Usage/History: 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:
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:
Description: 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:
BAUSCH & LOMB OPTICAL CO
ROCHESTER NY USA
NO 2451
with the serial number stamped on a blank metal field
Research: 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.
References:
1 Stock, John T. The Duboscq Colorimeter
and Its Inventor. Journal of Chemical Education71.
(Nov. 1994) 967-70; Turner, Gerard L'e. Nineteenth Century
Scientific Instruments. Sotheby/University of California
Press. 1983 p. 223
2 Skoog, 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.
