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Aim
To identify the chemical characters of a given sample.
Test and Observations
| Test | Observation | Inference |
|---|---|---|
| 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 formed | Distinction 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 diatoms | Sulphate 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.