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A new, rugged, precise and accurate gravimetric method has been developed for the determination of silver in various silver bearing materials. Several gravimetry and instrumental methods have been reported in the literature for silver determination, but the fire assay method E2295-03(2008) e1E 1335-08 reported in ASTM is the only standard test method accepted internationally. This method is cumbersome, time consuming, and only a well trained chemist can perform the test. In this method the determination of silver has been carried out as silver chloride. The silver chloride formed is highly hygroscopic and converts into silver metal on exposure to light, on keeping the silver chloride for up to a few hours to covert into metallic silver. But we do not consider this in our calculations, we calculate on the basis of silver chloride, so it may affect the final results. Considering these facts a gravimetry method has been developed, after reducing silver nitrate to metallic silver using hydroxylamine hydrochloride in ammoniacal medium. In the method proposed the metallic silver formed is non-hygroscopic and is stable for several months. A comparison study has also been carried out following the primary (gravimetry) method and the existing ASTM method. A primary method of measurement is a method having the highest metrological qualities, whose operation is completely described and understood in terms of SI units and whose results are accepted without reference to a standard of the same quantity. Gravimetry is a primary method, but parallel validation has been carried out by analyzing a certified reference material of silver procured from SCP Science, Canada. The formation of metallic silver and silver chloride has been confirmed by X-ray fluorescence and X-ray diffraction. The method has also been tested in the presence of several impurities of single or multi-elements, which is generally added to the silver metal. The calculation of uncertainty has also been done following the EURACHEM/GUM guideline. After the experiment it has been found that the uncertainty result mostly depends on the uncertainty due to repeatability, weighing balance and atomic mass of silver. On the basis of the proposed method and the ASTM method the purity of silver was found to be 99.841 ± 0.085% and 99.746 ± 0.105%, whereas the recovery of silver using the SCP reference standard was found to be 99.971 ± 0.20% and 99.941 ± 0.202% respectively with 95% confidence level (k= 2). The method proposed is highly reproducible, rugged and can be used for accurate and precise determination of silver in various silver materials.

Urea(U) can abstract H+ion from p-nitrophenol (PNP) forming a hydrogen bonded ion pair (proton-transfer complex PNP-···H+U) of 1 : 1 stoichiometry with a formation constant 0.42 at 303 K. Infrared spectral measurements of the uronium phenolate and uronium nitrate have supported that the proton transferred from PNP is attached to the oxygen center of the amide. The needle shaped light yellow urea–PNP adduct is fairly stable under ordinary conditions decomposing at 398 K. The standard free energy, enthalpy, and entropy of formation determined from spectrophotometric and calorimetric methods have been found to be 3.62 kJ mol-1, -13.30 kJ mol-1, and -57.5 J mol-1K-1, respectively at 303 K.

Altitude profiles of aerosol black carbon (BC) in the atmospheric boundary layer and above it were measured for the first time in India, over the urban location Hyderabad, onboard an aircraft during two consecutive days of February 2004. The profiles on both the days were consistent, and showed a rapid decrease in BC concentration within the boundary up to ∼550 m AGL (where convective activity prevailed). Sodar measurements from the nearby location revealed the mean boundary layer height to be ∼600 m during the flight period. The decrease in BC above the boundary layer was quite weak up to ∼2.2 km AGL.