Refractometer is an analytical instrument, which is used for measuring the refractive index of liquids, gases and translucent solids. The refractive index of liquid is measured for things like fluid concentration, specific gravity of urine, blood proteins and salinity. The instrument functions to determines how much the speed of light is reduced in a solution, gas, or solid. Prisms and lenses of refractometers show the shadow line, which can be seen through a magnifying eye piece only. The instrument is often used for measuring the sugar content of fruit, fruit juices, wine, milk, soft drinks and yeast cultures.