136 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



(ii) By Urease. 



Since the discovery of the enzyme, urease, in the soy bean which 

 converts urea into ammonia and carbon dioxide, this hydrolytic agent 

 has displaced hydrochloric acid on account of simplicity. An apparatus 

 consisting of a wash bottle, a gas cylinder or other tall vessel, and 

 a receiving bottle is required (Fig. 27). The gas cylinder is^ fitted 

 with a cork carrying a long tube reaching to the bottom and a short 



tube ; the receiving bottle is 

 fitted with a cork carrying a 

 tube with a bulb blown at its end 

 and pierced with several small 

 holes. The long tube in the gas 

 cylinder is connected by rubber 

 tubing to the wash bottle and 

 the short tube to the bulb tube 

 of the receiving bottle. Air is 

 drawn as rapidly as possible 

 through the apparatus by suc- 

 tion with a pump attached to the 

 short tube of the receiving bottle. 

 The wash bottle contains 

 sulphuric acid to remove am- 

 monia from the air drawn 

 through the vessels. The re- 

 ceiving bottle contains a known 

 volume (25 or 50 c.c.) of 'iN sulphuric acid coloured with a few 

 drops of alizarin red or methyl orange solution. 5 c.c. of the solu- 

 tion of urea (1-2 percent), 25 c.c. of water, and about 2 c.c. of kerosene 

 or liquid paraffin and 0*5 to I gm. of powdered soy bean are placed in 

 the gas cylinder, and air is drawn through the apparatus for -J to I hour 

 depending on the amount of urea present. The gas cylinder should be 

 placed in warm water at 40 or in a bath kept at 40 to hasten the 

 decomposition of the urea. At the end of this time the parts of the 

 apparatus are disjointed. I gm. of anhydrous sodium carbonate put into 

 ihe gas cylinder so as to liberate ammonia which may be retained as 

 ammonium salt, the connections are again made and the ammonia 

 drawn into the receiving bottle by air suction for another half-hour. 

 The excess of -iN acid in the bottle is titrated with 'iN alkali. The 

 amount of urea is calculated from the equation : 

 CO(NH 2 )., + H 2 O = CO 2 + 2NH 3 



60 34 



30 17 



i c.c. of 'iN alkali = 0*003 gm. urea. 



FIG. 27. 



