

DETERMINATION OF UREA 89 



rubber stopper and draw the connecting tube diagonally to near 

 1/3 the top of the inclined receiver. Continue the distillation for 

 one more minute and rinse off the lower outside part of the delivery 

 tube with a little water. Cool the distillate with running water, 

 dilute to about 20 c.c. and add 2.5 c.c. of the Nessler solution pre- 

 viously described. Fill to the 25 c.c. mark and compare in the 

 colorimeter with a standard containing 0.3 mg. of nitrogen in a 100 

 c.c. flask and Nesslerized with 10 c.c. of the Nessler solution. The 

 standard and unknown should always be Nesslerized as nearly 

 simultaneously as practicable. 



Calculation. Multiply 20 (the height of the standard in mm.) 

 by 15 and divide by the colorimetric reading to get the urea 

 nitrogen per 100 c.c. of blood. The reasons for this calculation 

 are, of course, to be found in the fact that the standard containing 

 0.3 mg. of nitrogen is diluted to 100 c.c. while the unknown, which 

 corresponds to 0.05 c.c. of blood, is diluted to only 25 c.c. 



Preparation of Urease. Urease solution is made from jack 

 bean powder in the following manner: Transfer to a 200 c.c. flask 

 or bottle about 3 gms. of permutit powder. Wash this by decan- 

 tation once with 2 per cent acetic acid, then twice with water. 

 Add to the moist permutit in the flask 100 c.c. of 30 per cent 

 alcohol (35 c.c. of 95 per cent alcohol mixed with 70 c.c. of water). 

 First introduce 5 gms. of jack bean meal and shake for ten minutes. 

 Filter and collect the filtrate in three or four different clean, small 

 bottles. Set one aside for immediate use; it will remain serviceable 

 for at least one week at ordinary room temperature if not exposed 

 to direct sunlight. Put the others on ice where they will remain 

 good from three to five weeks. This preparation is very active 

 and the use of permutit makes the extract free from ammonia, 

 nor does ammonia develop on standing. 



Preparation of Pyrophosphate Solution. This solution con- 

 tains 140 gms. of sodium pyrophosphate (U.S.P.) and 20 gms. of 

 glacial phosphoric acid per liter. 



2. Urea Determination by Means of Urease and Aeration 



The decomposition of the urea is made in the same kind of a 

 Pyrex test-tube and in the manner already described under 1. 

 One or 2 c.c. of 10 per cent sodium hydroxide are first added and 

 ammonia aspirated into a test-tube graduated at 25 c.c. and con- 



