Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Carl Zeiss introduced the butter refractometer in 18922 to satisfy the growing needs of government and industry industry to determine the purity of oils as described in their introductory leaflet, and in particular to distinguish butter from margerine. The Butter Refractometer is a specialized version of the Abbe refractometer designed specifically for work with butter and oils. The narrow scope of the specimen's enabled Zeiss to optimize the instrument in a number of ways. The narrower refractive index range (1.42-1.49) 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 butter 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 Butter (Butyro) refractometer is one of a variety of specialty designs adapting the Abbe 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 Abbe Refractometer, traces the development of the predecessor to this more specialized instrument.
The instrument stands 11 1/2" high in the closed, vertical position. It is finished in black enamel (may have been restored) with the exception of the prism assembly (black oxidized) and telescope assembly (nickel plate). The round, cast iron base is 5 1/2" diameter. The post is bolted to the base from below with three heavy screws. The Carl Zeiss acromat logo and serial number are engraved on the side of the telescope (see photo). The micrometer screw on the side of the telescope (side view of instrument) is graduated incrementally with numbering at 0, 5, and 10 (white filled on black scale below nickel plated knob). The telescope/prism assembly tilts to the vertical position for loading. This exhibit also includes a 1927 Carl Zeiss Butter Refractometer manual.
1 "the refractometer 11332 was delivered to Leipzig in November 26., 1913." Personal communication (2003), Dr. Wolfgang Wimmer, Archivar, Carl Zeiss Jena GMBH.
2 Carl Zeiss (internal document) Entwurf zu einer Chronik der Abteilung Mess (An Outline of the History of the Measurement Division)