Preparative isolation of aquatic humic substances.

The drop impact sampler developed by the Bureau of Mines is based on the stain technique for measuring airborne drops. The stain technique requires a calibration curve to relate stain and drop diameters a t a known impact velocity, usually the terminal value. However, physical constraints limit sampler location, making it difficult to attain the terminal value and thereby introducing complications; extrapolation of a calibration curve based on the spherical quiescent model to large drops results in an erroneously large diameter. The new sampler eliminates these difficulties and in addition makes it possible to determine rates of depositions and spatial concentrations. The sampler can measure drop diameters ranging from 0.005 to 2.5 mm and is suitable for water sprays, raindrops, and carry-over drops such as from cooling towers. Laboratory tests have shown that the sampler is reliable, rugged, lightweight, and easy to use.