Chart presentation of recent work on indicators / by George Stanley Walpole ; [communicated by H.H. Dale].

  • Walpole, George Stanley.
Date:
[1910?]
Catalogue details

Licence: Attribution 4.0 International (CC BY 4.0)

Credit: Chart presentation of recent work on indicators / by George Stanley Walpole ; [communicated by H.H. Dale]. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    8/14 (page 210)
    exponent of the liydroxyl ion concentration then we may write that for aqueous solutions PoH ~ 14 14 pj' This relationship is expressed in the diagram. On the right hand side the numerical value of the negative exponent of the hydroxvl ion concentration may be read off directly. On the left are drawn rectaugiilar spaces each indicating the range of hydrogen ion concentration over which tlie indicator repre.sented by that space changes its tint. Litmus, for example, it is seen, shows colour changes from about pf, = 4 u to 8‘3. The relationship of indicators one to another is shown at a glance, and it can be seen, at once, which indicators will be sensitive to slight changes of ionic (•oncentratiou for any given value of pj^. Sorensen has examined many indicators, and has divided tliem into ftve groups. The ranges of tiiese groups are repre.sented by the rectangles on the extreme left. At the right of the diagram I have inlroduced the results of a few observers on the values of p,*, for some of the more familiar physiological tliiids. Certain limitations of the colorimetric method of determiningp,*, must be recognised and corresponding j)recautions taken if reliable results are to be obtained. As these are dealt with under the heading ‘ Sources of error of the method ’ in Sorensen’s pajjer, tlieir re])etition here is unnecessary. An attempt has been made in the chart, by broken lines at the end of the frame in which the words ‘ congo-red ’ are placed, to show the peculiar nature of this indicator. 'J’he chart was first prepared for my own use in connection with a method for titrating pigmented physiological fluids.^ Its convenience for reference to laboratory workers who have to consider the behaviour of solutions whose reactions are nearly neutral, and the possibility of its use to teachers elucidating the theory and uses of indicators, have led me to its publication. I have added a few examples illustrating the use of the chart. 1-EXAMPLE \.—The determination of the hydrogen ion coneerUraiion of a giivn sample of urine. Small quantities of urine are placed in each of a series of test tubes, and trials ma<le uith a few indicators. It is found to be within the limits of the colour range of litmus and neutral 1. Froc. Physiol. Soe.. Vol. XL, p. 27. 1910.