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In Dumas method, a knownquantity of nitrogen containing organic compound is heated strongly with excessof copper oxide in an atmosphere of carbon dioxide to produce free nitrogen inaddition to carbon dioxide and water. The chemical equation involved in theprocess can be represented as
The traces of nitrogenoxides can also be produced in the reaction, which can be reduced to dinitrogenby passing the gaseous mixture over a heated copper gauge. The dinitrogenproduced is collected over an aqueous solution of potassium hydroxide. Thevolume of nitrogen produced is then measured at room temperature andatmospheric pressure.
On the other hand, inKjeldahl’s method, a known quantity of nitrogen containing organic compound isheated with concentrated sulphuric acid. The nitrogen present in the compoundis quantitatively converted into ammonium sulphate. It is then distilled withexcess of sodium hydroxide. The ammonia evolved during this process is passedinto a known volume of H2SO4. The chemical equationsinvolved in the process are
The acid that is leftunused is estimated by volumetric analysis (titrating it against a standardalkali) and the amount of ammonia produced can be determined. Thus, thepercentage of nitrogen in the compound can be estimated. This method cannot beapplied to the compounds, in which nitrogen is present in a ring structure, andalso not applicable to compounds containing nitro and azo groups.