Refractometer is an instrument used to measure the level / concentration of dissolved materials for instance: Sugar, Salt, Protein etc. The working principle of a refractometer as the name suggests is to utilize the refraction of light. As shown in Figure 28 below a straw dipped in a glass of water will look terbengkok. In the second picture a straw dipped in a glass containing sugar lauran.
Terbengkok straw looks sharper. This phenomenon occurs because of the refraction of light. The higher the concentration of the dissolved substance (Meetings type solution), then straws will increasingly look crooked proportionally. The amount of bending angle is called Refractive Index (nD). Refractometer discovered by Dr. Ernst Abbe a scientist of German at the beginning of the 20th century.
The working principle of a refractometer can be described as follows:
o From the picture below, there are 3 parts: Sample, Prisma and Scale Board. Refractive index prism is much larger than the sample.
o If the sample is a solution with a low concentration, the wide angle of refraction will be due to differences in refraction of the prism and a large sample. So on board beam scale “a” would fall on a lower scale.
o If the sample is a concentrated solution / high concentration, then the angle of refraction will be smaller because of the difference of refraction prism and a small sample. In terlihar image ray “b” falls on a large scale.
Figure 27. Refraction of light
From the above it is clear that the concentration will have an effect proportional to the angle of refraction. In practice refractometer will appraise them on a scale according to their use. For example refractometer is used to measure the concentration of sugar solution will appraise them on a scale of sugar. Likewise with a refractometer to dissolved salts, proteins etc. The concentration of dissolved materials is often expressed in units of Brix (%) that is pronsentasi of dissolved material in the sample (water solution).
Levels of dissolved materials is the total of all the material in the water, including sugar, salt, protein, acids, etc.. Basically, Brix (%) is expressed as the number of grams of cane sugar contained in 100g of cane sugar solution. So when measuring the sugar solution, Brix (%) should be completely appropriate to the concentration.
Salinity is measured with a refractometer by:
o refractometer to use calibrated beforehand with distilled water dripping into the windshield of a refractometer.
o Observe the salinity level of the rear lens to show the numbers 0 to while turning part of the calibration by using a small screwdriver at the top refractometer.
o Clean the glass front of the refractometer, uses paper towels until completely clean before being used to observe the sample salinity levels.
o Air samples taken in moderation, then dropped on the windshield refractometer,
o Then observed through the lens of the back,
o Appointment value of salinity on the device, recorded.
Figure 2 The use of hand refractometer