A: Duboscq type colorimeter, biological, with electric illuminator. Hollow black cast iron base attached to a sloping cast iron upright supporting the reader, prisms, and sample cups; reader detaches with two metal screws; upright also supports the sample cups (see B and C) and a mechanism for raising and lowering the sample cups on a focusing rail; two stainless steel knobs at the bottom of the upright control the height of the sample cups; a scale on the front of the upright indicates the height of the sample cups from zero to fifty millimeters, read against a 0-10 vernier scale; base has a circular hole for inserting the electric light bulb (see E) and a screw for holding the bulb in place; a swinging mechanism at the bottom rear of the base controls a metal shield inside the base, which can control the intensity of the bulb's light; two metal tags on the front of the upright identify the manufacturer, patent number, and serial number; an upside down metal tag on the rear of the base identifies a pending patent and serial number.

B: Armored sample cup with a glass bottom, metal collar, and glass-lined interior; stored in place on the colorimeter.

C: Armored sample cup with a glass bottom and metal collar; stored in place on the colorimeter; missing the glass-lined interior.

D: Cast iron shield; fits on the colorimeter to protect the prisms and sample cups; 4.75" tall, 3.625" wide, 3.125" deep.

E: Light bulb on a cast iron, cork, and metal base with an on-off switch, attached to a 34.5" electrical cord, stored in place in the colorimeter.

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 This method of identification was revolutionary when first introduced, but the colorimeter was superceded by the development of the more precise spectrophotometer in the early 1940s.