366 AGRICULTURAL ANALYSIS 



ter of six -centimeters and tapering out gradually in a long neck, 

 which is two centimeters in diameter at the narrowest part, and 

 flared a little at the edge. The total capacity is about 250 cubic 

 centimeters. 



(2) Distillation flasks. For distillation, a flask of ordinary 

 shape, of about 550 cubic centimeters capacity may be used. It 

 is fitted with a rubber stopper and with a bulb-tube above to pre- 

 vent the possibility of sodium hydroxid being carried over me- 

 chanically during distillation. The bulbs are about three centi- 

 meters in diameter, the tubes being of the same diameter as the 

 condenser and cut off obliquely at the lower end, which is fastened 

 to the tube of the condenser by a rubber tube. 



(3) Kjeldahl flasks for both digestion and distillation. These 

 are pear-shaped, round-bottom flasks, having a total capacity of 

 about 550 cubic centimeters, made of hard, moderately thick and 

 well-annealed glass. When used for distillation the flasks are 

 fitted with rubber stoppers and bulb-tubes, as given under distil- 

 lation flasks. 



Manipulation. (i) The Digestion. From seven-tenths to 

 three and five-tenths grams of the substance to be analyzed, ac- 

 cording to its proportion of nitrogen, are brought into a digestion 

 flask with approximately seven-tenths gram of mercuric oxid or 

 its equivalent in metallic mercury and 20 cubic centimeters of 

 sulfuric acid. The flask is placed in an inclined, position, and 

 heated below the boiling-point of the acid for from five to 15 

 minutes or until frothing has ceased. If the mixture froths 

 badly, a small piece of paraffin may be added to prevent it. 

 The heat is then raised until the acid boils briskly. No further 

 attention is required until the contents of the flask have become 

 a clear liquid, which is colorless or, at least, has only a very pale 

 straw color. The flask is then removed from the frame, held 

 upright and, while still hot, potassium permanganate is dropped 

 in carefully and in small quantities at a time until, after shak- 

 ing, the liquid remains of a green or purple color. Respecting 

 the time of boiling, it is suggested that the following be added to 

 the official methods in place of the sentence beginning "no 

 further attention, etc." "Boil for at least one hour or until the 



