230 THE URINE. 



thetically, but they are all more or less modifications of the one just 

 described. 



Isolation from the Urine. To isolate urea on a small scale, 50-100 

 c.c. of urine are evaporated to a syrup on a water-bath and ex- 

 tracted with 150 c.c. of strong alcohol by rubbing in a mortar. 

 The alcoholic extract is filtered, the alcohol distilled off, and the 

 syrupy residue treated with concentrated nitric acid in the cold. 

 The urea nitrate which crystallizes out on standing is filtered 

 off with a suction-pump, dissolved in hot water, and the aqueous 

 solution decolorized by gently heating with animal charcoal. The 

 colorless filtrate is then treated with barium carbonate in substance 

 so long as carbon dioxide is evolved, and finally rendered alkaline 

 with barium hydrate solution. The urea is thus liberated according 

 to the equation : 



'JCCHNH^HNOs + BaC0 3 = Ba(NO 3 ) 2 -f 2CO(NH 2 ) 2 + H 2 O + CO 2 . 



The solution is now evaporated to dryness and the residue extracted 

 with absolute alcohol. On concentrating this extract the urea crys- 

 tallizes out in colorless prisms, which may then be treated as above 

 indicated. 



Quantitative Estimation. In the clinical laboratory the old method 

 of Knop and Hiifner is almost exclusively employed. This is based 

 upon the decomposition of urea with sodium hypobromite in alkaline 

 solution, as already described. The nitrogen which is thus liber- 

 ated is measured and the corresponding amount of urea determined 

 by calculation. 



For scientific purposes, however, this method in any one of its 

 numerous modifications is not sufficiently accurate, as the actual 

 volume of nitrogen which is obtained always falls somewhat short 

 of the theoretical amount. The sodium hypobromite, moreover, 

 also causes a partial decomposition of other nitrogenous constituents 

 of the urine, and as the resulting amount of nitrogen is not con- 

 stant, a further error is incurred. In scientific research we are 

 hence forced to resort to some other procedure, such as that 

 proposed by Morner and Sjoquist, or the simpler method which has 

 recently been suggested by Folin. 



METHOD OF MORNER AND SJOQUIST. This is based upon the 

 fact that the organic nitrogenous constituents of the urine, with the 

 exception of urea and ammonia, are precipitated by an alkaline 

 barium chloride mixture. This precipitate is insoluble in ether- 

 alcohol, while urea and ammoniacal salts are dissolved together with 

 a small amount of barium hydrate. In the concentrated ether- 

 alcoholic filtrate the nitrogen is then determined according to Kjel- 

 dahl's method, after the ammoniacal salts have been decomposed, 

 and the resulting ammonia has been driven off. From the per- 

 centage of nitrogen the corresponding amount of urea is then cal- 

 culated by multiplying by 2.14. 



Five c.c. of urine are treated with an equal volume of baryta 



