XX.] URIC ACID, ETC. 135 



15. Mucus. A trace of mucus occurs normally in urine. Col- 

 lect fresh urine in a tall vessel, and allow it to stand for some 

 time, when fine clouds (" mucous clouds ") like delicate cotton- 

 wool appear. These consist of mucus entangling a few epithelial 

 scales. 



(a.) If the urine contain an excess of mucus, on adding a satu- 

 rated solution of citric acid to form a layer at the bottom of the 

 test-tube, a haziness at the line of junction of the urine and acid 

 indicates mucus. There is no deposit with healthy, freshly-passed 

 urine. Citric acid is used because it is heavier than acetic. 



16. Ferments in Urine. There is no doubt that urine contains 

 pepsin. Some observers state that it also contains trypsin and a 

 sugar-forming ferment ; but the latter statement is denied. 



(a.) Select the morning urine, place in it for several hours fresh 

 well-washed and boiled fibrin. The latter absorbs the ferment, 

 and on placing it in .2 per cent. HC1 at 40 C., the pepsin is 

 dissolved and peptones are formed. Test for the peptones by the 

 biuret reaction. 



17. Eeactions of Normal Urine towards Reagents. 



(i.) Add 5 cc. of HC1 to roo of urine. After twenty-four hours crystals of 

 uric acid separate out. 



(2.) Add caustic soda or ammonia = precipitate of the phosphates of the 

 alkaline earths, partly in an amorphous state, partly in acicular crystals. 



(3.) Acidulate with nitric acid and heat with phospho-molybdic acid = blue 

 coloration due to urates. 



(4. ) Add mercuric nitrate = white cloudiness, which disappears on shaking. 

 This is a precipitate due to the formation of sodium nitrate and mercuric 

 chloride (Hg(N0 3 ) 2 + 2NaCl = 2js T aN0 3 + HgCl.,), soluble in acid urine. After 

 all the N"aCl is decomposed but not until then a permanent precipitate, a 

 compound of urea and the mercury salt, forms. 



(5.) Silver nitrate = white precipitate of AgCl and Ag 3 P0 4 ; the latter falls 

 first, and afterwards all the silver combines with the chlorine. The precipi- 

 tate is insoluble in HN0 3 but soluble in NH 4 HO. 



(6.) Barium chloride = white precipitate of BaS0 4 and Ba.(P0 4 ) 2 . 

 ^ (7.) Lead acetate = whitish precipitate of PbS0 4 .. PbCl 2) Pb i (P0 4 ) 2 , and the 

 pigments. 



(8.) Ferric chloride after acidulation with acetic acid = precipitate of 

 Fe 2 (P0 4 ) 2 . 



(9. ) An ammoniacal solution of cupric oxide is decomposed and decolorised 

 at the boiling-point by the urates. 



(10.) Tannic acid = no precipitate (Krukenberg}. 



18. Estimation of Uric Acid. This is sometimes done by the method (2, a), 

 but it is not accurate, (a. ) Haycraft's Method depends on the formation of urate 

 of silver, which is practically insoluble in water or acetic acid (British Medical 

 Journa/, 1885). The urate of silver is of a slimy nature and must be washed 

 on an asbestos filter. The titration of the silver compound is by means of 

 Volhard's ammonium thio-cyanate method (Sutton's Volumetric Analysis, 5th 

 edit., 1886, pp. 116, 324). 



