Advanced Optics Experiments Using Nonuniform Aperture Functions

A method to create instructive, nonuniform aperture functions using spatial frequency filtering is described. The diffraction from a single slit in the Fresnel limit and the interference from a double slit in the Fraunhofer limit are spatially filtered to create electric field distributions across an aperture to produce apodization, inverse apodization or super-resolution, and apertures with phase shifts across their widths. The diffraction effects from these aperture functions are measured and calculated. The excellent agreement between the experimental results and the calculated results makes the experiment ideal for use in an advanced undergraduate or graduate optics laboratory to illustrate experimentally several effects in Fourier optics

The Cobalt-3,5-Dimethylpyrazole Reaction

The reaction of 3,5-dimethylpyrazole with cobalt (II) ion in aqueous solution was first observed by Fischer in 1925 (1). He investigated a series of organic compounds as precipitants for the common metal ions and noted that aluminum, cobalt, iron, and zinc (among others) formed precipitates with 3,5-dimethylpyrazole. Surprisingly enough, preciphation was not observed with copper and nickel. A reagent capable of differentiating between cobalt and nickel was thus potentially available. In 1930, Heim (2) used 3,5-dimethylpyrazole for the determination of cobalt ion in solutions of cobalt salts after separation of interfering ions. The blue-violet precipitate formed in basic solution was filtered, washed, dried, and weighed as Co(C5H7N2)2 . More recently, the use of the reagent as a precipitant for cobalt has been advanced (7). Procedures are outlined for the determination of cobalt in organic compounds after destruction of the organic matter by sulfuric acid and peroxide oxidation. Present interest in the cobalt-3,5-dimethylpyrazole system was concerned with the possible colorimetric determination of the metal ion with the reagent. Solubility of the colored material in a nonaqueous medium with retention of coloration would form the basis of such a method. Solubility to yield a colored solution (the precipitated species would remain as an undissociated species) might be expected from the similarity to the cobalt (1) acetylacetonate complex which is soluble in most organic solvents

Experiments on Stability of Bunsen-Burner Flames for Turbulent Flow

The results of a study of the stability of propane-air flames on bunsen-burner tubes are presented. Fuel-air ratio, tube diameter, and Reynolds number were the primary variables. Regions of stability are outlined in plots of fuel-air ratio as a function of Reynolds number for flames seated on the burner lip and for flames suspended well above the burner. For fully developed flow, turbulent as well as laminar, the velocity gradient at the burner wall is a satisfactory variable for correlating the fuel-air ratio required for blow-off of seated flames for fuel-air ratios of less than 15 percent. For turbulent flames, wall velocity serves as a correlating variable in the same fuel-air-ratio range. (author