Identification of Organic Compounds. 33 



prepared in a hard glass tube by heating sodium hydrogen 

 carbonate. The front part of the combustion tube is con- 

 nected with the nitrometer. All parts of the combustion tube, 

 except that in the immediate neighbourhood of the substance 

 mixed with copper oxide, are heated whilst a stream of 

 carbon dioxide is led through. The nitrometer is previously 

 filled with the solution of caustic soda which absorbs the 

 carbon dioxide which passes through. When all the gas 

 which collects in the nitrometer is absorbed, a fact which 

 indicates that no more air is left in the apparatus, the 

 nitrometer is filled up with alkaline solution by raising the 

 funnel d, the slight excess of alkali being driven through 

 the tap a, which is then closed. In this way the air which 

 has collected is expelled from the nitrometer. If, now, 

 the copper oxide is sufficiently hot (a dull red heat), the 

 actual combustion of the substance may be commenced by 

 lighting the burner under that part of the tube in which 

 it is contained. The burning is complete when the volume 

 of gas in the nitrometer no longer shows any increase. 

 After it has stood for some time to attain the atmospheric 

 temperature, the level of the alkaline liquid in the reservoir 

 is brought to that of the liquid in the graduated measuring 

 tube, and the volume is read. The height of the baro- 

 meter and temperature are noted, and the volume is then 

 corrected for normal pressure and temperature (760 mm. 

 and C.). 



(6) The Method of Kjeldahl This method has not 

 such a wide application as the previous one, as in the case 

 of a few substances incorrect results are obtained. It is, 

 however, of considerable value in biological chemistry, as 

 the nitrogen of that important class of compounds, the 

 proteins, is readily determined by this process. Owing to 

 its simplicity, and the small amount of labour involved in 

 the analyses, it is to be preferred to the Dumas method 



(1,997) 3 



