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WALTER A. WOLF Colgate Unlverslty Hamlltan. New York
The Use of an Eskimo YO-YOto Demonstrate Circular Dichroism and Optical Rotation Clifton E. Meloan Kansas State University Manhattan, Kansas 66506 a n d Dennis Gere Hewlett-Packard Company Philadelohia. Penmvlvania We have found that an Eskimo yo-yo can be used to more rlearlv illustrate the orinciole of ootical rotational in eenrral and &e difference between circuiar dichroism and optical rotary dispersion in particular. An Eskimo yo-yo consists of two felt or leather balls about 2 inches in diameter connected to each other with a string. Thestring isgrasped between the thumb and forefinger just off center. The hall on the "long string" rotates in a circular motion in one direction and the other ball rotates in the opposite direction. The hand holding the two halls must move up and down to keep the yo-yo in operation. At this stage we are illustrating the electrical component of normal radiation: i t is made of a right circular component and a left circular component and the resultant is a vertical oscillation of the field-the wave motion of a ray of radiation. By changing the relative string lengths, and the relative velocities, the differences between circular dicbroism and optical rotatory dispersion can be illustrated. Photos, diagrams and a more complete explanation are available from the authors.
Automatic Potentiometric Titrations Chester A. Pinkham Brownlee Field Tri-State University Angola, Indiana 46703 In our instrumental analysis course we performed a potentiometric titration on a chloride-iodide mixture by means of a point-by-point titration.' This was an extremely time consuming experiment, and the iodide equivalence point was frequently missed while the students were still learning the procedure. Thus, we decided to automate this experiment. A constant flow buret2 with a 2-1 separatory funnel as upper reservoir was used. The reference and indicating electrodes were connected to avariable speed Heath recorder. A potentiometer was connected across the input leads of the recorder. Samples of NaCl were run to calibrate the flow rate of the buret. The flow rate was reported in units of moles of AgN03/ min from measurements of distance to the equivalence point on the chart paper. Sample weights of NaCl from 0.01-0.08 g and a 0.01 M AgN03 solution were employed. A relative
standard deviation of 1.1% was obtained with the known samples. After the calibration, mixed samples of KI-NaCl were run as unknowns. The student results from this automated method were equivalent to the previous laborious titrations. Other advantages include the greater speed of the automated procedure and the low cost of the apparatus. 'Christian, G., "Analytical Chemistry", John Wiley and Sons, New York, 1971, pp. 287-8. 2Baxter, D., and Huber, C., J. CHEM. EDUC., 49, 535 (1972).
Preparation and Application of Carrier-Free 212Pb in a Radiochemical Teaching Laboratory
E. Broda T. Schonfeld Institute of Physical Chemistry and Institute of Inorganic Chemistry University of Vienna A-1090 Vienna, Austria Kvale and Skarestad have, under the above heading, described a simple and cheap method for the production of radioactive lead (212Pb).'They use a thin layer of solid Z28Th nitrate as the thoron generator. May we point out that the same isotope of lead can be obtained even more simply and cheaply by drawing a current of air through a solution of natural thorium nitrate and absorbing the thoron in water. This can be accomplished using two wash bottles in series, with filter fibres inserted in between to hold back dronlets of the thorium solution.2 When applying this method, no radionuclides-such as separated 228Th-need be purchased a t all. Only a small stock of natural thorium nitrate is required.
,...-., 'KvBle, E., and Skarestad, M., J. CHEM. EDUC., 51,756 (IY'i41.
2Broda, E., Fabitschowitz, H., and SchGnfeld, T., Monatsh. Chem., 83,482 (1952).
A Teaching Analogy to Catalyze Understanding of Energy-Rich Organic Phosphates Robert E. Kuttner Department of Physiology Louisiana State Unversity Medical Center New Orleans, 70112 The concept of the metabolic utilization and storage of energy-rich organic phosphates is sometimes difficult to convey to nonchemistry majors in short or elementary hioVolume 54, Number 9, September 1977 1 577
