A: Refractometer
Instrument has round base with black finish; on the base is a double-sided circular glass mirror mounted to allow full rotation; a black pillar supports the prism alidade, the black brass cylindrical telescope viewer, and another viewer/magnifier which looks down on the scale; telescope, prism, and scale can be moved together on a pivot; scale reading telescope can also be moved on a separate, lockable pivot; scale can also be refined using screw at bottom of instrument; prism apparatus can be opened and closed using a locking mechanism.

B: Box/Carrying Case
Rectangular hardwood case; brass latch on the front closes the box; metal carrying handle on top; inside of box door has several wooden attachments for instrument accessories; inside of box has wooden attachments for securing refractometer.

C: Glass Test-Block and Case
Small circular white case with a removable lid; small rectangular glass test-block is inside resting on cotton.

Refractometry is the process of measuring the extent to which light is "bent" (or refracted) when passing through a transparent solution or solid. The measurement is converted to a unitless value, which helps to determine a solution's purity, its concentration, and/or its composition. According to Dr. Richard Paselk, Curator of Humboldt State University's Scientific Instrument Museum, "[t]he Abbe refractometer provides a quick and easy means for determining refractive index and dispersion for liquids and solids. It is used in the examination of organic compounds (oils, solvents, etc.), solutions, food products, and serum protein concentration. The refractive index is measured by aligning the cross hairs in the telescope with the line of total reflection (seen as the edge between light and dark fields in the telescope)."