The Discrepancy between Electrometric and Colorimetric (Phenol Red) Determinations of cH according to the Salt-content of the Solution

THE method of Friedenthal [1904] and Salm [1904] for the approximate determination-of CH by addingvarious indicators to the solution was developed by Michaelis and Rona [1908, 1909] were the first to draw attention to aberrations of the colorimetric method due to the salt-content of the solution under investigation. For accurate work it is necessary to be aware of these and to correct for them. The entire blame was attributed to the indicator, until it was pointed out by Sorensen and Palitzsch [1910] that the addition of NaCl or KCI to a buffer solution of phosphates also altered the CH, as determined electrometrically, and that the discrepancy between the two methods was the algebraic sum of the influence of the electrolyte upon the dissociation of the weak acid of the buffer mixture and the indicator respectively.