132 MANUFACTURE OF FERTILIZING MATERIALS 



solving the ammonium citrate obtained from 

 dealers in water. 



Nitrogen. The absolute method for nitro- 

 gen consists in mixing the sample of fertilizer 

 with copper oxide, and then heating to redness 

 * in a tube. The carbon and hydrogen take oxy- 

 gen from the copper oxide becoming carbon 

 dioxide and water, while the nitrogen is set free 

 in the gaseous form. Copper oxide is intro- 

 duced on both sides of the mixture or sample 

 of fertilizer with the oxide in order to thor- 

 oughly burn up any volatile portions coming from 

 the sample. In order to destroy any nitrogen 

 oxides which may be present or be found during 

 the combustion, metallic copper, preferably in 

 the form of a roll of wire gauze, is interposed 

 in the path of the gases to the azotometer, the 

 function of which is to abstract the oxygen from 

 the nitrogen oxides under the conditions produced. 



It has been often found that the copper 

 gauze does more than is intended, and abstracts 

 some oxygen from the carbon dioxide as well, 

 giving small amounts of carbon monoxide; so 

 to remedy this a third layer of copper oxide is 

 interposed, which will reoxidize it to carbon 

 dioxide. 



To remove the air from the tube at the be- 

 ginning of the operation, the extreme end of the 

 tube is charged with coarsely crushed carbonate, 

 which on heating evolves carbon dioxide, and 

 sweeps the air from the tube before the combus- 



