UREA. 229 



Urea phosphate, CH 4 K 2 O.H 3 P0 4 , crystallizes occa- 

 sionally from evaporated urine (of swine) ; is always 

 produced when phosphoric acid is added to urea in 

 the proportion required by the formula of the salt, and 

 the solution evaporated down to a small volume. 

 Large, well-formed, rhomhic crystals, easily soluble in 

 water, but not deliquescent. 



Urea-mercury oxide, CH 4 N 2 0.2HgO, white pre- 

 cipitate, which a solution of mercury nitrate produces 

 in a solution of urea mixed with potassa. When a 

 solution of mercury chloride is employed, there is formed 

 a gelatinous, snowy- white precipitate 2(CHXN" 2 0).3HgO, 

 which, when washed with boiling water, becomes 

 yellow. 



Urea and sodium chloride, CHWO.NaCl + H 2 0. 



Shining crystals, which separate on the evaporation of 

 a solution of urea containing sodium chloride. 



Urea also unites with other chlorine compounds and 



a great many nitrates. Mercury nitrate precipitates 



from its solution insoluble compounds of varying com- 



position. By mixing very dilute solutions, there is 



roduced a heavy, white powder of the composition 



3HgO.* 



* This reaction is employed for the purpose of estimating urea quan- 

 titatively. For this object a solution of mercury nitrate prepared by 

 dissolving 77.2 grms. pure mercury oxide in nitric acid, evaporating to 

 dryness, and diluting with water so as to make 1000 cc. is added to the 

 solution of urea until an addition of sodium carbonate to a small por- 

 tion, removed each time for the purpose, commences to give a yellow 

 color. Every cc. of the mercury solution employed corresponds to 0.01 

 grms. of urea. Before the estimation of urea in urine, all sulphuric 

 and phosphoric acids must be removed. This is accomplished best by 

 means of a mixture of two volumes of a solution of barium hydroxide 

 (saturated at the ordinary temperature) with one volume of a similarly 

 prepared solution of barium nitrate. Two volumes of urine are mixed 

 with one volume of this mixture, filtered, and the urea precipitated 

 exactly from 15 cc. of the filtrate (corresponding to 10 cc. urine) by 

 means of the mercury solution. In the case of very exact estimations, 

 another correction of the result is necessary in consequence of the 

 presence of sodium chloride in the urine. 



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