518 PHYSIOLOGICAL CHEMISTRY 



Precipitate, Purine nitrogen, 



c.c. per cent 



(grams in 100 c.c.) 



20 o . 0275 



21 0.0283 



22 O.O286 



23 . o . 0299 



24 0.0312 



. 25. 0.0325 



Calculation. Multiply the purine nitrogen percentage by the total volume of 

 urine and divide by 100 to obtain the total purine nitrogen value. For example, 

 if the precipitate was found to be 12 c.c. and the total volume of the 24-hour urine 

 was 1300 c.c. the calculation would be as follows: 



12 c.c. = 0.0205 per cent purine nitrogen. 

 0.0205 X 13.0 = 0.2665 gram purine nitrogen. 



Interpretation. The endogenous purine nitrogen excretion (on purine-free 

 diet) averages about 0.15 gram per day, though variations are considerable. As 

 uric acid makes up about nine-tenths of this the amount varies much as uric acid 

 varies. The exogenous purine nitrogen excretion may be largely influenced by the 

 methyl purines of tea, coffee, and cocoa which are excreted unchanged, as well 

 as by the purine bases which are normally oxidized to uric acid (see Uric Acid, 

 page 511). 



Allantoin 



i. Method of Wiechowski-Handovsky. 1 Principle. The urine is precipitated 

 with phosphotungstic acid and lead acetate and in the presence of chlorides with 

 silver acetate. The heavy metals are removed with hydrogen sulphide. The allan- 

 toin is then precipitated as a mercuric compound and the amount of mercury and 

 hence of allantoin in the precipitate determined by titration with ammonium 

 thiocyanate. This method, though rather tedious, is probably the most accurate 

 method for the determination of allantoin. 



Procedure. The urine is diluted to about i per cent urea. As rabbit urine 

 contains in the day's output about 2-4 grams of urea, and that of other herbivora 

 usually forms about a 4 per cent urea solution, it is usually desirable to dilute 3-4 

 times. A greater dilution is not desirable. The urine is treated with i per cent of 

 sulphuric acid and about 3 c.c. of acetic acid for each day's volume. Test a small 

 quantity of the urine to determine the amount of 50 per cent phosphotungstic acid 

 required to completely precipitate it. The bulk of the urine is then treated on this 

 basis with sufficient solid phosphotungstic acid to precipitate it completely. Stir 

 to dissolve the acid and allow to stand for several hours. Filter with suction, first 

 lining the filter with infusorial earth by rubbing up a little of the substance with some 

 of the urine mixture and filtering with suction. To some ordinary lead oxide in a 

 mortar add a small amount of the filtrate and stir until it becomes warm, then add 

 the rest of the filtrate and stir, adding more oxide if necessary until the solution 

 reacts alkaline due to the formation of basic lead acetate. 



Filter again. The nitrate should give no precipitate with basic lead acetate. 

 A measured volume of the nitrate is then treated with measured volumes of acetic 

 acid and silver nitrate solution to completely precipitate any chlorides present. 

 Filter again preferably through infusorial earth. Pass hydrogen sulphide through 



1 Handovsky: Zeit. physiol. Chem., 90, 211, 1914. 



Wiechowski: Neubauer-Huppert: Analyse des Harns, Wiesbaden, 1913, p. 1076. 



