Identification of Organic Compounds. 3 1 



These various tubes are weighed both before and after the 

 combustion, and from their gains in weight the hydrogen 

 and carbon content of the substance are determined. 



J 



Fig. 11. 



There are various modifications of the above method ; 

 and several precautions must be taken, such as the com- 

 plete expulsion of all moisture and carbon dioxide from 

 the tube before analysis, to obtain correct results. These 

 can, however, only be learnt by direct experience, and it is 

 not possible in this place to give more than a general 

 outline of the method. 



When the substance contains nitrogen, oxides of 

 nitrogen will be formed, which will be retained by the 

 soda-lime, and lead thus to an incorrect result in the 

 carbon determination. To avoid this, it is usual to insert 

 a boat containing lead peroxide in the front part of the 

 tube (over burner c), to decompose the oxides. This sub- 

 stance will also retain sulphur and the halogens, which 

 may be quantitatively estimated afterwards. The nitrogen 

 will be retained in the form of lead nitrate, and the 

 sulphur as lead sulphate. 



ESTIMATION OF NITROGEN. 



Two methods can be employed for the estimation of 

 this element. 



