ANDREW MCCLENAGHAN / SCIENCE PHOTO LIBRARY. ANDREW MCCLENAGHAN / SCIENCE PHOTO LIBRARY.
Acid test: blue litmus paper turns red in the presence of lemon juice (citric acid). The blue test paper is impregnated with litmus solution (derived from lichens) which turns red in the presence of acids; red litmus paper turns blue on contact with alkaline solutions.
Model release not required. Property release not required.