LESSON X 

 URINE 



1. Test the reaction of urine on litmus paper. 



2. Determine its specific gravity by the urinometer. 



3. Test for the following inorganic salts : 



(a) Chlorides. 'Acidulate with nitric acid and add silver nitrate; a white 

 precipitate of silver chloride, soluble in ammonia, is produced. The object 

 of acidulating with nitric acid is to prevent phosphates being precipitated by 

 the nitrate of silver. 



(6) Sulphates. Acidulate with hydrochloric acid and add barium chloride. 

 A white precipitate of barium sulphate is produced. Hydrochloric acid is 

 added first, to prevent precipitation of phosphates. 



(c) Phosphates. i. Add ammonia; a white crystalline precipitate of 

 earthy (that is, calcium and magnesium) phosphates is produced. This 

 becomes more apparent on standing. The alkaline (that is, sodium and 

 potassium) phosphates remain in solution. 



ii. Mix another portion of urine with half its volume of nitric acid ; add 

 ammonium molybdate, and boil. A yellow crystalline precipitate falls. 

 This test is given by both kinds of phosphates. 



4. Urea. Take some urea crystals. Observe that they are readily soluble 

 in water, and that effervescence occurs when fuming nitric acid (i.e. nitric 

 acid containing nitrous acid in solution) is added to the solution. The 

 effervescence is due to the breaking up of the urea. Carbonic acid and 

 nitrogen come off. A similar bubbling, due to evolution of nitrogen, occurs 

 when an alkaline solution of sodium hypobroniite is added to another 

 portion of the solution. 



5. Heat some urea crystals in a dry test-tube. Biuret is formed, and 

 ammonia comes off. Add a drop of copper-sulphate solution and a few drops 

 of 20-per-cent. potash. A rose-red colour is produced. 



0. Quantitative estimation of urea. 



For this purpose Dupre's apparatus (fig. 41) is the most convenient. It 

 consists of a bottle united to a measuring tube by indiarubber tubing. The 

 measuring tube (an inverted burette will do very well) is placed within a 

 cylinder of water, and can be raised and lowered at will. Measure 25 c.c. of 

 alkaline solution of sodium hypobromite (made by mixing 2 c.c. of bromine 

 with 23 c.c. of a 40-per-cent. solution of caustic soda) into the bottle. 

 Measure 5 c.c. of urine into a small tube, and lower it carefully, so that no 

 urine spills, into the bottle. Close the bottle securely with a stopper per- 

 forated by a glass tube : this glass tube * is connected to the measuring tube by 



1 The efficiency of the apparatus is increased by having a glass bulb blown on 

 this tube to prevent froth passing into the rest of the apparatus. This is not 

 shown in the figure. 



