The magnetic resonance spectra of the ground 2P multiplets of 11B and 27Al have been remeasured by the method of atomic beams and the coupling constants A3/2, B3/2, and gJ(2P3/2) and gJ(2P1/2) for 11B, and A1/2 for 27Al, have been redetermined to higher precision. Measurements have also been made, by the triple resonance method, of two ΔMJ = 0, ΔMI = ± 1 transitions in both 11B and27 Al and from these the off-diagonal magnetic dipole coupling constants A3/2,1/2 have been determined.These measurements have enabled us to evaluate the magnetic dipole radial parameters [Formula: see text], [Formula: see text], and [Formula: see text] for both boron and aluminum. The departures of [Formula: see text] and the ratio [Formula: see text] from their restricted Hartree–Fock values are plotted as functions of the occupation number N for all elements with (2p)N and (3p)N ground configuration for which data are available. The trends are briefly discussed.

The adsorption from suspension of the humic-and fulvic-acid components of a soil organic-matter extract by bentonite was extremely rapid, and was unaffected by temperature. For the humic fraction the extent of adsorption was : Ca and Mg systems > acid systems > K and Na systems; for the fulvic fraction: acid > Ca > Mg > K and Na systems. Only in the K systems was there an approach to the saturation of adsorption, although cation-exchange-capacity reductions ceased at a low level of adsorption. In the absence of exchangeable calcium there was a sharp fall in the extent of adsorption with rise in pH, particularly above pH 3.5.Only a small proportion of the organic carbon in both the fulvic and humic fractions was usually adsorbed by the bentonite. The remainder of both fractions was found to be relatively unadsorbable, while the re-extracted adsorbed proportion remained highly adsorbable.Adsorption by kaolin in K systems was as extensive as that by bentonite, but in the acid and Ca systems it was much less. For adsorption of humic carbon the order of effectiveness was Ca > acid > K, and for fulvic carbon, acid > Ca > K, as in the bentonite systems. Lepidocrocite, goethite, &Fe,O,.HaO, and gibbsite also removed much fulvic and humic carbon from suspension, particularly at lower pH values.Mechanisms for the adsorption of organic colloids by clays are considered in the light of these results. THE interaction of organic colloids with the clay fraction probably takes place in many soils, and may affect the structural condition, the extractability of the humus, and the rate of decomposition of the organic matter in soils. While the nature of the bonding forces involved in the interactions of many organic com ounds with clays has been widely studied organic matter with clays is still obscure. The object of the work reported here was to study the mechanism of this association, and to examine the possibility that some fractions of soil organic matter are more readily sorbed by clays than others.(Grim, 1g53), the nature o P those involved in the interaction of soil Experimental MethodsThe humic colloids used were extracted from the neutral topsoil of the pastures in the Oxford University Parks with a 0.4 N 2 : I NaHCOd Na,CO, solution of H 9-1 for 2 days at 35" C. This rocedure extracted centrifuged in a bucket-type centrifu e at 3,000 r.p.m., and then slowly about I I per cent. o f! the organic carbon from the soil! The extracts were run through a Sharples supercentri H uge to remove the deflocculated

The extent of organic-matter extraction tended to rise with the pH of the extractant solution, as did the proportion of the humic-acid fraction in the extracts. Chelating reagents extracted more organic matter than other extractants of comparable pH, but extraction by all reagents rose with increasing time and temperature of extraction. The equivalent weights of both the humic and fulvic fractions of alkaline extracts rose with the temperature of extraction, as did the extent of conversion of the humic-acid fraction to acid-soluble compounds. The humicacid fraction was flocculated by various salts to a much greater extent than the fulvic fraction. The nature of soil organic-matter extraction is considered in the light of these results.ALTHOUGH the classical method of extracting soil organic matter with caustic soda still remains quantitative1 the most efficient available, there is evidence that the materials extracte B may have undergone considerable modification in the process, by oxidation and hydrolysis. Hobson and Page ( I 32) found 0.2 N Na,CO, to be rather less than half as effective as 0-5 d NaOH in extraction, but little is known of the effect of pH on the efficiency of extraction or on the degree of modification of the organic matter extracted.Extraction of organic matter by neutral solutions is generally slight, but Simon (1929) found sodium fluoride to be an efficient extractant. Subse uently Bremner et al. (1946, 1949) and Hamy and Leroy (1952) form chelates or co-ordination complexes with calcium an the trivalent metal cations, which often prevent the ready deflocculation of much of the organic matter in soils, are ve efficient in the extraction of humus. of extraction, and pretreatment of the soil with acid, did not great y affect the efficiency of extractions by pyrophosphate, whereas they did influence the efficiency of extractions by NaOH. Such results may imply that, unlike NaOH, the chelating reagents extract only a s ecific fraction of cations which can be chelated by the extractant anion. If such reagents are fairly specific a procedure, more rapid and efficient than that of Tiulin (1938), for the fractionation of soil or anic matter according to purpose of this paper to examine this possibility further.x have s x own that neutral solutions of anions which can recipitate or Bremner and Lees (1949) found x t at time, temperature, and re etition the organic matter present in a soil, namely that floccu H ated by the metal the dominant cation rendering it insoluble cou 'i d be devised, and it is the P Experimental MethodsThe soil used in all extractions was a sample of neutral topsoil from the pasture in the University Parks, Oxford, prepared to pass the I-mm.