AbstractThe total unit cell planar specific surface was computed as the sum of planar sorption surface (by a glycerol gravimetric method) and the mica unit cell interplanar surface (corresponding to the K). This sum was found to be constant for a given unit cell formula weight, averaging 773 m.2/g. with a standard deviation of ±12.7 or about ±2%. For example, a Colorado vermiculite had 1.63% K2O equivalent to 16.3% mica residue with a unit cell interplanar surface of 124 m.2/g.; this added to the measured 631 m.2/g. of planar sorption surface (glycerol sorbed on expanded or cleavage planes) gives a total planar surface of 755 m.2/g. Similarly, for coarse clay from Fithian, Illinois, the 5.61% K2O is equivalent to 56.1% of illite, with unit cell interplanar surface of 426 m.2/g. This, added to 235 m.2/g. of measured planar sorption surface, gives a total of 661 m.2/g. which when corrected to exclude 15% unexpanded minerals (kaolinite and chlorite) gives a total planar specific surface of 775 m.2/g. Wyoming montmorillonite had 803 m.2/g. of planar specific surface, comparing well with the theoretical, 808 m.2/g. This principle of unit cell planar specific surface constancy of 2:1 layer silicates shows that the mechanism of K release from mica is by cleavage, and gives an accurate tool for analysis of the rather generally occurring interstratified mixtures of expanding 2:1 layer silicate minerals with micas in soils and sediments.

AbstractIn a new method for specific surface determination, montmorillonite is made to sorb exactly two interlayers of glycerol (a true monolayer on each planar surface) at 35° C. in a vacuum of < 1 mm. of Hg. Vermiculite sorbs only one interlayer under these conditions. Both montmorillonite and vermiculite sorb only a mono‐interlayer of glycerol at 110° C. in a previous method. The two analytical methods thus give the amount of glycerol corresponding to the second interlayer in montmorillonite, and this makes possible quantitative analytical determination of montmorillonite and of vermiculite.To illustrate, Wyoming montmorillonite sorbs 21.1% glycerol at 110° C., and 41.6% at 35° C. in vacuum, which gives an analysis of 98% montmorillonite, whereas Colorado vermiculite sorbs the same amount of glycerol under both these conditions, equivalent to only a monointerlayer. The presence of fine amorphous material in montmorillonitic fine clays is revealed by a higher specific surface than obtained with 100% montmorillonite. Dissolution of the allophane from Black Cotton soil (India) resulted in a specific surface analysis of 94% montmorillonite (5 to 10% kaolinite is present). Ladybrook fine clay fraction (Queensland, Australia) showed 90% montmorillonite and 10% of mono‐interlayer expanding mineral.

The oxidation potential of dithionite (Na2S2O4) increases from 0.37 V to 0.73 V with increase in pH from 6 to 9, because hydroxyl is consumed during oxidation of dithionite. At the same time the amount of iron oxide dissolved in 15 minutes falls off (from 100 percent to less than 1 percent extracted) with increase in pH from 6 to 12 owing to solubility product relationships of iron oxides. An optimum pH for maximum reaction kinetics occurs at approximately pH 7.3. A buffer is needed to hold the pH at the optimum level because 4 moles of OH are used up in reaction with each mole of Na2S2O4 oxidized. Tests show that NaHCO3 effectively serves as a buffer in this application. Crystalline hematite dissolved in amounts of several hundred milligrams in 2 min. Crystalline goethite dissolved more slowly, but dissolved during the two or three 15 min treatments normally given for iron oxide removal from soils and clays. A series of methods for the extraction of iron oxides from soils and clays was tested with soils high in free iron oxides and with nontronite and other iron-bearing clays. It was found that the bicarbonate-buffered Na2S2O4-citrate system was the most effective in removal of free iron oxides from latosolic soils, and the least destructive of iron silicate clays as indicated by least loss in cation exchange capacity after the iron oxide removal treatment. With soils the decrease was very little but with the very susceptible Woody district nontronite, the decrease was about 17 percent as contrasted to 35–80 percent with other methods.