Steam distillation is used for separating substances which
are immiscible with water, volatile in steam & having high vapour pressure
at the boiling temperature of water
It is a method of distillation carried with the aid of steam
and used for the separation of high boiling substance from non-volatile
It is the most common example of differential distillation
• A mixture of immiscible liquids begins to boil when the
sum of their vapor pressure is equal to the atmospheric pressure.
• In case of a mixture of turpentine oil and water, mixture
boils below the BP of water, though the turpentine boils at a much higher
temperature than that of water.
• For example, the BP of turpentine is about 1600C.
on mixing with water and heated the mixture boils at about 95.60C
• At this temperature, the VP of water is 86.24 kPa (647 mm
Hg) and that of turpentine is 15.05 kPa (113 mm Hg)
• The sum of VPs is 101.31 kPa (760 mm Hg) which is normal
• Thus high boiling substances can be distilled at a
temperature much below its BP when steam is used
• It consists of a metallic ‘steam can’ fitted with a cork
having two holes.
• Through one of the holes, a long tube is passed so as to
reach almost the bottom of steam generator.
• This tube acts as a safety tube, so that in case the
pressure inside the steam generator becomes too much, water will be forced out
of it and the pressure will be relieved. Moreover, when steam start coming out
from the safety tube; it indicates that the steam can is almost empty.
• Through another hole a bent tube is passed.
• Another end of the bent tube is connected to the flask
containing non-aqueous liquid (for example, crude containing volatile oil)
through a rubber bung. The tube should reach almost the bottom of the flask.
• Through the other hole of the rubber bung, a delivery tube
is inserted which connects the flask and the condenser.
• The condenser is connected to a receiver flask using an
Provisions are made to heat the steam can and flask.
The non- aqueous liquid is placed in the flask. A small
quantity of water is added to it. Steam can is filled with water.
The steam generator and the flask are heated simultaneously,
so that a uniform flow of steam passes through the boiling mixture. The mixture
The steam carries the volatile oil and passes into the
condenser, which is cooled by cold water.
The condensed immiscible liquid is collected into receiver.
Distillation is continued until all the non- aqueous liquid has been distilled.
In the receiver, water and organic liquid form two separate layers, which can
be easily separated using a separating flask.
• It is used for the separation of immiscible liquids
(toulene and water)
• Extracting most of the volatile oils (anise, clove and
• Purification of liquid with high BP (essential oil of
• Camphor can be distilled
• Aromatic water are prepared by this method