Laboratory Instruments for Health and Industry

c. 1850 – c. 1950

Richard Paselk, Curator

Duboscq colorimeter

The Duboscq colorimeter was invented by Jules Duboscq in 1870. This version by Leitz is nearly identical in construction to the instrument manufactured by Duboscq and Pellin in the late nineteenth century. The Duboscq colorimeter was the most widely manufactured and used of the various colorimeter designs.* The catalog scan is from E. Leitz, Inc., New York; Catalog No. 2 Laboratory Apparatus, Etc. (1919).

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:

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

Description

The instrument is constructed from a 15” h x 4”w x 1/4” solid brass plate mounted through the center slot in a double coved brass molding to a heavy cast iron 7” x 7” x 1 1/8”h base, shown in the side view photograph below. Two 20 cm scales run down the center of the plate between slots carrying the rack and pinion controlled specimen holders, as can be seen in the main photograph above. A 5 1/4” long telescope is mounted at the top of the plate above an enclosed beam-splitter carrying the two 4” long, octagonal, glass dipping prisms. The prisms and a replacement sample cup are shown in the photo of the instrument with the cover removed below. The prisms and specimen cups are protected by a black painted brass shield of U cross section, 9 1/2”h x 4”w x 2 3/4”d, as shown in the view from the back of the instrument, below. Illumination is by a double sided mirror/opaque white glass reflector mounted between pinions on the base. The original specimen cups are missing. The silver backing on the mirror is partially gone. The condition of the instrument is otherwise excellent, with the original finish throughout, noting some chemical stains on the plate and base, and some corrosion of the small steel assembly screws. The instrument is engraved on the brass plate: Duboscq-Leitz Colorimeter / E. Leitz Inc. / New York / 506, see image below.

* Turner, Gerard L’e. Nineteenth Century Scientific Instruments. Sotheby/University of California Press. 1983 p. 223

** The 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]

© R. Paselk 2013, Last modified 31 December 2020