File:Bausch & Lomb Duboscq Type Colorimeter - DPLA - 9714e4e623cc87c9e0c59fa4a2c97691 (page 3).jpg

A: Cast iron base attached to a sloping cast iron upright supporting the reader, prisms, sample cups, plungers, and a mechanism for raising and lowering the sample cups; two metal knobs control the height of the sample cups; two scales on the back indicate the height of the sample cups; a metal tag on the front of the upright identifies the manufacturer; a magnifying lens on the front of the upright allows scales to be read from eye point; a swiveling mirrored plate is mounted on the base; a detachable cast iron cover protects the sample cups and prisms. B: Two armored sample cups for use in A; each cup consists of a glass tube with a separate round glass base enclosed in a metal casing screwed into a metal base. C: Wooden carrying case for A with metal handle on top; interior shelf includes slots for sample cups and plungers. The Duboscq type colorimeter was invented by Jules Duboscq in 1870. It was a popular and enduring design, manufactured by several companies well into the 20th century, including this later model made by Bausch & Lomb. A Duboscq colorimeter determines the concentration of a substance through a visual comparison of the substance's color intensity against that of a standard solution--hence the two adjacent sample cups. This method of identification was revolutionary when first introduced, but the colorimeter was superceded by the development of the more precise spectrophotometer in the early 1940s.