REFRACTIVE INDEX: The spheres shall have an average index of refraction not less than 1.50 when tested by the liquid immersion method at 25 degrees centigrade. SIZE The glass spheres shall conform to the following graduation when tested according to ASTM D-1214: U.S. Standard-Sieve No. 16 100% passing No. 40 40% - 60% passing No. 100 0% - 3% passing IMPERFECT GLASS SPHERES: The glass spheres shall not contain more than twenty (20) percent irregular particles when tested by ASTM D-1155. Imperfect glass spheres are defined as spheres which are ovate or otherwise non-spherical in shape, two or more beads fused together, opaque spheres or pitted spheres. MOISTURE RESISTANCE: Spheres shall pass the “Free Flow Test”. REQUIRED APPARATUS: Standard one-pint screw cap mason jars: With two piece covers consisting of a flat cover plate with sealing gasket attached and a crew ring to hold the cover plate on the jar. Special sixty-degree brass funnel with four-inch stem: Inside diameter of the stem shall be 0.25 inches plus or minus 0.004 inches...
