The Sedgewick-Rafter Cell Counting Chamber is of all glass construction. A 50 x 20 x 1 mm deep cell is formed by four polished strips cemented to a 75 x 33 mm base. It is primarily designed for use in the microscopy of drinking water. The employment of a cement which is not soluble in methyl alcohol renders it useable for dust examination. As the chamber is not of open moat construction, it cam be hermetically sealed and employed in the study of the growth of microorganisms. The Whipple eyepiece micrometer, 21.0 mm diameter, is recommended for use with the instrument for most operations. The cover glass, 60 x 25mm, is optically plane on both sides and is 0.5 mm thick.