SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Universal indicator paper. Strips of universal indicator paper that have been dipped into solutions of various pH values (hydrogen ion concentrations). From left are strongly acidic solutions (red, pH 1-3), then weaker acids (orange and yellow, pH 4-6), then weak alkalis (blue-green and blue, pH 8-10) and finally at far right strong alkalis (purple, pH 11-14). Neutral solutions (pH 7) show as green.
Model release not required. Property release not required.