Duboscq colorimeter

Du·boscq col·or·im·e·ter

(dū-bosk'),
an early apparatus for measuring the depth of tint in a fluid by comparing it with a standard fluid; glass cylinders are immersed in each of two cups, one containing standard fluid and the other the fluid to be tested; on looking through the cylinders, the tints are equalized by raising or lowering the cylinder in one cup; the extent of this raising or lowering is indicated on a scale and gives the exact difference in tint.
[Jules Duboscq]

Duboscq,

Jules, French optician, 1817-1886.
Duboscq colorimeter - an apparatus for measuring the depth of tint in a fluid.
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Of course, the contributions and impact of Donald Dexter Van Slyke, Stanley Benedict, and Otto Folin are prominently featured, as is the introduction of analysis by color comparison and the Duboscq colorimeter, invented by Jules Duboscq in 1870.
Chemistry procedures were performed by color comparison with a standard on a Duboscq colorimeter until the Klett-Summerson colorimeter brought electronics into the arena.
In less than 90 years, the chemistry laboratory moved from the Duboscq colorimeter (circa 1919) to the most advanced of automated analytical instruments, virtually eliminating all manual procedures while simultaneously expanding the number of diagnostic tests.
The Duboscq colorimeter became a predominant instrument for comparing the colors of unknowns with those of standard solutions; matching of colors depended on the technologist's color perception.