Humboldt State University
Robert A. Paselk Scientific Instrument Museum
This instrument, by a Japanese company, illustrates the features of the final Zeiss Abbe refractometer design. In appearance, it is nearly identical to Zeiss instruments, with the exception of the "D" handle on the casting beneath the eyepiece. Similar instruments,apparently inpired by the original Zeiss design, are still being manufactured and sold by various companies. The current specimen has built illumination of both the specimen and the refractive index scale.
Compared to the previous Zeiss design (see the 1926 example in this exhibit), the instrument now has an optical readout of the refractive index through the eyepiece and a horizontal prism surface, both making the instrument more convenient for the user. Zeiss introduced their "new design" in 19502. According to The Zeiss Historica Society3. Zeiss scientists in West Germany designed new instruments from scratch following "denazification" after WW II. Though Zeiss had a tradition of optical reading in refractometer in their sugar and butter refractometers, the loss of their prototypes etc. to East Germany apparently inspired this new and very elegant design. The new design also has clear precedent in the 1935 butter refractometer, as seen in the illustration on the manual cover. Perhaps the slightly preceeding new Abbe 56 from Bausch & Lomb also influenced them. Certainly the Bausch & Lomb 3L seems to owe some of its features (e.g. the horizontal prism, new optical readout) to the new Zeiss design.
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 charecteristics, 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. This particular instrument was used in the Biology Department at Humboldt State University. It has been on loan to the Museum since 2000.
The instrument stands 8 1/2" high in the closed position. The base is 5 1/2" x 4". The instrument is finished in light brown "satin" enamel, with exposed metal parts finished with a satin-chrome plate. In the photograph the large knob adjusts the refractive index, while the smaller knob above it, just behind and above the prism mount, adjusts the Amici prism compensator, and is graduated incrementally from 0-60-0, numbered decadally. The knob on the oposite side of the instrument locks the illuminating prism in the closed position. There is a knurled cap above the compensator know which covers an adjustment screw. The yellow-backed thermometer is graduated from 0-50 °C by half-degree increments. There is an aluminum property tag on the left side of the instrument below the eyepiece: HUMBOLDT STATE UNIVERSITY / 48629.
The instrument has its original fitted plywood case (14"h x 8 3/4"w x 8 1/2"d) with an apparently original bottle of monobromonapthalene (labeled "ATAGO OPTICAL WORKS CO., LTD. / TOKYO JAPAN"), glass test block, (nD = 1.5163; 0.633" x 0.417" x 0.160", polished on one side and one end), original thermometer, 'jewelers' screwdriver, a heavy, notched, antireflective-chromed metal plate and power supply.
1 According to Humboldt State University property records this instrument was aquired in 1977.
2 The Carl Zeiss document Reifezeit für High-Tech, under the column "Refraktometrie" has the following listing: 1950 neues Abbe-Refractometer.