Chemical Test for Agar

Aim

To identify the chemical characters of a given sample.

Test and Observations

TestObservationInference
Boil 1gm of agar with 10ml of water
until the solution is affected, cool to room
temperature
A slip jet is formed. (Jelly like
mass is formed)
Agar
0.2% solution of agar, + aqueous solution
of tannic acid
No Precipitate is formedDistinction from
gelatin
Warm little sample in alcoholic solution
of pot. Hydroxide
Canary yellow colour is
produced
Agar present
Mount a small quantity of powder in the
solution of ruthenium red and examine
microscopically
Particles acquire red or pink
colour
Presence of
the mucilage in agar.
Add 1 drop of N/10 solution of iodine to
10ml of decoction of agar. Rapidly cool
under tap water to room temperature.
Crimson or Pale yellow colour
is produced
Agar is present
Add 0.5ml of conc. HCl to 4ml of 0.5%
solution of agar. Heat it on the water bath for
30minutes, cool at room temperature and
divide into two portions.
a) Add 3ml of 10% NaOH solution
and Fehling’s solution A and B in equal
quantities and warm over the water bath.
b) Add 10% of barium chloride
solution.
Red ppt of cuprous oxide is
obtained

Slight white ppt of barium
sulphate is
obtained
Reducing sugars
are present
Incinerate agar to ash, add a drop of
con.HCl observe under the microscope
Fragments of diatomsSulphate in agar

Conclusion

From the above morphological characters and chemical tests, the given crude drug is identified as Agar.

References

1.Kokate CK. Practical Pharmacognosy, 4 edition, VallabhPrakashan. Delhi; 1994: 98.

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