Hydrogen compounds that test low on the pH scale. Acids may be liquids, gasses, or solids—organic or inorganic. Acids were used frequently in 19th-century photographic processes, and they are addressed in this encyclopedia under specific entries.
↑Osterman, Mark. 2007. Acids. In The Focal Encyclopedia of Photography: Digital Imaging, Theory and Applications, History, and Science, ed. Michael R. Peres, 37, Focal Press.