METHOD OF KJELDAHL 349 



the acid or near thereto, since at a lower temperature, for instance, 

 from 1 00 to 150, the formation of ammonia is incomplete. 

 Since all organic substances of whatever kind are dissolved by 

 the boiling acid, the previous pulverization of the material need 

 be carried only far enough to secure a fair sample. Many sub- 

 stances give up practically all their nitrogen as ammonium sul- 

 fate when heated with sulfuric acid, as, for instance, urea, as- 

 paragin, and the glutens. In most of the other organic bodies 

 fully 90 per cent, of the nitrogen is likewise secured as the am- 

 monium salt. In the aromatic compounds, or even in the form 

 of amid in anilin salts, the nitrogen is more resistant to the action 

 of sulfuric acid. In the alkaloids where the nitrogen is probably 

 a real component of the benzol skeleton, the formation of am- 

 monia is very incomplete. But even in the cases where the con- 

 version of the nitrogen into ammonia is practically perfect, it is 

 advisable to finish the process by completing the oxidation with 

 potassium permanganate. The permanganate should be used in 

 a dry powdered form and added little by little to the hot con- 

 tents of the digestion flask, the latter being held in an upright 

 position and removed meanwhile from the lamp. When carefully 

 performed there is no danger of loss of ammonia, although the 

 oxidation is at times so vigorous as to be attended with evolu- 

 tion of light. The permanganate must always be added in excess 

 and until a permanent green color is produced. The flask is 

 . then gently heated for from five to 10 minutes over a small flame, 

 but this is not important. The heating must not be too strong, 

 or else a strong evolution of oxygen will take place, with a con- 

 sequent reduction of the manganese compound. When this hap- 

 pens the liquid again becomes clear and there is a loss of am- 

 monia. 



After cooling, the contents of the flask are diluted with water, 

 the green color giving place to a brown, with a rise of tempera- 

 ture. After cooling a second time, the whole is brought into a 

 distillation flask of about three-quarters of a liter capacity and 

 attached to a condenser which ends in a vessel containing titrated 

 sulfuric acid. About 40 cubic centimeters of sodium hydroxid 

 .solution of 1.3 specific gravity are added and the stopper at once 



