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Estimation of nitrogen by fumeless digestion. Part III

Extension of chromo-sulphuric acid digestion to include large quantities of nitrates

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Proceedings / Indian Academy of Sciences

Summary

  1. (1)

    The incomplete reduction of nitrate (over 50 parts per million) in the chromo-sulphuric acid digest by zinc is traceable to the presence of the mercury salt in the digesting mixture. The mercury forms a coat of hydride around unattacked zinc and thus prevents further action with acid.

  2. (2)

    The interference of mercury can be eliminated and accurate estimates of nitrates in soils (upto 300 parts per million) obtained by adding extraquantity of sodium sulphite to the digest until a black precipitate is obtained. The suspension is then raised to boil and treated with zinc in the usual way.

  3. (3)

    The efficiency of zinc in reducing nitrate in the digest is traceable to the joint action of chromium and sulphite. On treatment of acid with zinc the latter forms hydrogen sulphide which is directly responsible for the removal of small quantities of nitrous acid that may be formed during reduction. The mechanism of the related processes has been discussed.

  4. (4)

    The commoner samples of reduced iron contain ferrous sulphide, so that the non-formation of nitrous acid during reduction of nitrate by that reagent is traceable to hydrogen sulphide. The ferrous salt present in solution behaves in a manner similar to the chromium salt and thus prevents loss of nitrogen during reduction.

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References

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Authors and Affiliations

  1. Department of Biochemistry, Indian Institute of Science, Bangalore

    C. R. Harihara Iyer & R. Rajagopalan

Authors
  1. C. R. Harihara Iyer
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  2. R. Rajagopalan
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Additional information

Communicated by Prof. V. Subrahmanyan,d.sc., f.i.c.

Our thanks are due to Professor V. Subrahmanyan for his keen interest in the work.

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Iyer, C.R.H., Rajagopalan, R. Estimation of nitrogen by fumeless digestion. Part III. Proc. Indian Acad. Sci. 4, 122–127 (1936). https://doi.org/10.1007/BF03049766

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  • DOI: https://doi.org/10.1007/BF03049766

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