07-016. German, 2nd quarter 20th century, signed on the face of the circle "CARL ZEISS, Jena, Germany" and serial numbered Nr. 66478. Made of black painted cast iron, with nickel silver & aluminum fittings, and standing 17 1/4" high overall on its 7 1/2" diameter very heavy base. This apparatus is 13" wide x 6 3/4" deep, with a 4 1/2" graduated circle, vernier readout by magnifier, and tangent screw fine adjustment. This unusual refractometer is in very good display condition and could probably even be used today to determine optical properties of minerals as it was originally designed to do.
Used in laboratories for accurately measuring refractive index and dispersion of transparent liquids and solids, its operation is described in the 1936 Eimer & Amend catalog as follows: "Principle of apparatus is the use of a right angled prism of highly refractive glass, placed so one face is horizontal and the other vertical. Substance to be examined is brought into contact with upturned horizontal face, while through vertical face, border line of light striking object at grazing incidence is observed. From the angle measured by means of telescope and graduated circle, at which border ray leaves face of prism, and known refractive index of prism, refractive index of substance under examination can be obtained by means of a table."
