How to Adjust Refractometer Readings

Light becomes bent or "refracted" when it passes between different substances or media where it travels at different speeds. Measuring the index of refraction can help you to determine the concentration of certain solutions such as maple syrup. You can measure the index of refraction for a solution using an instrument called a refractometer. Before you use a refractometer, however, you have to make sure it is calibrated properly. Fortunately, this procedure is pretty simple.

Things You'll Need

• Distilled water
• Flat-head screwdriver
• Tissue paper

Instructions

1. Open the cover on the sloping wedge-shaped end of the refractometer. Below the cover you'll see a kind of rectangular glass plate -- the surface of the prism.

2. Place a drop of distilled water in the middle of this glass plate and shut the cover. The water will spread out across the plate to form a thin film.

3. Look through the eyepiece of the refractometer while pointing it toward a light source. You will see a shadow or circular field with a scale superimposed on it. Using a flathead screwdriver, turn the calibration screw to adjust the position of this circular field until its rim is dead on zero on the scale.

4. Open the cover again and wipe the glass plate and cover dry.

Tips & Warnings

• The location of the calibration screw may vary depending on the model, but it should typically be close to the cover on the prism.

References

• Cornell University Sugar Maple Research and Extension Program: Kids Section, Using a Refractometer to Measure the Sugar Concentration of Sap and Syrup
• GrapeStompers: How to Use a Refractometer