452 EXCRETION 



The Mwexide Test. Add to 2 cc. of uric acid solution in a test-tube an 

 equal quantity of nitric acid. Heat gently, a reddish ring forms at the point 

 of contact between the nitric acid and uric acid solution. Cool and add 

 ammonia carefully. The color ring deepens to a purple color. This test 

 succeeds well by evaporating a few drops of uric acid on a porcelain plate. 

 Add to the stain a drop of concentrated nitric acid and evaporate. Concen- 

 tric rings of reddish color will be formed. This color deepens to reddish- 

 purple when a drop of ammonia is added. 



13. Creatinin. Test 20 cc. of urine in a beaker for creatinin by 

 adding a cubic centimeter of dilute solution of sodium nitroprusside and then 

 weak sodium hydrate. A ruby-red color, which quickly turns yellow, indi- 

 cates the presence of creatinin (Weyl's reaction). If the yellow solution 

 has an excess of acetic acid added and is then boiled, it turns first green and 

 later blue, forming ultimately a precipitate of Prussian blue. Urine mixed 

 with picric acid gives a red coloration when made alkaline with caustic 

 alkali solution. 



14. Total Nitrogen in Urine. Determine the total nitrogen in a sample 

 of urine by the Kjeldahl method. This method depends upon the con- 

 version of all the nitrogen to ammonia, the distillation of this ammonia 

 into a known quantity of sulphuric acid, and the final titration of the excess 

 of sulphuric acid when the distillation is complete. The computation is 

 made on the basis that i cc. of a normal sulphuric acid is equivalent to 

 i cc. normal sodium hydrate, and that in turn to i cc. of ammonium 

 hydrate. The ammonia neutralizes a portion of the sulphuric acid in the 

 distillation. One cc. of normal ammonium hydrate contains 0.014 gram 

 nitrogen, from which the total nitrogen in the sample used can be readily 

 computed. 



15. Pigments of Urine. The normal color of the urine is due to the 

 presence of a pigment, urobilin. Prepare urobilin by adding lead acetate 

 to a 200 cc. sample of urine. A precipitate forms which carries down the 

 coloring mater. Filter. Add acid alcohol to the precipitate to extract the 

 coloring mater, refilter, which gives a deep yellow solution. Shake up with 

 a few cubic centimeters of chloroform which dissolves the pigment. Draw 

 off the chloroform solution and allow to evaporate. The residue is a brown- 

 ish mass of urobilin. 



1 6. Test for Indican, Obermayer's. Take in a test tube i cc. Ober- 

 mayer's reagent (.2 to .4 per cent, ferric chloride in concentrated hydro- 

 chloric acid) and an equal part urine to be tested, then add 2 cc. of chloro- 

 form. Thoroughly shake. A blue color will develop if indican be present. 



ABNORMAL CONSTITUENTS OF URINE. 



Many abnormal constituents may appear in the urine under pathological 

 conditions, only two of which will be mentioned here. 

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