Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Chemical Heritage Foundation*
The Pulfrich refractometer was advertized as being particularly suited for 1) measurement of refractive index and dispersion for any given light (e.g. sodium D lines, Hydrogen, C, F, G' etc.) of all transparent liquids and solids, 2) studies of fluids at high temperatures, and 3) measurements of differences of refraction or dispersion over small ranges. The basic theory of the instrument is diagramed and explained in the catalog scan from Arthur H. Thomas Co. Laboratory Apparatus and Reagents. Philadelphia (1921). The Pulfrich refractometer was considered a higher precision and more flexible instrument than the standard Abbe refractometer.2 Though its direct reading specifications show it to be good to 0.0001 unit of refractive index (one part in the "fourth place") like the Abbe, as a differential instrument it is good to 0.00002 (two parts in the "fifth place"). Thus the graduated circle can be read to one minute by vernier for direct measurements, while the tangent screw, which clamps to the graduated disk, has a range of six degrees, and is divided to 6 seconds for differential measurements.
The original "Refractometer for Chemists" was designed by Carl Pulfrich and described in 1888.3 This earlier, somewhat simpler instrument was constructed and sold by Max Wolz in Bonn, Germany. The instrument in this exhibit was designed by Pulfrich after joining Carl Zeiss, and was described by him in 1895, as seen Fig 1 from the 1895 Pulfrich manual.4 This second version of the refractometer for chemists was sold as the Pulfrich Refractometer by Carl Zeiss, and has been known as a Pulfrich refractometer since. The catalog scan is taken from Eimer & Amend BCM Catalog: Biological, Chemical and Metallurgical Apparatus. New York. (1927) .Zeiss offered a new design of the Pulfrish refractometer in the 1930's, as described in the catalog scan from the Eimer & Amend 85th Anniversary Catalog: Laboratory Apparatus and Supplies. New York (1936) catalog. The body (front view, end view) and accessories for one of these instruments is held by the Chemical Heritage Foundation collection.
A brief essay, The Chemical Refractometer, describes the characteristics, designs, and use of refractometers.
The instrument stands 15 7/8" high including the wood slide to which it is attached. The finish is the original laquered brass and black japanned enamel. The main scale is divided on an inlaid 'silver' disk (detail view).The tripod base is of heavy cast iron. The instrument is in its original light hardwood ("alderwood"3) case (20 3/8 "h x14 7/8"w x 12 1/5"d).
A complete set of accesories, as described in the catalog scan, accompanies the refractometer in their own case (closed, open-top view, open-front view). Included are two thermometers in a box within the case, bottles for oil, a couple of thermally jacketed prisms, one with mounted fluid cell for differential readings of fluids (right-hand side of image).
* 315Chestnut Street, Philadelphia PA 19106-2702.
** All photographs are courtesy of the Chemical Heritage Foundation.
1 "3012 was delivered to Carl Zeiss in Peterburg in 01.23.1905." Personal communication (2005), Dr. Wolfgang Wimmer, Archivar, Carl Zeiss Jena GMBH.
2 A detailed treatment of refractometry and refractometers is given in: Tilton, Leroy W. and John K. Taylor. "Refractive Index Measurement." in Physical Methods in Chemical Analysis Vol. 1, 2nd ed. ; Walter G. Berl, editor (1961) pp41162.
3 Pulfrich, C. (1888) Zeitschrift für Instrumentenkunde. 8. p 47; C. Pulfrich (1890) das Totalreflectometer und das Refractometer für Chemiker etc. W. Engelmann, Leipzig.
4 Pulfrich, C. (1895) Zeitschrift für Instrumentenkunde. 15. p 389; C. Pulfrich (1895) Zeitschrift für physikalische Chemie. p 294.
5 As noted on p 2 of the Carl Zeiss Sugar Refractometer instruction manual.