I would use it to measure an index of refraction.
See the related link listed below for more information:
it works on the principle of refraction
Refractometer
Some labs store the refractometer with a piece of tissue in the prism assembly to keep the prism glass from being scratched.
An Abbe refractometer is an instrument used to measure the refractive index of a liquid, by utilizing the critical angle for total reflection.
Examples are: oven, burette, muffle furnace, spectrophotometer, refractometer, analytical balance, stirrer and hundred others.
Any of several instruments used to measure the index of refraction of a substance. it is commonly known to be used in wine making, where the refractometer is used to measure the sugar content in the fruit juices.
A refractometer measures the refraction of light through a medium. In beer manufacture it tests for the density of sugars in the beer and is able to tell you the sweetness.
A hand-held refractometer is a simple to operate, moderately priced instrument that is suitable for field use. In most cases sample preparation is limited to suitable dilution of a wet concentrate or blending of a dry concentrate with water. Although many refractometer are temperature compensated to allow accurate readings over a range of solution temperatures, they are sensitive to large temperature changes to which they may be subjected during field work.
To make real slush you need a concentrate which is 12 brix. This is the optimum sugar level to prevent the water from freezing into solid ice. The mixture should be agitated while it freezes. The brix can be measured with a refractometer.
Deionized, distilled water
Hydrometer or refractometer.
Instrument used to measure the index of refraction of a substanceSource: refractometer