IMUNK 1 I.") 



diet containing about 100 grammes of protein) in the twenty-four 



hours : 



Water . . 1500-00 grammes 



Total solids 72-00 



Urea 33-18 



Uric acid ..... 0-55 



Hippuric acid .... 0'40 



Creatinine ..... 0'91 



Pigment and other organic substances . 10*00 

 Sulphuric acid . . 2'01 



Phosphoric acid .... 3'16 



Chlorine . . . . . 7-50 



Ammonia ..... 0'77 



Potassium ..... 2'50 



Sodium 11-09 



Calcium . . 0'26 



Magnesium ..... 0'21 



The most abundant constituents of the urine are water, urea, and 

 sodium chloride. In the foregoing table the student must not be 

 misled by seeing the names of the acids and metals separated. The 

 acids and the bases are combined to form salts : urates, chlorides, 

 sulphates, phosphates, &c. 



UREA 



Urea or Carbamide, CO(NH 2 ) 2 , is isomeric (that is, has the same 

 empirical, but not the same structural formula) with ammonium 

 cyanate (NH 4 )CNO, from which it was first prepared synthetically 

 by Wohler in 1828. Since then it has been prepared synthetically 

 in other ways. Wohler's observation derives interest from the fact 

 that this was the first organic substance which was prepared syntheti- 

 cally by chemists. 



When separated from the urine, it is found to be readily soluble 

 both in water and in alcohol : it has a saltish taste, and is neutral to 

 litmus paper. The form of its crystals is shown in fig. 43. 



When treated with nitric acid, nitrate of urea (CON 2 H 4 .HN0 3 ) 

 is formed ; this crystallises in octahedra, lozenge -shaped tablets, or 

 hexagons (fig. 44, a). . When treated with oxalic acid, prismatic 

 crystals of urea oxalate (CON 2 H 4 .H 2 C 2 O 4 -f H 2 0) are formed (fig. 

 44, 6). 



These crystals may be readily obtained in an impure form by 

 adding excess of the respective acids to urine which has been con- 

 centrated to a third or a quarter of its bulk. 1 



Under the influence of certain organised ferments, such as the 

 micrococcus urese, which grows readily in stale urine, urea takes up 



1 The preparation of urea nitrate and urea oxalate is postponed to the next 

 lesson, when other microscopic crystals will also be under examination. 



