ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Blackcurrant juice indicator in an acidic solution (image 1 of 2). Changes in colour (here from purple, the colour of the juice, to red) are a common way to test the pH of a solution. Alkali and acid are the two parts of the pH scale, indicating the hydrogen ion concentration in a solution relative to that found in water. Alkalis (pH 8-14) contain fewer free hydrogen ions than water, while acids (pH 1-6) contain more. Water (pH 7) is considered neutral. See A500/521 for blackcurrant juice in an alkali solution.
Model release not required. Property release not required.