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Refractometer Use

1. Plug in the refractometer and turn it on using the switch on the cord. The light in front should illuminate.

2. Look in the eye-piece, push in the push-button on the left hand side of the machine. You will see a scale become illuminated in the eye-piece. Use the knob on the right hand side of the machine to bring the line to about 1.35 on the upper scale. Release the push-button

3. Open the prism, and place a drop of distilled water on the prism. Do not scratch the prism!

4. Close the prism

5. Using the knob, adjust the light/dark interface to the cross-hairs. (You sharpen the interface by both focusing the eye-piece (in/out) and by turning the rotary dial on the FRONT of the machine.

6. Press the push-button. The lower scale should read 0 - IF the machine has been calibrated.

7. To calibrate the machine: while pressing the push-button in, turn a hex-wrench in the screw under the small cap in the middle of the right-hand side of the machine. Turn until the lower scale = 0. This lower scale reads in percent dissolved solids in WATER. Thus you can rapidly determine the concentrations of salts and sugars in water.

8. Once the refractometer has been "zeroed," you are ready to use it to measure the refractive indeces of other liquids.

   ------ Here are the usual steps with a series of readings ------

9. Using a soft and absorband paper (toilet tissue or hand-towels) dry the prism interfaces - both top and bottom.

10. Add a few drops of your experimental liquid, to the top of the lower prism and close the top prism on it. Do not allow the prisms to be open for any longer than necessary - evaporation leads to increasing concentration.

11. Move the interface to near the cross-hairs; refocuse as in step #5; and then move the interface to the cross-hairs.

12. Press the push-button and read the scales. Again, the bottom one is percent dissolved solids IN WATER. Thus if you are dealing with NaBr solutions and you get a reading of 38.22% (notice all the significant figures!), the density of the solution is 1.3822 g/cc.

13. ALWAYS thoroughly blot dry the prisms between readings and even measure some distilled water to make sure the prisms are free of salt before storing. If need be, to clear any spillage of salts, use a damp towel to wipe the lower metal parts of the machine below the prisms. Remember any residual salts may be hygroscopic in humid weather and corrode the metal parts.