Page 46 - phytochemistry I - PharmD Clinical

The principle of these methods is that, the boiling water or steam
penetrate the plant tissue and vaporizes all volatile substances.

 Before distillation the plant material must be subjected to size
reduction in order to expose a great number of oil glands. This process
termed "Comminution". Flowers, leaves and other thin and non-fibrous
parts of the plant can be distilled without comminution. Seeds and fruits
must be crushed. Roots, stalks and all woody materials should be cut into
short length.

There are three types of hydrodistillation:
a- Water distillation
b- Water and steam distillation
c- Direct steam distillation

Some plant materials (e.g., powdered almonds, rose petals, and orange
blossoms) must be distilled while fully immersed and moving freely in
boiling water, because on distillation with injection live steam (direct
steam distillation) these materials agglutinate and form large compact
lumps, through which the steam cannot penetrate.

a- Water distillation:
The plant material is mixed directly with water in a still pot.
It may float on the water or be completely immersed, depending upon its
specific gravity and the quantity of material handled per charge.

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