On chromic acid as an antiseptic disinfectant, etc. : more especially as compared with carbolic acid / by John Dougall.

  • Dougall, John
Date:
[1871]
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Licence: Public Domain Mark

Credit: On chromic acid as an antiseptic disinfectant, etc. : more especially as compared with carbolic acid / by John Dougall. 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.

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    hands of two professors—one a celebrated toxicologist—when attempting to show it to their class; and am not aware that any explanation of the cause has been given, though it seems to me as follows:—It is obvious from the fact of chromic acid giving the coloured test at all, that to it alone the reaction is due when bichromo is used ; that neither the potash in the latter, nor the sulphate of potash resulting from the addition of sulphuric acid, are indispensable agents in developing the reaction. Further- more, as strong sulphuric acid is necessary both when using bichrome and chromic acid, per se, it is evident that when added to the first, the result is the formation of sulphate of potassium, water, and free chromic acid; indeed this is exactly the method by which the latter is prepared, as shown in the following equa- tion :—K2O 2CrOg -f H2SO4 = K2SO4 + H^O X SCrOg. The chromic acid, being thus liberated, oxidises the strychnia, and the coloured reaction is afterwards developed by the strong sulphuric acid. But it may happen that the sulphuric acid, which might have proved strong enough for isolated chromic acid, is rendered too weak for bichrome in consequence of being partially neutralised by the base of the latter, and further diluted by the water, which, as seen in the foi-mula, is generated by the hydrogen of the sul- phuric acid combining with the oxygen of the potash ; and this, I believe, is the most frequent cause of non-success of the test. With isolated chromic acid failure is of course impossible from such a source; and when used as described, the reaction is not only con- stant, but greatly more delicate. Another cause of lapsus with the bichrome, also applying in part to chromic acid, is seen in the following table of results :— Bichrome added to solution of strychnia, then sulphuric acid added = much colour. Sulphuric acid added to solution of strychnia, then bichrome added = considerable colour. Sulphuric acid added to bichrome, then solution of strychnia added = almost no colour.
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