THE COLORIMETRIC DETERMINATION OF HYDROGEN ION CONCENTRATION AND ITS APPLICATIONS IN BACTERIOLOGY PART III

Abstract

SECTION XIV. ELECTROMETRIC AND COLORIMETRIC COMPARISONS As indicated in a previous section, the solutions which must be dealt with in bacteriological investigations are diverse in-deed and are not subject to a classification which facilitates sys-tematic study of the indicator errors. We have. considered it wise, therefore, to omit, for the present, detai.led consideration of particular media, and have studj0ed,Qniderable variety of solutions upon which we havema de more than 400 electrometric measurements and many more colorimetric comparisons. These comparisons between the colorimetric and electrometric meas-urements are given iwr tables 4 to 19. In these comparisons we shall consider the hydrogen electrode measurements as the standard, since they were made with an equipment and iui a manner which has proved accurate and reli-able. The details of the special electrometric methods used will be found in previous papers by Clark (1915 d) and Clark and Lubs (1916). Occasionally an electrometric determinator was made upon a solution not well adapted to hydrogen electrode meusurements.s Those familiar with the subject will recognize such a solution in Dorset's egg medium, for instance. In one or two other cases electrometric determinations with solutions in a P. region where their buffer effect is small have been somewhat uncertain. In general, however, the electrometric measurements may be trusted to the second decimal of PH if it be granted that the correct order of magnitude of liquid contact potentials has been properly determined (Clark and Lubs 1916). Where the measurements are not to be so trusted the second decimal place will be omitted. In the colorimetric comparisons we have purposely avoided, in this preliminary survey, some of the best colorimetric methods which we might have applied, such as the use of optical instru-ments of correct design, and we have used the somewhat wide interval of 0.2 P. in the standard comparison solutions between