Photoelectric Colorimeter

Photoelectric colorimetry was a hot topic in the mid-1930s when Arnoldus Goudsmit Jr. and William Henry Summerson described a photoelectric colorimeter of their own design. As graduate students at the Cornell University Medical College, Goudsmit and Summerson knew that the "progress of analytical biochemistry in the past 30 years has been closely associated with the use of the colorimeter as a measuring instrument," and they believed that an instrument that used standard photocells to measure the intensity of light would give more reliable results than one that depended on the eyesight of individual people.
Summerson applied for a patent in 1938, one year after receiving a PhD in biochemistry. The Klett Manufacturing Co. of New York began marketing this instrument in 1939, noting that it would "bring the convenience, speed, accuracy and other advantages of photoelectric colorimetry to the laboratory" and provide "analytical precision in an instrument that is simple and easy to operate." The original model was still available in 1965; the same in a slightly different housing could still be had in 1974.
This example is marked "KLETT-SUMMERSON / PHOTELECTRIC COLORIMETER / PAT. NO. 2193437-1940 / KLETT MFG. CO. / N.Y. U.S.A. / MODEL 900.3 / SERIAL 12 246 / VOLTS 115 / MAX. WATTS 100. It was made after the issuance of Summerson's patent (#2,193,437) in 1940. The National Institutes of Health transferred it to the Smithsonian in 1980.
Ref: A. Goudsmit Jr., and W. H. Summerson, "A Variable Layer Photoelectric Comparison Photometer," Journal of Biological Chemistry 111 (1935): 421-433.
Summerson, "A Simplified Test-Tube Photoelectric Colorimeter, and the Use of the Photoelectric Colorimeter in Colorimetric Analysis," Journal of Biological Chemistry 130 (1939): 149-166.
Currently not on view
Klett Manufacturing Company
place made
United States: New York
Physical Description
aluminum (overall material)
steel (overall material)
rubber (overall material)
overall: 22 cm x 46 cm x 17.8 cm; 8 21/32 in x 18 1/8 in x 7 in
overall: 8 3/4 in x 6 1/4 in x 17 1/4 in; 22.225 cm x 15.875 cm x 43.815 cm
ID Number
catalog number
accession number
Credit Line
National Institutes of Health
See more items in
Medicine and Science: Chemistry
Measuring & Mapping
Data Source
National Museum of American History, Kenneth E. Behring Center


Another comment on the Klett. It used glass filters (those should be in a little wooden box next to your example instrument), because interference filters were not yet commercially available. Probably interference filters would not have enough transmittance for the Klett's detector system, but a modernized version ought to have them.
Possible addendum to my previous note; I recall that the lamp reference beam was directed at a solid-state detector, some sort of sulphide (how strange that I cannot immediately recall it after fifty-odd years! I could consult my Analytical Chemistry notebook...), and I suspect the photomultiplier gain was very low compared to modern instruments--both of which would increase its service life. I would willingly bet a modest sum that any Klett pulled out of storage (if not burnt up or flooded), dusted out and plugged in would work today. I see that your example has the old black crinkle finish--later ones had a smooth gray finish.
The Klett Summerson Photoelectric Colorimeter is often underestimated by people who are not familiar with its technology. Besides being extremely rugged, it was the first photoelectric colorimeter to have a readout linear in concentration instead of transmittance ("Klett Units" rather than absorbance, but they are proportional). In addition to that, it was the first to have a split beam double detector to compensate for variations in line current (the mains power was in those days not nearly as well regulated as today). Even decades later many single-beam photometers and spectrophotometers were powered by automobile batteries rather than mains power, because the latter was too unstable and the electrictronic power supplies of the day couldn't smooth it out adequately. The "Klett" also had an optical beam galvanometer to balance the readout, rather than an electromechanical absorbance/transmittance readout device. If I were working in a remote location, I might well suggest a Klett for use today.
"This device was described in the following paper:William H. Summerson. 1939. A simplified test tube photoelectric colorimeter, and the use of the photoelectric colorimeter in colorimetric analysis. Journal of Biological Chemistry, Vol 130, pages 149-166..When I was undertaking graduate studies in the mid 1970s, I used a Klett Colorimeter to perform some of my analyses."
"Valuable information about Klett Somerson Colorimeter. I used to service and maintain it during the late 1980's at the National Institute of Nutrition, Instrumentation Department, Hyderabad - India."

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