Hissink, D. J.

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Soil Research—Bodenkundliche Forschungen Recherches sur le Sol Supplements to the Proceedings of the International Society of Soi lScience— Beiheft zu den Mitteilungen der Internationalen Bodenkundlichen Gesellschaft — Supplements aux Comptes Rendus de l'Association de la Science du Sol Vol./Bd.n 1930 No 2 Report of the Committee on Soil Reaction Measurements Second Internat ional Commission President: Prof. Dr. Alex. A. J. von 'Sigmond Part II. Conclusions and Recommendations The Committee has already published (Soil Research, Vol. 2, 1930, p. 77—139) the methods and the results of its work. It has held one meeting on July 8th, 9th, 10th and 11th 1930, in the Geologische Landes-anstalt, Berlin. The following members were present: Dr. D. J. His sink, Groningen (Holland) (Chairman); Dr. E. M. Crowther, Harpenden (England); Dr. S. B. Hooghoudt, Groningen (Holland); Prof. Dr. S. Tovborg-Jensen, Lyngby (Denmark); Dr. S. Kuhn, Budapest (Hungary); Dr. M, Trenel, Berlin (Germany) and Dr. Presenius, Berlin (Ger-many) (representing Prof. Dr. 0. Lemmermann, Berlin, Germany). Detailed comments and statistical analyses of the results had previously been circulated by several members, and, after a full dis-cussion, it was unanimously agreed to make the following report and recommendations. Comparison of methods "With a few exceptions, the pH values obtained by four independent methods in several Institutes showed satisfactory agreement. Quinhydrone method Since this Committee was set up primarily as the result of criticisms at Budapest of the quinhydrone method, we have directed our attention primarily to this method. Our work has shown conclusively that many soils give much higher (more alkaline) equilibrium pH values by the Beiheft Bodenkundliche Gesellschaft 10 — 142 — quinhydrone than by other methods (see Heintze and Crowther's paper, Budapest Trans. A) and, further, that these soils are the ones which show a rapid increase in pH within the first few seconds after the addition of quinhydrone (see Kiihn and Scherf's paper, ibid.). All Institutes obtained similar equilibrum pH values for these erratic soils. Out of a total of 28 soils examined, 8 gave erroneous results by the quinhydrone method, the excesses of the Qh pH over the H2 pH being 0.3, 0.4,0.5,0.6,0.7,0.8,0.8, 1.3. In some of the Institutes each of the 8 erratic soils, but none of others, showed a marked initial potential drift from 15 (or 8) seconds to 60 seconds after adding the quinhydrone. One Institute failed to detect this initial drift because the soil and quinhydrone were shaken together for several seconds before the time readings commenced. At Rothamsted similar errors in these 8 soils when quinhydrone was added in colorimetric measurements. Proposed Quinhydrone Method Apparatus: The quinhydrone, electrodes, and KC1 bridge should be prepared in accordance with the instructions in Part 1 of this Report (Soil Research, Vol. 2, 1930, p. 81—83). The ratio of soil to liquid has not been examined by us and we therefore retain the 1 : 2.5 ratio adopted at the Groningen Conference. Preliminary approximate measurement It is necessary to make a rapid measurement in order to ascertain whether or not the soil is suitable for the quinhydrone method. The soil and water are shaken together for one minute, the quinhydrone added, and the mixture is immediately shaken vigourously for not more than 2 seconds. All time intervals are measured from the time of adding the quinhydrone to the soil. The electrode and KC1 bridge are introduced and the potential measured at 10 (or at most 15) 30 and 60 seconds. Final more accurate measurement _ Where the increase in apparent pH value from 10 to 60 seconds in the preliminary measurement is less than 0.2, the soil may be regarded as suitable for the quinhydrone method, but the determination should be repeated with less rapid manipulation. The soil and water are shaken or one minute, as in the preliminary measurement, but, after adding the quinhydrone, the mixture is shaken for 10 seconds and the potential measured at 60 seconds. — 143 — Where the increase in apparent pH value from 10 to 60 seconds