Mounted on the base are two shaded lamps, which direct the center of their beams of light at about a 45° angle to the plane of the sample and standard surfaces. The comparator is rigidly mounted on a vertical stand attached to a base in which arrangement is provided for securely and accurately positioning two cans of size 307 × 113 in the two fields of view. The passed wavelength band is of a monochromaticity sufficient to cause a sample and a neutral standard of equal reflectance to appear of the same hue. The filter does not pass appreciable visible radiation of wavelengths below 540 mµ or above 570 mµ. The eyepiece contains a color filter centering at a wavelength between 550 mµ and 560 mµ. Light reaching the eye is rendered sufficiently diffuse, by design of eyepiece and comparator, so that detail of the sample surface will remain undefined, to a degree such as to avoid visual confusion in observation of a match of over-all intensity of reflected light. The scanned areas of sample and standard surface are not smaller than 2 square inches. The following method may be used, employing an optical comparator, consisting of a lens and prism system which brings two beams of light, reflected from equal areas of sample surface and standard surface, respectively, together, within an eyepiece, so as to show an equally divided optical field. (i ) Determine the Munsell value of the sample surface so prepared. Within 10 minutes after sieving through the 1⁄ 4-inch mesh woven-wire cloth, determine the Munsell value of sample surface. Mix the sieved material and place a sufficient quantity into a 307 × 113 size container (bearing a top seam and having a false bottom approximately 1⁄ 2-inch deep and painted flat black inside and outside) so that after tamping and smoothing the surface of the sample the material will be 1⁄ 8-inch to 1⁄ 4-inch below the top of the container. For information on the availability of this material at NARA, call 20, or go to. Copies may be obtained from the AOAC INTERNATIONAL, 481 North Frederick Ave., suite 500, Gaithersburg, MD 20877, or may be examined at the National Archives and Records Administration (NARA). Standard Series),” under the heading “Definitions of Terms and Explanatory Notes,” which is incorporated by reference. (1980), Table 1, “Nominal Dimensions of Standard Test Sieves (U.S.A. Pass the combined portions through a sieve fitted with woven-wire cloth of 1⁄ 4-inch mesh complying with the specifications for such cloth set forth in “Official Methods of Analysis of the Association of Official Analytical Chemists,” 13th Ed. (7 ) For determination of the color designations specified in paragraph (a)(4) of this section, the following method shall be used: Recombine the separations of pressed cake resulting from the method prescribed in paragraph (c)(2) of this section.
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