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A simple, sensitive, highly selective, automatic spectrofluorimetric method for the simultaneous determination of selenium (IV) and (VI) as selenite-selenate by flow injection analysis (FIA) has been developed. The method is based on the selective oxidation of the non-fluorescent reagent 2-(alpha-pyridyl)thioquinaldinamide (PTQA) in acidic solution (1.5-3.0 M H2SO4) by SeIV to give an intensely fluorescent oxidation product (lambda ex =350 nm; lambda em = 500nm). Selenium (VI) is reduced on-line to SeIV, in a reduction coil installed in a photo-reactor, which is then treated with PTQA and the fluorescene due to the sum of SeIV and SeVI is measured; SeVi is determined from the difference in fluorescence values. Various analytical parameters, such as effect of acidity, flow rate, sample size, dispersion coefficient, temperature, reagent concentration and interfering species were studied. The photo-reduction conditions were optimized, with an FIA procedure, for SeVI on the basis of its reduction efficiency. The calibration graphs were rectilinear for 0.1-2.4 micrograms ml-1 of SeVI and 10 ng ml-1-2.2 micrograms ml-1 of SeIV, respectively. The method was applied to the determination of Se in several Standard Reference Materials (alloy, sediments and tea), as well as in some environmental waters (tap and surface water), food samples (flour and egg), a biological sample (human hair), soil sample and in synthetic mixtures. Up to 25 samples per hour can be analysed with an RSD approximately 0.1-2%.

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Densities and viscosities have been measured for twelve 1-alkanols from methanol to 1-dodecanol at temperatures ranging from 303.15 to 323.15 K. Molar volumes, V m , have been calculated from the density data, which have been found to follow the additive equation,where n is the number of CH 2 groups. V m have been plotted against n, showing an excellent linear relationship. The average values of V CH 2 at 303.15 K and 323.15 K have been determined from the slopes of this equation. The viscosities have been found to increase almost exponentially with the number of carbon atoms at different temperatures. The thermodynamic activation parameters, free energy, ÁG 6 ¼ , enthalpy, ÁH 6 ¼ , and entropy, ÁS 6 ¼ for viscous flow have been plotted against the number of C atoms -all have been found to increase with the chain length of 1-alkanols.

Tropical forests of the world are degrading at an alarming rate because of human-induced activities. This study was conducted to determine the consequences of deforestation on the natural regeneration of vegetation and soil quality in tropical, semievergreen protected and degraded forest ecosystems of Bangladesh. In each forest ecosystem, 20 matured trees were randomly selected for laid-out experimental plots by placing the tree stand at the center of the plot. The number of vegetative species, height, basal area, crown percentages and species richness were measured. The selected soil properties were determined. The vegetation in the protected forest site was denser with an abundance of species than in the degraded forest site. The primary forest regenerative species were dominated by the dipterocarps in both forest sites. The most alarming difference was that of an abrupt decline in regenerative forest species accompanied by an increase in exotic shrubs, grasses and vines typical of open habitats in the degraded forest site. These shrubs (e.g. Melastaoma, Lantana camara, Clerodendrum infortunatum and Jasminium spp.) and grasses and vines (e.g. Imperata cylindrica, Imperata arundinacea, Mikania scandenes, Saccharum spontaneum and Eupatorium odoratum) are gradually replacing the primary forest regenerative species in the degraded forest site. The soil quality of the degraded forest site has deteriorated over time due to preferential removal of ®ner particles and organic matter by accelerated water erosion. As a result, natural regeneration of primary forest species, especially dipterocarps, is severely affected by the direct effects of biotic interferences and attendant processes of soil quality degradation from deforestation. In contrast, degraded forest sites under regular protection have shown slow, but gradual, increase in crown frequency, enhanced recruitment and recovery of primary forest species, species abundance, and an improvement in soil quality.

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