Refractometer When light passes from the air into water it is refracted - that is, its direction changes. The illusion of bending when a straight stick is submerged in water illustrates this principle. The amount of refraction is affected by the temperature and the amount of dissolved solids in the water. A refractometer is an optical device that magnifies this effect in a single drop of water and quantifies it on a scale. Refractometers are widely used in food processing to measure the concentrations of both sugar and salt.
Refractometers are very handy and require no batteries or reagents.
The most convenient units are hand-held and include temperature compensation. The more salts dissolved in a water sample, and the warmer the temperature, the better the water sample conducts electricity. The concentration of dissolved material in a water sample may be estimated by multiplying the conductivity by a factor that depends on the unique mixture of dissolved material in the water. The conversion factor also varies with concentration and temperature. Each of these features has a cost associated with it, resulting in meter prices that range widely.