A MAILING-TUBE POLARIMETER1 WILLIAM H. R. SHAW The University of Texas, Austin, Texas T w o flat round corks (Figure 1)are bored. A Polar- PROCEDURE oid square2 is placed between them and secured with The procedure for conducting measurements with the a strip of plastic tape. Two such units, the polarizer apparatus is as follows. The polarimeter tube is filled and the analyzer, are constructed. A metal-ended with water and placed in the polarimeter. The instrumailing tube3 is drilled, forming a circular hole a t each ment is pointed toward a source of light (a window was end. The polarizer is then mounted in the mailing used), and one end of the mailing tube rotated with retube with three small nails. The analyzer is likewise spect to the other end until the field turns deep purple. mounted. Two strips of white paper are glued about The zero of the instrument is recorded by making a the mailing tube, one on each side of the mailing tube mark on the white paper opposite the zero on the graph paper. Various sugar solutions are then placed in the polarimeter tube and readings are made in terms of the arbitrary graph-paper units. The readings in graph paper units may, of course, be readily converted to degrees by using the conversion factor obtained by determining the circumference of the mailing tube in graph-paper units and equating to 360'. RESULTS
IXPLODFD V I E W Of
POLARIZING ELEMENT
POLARIZING ELEMENT
COMPLETE
Figure 1.
The extent of optical rotation,^, is proportional to the number of optically active molecules in the light path. The results may be analyzed in terms of the following e q u a t i ~ n : ~
Student Polarimeter
joint. A strip of plastic-sprayed4 graph paper is then where I is the length of the path in decimeters, and mounted over one of the strips to serve as a scale. The g is the number of grams of optically active material in polarimeter tube (Figure 2) is made of a length of glass v milliliters of solution. (a)&'is the specific rotation, tubing. Microscope cover ?lasses are afied t o two a constant for a given temperature, t , and wave length, drilled rubber stoppers by means of 3M Weatherstrip X. The equation predicts that a plot of a versus conCement. One of these stoppers has a small hole drilled centration (glv) will be linear, and such a result was just a t the edge of the cover glass t o permit the escape obtained with this instrument. The ~olarimeteris used in the Dhvsical chemistrv of air on s t o ~ ~ e r i the n e tube. laborat& a t this institution not onlyfor polarimetrk Presented before the Division of Chemical Education a t the Regional Conclave of the American Chemical Society, December experiments but in kinetic studies. The quality of the experimental results is somewhat surprising. 11, 1953, New Orleans, Louisiana. Polaroid film can be obtained from E. H. Sargent and Com- The excellent agreement of the specific rotation with the pany, Dsllss, Texas, or the material distributed a t "3D" theaters value is doubtless fortuitous, can be used. The cost of materials for the manufacture of the Wetal-ended mailing tubes 18in. Long and Z1/rin. in diameter like those used by the Matheson Company, Joliet, Illinois, for instrument comes to a little under a dollar, in sham contrast to the cheapest commercial instrument retailshipping bottled gases, were employed. ' The scale and the entire polarimeter were sprayed with trans- ine for about four hundred. The chief advantaee of parent plastic from one of the new pressurised dispensers. the ~olarimeter. however. lies in the fact that the student can take it apart, and find out for himself SMALL YDLI 41101 A,R exactly how the "magic box" works. I
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ACKNOWLEDGMENT The author is indebted to Mr. Thomas L. Keelen for obtaining the experimental results published in this paper.
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6 DANIELS, F., "Outlines of Physical Chemistry," John Wiley 61 Sons, Ine., New York, 1948.
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