A critique of certain methods of gastric analysis / by David L. Edsall.

  • Edsall, David Linn, 1869-1945.
Date:
[1901]
Catalogue details

Licence: In copyright

Credit: A critique of certain methods of gastric analysis / by David L. Edsall. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    gives much lower results than Congo red even in solutions containing no acid salts but containing albu- mins. It seems wholly proper therefore to decide that Congo red is not an accurate indicator of free acids. I have personally recommended Congo red as an indi- cator for free acids, but am quite willing to acknowl- edge my error in so doing, since I have used the phosphotungstate method and compared results. The more serious portion of the error in using Congo red lies, however, in considering it to be an indicator of the amount of acid salts. There is a general statement in many works which discuss gastric analysis that Congo red reacts to acid salts, but I am not aware that there is any statement that it is a good indicator for these salts. If such a statement is made I think it is wholly erroneous. I have made solutions of monosodic and monocalcium phosphates in about 0.2 per cent strength (about the maximum strength in which acid phosphates are found in the stomach contents) and have titrated these solutions with phenolphtha- lein, rosolic acid and Congo red as indicators. With the monosodic phosphate solution Congo gave no recognizable reaction. With monocalcium phosphate solution a slight though distinct reaction was obtained, but the reaction vanished after the addition of 0.3 cubic centimetres of decinormal sodium hydrate, while it took 2.3 cubic centimetres and 2.5 cubic centimetres of the soda solution to give a reac- tion with the other indicators. It is evident, there- fore, that while Congo red reacts to monocalcium phosphate, it does so only in solutions of consid- erable strength, and is by no means an accurate indi- cator of the amount present, as it shows only about one-eighth of an acidity which is due to this salt. This error is sufficient to make the method unre- liable. But one of the most serious errors in this method, as well as in Topfer's, is the use of three