pH is an estimate of the concentration of hydrogen ions, so it refers to whether the paper is acidic or basic. pH is equal to the negative logarithm of the hydrogen ion concentration. Paper with a pH less than 7 is acidic; a pH greater than 7 is alkaline, and 7 is neutral. This property is related to the "permanence" of the paper. The pH of paper can be determined in a number of ways, such as:
(1) Determine the pH of the paper extract obtained by disintegration in hot distilled water.
(2) Measure the pH of the paper extract obtained by disintegrating in cold distilled water.
(3) Measure the pH value directly on the surface of the test paper with a wet electrode. These three modes give different test results on the same paper sample.
