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W M Stewart

Publications and source records attributed to W M Stewart.

48 records · Page 3Linked to original sources
PubMedDate not supplied

Factors affecting the ratio of cation exchange capacity to clay content in lignite overburden.

Unusually high cation exchange capacity (CEC) values relative to clay content are frequently reported for lignite overburden and minesoils. The CEC to percent clay ratio is commonly greater than one and would require that the average charge of the clay fraction be greater than 100 cmol(c) kg(-1). A comparison of methods for particle-size distribution suggests that the major reason lignite overburden samples have CEC to percent clay ratios greater than one is incomplete dispersion of aggregates of clay minerals or shale fragments. Preliminary investigations revealed the presence of shale fragments, smectite, and partially weathered mica in the silt fraction. Methods commonly used in soil textural analysis underestimated clay content by approximately 24%. The silt fraction may, therefore, provide a "hidden" source of CEC. Another important factor influencing the CEC to percent clay ratio was the presence of organic materials (lignite) in the samples. Lignite may make a significant contribution to CEC in overburden materials. In a study designed to estimate the pH-dependent charge of both the mineral and organic fractions, the CEC of overburden organic constituents was determined to be approximately 158 cmol(c) kg(-1) at pH 8.2. The high CEC to percent clay ratio in lignite overburden and minesoils may be resolved by adjusting methods for clay determination to optimize dispersion and by accounting for CEC due to organic materials. An alternative approach is to use existing methodology and use correction factors to account for incomplete dispersion of clay minerals and the charge contributions of organic materials.

Aluminum Silicates↗
PubMedDate not supplied

[Report on two cases of bullous manifestations, one of which being a pemphigus, induced by penicillamine (author's transl)].

Cutaneous bullous disease may be induced by D-penicillamin. We have briefly reviewed what was then possible: bullosa epidermolysis, pemphigus, bullous toxiderma. We have had the opportunity to observe twice this phenomenon. In one case, as already mentioned about fifteen times in the literature, it was a pemphigus. Its clinical, histological and immunological features are mentioned, and its good prognosis confirmed. The other case gives matter to discussion about toxic pre-pemphigus.

Drug Eruptions↗