156 THE URINE. 



find that less is excreted in carcinoma and cirrhosis of this 

 organ. 



The fermentation of urea to ammonium carbonate, 

 caused by the action of micro-organisms, has been already 

 referred to. 



PREPARATION OF UREA. 



342. PROM URINE. (a) If only a small amount is 

 desired, evaporate half a test-tubeful of urine to dryness 

 on the water-bath. Dissolve the urea from the residue 

 with 95-per-cent. alcohol. Allow a drop of the alcoholic 

 filtrate to evaporate on a microscope-slide without the aid 

 of heat. Examine the crystals under the microscope. If 

 the form is not distinct, dissolve in a drop of water and 

 again observe the crystals after this has evaporated. Add 

 a drop of dilute nitric acid to the slide, let it stand a few 

 minutes, then examine the crystals of urea nitrate. (Plate 

 1,6.) 



(b) A larger quantity can best be obtained by evapo- 

 rating half a liter to a liter of urine to a thin syrup upon 

 the water-bath, then cooling it in ice-water, and adding 

 about three times its volume of nitric acid of a specific 

 gravity of 1.3 which has been boiled to expel the oxids 

 of nitrogen and cooled with ice-water. Filter off the 

 urea nitrate through an asbestos or glass-wool filter, wash- 

 ing with a small quantity of ice-cold concentrated nitric 

 acid. Dissolve the crystals in hot water and decolorize by 

 chlorin-water or a small quantity of potassium chlorate. 

 Add, then, small portions of pure barium carbonate as long 

 as it dissolves and until the liquid is neutral. Evaporate 

 the whole upon the water-bath to dryness. Pulverize the 

 residue and dissolve the urea in absolute alcohol, which 

 does not dissolve the barium nitrate. If the alcoholic solu- 



