acid filtrate from the separated uric acid. This filtrate is evaporated with mag- 

 nesia until all the ammonia has been expelled and the residue used for the KJEL- 

 DAHL determination. 



The nitrogen of the purine bases is also determined as the difference between 

 the uric-acid nitrogen and the total nitrogen of the purine bodies of the silver 

 precipitate (CAMERER, ARNSTEiN 4 ). Certain objections have been raised 

 against this method but they can be overcome by using the modified method 

 as suggested by KENNAWAY. 5 



According to the method of KRUGER and SCHMID 6 the uric acid and the 

 purine bases are precipitated as a cuprous compound by copper-sulphate solu- 

 tion and sodium bisulphite. The precipitate is decomposed in sufficient water 

 by sodium sulphide, and the uric acid precipitated from the concentrated filtrate 

 with hydrochloric acid, and the purine bases again precipitated from this filtrate 

 as cuprous or silver compounds. Finally, the nitrogen in the uric-acid part and 

 the part containing the mixture of purine bases is estimated. 



Oxaluric Acid, C 3 H 4 N 2 O4 = (CON 2 H3).CO.COOH. This acid, whose relation 

 to uric acid and urea has been spoken of above, does not always occur in the 

 urine, and then only in traces as the ammonium salt. This salt is not directly 

 precipitated by CaCl 2 and NH 3 , but on boiling it is decomposed into urea and 

 oxalate. In preparing oxaluric acid from urine the latter is filtered through 

 animal charcoal. The oxalurate retained by the charcoal may be obtained by 

 boiling with alcohol. 



1 Pfliiger's Arch., 69. 



2 In regard to the details we refer the reader to the original paper. 



3 Centralbl. f. innere Med., 1897. 



4 Camerer, Zeitschr. f. Biologic, 26 and 28; Arnstein, Zeitschr. f. physiol. Chem., 23. 

 6 Journ. of Physiol., 39. 



6 Zeitschr. . f. physiol. Chem., 45, and Hoppe-Seyler-Thierfelder's Handbuch, 8. 

 Aufl., 590. 



