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These instruments were used for the determination of concentration of an unknown solution c. 1913. One cup is half filled with standard solution, placed on the right hand carrier and racked up to a set reading. The other cup is half filled with the unknown solution, placed on the right hand carrier and racked up until the plunger touches the fluid. The light source is turned on and the unknown is racked up until a perfect match is obtained. Material: Metal, brass and glass. Colour: Painted black, brass and clear, c. 1913.