KJELDAHL METHOD 



361 



ping into the standardized acid in the erlenmeyer receiver. The 

 general arrangement of the distilling apparatus is shown in 

 Fig. 1 6. Since the contents of the vessel are warmed by mixing 

 with the soda-lye, the flame can be turned on at full head at once 

 at the commencement of the operation. In about a quarter of 

 an hour the liquid in the receiver will be at the boiling-point, 

 and the boiling should be continued for five minutes more, making 

 20 minutes in all for the completion of the distillation. By this 

 boiling the contents of the receiver are not charged with carbon 

 dioxid, as might happen if a condenser were used. The receiver 

 contains 20 cubic centimeters of a standardized sulfuric acid solu- 

 tion and about 50 cubic centimeters of water. 



The acid used should contain 38.1 grams of sulfuric acid of 

 1.845 specific gravity in a liter; and it should be set by titration 



Fig. 16. Distillation Apparatus of the Halle Agricultural Laboratory. 



with chemically pure sodium carbonate. For this purpose 0.7 

 gram of sodium carbonate is heated in a platinum crucible for 

 two hours over a small flame, weighed, and placed in an erlen- 

 meyer together with 20 cubic centimeters of the sulfuric acid, 

 care being taken to avoid loss from the vigorous evolution of 

 carbon dioxid. After boiling for 10 minutes all the carbon dioxicl 

 is removed from solution. After cooling, the excess of acid is 

 determined by titration with a standardized barium hydroxid 

 solution, using rosolic acid as indicator. 



The solution of barium hydroxid is made as follows: Digest, 

 with warm water, 260 grams of caustic baryta, Ba(OH),, until 

 it is nearly all dissolved, filter, and make up to a volume of 10 



