/ 



is 



-,,:\\ THE SECRETIONS. 



ill fall. This consists of chloride of silver and phosphate 

 of silver ; and adding nitric acid to the mixture, the phosphate 

 of silver is dissolved, leaving a quantity of perfectly white 

 chloride of silver, which, after the test-tube has been shaken 

 for some time, sinks to the bottom, leaving a clear supernatant 

 fluid. 



4. To 15 cubic centimetres of urine which have been strongly 

 acidulated with nitric or hydrochloric acid, add two or three 

 T a solution of barium chloride. A precipitate of barium 

 sulphate will fall. 



... 1'our a strongly acid solution of ammonium naolybdate 



hi a few drops of urine and boil ; the fluid 



will I - -llo\v, and a canary-yellow precipitate will fajl, 



of'phospho-molybdate of ammonium ; this indicates 



the presence of phosphoric acid. 



To 1.") cubic centimetres of urine, in a test-tube, add an 

 equal quantity of a solution of caustic baryta. An abundant 

 j.itate will fall, composed chiefly of barium sulphate and 

 phosphate. 



7. To the same quantity of urine add about one-third of its 



volume of a solution of acetate of lead. A white precipitate, 



consisting of chloride, sulphate and phosphate of lead, will 



Mud it will be observed that the urine is to a great extent 



decolorized. 



ON THK MKTH<> .VRATING, AND ON THE REACTION OF THE 



PKIM ir-AL OKGANIC CONSTITUENTS OP UKINE. 



** 185. Preparation of Urea (CH.Y.O) from Urine. 

 Take loo cubic centimetres of urine, and add to it 50 cubic 

 centimetres of a solution made b}' mixing one volume of a 

 saturated solution of nitrate of barium, with two volumes of a 

 saturated solution of caustic bar3*ta. 



A precipitate will form, which is chiefly composed of phos- 

 phate and sulphate of barium. On filtering, a clear fluid is 

 obtained which is evaporated to dryness on a water bath. The 

 residues treated with hot spirits of wine, and the alcoholic 

 solution i* likewise evaporated to dryness. On now adding 

 absolute alcohol to the residue the urea is separated, and is 

 obtained from the solution by evaporation. To purify it further 

 fr<>m traces of other organic and saline matters, the crystals 

 of urea must be collected on blotting-paper, strongly pressed 

 between folds of filtering paper, dried on a porous tile, and, if 

 i in dissolved in spirit and re-crystallized. 



Although urea can be readily obtained from urine, it is more 

 convenient to make use of artificial urea in the experiments 

 which are required to demonstrate its characteristic properties.' 



As it is altogether beyond the province of this book to refer 



