§ 85. DETEKMINATIOX OF NITROGEN. 121 



ed with fresh, live coals, large coals being used to brido-e 

 over the top, in order that there shall be no weight there 

 on the tube when softened by heat, to bend it inwards 

 and close the j)assage above the soda-lime. 



When this part of the tube is red-hot, move the screen 

 along about 8 cm., and apply more coals in the same man- 

 ner as around the first 8 cm. of the tube. 



When that part of the tube is approached, Avhere the 

 mixture of soda-lime and substance is contained, care 

 must be exercised in applying the coals, so as not to have 

 too rapid an evolution of the gas ; there is little danger 

 that any ammonia will pass through the acid unabsorbed, 

 but it will be safer not to have so rapid a flow of gases that 

 the bubbles in the bulbed apparatus cannot be counted ; 

 nevertheless, a continuous current should be maintained, 

 and, all the while, the front end of the tube must be kept 

 well heated by supplying fresh coals as often as is nec- 

 essary. 



When the tube has been heated throughout, and quite 

 intensely around the mixture of substance and soda-lime, 

 and the passage of bubbles through the acid has ceased, 

 break oiF the point of the beak at A, and draw a consid- 

 erable quantity of air through the whole apparatus by 

 applying suction at the mouth of the bulbed tube, in or- 

 der to carry all ammonia remaining in the combustion- 

 tube into the acid ; disconnect the bulbed tube from the 

 other, add a little cochineal, and then the standard sodic 

 solution until the acid is almost neutralized, empty the 

 contents of the bulbs into a beaker, rinse with a little 

 water, and finish the titration (§ 45). 



For each cubic centimetre of the acid that was neutral- 

 ized by the ammonia set free, the substance analyzed con- 

 tained 0.014 grm. of nitrogen. 



When very great accuracy is required, the ammonia 

 should be collected in hydrochloric acid, oily matters fil- 

 tered out, if any are seen in the acid after the combustion 

 6 