in the preliminary measurement is more than 0.2, the soil is unsuitable for the quinhydrone method and it is better to use some other method. In this case approximate pH values may, however, be obtained by the quinhydrone method if the preliminary measurement is repeated on a new soil sample and the reading taken at 10 seconds. In recording such approximate results it should be clearly stated that they are „10 second values". Hydrogen electrode We have found that the sintered glass crucibles of Schott, Jena, are convenient as hydrogen electrode vessels. The flask and funnel shown in Fig. Ill, p. 99 of Part I of this.Report are not necessary and may with advantage be replaced by a rubber stopper inserted below the sintered glass plate (Fig. I). Alternatively a Schott, Jena, sintered glass funnel may be used (Fig. II). Constant potentials may be obtained within about one minute provided that: a) the filter is sufficently coarse-grained to allow a rapid stream of hydrogen; b) the film of platinum or palladium deposited on the electrode is very thin and c) only a few millimetres of the electrode are immersed in the suspension. The KC1 bridge should not be lowered into the suspension until immediately before the potential measurement. With alkaline soils, especially in the naturally moist state, the removal of carbon dioxide by the current of hydrogen introduces an error and it is better to use a vessel of the Clark type. Commercial hydrogen, preferably electrolytic, is often suitable for use without further purification. Colorimetric Measurements Some Institutes found very good agreement between colorimetric and electrometric measurements, but others did not. Although it is possible to obtain satisfactory results by working with great care, the colorimetric method is not at present a simple one. The selection of the appropriate indicator is of the highest importance. It is essential that indicators such as methyl red, which are adsorbed by the soil, should not be used in soil suspensions. We have found that the barium sulphate method of Kuhn for clearing the suspension is very useful 10* — 144 — . and we recommend its trial in other laboratories. Several of the cooper-ating Institutes propose to repeat the colorimetric determinations with a "better technique. Antimony Electrode We make at present no proposals on this method as it has not been sufficently tested. Aqueous and potassium chloride suspensions "We would urge the more general adoption of the Groningen re-commendation that reaction measurements should be made both in aqueous and in 1 N KC1 suspensions. The pH values in 1 N KC1 appear to be less influenced by changes in biological and meteorological v conditions and thus measure a more permanent characteristic of the soil. Aqueous suspensions should, of course, be used in studying seasonal and similar fluctuations. Berlin, July 11th 1930 D. J. Hissink E. M. Crowther S. B. Hooghoudt S. Tovborg Jensen St. Ktihn M. Trenel Bericht des Ausschusses zur Prlifung der Methoden zur Bestimmung der Bodenreaktion Zweite Internationale Kommission Vorsitzender: Prof. Dr. Alex. A. J. von 'Sigmond II. Teil. Beschlusse und Vorschlage ' Die Ergebnisse der internationalen Prufung der Methoden zur Be-stimmung der Bodenreaktion sind bereits in Soil Research, Bd. II, 1930', S. 77—139 veroffentlicht worden. Die Sitzung wurde am 8. bis 10. Juli auf Einladung von Dr. Trenel in der Geologischen Landes-anstalt, Berlin, abgehalten. Anwesend waren als Vorsitzender Dr. D. J. Hissink, Groningen (Holland); Dr. E. M. Crowther, Harpenden (England); Dr. S. B. Hooghoudt, Groningen (Holland); Professor Dr. S. Tovborg-Jensen, Lyngby (Danemark); Dr. S Ktihn, Buda-pest (Ungarn); Dr.M.Trenel, Berlin (Deutschland) und Dr Fresenius, Berlin (Deutschland) als Vertreter von Prof. Dr. 0. Lemmermann, Berlin (Deutschland). 

Report of the Committee on soil reaction measurements Pt 1 Results of the comparative investigation on quinhydrone electrode method

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Report of the Committee on soil reaction measurements Pt 1 Results of the comparative investigation on quinhydrone electrode method

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