1.2.1.2  Spot tests for detection of various types of adulteration

Mahua cake

To water extract of the test feed, add concentrated H SO (sulphuric acid). Violet or pink colour indicates the presence of mahua cake.

Argemone seeds

To water extract of test feed, add conc. HNO (nitric acid). Appearance of brown-reddish colour indicates the presence of argemone seeds.

Detection of castor cake in feedstuffs

When feed is treated with potassium chlorate, the castor cake is destroyed and settles down at the bottom.

Detection of neem seed cake in feedstuffs  and edible oil cakes

The coarsely powdered feed stuffs are percolated three times at room  temperature with 95 per cent alcohol. The total percolate is concentrated under reduced pressure till a thick syrupy amber coloured residue is obtained, which is treated with different solvents to extract a crystalline product (Nimbine). It is cautiously dissolved in concentrate sulphuric acid, the resultant brown solution changes to cherry red on addition of small quantity of concentrated nitric acid. The crystalline product gives a yellow colour with tetranitromethane. Alcoholic solution of the crystalline product shows a sky blue fluorescence under ultraviolet light.

Detection of linseed meal in animal feeds

A small quantity of feed is treated with 1 or 2 drops of dilute sulphuric acid in a test tube. It is some time necessary to add some granulated zinc and more acid. The mouth of the test tube is covered with a disk of filter paper moisten with a drop of reagent. Depending upon the amount of hydrogen cyanide produced a more or less intense blue colour appears on the reagent paper. Gentle warming in water bath is advisable when small quantity of cyanide is suspected.