Carbon and hydrogen in the organic compound are estimated by Liebig’s method. The proportions of carbon and hydrogen in an organic compound can be detected by burning the compound in the presence of excess oxygen and cupric oxide.
For estimating the proportion of nitrogen, two methods are used - the Dumas method and Kjeldahl’s method. In Dumas method a known mass of an organic compound is heated strongly with coarse cupric oxide in an atmosphere of carbon dioxide.
In Kjeldahl’s method, the organic compound is heated with concentrated sulphuric acid. Kjeldahl method is not applicable when nitrogen is present in the ring and also in nitro and azo compounds. For the estimation of halogen a known mass of organic compound should be heated with fuming nitric acid in the presence of silver nitrate in a Carius tube.