PHILIPPE PSAILA / SCIENCE PHOTO LIBRARY PHILIPPE PSAILA / SCIENCE PHOTO LIBRARY
Fingerprint detection. Forensic scientist dipping a letter in a solution of ninhydrin in order to detect any fingerprints on it. Ninhydrin is a chemical that binds to the proteins in the sweat in fingerprints. It changes colour during this reaction, allowing previously invisible prints to be detected. Ninhydrin is typically used to detect prints on porous surfaces such as paper. Fingerprints are unique to every individual and can thus be used to determine who has handled the letter.
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