DETERMINATION OF UREA AND NITROGEN. 159 



side of C in A put 20 or 25 cubic centimeters of the hypo- 

 bromite. Insert the stopper (E) tightly, thus filling the 

 tube D with water. If it remains full, showing that the 

 apparatus is tight, place an empty beaker under D and 

 gently mix the urine and hypobromite. Avoid as much 

 as possible raising the temperature by holding the bottle 

 in the hand, as the expansion of the gas causes a consid- 

 erable error. Allow it to stand until no more water passes 

 from D, which must remain full of water during the whole 

 test; then measure the expelled water in a graduated cy- 

 linder. 



One gramme of urea contains 371 cubic centimeters 

 of nitrogen; but, when it is decomposed in this manner, 

 only about 354 cubic centimeters are obtained. For ordi- 

 nary clinical purposes the percentage of urea in urine can 

 be calculated from the following formula: 



100 x number of c. c. of N 

 percentage of urea = " 



350. DETERMINATION OF THE TOTAL NITROGEN IN URINE 

 (KJELDAHL'S METHOD* 1 ). I. Prepare the following solutions: 



1. Standard sulphuric acid containing about 25 grammes per 

 liter, of which the strength has been accurately determined. 



2. Standard ammonia, of which about five volumes are neces- 

 sary to neutralize one of the acid. Determine this accurately and 

 calculate the amount of ammonia by weight in 1 cubic centimeter. 



3. Sodium hydrate free from ammonia, and nitric acid, about 

 270 grammes per liter. 



4. Congo-red, of which the solution contains 0.2 gramme in 

 100 cubic centimeters. This is turned red by alkalies and blue by 

 acids the opposite of litmus. 



1 This method can be used for finding the amount of N in 

 most animal and vegetable compounds. 



