Humboldt State University
Robert A. Paselk Scientific Instrument Museum
"Abbe 56" Refractometer
Bausch & Lomb
Ser. No. DB597
Chemical Heritage Foundation
Bausch & Lomb introduced the "Abbe 56", an innovative Abbe refractometer design, around 1949.2 Though the appearance of this instrument is radically different from their previous instrument, the basic instrument remains the same. The major change is the enclosure of the prism arm within the casting, and the attachment of an etched glass scale to the arm such that the scale moves past a fixed telescope to read the refractive index. Movement of the prisms and scale is accomplished via a screw-thread (see the internal view) which is turned with the knob and crank on the right side of the instrument. Additional features of this design include built-in illumination via a low-voltage light bulb on an adjustable arm (rotating around the prism holder axis), built-in or ambient illumination of the glass scale, and convenient placement of the index determination and scale reading telescopes in close proximity. The development of this instrument seems to have just preceded the development of a more elegant and compact optically reading refractometer by Carl Zeiss in 1950. The Abbe 56 was succeeded in about 1956 by the more convenient and sophisticated Abbe 3L. The catalog scan is courtesy of Cenco, taken from their catalog: Cat J- 150 General Catalog Laboratory Apparatus & Scientific Instruments. Chicago. (1950).
The Abbe refractometer provides a quick and easy means for determining refractive index and dispersion of liquids and solids. Its most common use is the determination of the concentrations of solutions. A brief essay, The Chemical Refractometer, describes the characteristics, design, and use of these instruments. A detailed history, The Evolution of the Abbe Refractometer, traces the development of this valuable instrument to around 1980.
The instrument stands 12 3/4" high at the top of the case (not including the handle) while the base is 10" long and 6 1/4 across the tips of the tripod feet. The body of the instrument consists of a hollow, heavy aluminum casting, with large access ports on both sides and the front covered by thin steel plates, all finished in a heavy gray enamel. The prism assembly, telescope tubes, scale adjustment wheel, dispersion wheel etc. all appear to be chrome plated brass, with the prism assembly gray enameled as well on its outside surfaces. Both the prisms and the scale are provided with built-in electric illumination (note the movable arm with the lamp housing visible in both the photograph and the catalog illustration). A frosted window is also provided so that ambient light can be used to illuminate the scale, as seen as a white circular window in the photo of the left side of the instrument.
1 See Bracegirdle, Brian. Notes on Modern Microscope Manufacturers. Quekett Microscopical Club, Oxford (1996), for a list of serial number letters and their years of use.
2 A patent application for this instrument was filed in 1949 and issued in 1951. Production appears to have commensed immediately, as the Abbe 56 is illustrated in: MacAlaster Bicknell Co. General Catalog of Laboratory Supplies and Equipment Catalog M-E. New Haven (1949).