This document discusses astringents and their properties. It provides information on zinc sulfate and potash alum, including their formulas, preparation methods, properties, assay methods, and common uses. Zinc sulfate and potash alum are both used as astringents to constrict tissues and stop bleeding from minor wounds. They are also used as nutritional supplements or in water treatment processes.

2. INTRODUCTION
 An astringent is a chemical that shrinks or constricts body
tissues. The word derives from the Latin adstringere, which
means "to bind fast". Calamine lotion, witch hazel, and
yerba mansa, a Californian plant, are astringents.
 These are the drugs used to harden and protect the skin
and to stop bleeding from minor scratches. These drugs
cause contraction of cells by precipitating proteins from
their surfaces , there by , protects the skin.
 Astringents can be very drying for the skin. Avoid alcohol-
based and chemical-based astringents if you have dry or
sensitive skin.

3.  If you have acne and dry skin, an astringent may further
irritate breakouts, leading to peeling and additional
redness. Also, avoid alcohol-based astringents if you have
eczema or rosacea. Instead, try a hydrating toner or oil-free
moisturize, or ask a dermatologist for recommendations.
They may be able to prescribe a more effective treatment.
 If you have oily skin and are going to use an alcohol-based
astringent, consider spot treating only the oily parts of your
skin. This can help prevent irritation . Always follow up
astringents with sunscreen. This will help protect your skin
from sun damage.

4. ZINC SULPHATE
 Zinc sulfate is an inorganic compound. It is used as a
dietary supplement to treat zinc deficiency and to prevent
the condition in those at high risk. Side effects of excess
supplementation may include abdominal pain, vomiting,
headache, and tiredness.
 Formula : ZnSO₄.7H2O
 Molar mass : 287.6 g/mol
 Density : 3.54 g/cm³
 Boiling point : 740 °C
 ChEBI ID : 35176
 Classification : Sulfate , Inorganic compound

5. PREPARATION
1. It is prepared by treating zinc chloride with sodium
sulphate.
ZnCl2 + Na2SO4 = ZnSO4 + 2NaCl
2. It is also prepared by boiling metallic zinc with dilute
sulphuric acid
Zn + H2SO4 = ZnSO4 + H2

6. PROPERTIES
 It occurs as transparent crystals or white crystalline powder
, odourless , has metallic or astringent taste.
 Soluble in water and the aqueous is acidic in nature.
 It is soluble in alcohol.
 It forms double salt with potassium and ammonium
sulphate ( M2SO4 , ZnSO4 . 6H2O ) in dry air it
efflorescent in nature.
IP LIMIT
 contains not less than 99.0% and not more than 104.0% of
ZnSO4 . 7H2O

7. ASSAY
Dissolve an accurately weighted amount of substance in
water , add ammonia – ammonia chloride buffer to
maintain pH 10 , add erichrome black T as an indicator and
titrate against 0.05m di sodium EDTA until the color
changes to yellow.

8. USES
 It is used as astringent and reflux emetic ( dose 0.6 to 2.0
gm )
 Zinc sulphate Astringent used topically for skin
wounds/ulcers to assist healing. Also included in some eye
drops for minor allergic conjunctivitis. Orally it is an
emetic, but is not used for this purpose due to toxic effects.
In smaller, sustained release doses, it is used for
nutritional zinc deficiency.
 Zinc is a naturally occurring mineral. Zinc is important for
growth and for the development and health of body
tissues. Zinc sulfate is used to treat and to
prevent zinc deficiency. Zinc sulfate may also be used for
purposes not listed in this medication guide.

9. POTASH ALUM
 Potash alum is a chemical compound widely used as
the potassium sulfate dodecahydrate. It is double salt that
is used commonly in medicine and the water treatment
process. Potash alum is also known as potassium
alum or potassium aluminium sulfate.
 Potassium alum, potash alum, or potassium aluminium
sulfate is a chemical compound: the double sulfate of
potassium and aluminium, with chemical formula
KAl(SO₄)₂. It is commonly encountered as the
dodecahydrate, KAl(SO₄)₂·12H₂O

10.  Formula : KAl(SO₄)₂·12H₂O
 Molar mass : 474.39 g/mol
 Melting point : 92.5 °C
 Density : 1.76 g/cm³
 Solubility in water : 14.00 g/100 mL (20 °C); 36.80
g/100 mL (50 °C)
 Solubility in other solvents : Insoluble in acetone

11. PREPARATION
 Mixing hot concentration solution of potassium sulphate
with an equivalent quantity of hot solution of aluminium
sulphate , after cooling , gives potash alum.
Al2(SO4).18H2O + K2SO4 = KAl(SO₄)₂·12H₂O + 6H2O
PROPERTIES
 It occurs as white powder or transparent crystalline mass.
 It is odourless and has sweet or astringent taste.
 It is soluble in water insoluble in alcohol.
 The burnt alum contains anhydrous aluminium and
potassium sulphate

12. IP LIMIT
 Contain not less than 99.5% of alum
ASSAY
FOR ALUMINIUM-GRAVIMETRIC METHOD
PRINCIPLE
The aluminium present in alum is first precipitated as
aluminium hydroxide by ammonia , which is then ignited
to leave the residue aluminium oxide. The weight of Al2O3
is calculated.
1 gm of residue is equivalent to 9.307 gm of alum

13. PROCEDURE
Dissolve an accurately weighted amount of substance in
water , add ammonium chloride , few drops of methyl red ,
sufficient ammonia solution. The reaction mixture is
boiled and filtered. The residue is washed with 2.5%
solution of ammonium nitrate until the washing is free
from chloride. The remaining residue Al2O3 is dried at
120°C and weighed.
USES
 Used as astringent
 Used as source of Al3 ion
 Used in styptic pencils to stop bleeding from small cuts.
 Used in the preparation of precipitated diphtheria and
tetanus toxoids.