Role of gold analysis in forensic science
Gold is a precious valuable metal.
The human beings are fascinated for their ornaments.
Physical properties of gold.
• It is a chemical element.
• Symbol= AU
• Atomic number = 79
• In its purest form -
It is bright ,dense,soft,malleable, slightly reddish yellow ductile metal.
• It is one of the least reactive element.
• It is solid under standard condition.
Chemical properties of gold.
• Resistant to individual acids, but can be dissolved by aqua regia .
• Aqua regia is a mixture of HCl + concentrated nitric acid in 3:1 ratio.
• It doesn’t react with air,water,bases under normal conditions.
Resources in India
Largest resources of gold are
• Bihar – 44%
• Rajashthan – 25 %
• Karnataka – 21 %
• West Bengal – 3 %
Analysis of gold.
– depends upon the nature of sample and examination.
Various colour test /chemical test / analytical techniques are used in labs.
Qualitative estimation of gold.
• pH paper test
Moist the pH paper with distilled water
Dip it with exibit or its distilled water extract
Observe the pH .
● pH less than 7 indicates the presence of acid .
●pH more than 7 indicates the presence of alkali.
• Ring test
Add about 3 ml of freshly prepared saturated solution of ferrous sulphate to
About 2 ml of the nitrate solution (filtrate of the exibit ) in a test tube
Pour 3-5 ml conc.sulphuric acid slowly down the side of the test tube
a brown ring will form where the liquids meet which indicates the presence of nitrate.
• Test for gold: Test with benzidine 4.
Reagent = 0.5 % solution of benzidine in 10 % acetic acid.
Procedure : Few drops of exibit solution is placed on filter paper + add 1-2 drops of benzidine reagent unit
A blue colour appears on filter paper which indicates presence of gold.
Quantitative estimation of gold in aqua regia
1. ICP – Inductively coupled plasma technique.
2. Ion chromatography
3. Atomic absorption spectroscopy
4. Atomic emission spectrography
5. Fluorescence – XRD technique.
Forensic significance of gold analysis.
Gold in dentistry – inert to saliva.
Never corrode and harmful if swallowed.
Gold in medicine-
Chemical compounds made from gold used to treat inflammation.
Eg: Gold sodium thiosulfate,
Gold sodium thiomalate
Gold in food and drink-
Because it is inert to all body chemistry.
It has no taste .
Gold in aerospace-
It offers excellent protection from EMR.
The wind sheilds of jets also uses see through layer of gold.
Different kinds of jwellery are made out of it.
In cleaning process criminals alleged to remove few milligrams of gold and cheat the customers .
The polishers explore various methods for stealing gold:
•Stealing gold from jewellery with chemical ( aqua regia ).
• Making jwellery having low carat mixed with other metal.
• Making jewelry mixing iridium for weight gain to fool the buyers
And many more.
In case of aqua regia
The solution is seized from the scene of crime by police then sent to lab under IPC section 420.
