$A$ liquid with a high boiling point decomposes on simple distillation,but it can be steam distilled for its purification. Explain how this is possible.

(N/A) In steam distillation,the vapour of the organic compound and water are distilled out. Steam (water vapour) is passed into the liquid that is to be purified.
Consequently,the vapour of the liquid and the vapour of water rise and pass into the condenser. The liquid and water are immiscible and form separate layers.
When the sum of the partial vapour pressures of the liquid $(p_1)$ and water $(p_2)$ becomes equal to the atmospheric pressure $(p)$,distillation takes place.
Mathematically,$p = p_1 + p_2$. Since $p_1 < p$,the liquid distills at a temperature lower than its normal boiling point.
Therefore,steam distillation takes place at a lower temperature than the boiling point of the organic liquid,preventing thermal decomposition.