Page 123 - Medicinal Plants_PharmD general
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Properties:
Tannins are soluble in water and sparingly soluble in organic
solvents, solutions of tannins precipitate heavy metals, alkaloids,
glycosides and gelatin
Tests for tannins:
A) Goldbeater’s Skin test:
1. Soak a piece of goldbeater skin (membrane prepared from the
intestine of the ox which behaves similarly to an untanned hide)
in 2% HCI, then rinse with water.
2. Place the soaked piece in the solution to be tested for 5 min.
3. Wash with distilled water and transfer to a 1% solution of
ferrous sulphate.
A brown or black colour on the skin denotes the presence of tannins.
B) Ferric chloride solution:
Tannins are extracted from vegetable powdered plant with hot water.
Add few drops of ferric chloride solution a blue colour or precipitate is
produced with hydrolysable tannins and green colour or precipitate with
condesed tannins.
Uses:
1- Tannins are used in diarrhea and as haemostatic in hemorrhoids.
2- Commercial tannins are used in leather industry and in manufacture
of ink.
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