Effect of Heat on the pH of Water and Aqueous Dye Solutions

Abstract

IT appears to be generally accepted that the spontaneous acidity of distilled water is due to dissolved carbon dioxide which can be expelled by boiling to restore the pH to about 7.0. Some of my recent work has involved a large number of experiments on the pH of water and staining solutions. This brought to light some interesting phenomena which may be of interest to research workers in the field of biology and medicine. In the first place it appears that freshly distilled water usually has a pH between 5.0 and 6.0, not 7.0. In the experiments referred to above, whatever the pH of the particular sample of distilled water at 20° C it rose gradually until at 100° C it had risen by pH 2.0. That is to say if at 20° C the pH of the water was 5.0, then at 100° C the pH became 7.0, and pH 5.5, for example, became 7.5 at 100° C. Graphs were perfectly linear in every case.