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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    to determine the end reaction definitely, as Hewes does not now consider the other indicator sufficiently accu- rate. The total acidity due to free acids and acid salts (chiefly phosphates) is then estimated by titrating with Congo red as an indicator, as Hewes states that Congo red is an indicator of the amount of phosphates as well as of free acids. By this means the total acidity and amount of free HC1 are of course directly indicated, and if free HC1 be present, the combined HC1 is indicated by the difference between the total acidity and the result obtained by titration with Congo red. If no free HC1 is present and one wishes to know whether any combined HC1 is present he may use Ewald's modification of Sjoeq- vist's method. The first error in this method is in the recom- mendation that the titration for total acidity (with phenophthalein) be carried to the point where a deep- red color is obtained and not stopped, as is usually recommended, when a pink color first appears. Top- fer pointed out that phenophthalein always gives too high results when used as an indicator in albuminous solutions. I have tested this statement and confirmed its accuracy, and any one can similarly convince him- self by titrating solutions: of peptones in HC1 of known strength with phenophthalein. To continue the titration until a deep color is obtained would therefore increase the error always attendant upon the use of phenolphthalein. The most important error lies, however, in the use of Congo red as an indicator for the free acids and acid salts. The statements that I have previously made concerning dimethylamidoazobenzol apply with equal force to Congo as an indicator of free acids. Phloroglucin-vanillin is generally recognized to be an accurate indicator, and its accuracy is well demon- strated by Cohnheim and Krieger's method—it always