Crime Scene Investigator Network Newsletter

The Chemistry of Gunpowder
Most historians agree that the ancient Chinese discovered what we refer to as gunpowder. During the 9th century Taoist monks (alchemists) searching for an elixir of immortality accidentally stumbled upon the basic formula for black powder—a mixture of saltpeter (potassium nitrate), charcoal and sulfur. Later versions of gunpowder contain these same basic ingredients, but the overall chemistry evolved to include modifications that produced "smokeless gunpowder," Cordite, which eliminated the sulfur. Other advances added materials such as nitrocellulose (guncotton) and glycerol trinitrate (nitroglycerine).

Gunpowder—regardless of the formulation—has one specific purpose: the creation of oxides of carbon; in particular, carbon dioxide. The rapid creation of this gas is the propelling force that pushes a projectile (bullet) down through the barrel and on toward its intended target.

What is GSR?
Gunshot residue contains burned particles (potassium nitrite) and some unburned particles (potassium nitrate), and for decades criminal investigators collected these particles by applying melted paraffin wax to a subject's hands. Upon removal of the wax cast, a reagent containing diphenylamine and sulfuric acid was applied to the cast. The development of blue specks was indicative of the presence of nitrates.

But in the 1970s the courts took the position that the presence of nitrates in the environment was a common occurrence, and the dermal nitrate test was no longer a valid means to determine that the subject had fired a gun.

Primer Residue
When a gun is fired, the gunshot residue particles—small particles produced during the gunpowder explosions—are emitted from the back of the weapon and the muzzle. These particles fly onto the skin and clothing of the person

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