Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Ser No 1101
Chemical Heritage Foundation
Carl Zeiss introduced the immersion or dipping refractometer designed by Pulfrich in 1899.2, 3 The Model 2 seen in this exhibit , modified by Lowe, replaced the original design in 1902.2 The dipping refractometer is basically an Abbé type refractometer of short range and without an illuminating prism. The lack of an illuminating prism makes it free of errors due to the shielding of grazing rays, while the short range and long focal length allow reading refractive index to about 3.5 x 10-5.4 The instrument thus has very good precision, however its accuracy is further limited by the fact that it must be calibrated against a known sample, so it is always operated as a differential instrument. The refractive index is read on a linear scale (0-100) at the focal plane of the eyepiece. A dial micrometer is used to read to the tenths place. With a range of 1.325 to 1.367 the instrument can thus be read directly to 4.2 x 10-5. "The dipping instrument is the only commonly used refractometer that handles liquids in such a manner that both illumination and purity of sample are above criticism.5 Its disadvantages include the need for 3-4 mL of sample, and the precise temperature matching and control of samples and prism. The catalog scan above is from the Eimer & Amend Catalog 1910, Chemical Apparatus & Laboratory Supplies, New York (1910).
The dipping refractometer is used primarily for determining solution concentrations, such as in the sugar industry, pharmaceuticals, and milk. It is particularly useful for acids since only the inert prism dips into the solution. The original instrument was introduced by Carl Zeiss in 18993 with a range of 1.325 to 1.367. Later instruments were developed with interchangeable prisms (B&L had six prisms with a range of 1.325-1.544), and the original became known as the A prism.
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 14 3/4" long from the tip of the prism to the top of the eyepiece, with a tube diameter of 1 1/3". The telescope tube is wrapped in leather, with exposed metal either finished in black japanned enamel or polished nickel plate. The eyepiece is black hard rubber. The instrument is engraved: Carl Zeiss. Jena Nr 1011 in script, and stamped with white fill No 1101 on the collar below the eyepiece which also carries the micrometer. The micrometer dial is graduated (white filled) in increments from 0-10, (numbered at 0, 5, and 10) over about 140°. The inner scale goes from -5 to 105, and is numbered from 0-100 with numbers every 10 increments and major lines at every 5 increments. The compensator collar is graduated from 0-10 (numbered at 0, 5, and 10) in increments over about a quarter of a circle.
The instrument is in a leather covered case (16 1/4"l x 3 1/2"h x 4 3/4"d) with two suitcase type locking snaps and a leather suitcase style handle All of the hardware is nickel plated. There is no key. The case is lined with an off-white velvet. An attachable beaker with removable bottom (both in nickel plated brass - see front of case in photo) and a small sample prism (on case top in photo) and spring retaining ring complete the accessories. A photrocopy of the 1907 edition of the manual is provided in the on-line exhibit.
1 the Dipping Refractometer with the number 1101 was produced on May 7, 1902. It is a model 2. On December 2, 1905 it was delivered to Hugerhoff in Leipzig from where it came back. On June 24, 1908 it was delivered to "Helige & Co." in Freiburg/Breisgau. Personal communication (1999), 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)
3 Pulfrich, C. (1899) Über das neue Eintauchrefraktometer des Firma Carl Zeiss. Zeitschr. f. angew. Chemie. pp1186 et. seq.
4 Bauer, N., K Fagans, and S. Z. Lewin (1960) Refractometry. in Technique of Organic Chemistry, Volume I Physical Methods of Organic Chemistry. Part Two. 3rd Ed. (Arnold Weissberger, ed.) Interscience Publisher, New York.
5 Tilton, Leroy W. and John K. Taylor. (1961) Refractive Index Measurement. in Physical Methods in Chemical Analysis Vol. 1, 2nd ed. ; Walter G. Berl, editor. p430.