SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Invisible writing. Etching of invisible writing being carried out using sodium hypochlorite (then known as Javelle water or Javel water), an alkaline disinfectant more commonly known as bleach. The word science has been written on a substrate using nitric acid. The word is invisible until dipped in the bleach, when it turns white due to the chemical reaction that takes place. Artwork from the ninth volume (first period of 1892) of the French popular science weekly 'La Science Illustree'.
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