Polarimeters

Instruments designed to measure a sample's refractive index or polarization of light.

Typical uses for refractometers:

Laboratory medicine: Used to measure total proteins in blood samples and specific gravity in urine samples
Gemology: Used to identify gems
Aquariums: Measure water salinity and specific gravity
Industry: Measure coolant concentrations
Homebrewing: Measure fermentable sugars that will be converted to alcohol