Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Chemical Heritage Foundation
Carl Zeiss introduced the sugar refractometer in 19112 to satisfy the growing needs of the sugar industry for an accurate and easy to use instrument for determining sugar concentrations, as described in their introductory leaflet. The Sugar Refractometer is a specialized version of the Abbé refractometer designed specifically for work with sugar solutions. The narrow scope of the specimen's enabled Zeiss to optimize the instrument in a number of ways. The narrower refractive index range (1.33 - 1.55 vs. 1.3 - 1.7) allows the use of a harder, lower refractive index glass for the prisms to give a more robust instrument. The narrow range also allows for easier readability and accuracy by spreading the range out over the readout arc. The scale is engraved on a glass cylinder, enclosed in the instrument body. It is brightly illuminated, and both the scale and refractive index border are visible at the same time, making for a very convenient instrument. The instrument reads directly in %solids rather than refractive index, indicating its narrower intended usage. The stand and prism assembly of the sugar refractometer are essentially the same as those components of the standard Abbe refractometer seen in the catalog illustration, and the 1920 example in this exhibit. The catalog scan is taken from the Arthur H. Thomas Co. catalog, Laboratory Apparatus and Reagents. Philadelphia (1921).
The sugar and oil refractometer is one of a variety of specialty designs adapting the Abbé design for specific purposes of the laboratory and/or industry. A brief essay, The Chemical Refractometer, describes the characteristics, design, and use of various refractometers. A detailed history, The Evolution of the Abbé Refractometer, traces the development of the predecessor to this more specialized instrument.
The instrument is in its original light hardwood ("alderwood"3) case ( h), with a black hard-rubber or bakelite carry-handle and nickel plated keyhole cover. The key
1 "Nr. 11553 ... was delivered to Carl Zeiss in Berlin in January 10., 1914. From there it was delivered to the "Institut für die Zucker-Industrie". It came back to Carl Zeiss in Jena in March 19., 1914. In February 20.1915 it was delivered to Bausch & Lomb in Rochester." Personal communication (2003), Dr. Wolfgang Wimmer, Archivar, Carl Zeiss Jena GMBH.
Dr. Wimmer also notes that this refractometer was delivered to the United States during World War I - a time when German overseas shipping was problematic at best. He suggested that perhaps "it was transported by the transportation submarine "Deutschland", which then delivered high value products to the United States." If so, an indication of the perceived value of these instruments at that time.
2 Carl Zeiss (internal document) Entwurf zu einer Chronik der Abteilung Mess (An Outline of the History of the Measurement Division)
3 As noted on p 2 of the Carl Zeiss Sugar Refractometer instruction manual.