[34] E. C. Hansen, Studies in Fermentation (Copenhagen), p. 98.
[35] Proc. Royal Soc. of Edin., xxxvii., pt. iv., p. 759.
[36] E. A. Schäfer, Text-book of Physiology, vol. i., p. 25 (W. D. Halliburton).
[37] "Denitrifying" means reducing nitrates.
[38] R. Warington, M.A., F.R.S., Journ. Roy. Agricultural Soc. Eng., series iii., vol. viii., pt. iv., pp. 577 et seq.
[39] The saltpetre beds of Chili and Peru are an excellent example of the industrial application of these facts. Nitrates are there produced from the fæcal evacuations of sea-fowl in such quantities as to form an article of commerce. A like form of utilisation of the action of these bacteria was once practiced on the continent of Europe. Economic application is also seen in the treatment of sewage referred to elsewhere.
[40] The course of nitrification may be followed by means of chemical tests. 1. The disappearance of ammonia. 2. The appearance of nitrite. 3. Its disappearance. 4. Appearance of nitrate.
[41] Professor Warington, in Report IV. (p. 526) of his admirable series of papers on the subject, draws attention to Müntz's criticism that the nitrifying organisms only oxidise from nitrogenous matter to nitrites, and not from nitrites to nitrates. Müntz held that the conversion of nitrite into nitrate is brought about by the joint action of carbonic acid and oxygen. Professor Warington's experiments, however, clearly illustrate that the production of nitrates from nitrites in an ammoniacal solution can be determined by the character of the bacterial culture with which the solution is seeded, and that in a solution of potassium nitrite conversion into nitrate can be determined by the introduction of the nitric organism. Professor Warington still adheres to the opinion, in favour of which he has produced so much evidence, that the formation of nitrates in the soil is due to the nitric organism which soil always contains.
[42] British Association for the Advancement of Science, Bristol, 1898, Presidential Address.
[43] British Association for the Advancement of Science, Bristol, 1898, Presidential Address.