Detecting free Iron :   Spray the surface with a solution of potassium ferricyanide. If free iron is present, a blue color will appear. This test is extremely sensitive and often gives false positive results, that is, it gives an indication of iron being present when it really is not. The ferroxyl solution must be made fresh each day by addition with Nitric acid. The ferroxyl tests are described in ASTM A380.


Ferroxyl indicator is a solution containing potassium hexacyanoferrate(III) and phenolphthalein. It turns blue in the presence of Fe2+ ions, pink in the presence of hydroxide ions, it can be used to detect metal oxidation. It is often used to detect rusting in various situations.

It can be prepared by dissolving 10g sodium chloride and 1g potassium hexacyanoferrate(III) in distilled water, adding 10 cm3 phenolphthalein indicator, then making up to 500 cm3 with distilled water.

Vinylidene Chloride (VDC)

Vinylidene chloride, also called 1,1-dichloroethylene, a colourless, dense, toxic, volatile, flammable liquid belonging to the family of organic halogen compounds, used principally in combination with vinyl chloride, acrylonitrile, or methyl methacrylate for the manufacture of a class of plastics called saran. Vinylidene chloride is also used as a starting material for making methylchloroform, or 1, 1, 1-trichloroethane, and a solvent useful in cleaning electrical machinery.

Indole TEST :  ( Indole produced by microorganisms )

The ability to degrade amino acid to identify end products to differentiate bacteria.Indole can be detected to the culture growth ( Pure bacterial culture must be grown in sterile tryptophan or peptone broth for 24-48 hours before performing the test. ) by reaction with 5 drops of Kovac’s reagent to produce a red  or red violet colour. 

KOVAC’S Reagent - ( para-Dimethylaminobenzaldehyde in isoamyl alcohol and Concentrated hydrochloric acid ) 

Ehrlich Reagent - ( para-Dimethylaminobenzaldehyde in ethyl alcohol and Concentrated hydrochloric acid ) 

INDOLE TEST is suitable for