binding en een hoogere uitbuiting van het fosforzuur van de gegeven meststof veroorzaakte. Het is bekend, dat humus groote hoeveelheden Fe+++ enAl+++ kan binden(4, 13, 18, 19, 22) en deze kationen a.h.w. desactiviteert, wat betreft de fosforzuur-vastlegging. Naar aanleiding van genoemde humuswerking moge volledigheidshalve nog gewezen worden op de analoge werking van het kiezelzuur inde bodem (4, 28).
SUMMARY. Experiments are worked out with a Na-permitute, which, as appeared from the total analysis and from a percolation experiment with a NH4CI sol., contains all Na-ions in an easily exchangeable form. From the original researches of Ganzen follows that quite probably the Na-ions are linked indirectly tot the Al-ions. In various graduated flasks of 100 cc., quantities of H3PO sol., increasing quantities of NaOH sol. and water to a total of 100 cc. have been added; in the filtrate after different duration of contact between the phases the pH, [PO4'"], [Na+] have been determined. About the fixation of the PO4-ions which has been examined over a pH range of 2.96 up to 12.32, the following theory has been developed. After H-ion exchange added in the form of H3PO4 sol. with Na-ions of the Na-permitute, Na-H-permutite is fórmed. The unstable H-Al-silicate will remain as such fora more or less extensive part depending on the H-ion concentration in the liquid, and will be changed into AIPO4 for the remaining part. This anionadsorption which is generally considered to be a more physicalchemical process, which takes place at the permutite surface (topochemical-reaction), can be considered now as a mere Chemical reaction. The decrease of the P04-concentration of the solution relates equivalently to the quantity of Na'-ions exchanged from the permutitesurface. In the alkaline medium as to the cation-adsorption the same results have been obtained as have been found by Jenny. The results however have been interpreted otherwise and there has been concluded to alkaline adsorption, consequently to a polar linking of NaOH molecules. This alkaline adsorption, however, is much less than the cation-adsorption which takes place in neutral and acid media. Ook op deze plaats betuig ik Prof. Ir. J. Hudig mijn welgemeenden dank voor de interesse en steun, ondervonden gedurende dit onderzoek, hetwelk verricht werd in het landbouwscheikundig laboratorium te Wageningen in 1935. LITERATUUR. 1. Cernescu, N. C. Kationenumtausch und Struktur. Diss. Zürich 1931. 2. Davis, L. E. Sorption of phosphates by non calcareous Hawaiian soils. Soil Sci. 40, 1935, 129—158. 3. Doughty, J. L. Phosphate fixation in soils, particularly as influenced by organic matter. Soil Sci. 40, 1935, 191—202. 4- Gaarder, T. Die Bindung der Phosphorsaure im Erdboden. Vestlandets Forstl. Forsdkssta. Meddel. 18, 1935.