What is steam distillation?

Question

this method is used when she sought substance is steam volatile or vaporizes with the steam.

Answer 1

Steam distillation is a special type of distillation (a separation process) for temperature sensitive materials like natural aromatic compounds.

Many organic compounds tend to decompose at high sustained temperatures. Separation by normal distillation would then not be an option, so water or steam is introduced into the distillation apparatus. By adding water or steam, the boiling points of the compounds are depressed, allowing them to evaporate at lower temperatures, preferably below the temperatures at which the deterioration of the material becomes appreciable. If the substances to be distilled are very sensitive to heat, steam distillation can also be combined with vacuum distillation. After distillation the vapors are condensed as usual, usually yielding a two-phase system of water and the organic compounds, allowing for simple separation.

Answer 2

Steam distillation uses the same glassware as any other distillation, but the heat source is a steam bath.

It is used when your solvent is very volatile or when it is highly flammable.  With a flammable solvent, you are not exposing it to naked flames or to electrical equipment which could spark.  With the latter, I always turned on the steam bath before introducing the solvent.