Daniel D. Ebeling

Impact of experimental factors in soil phosphorus tests: shaking vessel, filtration, and centrifugation.

In the analysis of Mehlich III, deionized water (DI), Bray, and Olsen soil phosphorus (P) extractions, variations in shaking vessel, centrifugation, and filter paper result in different soil test P (STP) values. Of these factors, centrifugation and type of filtration were found to have the greatest impact on the results of water‐extractable P (WEP), that is, extraction with DI. Further spectrophotometric experiments demonstrated that centrifugation removed fine soil particles from the extract. Without the commonly used 0.45‐µm filters or centrifugation, these particles scatter the radiation of the spectrometer. During colorimetric analysis, this scattering of radiation will be perceived as absorption. This misperception results in a falsely high STP. In WEP analysis with only qualitative filtration, the scattering is very significant and appears to be due to limited aggregation of soil particles in the low ionic strength extract.

UV refractive indices of aqueous ammonium sulfate solutions

Refractive indices of aqueous solutions of ammonium sulfate were measured over a wavelength range of 240 to 400 nanometers (nm) at a temperature of 292 K. The solutions examined cover a broad range from the saturation concentration of ammonium sulfate in water at 292 K down to low concentrations. Solutions studied were: 42.5, 30.4, 23.6, 16.3, 8.5 weight per cent ammonium sulfate. Optical field measurements of these aerosols require knowing the necessary optical constants, and these constants in the ultraviolet (UV) are given here. Our results were found to be in agreement with literature values at longer wavelengths. Additionally, a Lorentz-Lorenz analysis is presented to extend our results to other wavelengths and temperatures.