34 



PRACTICAL ORGANIC AND BIO-CHEMISTRY 



2. Nitrogen. 



(a) Dumas' Method. On heating an organic compound contain- 

 ing nitrogen with copper oxide, its nitrogen is given off as nitrogen. 

 The gas given off from a known weight of substance is collected and 

 its volume measured, from which value its weight can be calculated. 



The analysis in practice is carried out in a similar way to that 

 described for carbon and hydrogen, but the substance is mixed with 

 finely powdered copper oxide and introduced into the tube; and a roll 

 of reduced copper gauze is placed at the end of the combustion tube 

 so as to reduce any oxides of nitrogen, which may be formed, to 

 nitrogen. Instead of a current of air, a current of carbon dioxide 

 is passed through the tube. The gas is collected in a Schiff s nitro- 

 meter over caustic potash which absorbs the carbon dioxide leaving 

 the nitrogen (Fig. 1 8). 



CO* r*r- 



FIG. 18. 



There are several ways of passing the carbon dioxide through the 

 combustion tube ; it may be evolved from a Kipp apparatus or it may 

 be evolved by heating magnesite, either contained in a special tube or 

 in the combustion tube, which in this case is sealed at the end. It is 

 obvious that before carrying out the analysis all the air must be ex- 

 pelled from the apparatus. 



