2Q6 URINE. [CH. XII. 



353. Schiff's test. Treat a very small amount of uric acid 

 with a few cc. of sodium carbonate. Pour the solution on to 

 filter paper moistened with silver nitrate. A black stain of reduced 

 silver immediately results. 



NOTE. This useful test cannot be applied in the presence of chlorides. It 

 is important to note that the uric acid is dissolved in sodium carbonate, not 

 the hydroxide, as the latter gives a precipitate of the brown silver hydroxide, 

 which completely obscures the reduction. An amount of sodium carbonate in 

 excess of that required to dissolve the uric acid must be added, as the reduction 

 only takes place in the alkaline condition. 



354. Folin's test. To a very small pinch of uric acid in a 

 beaker add 20 cc. of a saturated solution of sodium carbonate. 

 Stir till the uric acid has completely dissolved, add I cc. of Folin's 

 uric acid reagent. A blue colour is obtained. 



NOTES. i. Preparation of Folin's solution. 100 grams, of pure sodium 

 tungstate, 102 cc. of pure ortho- phosphoric acid (B.P. 66-3%) and 750 cc. of 

 distilled water in a flask fitted with a reflux condenser are boiled for 2 hours. 

 On cooling the solution is diluted to i litre. 



2. The solution also gives a blue colour with polyphenols. It is used for 

 the microchemical estimation of uric acid in urine. 



355. Dissolve a little uric acid in sodium carbonate by boiling. 

 Add 5 cc. of Fehling's solution and boil for a considerable time. 

 Note the peculiar reduction of the copper, and compare it with the 

 reduction obtained with glucose. 



356. Similarly try the effect of uric acid on Nylander's (Ex. 

 105) and Benedict's (Ex. 100) solutions. A reduction is not obtained. 



357. Dissolve some uric acid in sodium carbonate, add an 

 excess of ammonia and treat with silver nitrate. A white amorphous 

 precipitate of a silver compound of uric acid is formed. 



NOTE. Xanthine, hypoxanthine and other substances in urine closely 

 related to uric acid are similarly precipitated by ammoniacal silver nitrate. 



358. A solution of sodium urate and urea is provided. To 

 prepare crystals of uric acid and of urea. 



Heat a test-tube nearly full of the solution to boiling point and 

 add strong hydrochloric acid till the reaction is distinctly acid. 

 Allow the tube to cool slowly ; the uric acid crystals separate out. 



