The Use of Litmus Paper as a Quantitative Indicator of Reaction

In dealing with nearly neutral solutions of feebly dissociated electrolytes, especially when they are highly coloured, it is frequently convenient to gauge reaction by the use of litmus paper, and so avoid either electric measurement or the introduction of a fluid indicator into a comparatively large volume of fluid. And it has been found that if suitable precauitions are taken quite reliable informiation can be obtained as to the HE ion concentration of such fluids in this way. The apparently contradictory results obtained in such cases by using different commercial samples of litmus paper, iTnmersing the paper for a short or a long time in the fluid, using one drop on a piece of paper or a small piece of paper in a considerable volume of fluid, and so on, are capable of simple interpretation.