Color Standards for the Colorimetric Measurement of H-Ion Concentration

Abstract

In an article of the above title recently published in this journal, Medalia (1920) presents a system of color standards somewhat similar to one published by me a little before (Gillespie, 1920). The work is evidently independent of mine, but the proposed tables are in serious disagreement with the results of my work. The cause of the disagreement apparently does not lie in a conflict of observations, but in the plan followed by Medalia in preparing the tables.

Hydrogen-Ion Concentration as Related to the Fusarium Wilt of Tomato Seedlings

“…It may be added, however, that the series of standard buffer solutions employed in this inves¬ tigation gave perfect agreement when compared with a corresponding series of standard buffer solutions (belonging to the Department of Bacteriology, University of Wisconsin), the hydrogen-ion concentration of which had been checked by the electrometric method. The method of obtaining the soil extracts was essentially that described by Gillespie (6).…”

Further Observations on “Color Standards” for the Colorimetric Determination of H-Ion Concentration

“…A criticism (Gillespie, 1921) of this method of preparing color standards based on theoretical mathematical calculations has no weight, if the colors, actually prepared as described, do actually match other solutions of known pH. The calibration of each "'pair" in the author's series has been made by such actual comparisons, and the pH values assigned are based upon actual visual agreements with known standards and not from hypothetical relations.…”