Abstract
DURING a general study of the fauna of the Manx intertidal zone, I have been trying to determine, among other environmental factors, the amount of organic matter in littoral deposits. Several methods of determining the organic content of deposits have been tried, but those involving the reduction of chromic acid have been found to be the most useful because of their rapidity. There are many variations of the chromic acid method1–3; but Allison's4 modification of Schollenberger's5 technique has been used on account of its reasonable accuracy4,6, and because it was supposed to distinguish true organic matter from coal and other ‘inert carbons’4,7. The deposit is heated with excess potassium dichromate and concentrated sulphuric acid, rapidly cooled and diluted, and the excess dichromate titrated against standard ferrous ammonium sulphate4,5. The result is expressed as a percentage of organic carbon, but the theoretical value (1.000 gm. carbon≡16.345 gm. potassium dichromate) has to be adjusted to allow for incomplete oxidation of the carbon4. Unfortunately, I have now found that coal does react with chromic acid under these conditions, and as coal and other reducing substances in addition to true organic matter may be present in littoral deposits, it seems desirable to direct the attention of other shore ecologists to this fact.
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SOUTHWARD, A. Organic Matter in Littoral Deposits. Nature 169, 888 (1952). https://doi.org/10.1038/169888a0
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DOI: https://doi.org/10.1038/169888a0
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