Humboldt State University

Robert A. Paselk Scientific Instrument Museum

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Duboscq Colorimeter

Bausch & Lomb Optical Co.

No. 2451


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The Duboscq colorimeter was invented by Jules Duboscq in 1870. The Duboscq colorimeter was the most widely manufactured and used of the various colorimeter designs.1 It is also an instrument design of remarkable longevity, with very similar instruments still being sold. A modern version, for example, is shown in the 1996 edition of a standard analytical chemistry text.2

Colorimeters are used to determine the concentrations of substances by measuring color intensities. The DuBoscq type of colorimeter works by comparing the colors of two solutions of a colored substance, a standard with a known concentration, and a sample with an unknown concentration. A clear crystal prism dips into each solution and may be adjusted so that the path lengths of the light through the two solutions can be adjusted. The instrument then takes the light from the two prisms and arranges it to form two halves of an illuminated field in the viewing telescope. In use the operator adjusts the prisms to give equal intensities in both fields, at which point the concentration of the unknown sample can be calculated by the following relation:3

(concentration 1)(pathlength 1) = (concentration 2)(pathlength 2)

This instrument was used in the Biology Department's physiology laboratory at Humboldt. The Chemistry Department also had a Duboscq Colorimeter by B&L, but it was surplused in the 1960's. The manual is held by the museum, and is linked below.
Contemporary/early descriptions of the colorimeter and its use are provided below:


The instrument stands 16" high (drawtube closed) on a hollow 5 x 6" cast iron base. The stand is also cast iron, with a fold-up cast iron handle on the back. The prism housing/telescope mount is cast brass, attached with nickel-plated brass knurled screws. The sample cups (55 mm deep) are glass in nickel-plated brass shields (total height 72 mm). Each cup is held in a bracket on a focusing rail with a 60 x1 mm scale read against a 0-10 vernier scale. Small mirrors mounted at 45° allow viewing the scales from the telescope eye-position. The hexagonal glass prisms are 55 mm long with an optical finish on all surfaces. The optical shield is formed of steel sheet. The mirror illuminator may be flipped over to give a flat white surface instead. A black enameled aluminum tag on the back of the stand reads, in raised metal letters:

NO 2451
with the serial number stamped on a blank metal field.


The apparently identical instrument, with 45° mirrors for scale reading, is shown in the Calkins Co Catalogue No. 9 Assayer Materials and Laboratory Supplies, Los Angeles (c. 1924). In the 1927 Eimer & Amend Catalog BCM and the 1934 Braun Catalog 34, similar instruments are shown by B&L, but with a different readout system. The 1940 Braun-Knecht-Heiman Catalog 40 shows the same instruments as the E&A catalog of 1927 for the 40 mm and 50 mm instruments, however it also pictures a 100 mm instrument with the 45° mirror readout system. In the 1950 Cenco Catalog J-150 the B&L Duboscq colorimeter only one of the cells has a graduated scale associated with it, though it is similar to the current instrument, but without the mirror. The B&L Duboscq Colorimeter does not appear in any of the subsequent catalogs consulted (1960 on). There is a good general description of Duboscq colorimeters and their usage in Victor C. Myers, Practical Chemical Analysis of Blood, 2nd ed (1924), including current (1924?) prices of various manufacturer's instruments, including B&L (see link above).

According to a table in Bracegirdle4 Bausch & Lomb began using a letter prefix system for serial numbers in 1941 for microscopes. It appears the same system was used for their other instruments as well, indicating a manufacturing date prior to 1941 for this instrument.


1Stock, John T. The Duboscq Colorimeter and Its Inventor. Journal of Chemical Education 71. (Nov. 1994) 967-70; Turner, Gerard L'e. Nineteenth Century Scientific Instruments. Sotheby/University of California Press. 1983 p. 223

2Skoog, Douglas A., West, Donald M., and Holler, F. James. Fundamentals of Analytical Chemistry 7th. ed. Saunders College Publishing, Fort Worth (1996).

3The relationship between pathlength and light intensity reduction, upon which this relationship is based, was first described by Pierre Bougouer, a French mathematician and astronomer, in 1729. This work was extended and put into a more mathematically rigorous form by Lambert, a German physicist and mathematician, which he published in his book Photometrica in 1760 (hence, "Lambert's Law"). Both worked with glass plates or filters, however, and a method relating color intensity to pathlength for determination of concentrations in solution was not described until 1853 by Müller. (from Szabadváry, Ferenc. History of Analytical Chemistry. Pergamon Press, Oxford 1966 [English translation, orig. Hungarian: 1960]

4Bracegirdle, Brian. Notes on Modern Microscope Manufacturers. Quekett Microscopical Club, Oxford (1996) p 11.

HSC 1936-53 Scientific Instruments

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HSTC (1921-34)
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HSC (1935-1953)
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Last modified 30 August 2010