COMPOSITION AND CHARACTERS OF URINE 1259 



finally converted into ammonia. On adding alkali to the mixture the ammonia 

 is set free from its combination with the sulphuric acid and can be distilled off 

 and received into a vessel containing a known amount of decinormal acid. By 

 titrating this acid after the operation we can determine the qiiantity of ammonia 

 which has been produced. To carry out this method 5 c.c. of urine are heated 

 with 20 c.c. sulphuric acid and a small quantity of copper sulphate and potas- 

 sium sulphate. The copper sulphate is to aid the oxidation of the organic sub- 

 stances, the potassium sulphate is to raise the boiling-point of the mixture. 

 The boiling is continued for half an hour. The flask is then cooled and 

 half filled with distilled water. A special form of distillation tube (Fig. 

 525) is now attached by a rubber cork which fits tightly, but just before 



FIG. 525. 



this is done an excess of strong caustic soda sufficient to neutralise the 

 concentrated sulphuric acid is run in under the acid. The other end of the 

 distillation tube is at once arranged to dip under the surface of a measured 



n 



quantity of standard acid (e.g. 10 c.c. TT: H 2 S(\), diluted with water, and con- 

 tained in a 600 c.c. Erlenmeyer flask. The flask is then shaken and heated. 

 In about a quarter of an hour the ammonia is completely distilled off, and its 



n 

 amount can be determined by titrating the acid in the flask with r:; NaOH, 



methyl orange being used as indicator. 



UREA. The method usually adopted for estimating the urea is that 

 devised by Hiiiner. It depends on the fact that urea is decomposed by an alkaline 

 hypobromite with the production of C0 2 and nitrogen. In the presence 

 of an excess of alkali the C0 2 is absorbed and the nitrogen may be collected and 

 measured, and serves as an index of the amount of urea present. The reaction 

 which occurs is as follows : 



CO(NH 2 ) 2 + SNaBrO + 2NaOH = SNaBr + N 2 + Na 2 C0 3 + 3H 2 



60 grin. 

 1 grm. 



Actually, however, only 354-33 c.c. nitrogen are evolved by 1 grm. urea. 



22-4 litres 

 372 c.c. 



28 grm. 



