URINE. 



49 



7- Urea. To urine evaporated to one-third, add a drop of nitric acid in a 

 watch-glass. Glistening scales of urea nitrate are abundantly formed in the liquid. 



8. Uric Acid. To a hundred c.c. of urine add 5 c.c. of strong hydro- 

 chloric acid. Allow the liquid to stand for forty-eight hours. Dark red 

 crystals of uric acid separate from the liquid. 



9- Urochrome. Precipitate about 50 c.c. with lead acetate and a drop 

 of ammonia. Filter. The filtrate is colourless. Scrape the precipitate from 

 the filter paper into a capsule. Mix with a few drops of strong sulphuric acid 

 and add to the pasty mass a little alcohol. Filter. The yellow filtrate on 

 boiling with excess of strong sulphuric acid turns black. Dilute the acid 

 liquid with a large quantity of water. The uromelanhie which separates 

 in flocks is characterized by its extreme solubility in ammonia. It can be 

 precipitated from its solution in ammonia by sulphuric acid. 



10. IndigO. To 500 c.c. of urine add 250 c.c. of pure hydrochloric acid. 

 Allow the liquid to stand twenty-four hours. A coppery scum floats on the 

 surface. Filter. Treat the filter first with ammonia to extract the urome- 

 lanine, secondly with cold alcohol, which acquires thereby a red colour. On 

 boiling the residue in alcohol a blue solution is obtained, which exhibits the 

 absorption spectrum of indigo-blue. 



N.B. In consequence of the large quantities which must be used, this 

 experiment cannot be carried out by each student. 



vin. i. Quantitative determination of Urea. Urea 



(CO N 2 H 4 ) when decomposed by suitable oxidizing agents, yields CO 2 , H 2 O 

 and N. The most convenient reagent for effecting this decomposition is an 

 alkaline solution of sodic hypobromite. The CO 2 is absorbed by caustic soda. 

 The nitrogen which is disengaged is collected and measured in a suitable 

 apparatus. Every 37^3 c.c. of nitrogen, at ordinary pressure and temperature, 

 corresponds to O'l grm. of urea. The hypobromite solution is prepared by 

 adding 25 c.c. of bromine to 250 c.c. of a solution containing 100 grm. of 

 caustic soda. 



a. If Russell and West's apparatus is used, measure off in a 

 pipette 5 c.c. of urine and introduce carefully into the bottom of the "re- 

 action-tube." Rinse the sides of the tube with distilled water until the liquid 

 reaches the constriction. Plug with the caoutchouc stopper, avoiding the 

 introduction of air. Fill up the tube with the hypobromite solution and half fill 

 the trough with water. Fill the measuring tube with water and invert it in the 

 trough. Lift out the stopper, and, without loss of time, place the measuring 

 tube over the reaction-tube. Warm the bulb of the latter until the liquid just 

 boils, and read off the quantity of gas collected. 



b. If Dupre'S apparatus be used, introduce 25 c.c. of hypobromite 

 into the flask c. Measure off 5 c. c. of urine into the test-tube, and close the 

 flask with the caoutchouc stopper to which the test-tube is attached. Open 

 the pinch-cock d and lower the measuring tube a, until the surface of the water 

 is at the zero point of the graduation. Close the pinch-cock and raise the 

 measuring tube. If the apparatus be tight, mix the urine gradually with hypo- 

 bromite solution by inclining the flask. Finally, tilt the flask so as to rinse out 

 the test-tube with the solution, and shake well for a few seconds. Immerse 



