APPENDIX 



199 



KJELDAHL'S METHOD OF ESTIMATING NITEOGElf 



This simple and accurate method has very largely replaced the older 

 •comphcated processes. 



I take the following account of the method with the modifications pro- 

 posed by Warington from Sutton's ' Volumetric Analysis.' 



From O'l to 1 gramme of the dry powdered substance is put into a boiling 

 flask holding about 100-120 c.c. The acid used for the destruction of the 

 organic material is made by mixing 200 c.c. pure oil of ^•itriol with 50 c.c. 

 Nordhausen oil of vitriol, and 2 grammes of phosphoric acid in sticks ; all these 

 must, of course, be free from ammonia : 10-20 c.c. of this mixture are poured 

 over the substance in the flask and heated on wire gauze over a small Bunsen 

 flame. The temperature must be kept below boiling ; with prolonged heating 

 the organic matter is gradually destroyed, and the liquid becomes clear and 



Fig. 82.— Kjeldahl's method. (Waller, after Argatinsky.) 



quiet. The nitrogen originally present is thus converted into ammonia, and 

 this may be hastened by adding to the hquid very minute pinches of pure 

 potassium-permanganate. A violent commotion takes place with every 

 addition, but there is no fear of any ammonia being lost. The operation is 

 ended when the mixture becomes permanently greenish (from one to two 

 hours), and moderate heat is continued for a few minutes more. The flask 

 is cooled, some water added, and the contents washed out into a large flask 

 of 700 c.c. capacity with as little water as possible. It is then made alkaline 

 with excess of either pure caustic soda or potash solution (sp. gr. 1-3). A little 

 metallic zinc is added to prevent bumping during the subsequent distillation. 

 The flask is then rapidly closed with a perforated caoutchouc stopper, through 

 which passes an upright tube with two bulbs about an inch in diameter 

 blown upon it : these arrest and carry back any spray of soda from the liquid. 

 The tube above the bulbs is bent over and connected to a condenser, and the 

 delivery end of the condenser leads into a flask, containing a measured excess 

 of standard acid. The mixture in the flask is then distilled, and the ammonia 

 passes over into the acid. Distillation is continued from forty-five to sixty 

 minutes. The amount of acidity is then determined in the distillate by 



the 



titration with standard potash or soda, methyl 



01 



