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DIY Polarimeter Design - The idea is to utilize a yellow 585nm wave-length light emitting diode(L.E.D.) as the light-source. Two peices of polarizing film will be utilized to polarize the light-source. A large Poyvinyl chloride drain-age tube is used to house the cell, and light-source while blocking external non-polarized forms of light. A 360 degree protractor is printed out and fastened to the top of the P.V.C. tube to keep track of angles and measure observed rotation. The wiring is very primitive, and that is being generous. A 5 volt 0.7 Amp cell-phone charger's cord was cut to expose the positive and negative lines. The positive line is soldered to a SPST switch and lead to a 270ohm 0.5watt with 5% tolerance resistor. Wired shortly after the resistor is the yellow LED. *note* The LED is over-loaded, watts = amps * volts; 5v * 0.7A = 3.5 watts(cell-phone charger). The LED is only rated at 3V current. However there has been no issue yet. It's life-time will likely be fairly short, so should you decide to build your own at your own risk do the math and don't wing it. A stand was built to fit inside the P.V.C. tube. It consists of two rectangles cut from thin ply-wood(1/4"). A hole was drilled through them as close to the center as possible. Inbetween the sheets was placed the first sheet of polarizing film. The wood was taped together, and a clean micro-scope slide was taped over the hole. The micro-scope slide serves as a means to hold the cell-level. Pictures - 
click on the image thumb-nails to view the photo-graph Experimental Determination of the Specific Rotation of Sucrose- 12.00 grams of table sugar(sucrose) was added to to 11.0mL of distilled water. Heat was supplied with agitation to encourage dissolution. After 20 minutes full dissolution appeared to occur and the solution had cooled to room-temperature. The vial was placed on the stand and the protractor was turned clock-wise until the lightsource was no longer visible. It measured at 27* maybe a slightly less but I have no way to quantify with precision beyond the 1+/- degrees. The solution heigh was then measured. The hieght of which was 6.1cm(0.61dm). The solution was carefully poured into a graduated cylinder and it read 18.0mL. Calculations -
Observed* / (Path dm * g/mL) = Specific*
Conclusion - The apparatus appears to work as intended for obtaining the specific rotation of sucrose solutions in high concentrations. More tests will elucidate a trend or a lack-of a trend. This page will be updated. References -
A New Cost-Effective Diode Laser Polarimeter Apparatus Constructed by Undergraduate Students |