Describe the Kjeldahl's method and the principles for the estimation of nitrogen present in an organic compound.

(N/A) Method:
$(i)$ In this method,the organic compound containing nitrogen is heated with concentrated sulphuric acid $(H_2SO_4)$ in a Kjeldahl's flask. The nitrogen in the compound is converted into ammonium sulphate $((NH_4)_2SO_4)$.
$(ii)$ The resulting acid mixture in the Kjeldahl's flask is then heated with an excess of sodium hydroxide $(NaOH)$. The liberated ammonia $(NH_3)$ gas is absorbed in an excess of a standard solution of sulphuric acid $(H_2SO_4)$.
$(iii)$ The amount of ammonia produced is determined by estimating the amount of sulphuric acid consumed in the reaction.
$(iv)$ This is done by estimating the unreacted sulphuric acid left after the absorption of ammonia by titrating it with a standard alkali solution. The difference between the initial amount of acid taken and the amount left after the reaction gives the amount of acid that reacted with the ammonia.