Instrument has round cast iron base; on the base is a rectangular glass mirror mounted to allow rotation; a single black pillar supports the prism alidade, the black cylindrical telescope viewer, and another viewer/magnifier above the scale; scale and telescope are in fixed position; scale-reading telescope can be moved on a pivot that also moves the prism alidade; knob at base of telescope turns to control dispersion; prism apparatus can be opened and closed using a locking mechanism.
B: Box/Carrying Case
Rectangular hardwood case; brass key is in lock and operates locking mechanism; 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 cardboard box with a removable lid containing small rectangular glass test-block resting on bed of cotton.
Glass mercury thermometer in black casing stored in a round cardboard container with white label; fits in wooden casing on box door.
Small metal flat-head screwdriver stored in slot on door of B.
F: Glass Vial
Small glass vial with silver metal top; fits in wooden attachment to box door; inside vial is a small glass tube with a pointed wooden stick inside; lid of vial stuffed with brown paper.
G: Glass Vial
Small glass vial with cork stopper; fits in wooden attachment to box door; vial has a brown paper label covered by another layer of dark brown paper; silver paper tied in place with brown string around top of vial.
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)."
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