Add a few drops of tincture of Iodine or Iodine solution.
Formation of blue colour indicates the presence of starch.
Procedure - Test for Urea
Take a teaspoon of milk in a test tube.
Add ½ teaspoon of soybean or arhar powder.
Mix up the contents thoroughly by shaking the test tube.
After 5 minutes, dip a red litmus paper in it.
Remove the paper after ½ a minute.
A change in colour from red to blue indicates the presence of urea in the milk.
Procedure - Test for Formalin
Take 10 ml of milk in a tests tube and add 5 ml of conc. sulphuric acid from the sides of the wall without shaking.
If a violet or blue ring appears at the intersection of two layers then it shows presence of formalin.
Observations and Findings:
After the solvent has risen about 15 cm you will notice two different spots of blue and red colors on the filter paper. The pattern is called chromatograph.
Conclusions:
Over time, we see a pattern composed of various colors / components of the ink
Theory:
Household milk generally contains starch an impurity. In some cases, it might have urea or formalin (added to increase shelf life of milk).
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