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 hne 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. HCl at 40° C, the pepsin is 

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

 biuret reaction. 



17. Reactions of Normal TJrine towards Reagents. 



(i.) Add 5 cc. of HCl to 100 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(N03)2 -f- 2NaCl = 2N"aN03 + HgCl.^), soluble in acid urine. After 

 all the NaCl 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 Ag3P04 ; the latter falls 

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

 tate is insoluble in HNO3 but soluble in NH4HO. 



(6.) Barium chloride - white precipitate ofBaS04 and Ba.{(P04)2. 



(7.) Lead acetate = whitish precipitate of PbS04, PbClg, Pb3(P04)2, and the 

 pigments. 



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

 Fe,(P04)2. , , , . . 



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

 at the boiling-point by the urates. 



(10.) Tannic acid = no precipitate {Krukenlerg), 



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

 but it is not accurate, {a. ) Haycraf t's Method depends on the formation of urate 

 of silver, which is practically insoluble in water or acetic Ticid {British Medical 

 Journal, 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'g Volumeiric Analysis, 5th 

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



