ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Litmus solution being added to an acid. Litmus is an indicator, a chemical that has a different colour depending on whether it is in an acidic or alkaline environment. In acids it is red. In alkalis it turns purple/blue. Litmus is derived from the lichen Lecanora tartarea. For litmus being added to an alkali, see image A500/483.
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