Paraffin Test

The detection of nitrates and nitrites present in FDR using a color reaction with diphenylamine in sulfuric acid was first applied to firearms related examinations about 1911, and in 1914 Doctor Iturrioz used paraffin wax as a lifting medium for propellant residue on clothing prior to treatment with

HNO3 Diphenylamine (colorless)

HNO3 Diphenylamine (colorless)

Diphenylbenzadene HNO3 (colorless)

Diphenylbenzadene HNO3 (colorless)

Figure 16.1 Quinoil immonium ion (blue).

Figure 16.1 Quinoil immonium ion (blue).

diphenylamine/sulfuric acid reagent. The use of paraffin wax as a lifting medium led to the test being popularly referred to as the paraffin test.

In 1922, F. Benitez recorded this technique as a method for revealing the presence of propellant particles on the hands of a firer.112-114 In Mexico in 1931, T. Gonzales performed a modified version of Iturrioz's test using molten paraffin wax on the hands of a firer and in 1933 demonstrated the test in the United States. The test has also been referred to as the dermal nitrate test, the diphenylamine test, and the Gonzales test.115,116

The test is conducted by applying melted paraffin wax to the back of a suspect's hands. With a brush, the back of the hand is coated with paraffin wax which on cooling solidifies and can be peeled off the hand. The surface of the cast that has been in contact with the skin is treated with diphenyl-amine/sulfuric acid reagent by dropwise addition or spraying. The reagent produces a blue color with individual particles of nitrates and nitrites. The reaction sequence is as shown in Figure 16.1.117 The detection of dark blue spots was considered as indicative of the presence of nitrates and/or nitrates from FDR.

In 1935, the American Federal Bureau of Investigation pointed out that the test was not specific and had reservations about its use.118 Other evaluations of the technique proved it to be completely unreliable as an indicator of FDR. Common substances such as tobacco, tobacco ash, fertilizers, certain pharmaceuticals, certain paints, and urine also give positive results.119,120 In addition a number of oxidizing agents such as chlorates, bromates, iodates, permanganates, chromates, vanadates, molybdates, antimony(V), and ferric salts also give a reaction.121,122 At the Interpol Conference in Paris in 1968 it was officially concluded that the paraffin test should no longer be used.123

+1 0

Responses

  • Calimero
    Can a parrafin ballistics test burn a suspects hands?
    6 years ago
  • Paula Timonen
    Are paraffin test valid on modern guns?
    3 years ago
  • sanna veitonen
    Why is paraffin test called Dermal Nitrate Test?
    1 year ago
  • alan sinclair
    Who founded paraffin test?
    1 year ago
  • wilma
    What is detected in laraffin test?
    1 year ago
  • MANDY
    What is paraffin casting?
    1 year ago

Post a comment