Forensic Ballistics: GSR Chemistry: Walker, Griess and Rhodizonate Tests

UGC-NET Forensic Science Unit V drill on the chemistry of gunshot residue (GSR) and the colour-spot tests used to detect it on the shooter's hands, clothing and target surfaces at the foundations level. Covers the historical dermal nitrate or paraffin test (Teodoro Gonzalez 1933) and the reasons it was discredited after Calvin Goddard's 1935 critique by widespread false positives from urine, fertiliser, tobacco and many household oxidisers, the Walker test for the transfer of nitrite residues from a bloodstained or sooted cloth onto desensitised photographic paper using sulfanilic acid and alpha-naphthylamine, the modified Griess test for nitrites with sulfanilic acid coupled to alpha-naphthol (or N-(1-naphthyl)ethylenediamine) producing an orange-red azo dye for distance estimation, the sodium rhodizonate test for the lead residues left by primer cups and bullet wipe (pink-to-purple with the confirmatory bright-pink shift on acidification with dilute HCl), the diphenylamine test for nitrate and nitrite oxidisers in propellant residue and its specificity limits, the dithiooxamide (rubeanic acid) test for copper from cartridge jackets and primer cups, and the Indian collection workflow under BNSS 2023 (adhesive lifts and tape lifts from hands and cuffs, cotton swabs in dilute nitric acid for SEM-EDX and atomic absorption confirmation of the three-element Pb-Ba-Sb primer-residue particle signature, sample sealing, labelling and chain of custody requirements). Easy-band questions calibrated for first-pass UGC-NET preparation and quick concept refresh.

Targeted at MSc and BSc Forensic Science students preparing for UGC-NET Paper II, NFSU MSc Forensic Ballistics entrance, and FACT chemistry modules, the mock is also a quick refresher for working laboratory staff who handle firearm cases.

Topics covered:

• Dermal nitrate (paraffin) test history, reagent and discontinuation
• Walker test on filter paper for distance estimation by nitrite pattern
• Modified Griess test reagents, colour and distance-estimation use
• Sodium rhodizonate test for lead with HCl confirmation step
• Diphenylamine and dithiooxamide tests for nitrates and copper
• Adhesive lifts and cotton-swab collection for SEM-EDX and AAS work
• Pb-Ba-Sb three-element primer-residue particle signature
• Chain-of-custody and sampling time window under BNSS 2023

Useful for self-assessment before a deeper Unit V GSR revision push. Allow 30 minutes.